Columbia ^mtifrsJitp 1 90Z 
 
 CoUcge of ^{jpsitiansi anb giurgeonK 
 Hibrarp 
 
 ^\nof 
 
 W\: 
 
 Pr. C. F. MsLcDo-n^ld 
 
./ 
 
Columbia ©nitJersitp 1 902. 
 mtl)fCtipoflrttigm"k 
 
 College of ^{jpfiicians anli §• 
 
 llibrarp 
 
Digitized by the Internet Archive 
 
 in 2010 with funding from 
 
 Open Knowledge Commons 
 
 http://www.arGhive.org/details/anatomyhistology1902broo 
 
ANATOMY AND HISTOLOGY 
 
 MOUTH AND TEETH 
 
 I. NORMAN BROOMELL, D.D.S. 
 
 PROFESSOR OF DENTAL ANATOMY, DENTAL HISTOLOGY, AND PROSTHETIC TECHNICS IN THE 
 PENNSYLVANIA COLLEGE OF DENTAL SURGERY, PHILADELPHIA 
 
 SeconJ) Edition, IRevlseJ) anb ]Enlarge&, witb 
 337 miustrations 
 
 PHILADELPHIA 
 
 P. BLAKISTON'S SON & CO. 
 
 IOI2 WALNUT STREET 
 1902 
 

 Copyright, igoz, by P. Blakiston's Son & Co. 
 
 Press of Wm. F. Fell & Co, 
 
 I220-24 SANSOM ST., 
 
TO 
 
 C. N. PEIRCE, D.D.S. 
 
 AS A SOUVENIR OF A LONG AND VALUED FRIENDSHIP AND A 
 
 TESTIMONY OF ESTEEM FOR HIS PROFESSIONAL 
 
 AND PRIVATE WORTH 
 
 ?Ibis IDolume is IRcapcctfuUg DeOicateO 
 
 BY THE AUTHOR 
 
PREFACE TO SECOND EDITION. 
 
 In submitting to the dental profession a revised edition of 
 this work, the author has embraced the opportunity to make 
 such corrections and additions as were deemed advisable to fur- 
 ther increase the value of the book, and to make it worthy of 
 at least a portion of the approval accorded the first edition. 
 The general plan of the work has not been altered, and while 
 some exceptions have been taken to including within its pages 
 chapters devoted to the general anatomy of the mouth and its 
 associated parts, it was decided, after due consideration, to allow 
 this to remain. 
 
 In the description of the teeth, the terms "superior" and 
 "inferior" have been changed to "upper" and "lower," and 
 the term " palatal " as applied to one of the tooth surfaces has 
 been discarded, and the word " lingual " substituted. 
 
 Considerable care has been bestowed upon part second, and 
 as a result much of value, both as to descriptive matter and 
 illustrations, not included in the first edition will be here found 
 recorded. A chapter dealing with the Embryology of the Mouth 
 has been added, as has also a short chapter on Anomalies of 
 Tooth Form and Structure. 
 
 Fifty-three new illustrations have been added, all of which, 
 with one or two exceptions, are the original work of the author. 
 
 Acknowledgment is due the " Dental Cosmos " and "Items 
 of Interest " for the loan of cuts in their possession, and to 
 Miss Emma A. Graham, who so faithfully assisted in the work 
 of revision. 
 
 The author indulges the hope that his efforts to improve the 
 book will be found satisfactory to its readers. 
 
 1420 Chestnut Street, Philadelphia, 
 Angus/, igoz. 
 
PREFACE TO THE FIRST EDITION. 
 
 In the preparation of this work it has been the aim of the 
 author to systematically describe those parts of human anatomy 
 which come directly under the care of the stomatologist. In the 
 earlier chapters, which are devoted to a gross description of the 
 mouth and those tissues which enter into its construction, there 
 has been no attempt at originality other than in the arrangement, 
 which includes a complete description of one part before another 
 is taken up. 
 
 In the writing and classification of the succeeding chapters 
 the writer has attempted what others, though wiser and better 
 qualified, appeared unwilling to undertake, and it is from the 
 works of such as these that the foundation for the present 
 work has been derived. 
 
 Within the last few years the progress in nearly every branch 
 of dental education has made a work of this character an imper- 
 ative want. Dental therapeutics and dental chemistry have 
 been well-nigh reconstructed, while the investigations of the 
 microscopist and physiologist have brought forth many valuable 
 revelations. Next in importance has been the advance in, or 
 rather the introduction of, technic teaching. Considerable space 
 has, therefore, been devoted to the surface anatomy of the 
 individual teeth, with a hope that it may be of value in dental 
 anatomy technic. 
 
 While in one or two instances the writer has departed from 
 the field assigned as a text, the parts thus included are so 
 closely associated with the mouth, both in a constructive and in 
 a functional manner, that the work would be lacking in com- 
 pleteness if they were omitted. 
 
 The illustrations are, with but few exceptions, the original 
 work of the author, being reproduced by photograph from the 
 actual subject. In many instances dissections were required to 
 
reveal the parts, this being particularly true of those illustrations 
 included in the chapter on the Development of the Teeth, about 
 one hundred dissections being required to accomplish the pur- 
 pose. In preparing the illustrations descriptive of the various 
 surfaces of the individual teeth, the progress of the work was 
 materially interfered with by the difficulty experienced in secur- 
 ing normal teeth out of the mouth ; may their number ever 
 grow less. 
 
 The author desires to thus publicly acknowledge obligations 
 to the works of Tomes, Black, Morris, Stohr, Klein, and Strieker. 
 He is also indebted to Prof A. P. Brubaker and to Dr. C. P. 
 Shoemaker for valuable assistance rendered, and to P. Blakiston's 
 Son & Co. for their many courtesies during the preparation of 
 the volume. 
 
 That there is a place for such a work as this purports to be 
 the writer has but little doubt ; that the following pages will 
 fill that demand is his earnest dfesire, and it remains for the 
 reader to ascertain how far these demands have been met in 
 the direction of its aim and endeavor. 
 
 302 North Fortieth Street, Oct. 20, iSgS. 
 
TABLE OF CONTENTS. 
 
 PART I.— ANATOMY. 
 
 CHAPTER I. 
 
 General Description of the Mouth.- — The Buccal Orifice ; The Lateral 
 Walls of the Mouth ; The Hard Palate, or Dome of the Mouth ; 
 The Soft Palate and Fauces ; The Floor of the Mouth ; The 
 Tongue and its Attached Muscles, 17-50 
 
 CHAPTER II. 
 
 The Bones of the Mouth. — The Superior Maxilla; The Palate 
 
 Bones; The Inferior Maxilla, or Mandible, 51-81 
 
 CHAPTER III. 
 
 The Temporomandibular Articulation. — The Muscles of Mastication, S2-93 
 
 CHAPTER IV. 
 
 General Description of the Teeth ; The Permanent Teeth ; Classifi- 
 cation, Surfaces, etc.; The Roots of the Teeth; The Dental 
 Arch, 94-107 
 
 CHAPTER V. 
 Occlusion of the Teeth, 108-114 
 
 CHAPTER VI. 
 The Blood- and Nerve-supply to the Teeth, . . ; 1 15-123 
 
 CHAPTER VII. 
 
 Other Structures Within the Mouth. — The Gums ; The Mucous Mem- 
 brane; The Alveolodental Membrane; Glands, Ducts, etc., . 124-135 
 
 CHAPTER VIII. 
 
 A Description of the Upper Teeth in Detail. — Calcification, 
 Eruption, and Average Measurements ; Their Surfaces, Ridges, 
 Fossae, Grooves, etc., 136-207 
 
 CHAPTER IX. 
 
 A Description of the Lower Teeth in Detail. — Calcification, Erup- 
 tion, and Average Measurements ; Their Surfaces, Ridges, 
 Fossae, Grooves, etc. , 208-237 
 
X TABLE OF CONTENTS. 
 
 CHAPTER X. 
 The Pulp-cavities of the Teeth, 238-267 
 
 CHAPTER XI. 
 
 The Deciduous Teeth, Their Arrangement, Occlusion, etc.; Calcifi- 
 cation, Eruption, Decalcification, Shedding Process, and Average 
 Measurements ; Their Surfaces, Grooves, Fossae, Ridges, and 
 Pulp-cavities, 268-285 
 
 CHAPTER Xn. 
 
 Development of the Teeth. — The Dental Germs, Enamel Organ, 
 and Dentin Organ ; The Dental Follicle; Calcification, Erup- 
 tion, etc., 286-343 
 
 PART ll.-HISTOLOGY. 
 
 CHAPTER I. 
 
 General Histology. — The Tissues of the Body ; The Epithelial 
 Tissues ; Connective Tissues ; Muscular Tissues, and Nervous 
 Tissues, 344-363 
 
 CHAPTER II. 
 
 The Mucous Membrane of the Mouth. — Of the Lips; Of the Cheeks ; 
 Of the Gums; Of the Roof of the Mouth, Hard and Soft 
 Palate; Of the Floor of the Mouth and the Tongue, 364-375 
 
 CHAPTER III. 
 
 Glands and Ducts of the Mouth. — Of the Lips ; Of the Cheeks ; Of 
 
 the Hard and Soft Palate ; Of the Tongue ; The Salivary Glands, 376-384 
 
 CHAPTER IV. 
 
 Muscular Tissues of the Mouth.— Of the Lips ; Of the Cheeks ; Of 
 
 the Soft Palate ; Of the Tongue, 385-388 
 
 CHAPTER V. 
 
 Tissues of the Teeth. — Enamel ; Dentin ; Cementum ; The Tooth- 
 Pulp ; The Alveolodental Membrane, 389-454 
 
 CHAPTER VI. 
 Embryology of the Mouth and Teeth, 455-480 
 
 CHAPTER VII. 
 Anomalies of the Teeth, . 481-491 
 
 Index, 493 
 
ANATOMY AND HISTOLOGY 
 
 MOUTH AND TEETH 
 
 PART I.— ANATOMY. 
 
 CHAPTER I. 
 
 GENERAL DESCRIPTION OF THE MOUTH.— THE BUCCAL ORIFICE 
 (THE LIPS).— THE LATERAL WALLS OF THE MOUTH (THE CHEEKS). 
 -THE HARD PALATE OR DOME OF THE MOUTH.-THE SOFT 
 PALATE AND FAUCES.— THE FLOOR OF THE MOUTH.-THE 
 TONGUE AND ITS ATTACHED MUSCLES. 
 
 The mouth (Fig. i) {stoma, pL stoinata) is the entrance or gate- 
 way to the ahmentary canal, and is situated between the supe- 
 rior and inferior ma.Killary bones and their attached tissues. It 
 contains the active organs of mastication, the teei/i, the organs 
 of taste, of which tlie tongue is chief together with some of the 
 parts which assist in articulate speech. Anatomists usually 
 divide this cavity into two compartments, the teeth serving to 
 separate one from the other, the inner space being called the 
 month, while that between the teeth and lips or cheeks is known 
 as the vestibule of the mouth. In this description all that space 
 bounded anteriorly by the lips, posteriorly by the pillars of the 
 fauces, and latterly by the cheeks, will be considered as a single 
 cavity, and the organs and structures contained therein, together 
 with all parts directly interested in its formation, will constitute 
 a text for this work. The entrance to the cavity of the mouth is 
 formed by a freely movable transverse orifice or slit, the buccal 
 2 17 
 
orifice, while it communicates with the pharynx posteriorly 
 through the fauces. Entering into the construction of the mouth 
 and assisting in the performance of its functions are bones, 
 ligaments, muscles, blood-vessels, nerves, glands, ducts, etc., 
 each of which will be described in turn. 
 
 THE BUCCAL ORIFICE, 
 
 or entrance to the cavity of the mouth, is a transverse opening- 
 somewhat variable in extent, the extremities of which are known 
 as the corners or angles of the mouth. The orifice is bounded 
 
 Fig, I. — A General Vjew of the Mouth. 
 
 by two fleshy folds, the upper and lozi<er lips [labia), the former 
 usually being in the form of a double curve, coming together at the 
 median line and forming a small teat or tubercle, while the latter 
 is made up of a single curve extending from angle to angle. 
 While this general descripdon applies to the labial forms most 
 frequently met with, it must not be mistaken for a constant con- 
 
THE BUCCAL ORIFICE. 19 
 
 dition. In some instances the lips are tliin, with straight parallel 
 margins, firmly set against the teeth, and seldom separated from 
 each other when at rest. In another class they are thick, full, 
 and prominent, with their margins strongly curved, resting 
 lightly against the teeth, and more or less separated from each 
 other during rest. Accompanying the extreme as well as the 
 intervening conditions are various other peculiarities, such as 
 the color, the rigidity or flexibility of the muscular structure, 
 etc. The upper lip generally overhangs the lower, but in some 
 instances the lower lip is the most prominent. Externally the 
 lips are covered by the common integument, internally and over 
 their contiguous surfaces by a continuation of the integument, 
 the mucous membrane. Between the external and internal 
 coverings and forming the substance of these fleshy folds are 
 muscular fibers in which are imbedded numerous blood-vessels, 
 nerves, and glands (Jabial glands). By the various muscles 
 which enter into their construction the lips are attached to the 
 surfaces of the maxillary bones. 
 
 The integument, or external covering of the lips, is similar 
 to the skin covering other parts of the body. In the male it is 
 subject to a peculiar change and modification of its outer layer, 
 resulting in the production of a hairy growth. 
 
 The mucous membrane, or internal covering of the lips, 
 the beginning of which is strongly manifest by its bright-red 
 color, is without moisture on the contiguous surfaces, is ex- 
 tremely sensitive, and contains a number of vascular papillae, 
 many of which are accompanied by nerve terminals. Mucous 
 membranes are described as lining certain cavities or tracts, as 
 the digestive tract, the respiratory tract, and the genito-urinary 
 tract, and it is upon the contiguous surfaces of the lips that the 
 digestive tract begins. The line of junction between the integu- 
 ment and the mucous membrane, is quite variable in form, but 
 usually corresponds with the general curvature of the lips. 
 Internally at the median line each lip is provided with a pro- 
 nounced fold of mucous membrane, which is attached to the 
 basal portion of the gum, the fremim of the lip (fraenum labium 
 superloris and inferioris), which, in a measure, check the move- 
 ments of the lips. 
 
20 ANATOMY. 
 
 Muscles of the Lips. 
 
 The muscular fibers within the substance of the lips are prin- 
 cipally those of a single muscle, the orbicularis oi'is, but asso- 
 ciated with it is a portion of the elevator and depressor muscles 
 of the lips, the levator labii superioris aliEqiie nasi, levator labii 
 siiperioris, depressor labii inferioris or qiiadratus luenti, and the 
 zygoinaticus minor. 
 
 Orbicularis Oris. — This is the sphincter muscle which sur- 
 rounds and controls the buccal aperture. In form it is an oval 
 sheet with the long axis placed transversely, the fibers being 
 continued from one lip to the other by passing around the 
 angles of the mouth. It is divided into an internal or labial 
 portion, and an external or facial portion. The labial portion 
 forms the red part of the lips, and has no bony attachment 
 except through the medium of the adjacent muscles. The 
 external or facial portion forms the deeper layer and blends 
 with the surrounding muscles, works in conjunction with them, 
 and is provided with the following small bony attachments : 
 The nasolabial slips are attached to the septum of the nose, 
 other fibers are attached to the incisive fossa of the superior 
 maxilla over the position of the lateral incisor tooth, and to the 
 incisive fossa of the inferior maxilla near the socket of the lateral 
 incisor or cuspid tooth. 
 
 Structure. — The muscle consists of three sets of fibers, one of 
 which runs transversely, one in a vertical, and one in an antero- 
 posterior direction. The transverse set is continuous with the 
 fibers of the buccinator or cheek muscle, and forms the greater 
 part of the muscle. The red or labial portion of the muscle is 
 also formed from the same fibers, while the vertical fibers form 
 the superficial part of the facial portion and are continuous with 
 the fibers of the levator and depressor muscles. Some of these 
 latter fibers pass around the corners ot the mouth, thus becom- 
 ing transverse, those from above passing to the lower lip, while 
 those from below pass to the upper lip. The anteroposterior 
 fibers pass from before backward between the transverse fibers, 
 and unite the mucous membrane to the skin. These are chiefly 
 found in the labial portion of the muscle. 
 
 Relations. — The inner margin of the superficial surface is 
 
THE BUCCAL ORIFICE. 21 
 
 closely connected with the integument, while superimposed 
 between this and the outer portion is a layer of fatty tissue. 
 Upon the deep surface lies the mucous membrane of the mouth, 
 separated from the muscular tissue by blood-vessels, mucous 
 glands, and small salivary glands. 
 
 Action. — To bring the lips together, to draw the upper lip 
 downward, and the lower lip upward ; to draw together the 
 corners ot the mouth ; to throw both lips outward ; to draw 
 them back against the teeth, and to oppose the action of all 
 other muscles that blend into it and inclining to draw it in 
 various directions. 
 
 Levator Labii Superioris Alaeque Nasi. — As its name 
 implies, this muscle is an elevator of the upper lip and the wing 
 of the nose. It is one of the superficial facial muscles, is thin 
 and triangular, and is situated by the side of the nose, extending 
 from the infra-orbital ridge to the upper lip. 
 
 Origin. — From the nasal process of the superior maxilla near 
 its orbital margin. 
 
 Insertion.— Vxoxw its origin it passes almost directly down- 
 ward, dividing into two portions, the smaller of which is inserted 
 into the nasal wing, while the larger portion is prolonged down- 
 ward, blending into the orbicularis oris and levator labii superi- 
 oris, and forming a part of the substance of the upper lip. 
 
 Relations. — Superficially, by the integument ; deeply, by the 
 levator anguli oris and compressor narium. 
 
 Action. — By its smaller and shorter portion to raise the wing 
 of the nose and to dilate the nostril ; by its larger and longer 
 portion to elevate the inner half of the upper lip. 
 
 Levator Labii Superioris. — This muscle belongs to the 
 superficial layer, and derives its name from its action. 
 
 Origin. — From the facial surface of the superior maxilla, at a 
 point between the orbital cavity and the infra-orbital foramen. 
 Also by the attachment of a few fibers to the malar bone. 
 
 Insertion. — Passing downward and inward, it is inserted into 
 the orbicularis oris and the integument of the upper lip. Near 
 its lower third it joins the levator labii superioris alaeque nasi, 
 and acts in conjunction with it. Occasional!)- it is reinforced by 
 
fibers from the orbicularis palpebrarum, which it receives at its 
 outer border. 
 
 Relations. — Superficially, by the orbicularis palpebrarum and 
 the integument ; deeply, by the levator anguli oris ; the com- 
 pressor nasi at its origin, and by the infra-orbital vessels and 
 nerves. 
 
 Action. — To elevate the upper lip. 
 
 Levator Labii Inferioris. — This muscle, also known as 
 levator menti, lies immediately beneath the mucous membrane 
 of the lower lip, and can best be dissected by everting the lip 
 and lifting off the membrane. 
 
 Origin. — From the incisor fossa of the lower jaw at its upper 
 border. 
 
 Insertion. — Into the integument of the skin. 
 
 Relations. — With the labial integument, the lower border of 
 the orbicularis oris muscle, and its superficial surface with the 
 oral mucous membrane. Deeply it is in close contact with the 
 periosteum and the depressor labii inferioris. 
 
 Action. — To raise and cause to protrude the integument ot 
 the chin. 
 
 Depressor Labii Superioris. — This small muscle with its 
 fellow of the opposite side is sometimes found within the mucous 
 membrane forming the frenum of the upper lip. 
 
 Origin. — It arises from the incisive fossa along its lower mar- 
 gin and some of its fibers are attached to that part of the alve- 
 olar process closely associated with the fossa. 
 
 Insertion. — From the point of origin the fibers pass upward 
 and are attached to the lower border of the nostrils and parti- 
 tion of the nose. Some of the fibers of this muscle are also 
 attached to the integument covering the wing of the nose. The 
 balance pass downward and mingle with the fibers of the mus- 
 cular structure of the upper lip. 
 
 Relations. — At its point of origin the fibers are closely asso- 
 ciated with the mucous membrane forming the gums. Above 
 this the muscular structure of the lip overlies these fibers. Deeply 
 it rests upon the surface of the superior maxilla, and joins its 
 fellow of the opposite side at the median line. 
 
 Action. — To depress the upper lip. 
 
THE BUCCAL ORIFICE. 23 
 
 Depressor Labii Inferioris, or Quadratus Menti. — The 
 
 name of this muscle is derived from its form and action. It 
 belongs to the second layer of facial muscles, Is quadrilateral in 
 shape, and consists of parallel fibers which meet above in the 
 median line. 
 
 Origin. — At the outer aspect of the lower border of the infe- 
 rior maxilla, from a point near the symphysis to the space be- 
 neath the first bicuspid tooth. 
 
 Insertion. — Its fibers pass upward and inward, and after unit- 
 ing with its fellow of the opposite side, blend into the body of 
 the orbicularis oris of the lower lip. 
 
 Relations. — By its superficial surface with the integument and 
 a portion of the depressor anguli oris ; deeply, with the mental 
 nerve and vessels, a portion of the orbicularis oris, the mucous 
 membrane lining the lower lip, and the labial glands. 
 
 Actioji. — To draw down and somewhat evert the lower lip. 
 
 Zygomaticus Minor. — An extremely slender muscle belong- 
 ing to the superficial set of facial muscles. It is closely associ- 
 ated with a larger muscle, the zygomaticus major, belonging to 
 the angular series, to be described in connection with the mus- 
 cles of the cheek. 
 
 Origin. — From the anterior inferior part of one of the facial 
 bones, — the malar, — close to its junction with the superior maxilla. 
 
 Insertion. — It passes downward and forward, its fibers becom- 
 ing lost in the special elevator muscle of the upper lip about 
 midway between the median line and the angle of the mouth. 
 
 Relations. — Superficially, by the integument, by its deep sur- 
 face with the levator anguli oris, facial portion of the orbicularis 
 oris, and the infra-orbital branch of the facial nerve. 
 
 Action. — To elevate and somewhat evert the upper part of 
 the lip. 
 
 The Blood-supply to the Lips. 
 
 The blood-supply to the lips is principally through the superior 
 and inferior coronary arteries, both of which are branches of 
 the facial artery. In addition to these the inferior labial artery 
 and the sub-mental, also branches of the facial, and the mental 
 branch of the inferior dental artery supply a part of the lower lip. 
 
The superior coronary artery courses along the inferior 
 margin of the upper Hp, between the mucous membrane and 
 the fibers of the orbicularis oris muscle. At the median line it 
 anastomoses with its fellow of the opposite side. 
 
 The inferior coronary artery, somewhat smaller than the 
 superior, supplies the lower lip by coursing through its substance 
 in a manner similar to the superior coronary and also anasto- 
 moses with its fellow of the opposite side at the median line. 
 
 Course of the Blood From the Heart to the Lips. — From 
 the heart to the aorta, to the common carotid, to the external 
 carotid, to the facial, to the superior and inferior coronary and 
 the inferior labial arteries. After passing through the labial 
 capillaries the blood is returned to the heart through the 
 superior" and inferior coronary veins, and the larger veins of 
 which they are branches. 
 
 Nerves of the Lips. 
 
 The general nerve-supply to the lips is principally by small 
 branches of the infra- orbital nerve for the upper lip, and by 
 branches of the mental nerve for the lower lip. The bttccal and 
 superior maxillary branches of the lower division of the facial 
 nerve supply the orbicularis oris muscle ; the upper division of 
 the facial nerve sends branches which supply the levator labii 
 superioris alajque nasi, as well as the levator labii superioris 
 and the zygomaticus minor, while the superior maxillary branch 
 of the lower division of the facial supplies the depressor labii 
 inferioris. 
 
 THE LATERAL WALLS OF THE MOUTH. 
 
 The Cheeks [bucccs). 
 
 The cheeks are continuous with and similar in structure to 
 the lips, being covered internally by mucous membrane and ex- 
 ternally by the common integument. Immediately beneath the 
 mucous membrane are a number of transverse muscular fibers, 
 covered externally by a layer of subcutaneous fat, and lying 
 between this and the integument other muscular tissue, the 
 fibers of which radiate in various directions, according to the 
 action of the muscle to which thev belong. Besides muscular 
 
THE LATERAL WALLS OF THE MOUTH. 25 
 
 and fatty tissue, there are imbedded within the substance of the 
 cheek blood-vessels, nerves, and glands. The fatty tissue 
 spoken of as intervening between the muscular fibers gives to 
 the cheek the fullness and rotundity desired by so many but 
 possessed by so few. 
 
 The integument, or external covering of the cheek, is similar 
 in structure to the skin covering other parts of the body, and, 
 like the lips in the male, is productive of a hairy growth. 
 
 The mucous membrane, or internal covering of the cheek, 
 is similar to that of the lips, containing numerous glands {Imccal 
 glands) which are almost identical to, but smaller than, the labial 
 glands. In addition to the buccal glands which are distributed 
 over the entire membrane, there are about five of larger size, 
 which open into the mouth in the region of the molar teeth, and 
 are called molar glands (see Glands of the Mouth). 
 
 The Muscles of the Cheeks. 
 
 The transverse muscular fibers referred to as being immedi- 
 ately beneath the mucous membrane are those of the bticcmator, 
 a muscle named from its action, that of being the chief muscle 
 employed by the trumpeter. External to the buccinator is the 
 masseter, one of the muscles of mastication, the elevator and 
 depressor muscles of the angle of the mouth, the levator angtdi 
 oris, and the depressor angnli oris, and the dermal muscles, 
 zygoviaticiis majo7^ and zygoniatiais minor, and the risomts. 
 
 Buccinator. — This muscle forms the greater portion of the 
 lateral wall of the mouth. It is deep-seated in the cheek, being- 
 one of the third stratum of facial muscles. 
 
 Origin. — The fibers are distinct in their origin from a part ot 
 the alveolar process of the superior maxillary bone, at a point 
 immediately over the second and third molar teeth, from the 
 anterior border of the pterygomaxillary ligament, a narrow 
 band of tendinous fibers or raphe extending from the pterygoid 
 plate of the sphenoid bone to the mylohyoid ridge of the interior 
 maxilla near the position of the third molar tooth. Some of its 
 fibers also arise from the outer wall of the alveolar process of 
 the inferior maxilla below the second and third molars. 
 
 Insertion. — The fibers pass forward and converge as the)" 
 
reach the lateral margins of the orbicularis oris ; here the fibers 
 of the upper portion pass downward and blend into the mus- 
 cles of the lower lip, while the lower fibers pass upward and 
 blend into those of the upper lip. Those fibers which arise from 
 the inferior maxilla pass forward and also blend into the lower 
 
 lip- 
 
 Relations. — Superficially, by the skin and subcutaneous iat, 
 the duct of Steno, the masseter muscle, a portion of the angular 
 group, and the facial artery and vein. Passing over it are 
 branches of the facial and buccal nerves, also a layer of deep 
 fascia continuous with that which covers the upper part of the 
 pharynx. By its deep surface it is in relation with the mucous 
 membrane and buccal glands. 
 
 Action. — To draw outward or backward the angles of the 
 mouth, thus enlarging the buccal orifice and pressing the lips 
 tightly against the teeth ; to force the food between the occlusal 
 surfaces of the molar and bicuspid teeth during mastication ; to 
 diminish the concavity of the cheek, compressing the air con- 
 tained therein and forcing it forward. It becomes an auxiliary 
 in deglutition by shortening the cavity of the pharynx from 
 before backward, through its connection with the superior con- 
 strictor. 
 
 Masseter. — This muscle is placed immediately external to 
 the buccinator, and is one of the principal muscles of mastica- 
 tion. It is short, thick, and somewhat quadrate in form, and is 
 composed of two sets of fibers, superficial and deep. The fibers 
 of the former are directed obliquely downward and backward ; 
 those of the latter, which are much shorter, pass almost verti- 
 cally downward. 
 
 Origin. — The superficial layer, from the malar process of the 
 superior maxilla, and from the anterior portion of the zygomatic 
 arch of the malar bone. The deep layer from the posterior 
 third of the zygomatic arch, as well as from the greater part ot 
 its inner surface. 
 
 Insertion. — The superficial fibers are inserted into the ramus 
 and angle of the Inferior maxilla, and the deep fibers into the 
 upper half of the outer surface of the ramus. 
 
 Relations. — By its external surface with the zygomaticus 
 
THE LATERAL WALLS OF THE MOUTH. 27 
 
 major, risorius, and platysma myoides muscles, the parotid 
 gland and its duct ; by the transverse facial artery, the facial 
 vein, and facial nerve, and by the integument. By its internal 
 surface with the ramus of the inferior maxilla, a mass of fat 
 which separates it from the buccinator, and with the temporal 
 muscle. Its posterior margin is in relation with the parotid 
 gland, and its anterior with the facial artery and vein. 
 
 Action. — The principal action of this muscle is to close the 
 jaw and to draw it slightly forward. (For further description, 
 see Muscles of Mastication, part i, chap, iii.) 
 
 The Angular Series. — The remaining muscles of the cheek 
 are those of the angular series, or those muscles which are 
 inserted into the angle of the mouth, two coming obliquely from 
 above, — the levator angiili oris and the zygomaticus major, — one 
 running almost horizontally forward, — the risorius, — and one 
 ascending from below, — the depressor anguli oris. 
 
 Levator Anguli Oris. — This muscle, which receives its name 
 from its action, belongs to the second layer of facial muscles. 
 It is formed in the shape of a triangular sheet. 
 
 Origin. — From the canine fossa of the superior maxilla, im- 
 mediately below the infra-orbital foramen. 
 
 Insertion. — Passing downward and outward it is inserted into 
 the angle of the mouth, its fibers blending with those of the 
 orbicularis oris and the other angular muscles. 
 
 Relations. — Superficially, with the levator labii superioris, the 
 zygomaticus minor, and the infra-orbital vessels and nerves ; 
 deeply, with the facial portion of the orbicularis oris anci bucci- 
 nator muscles, and the mucous membrane of the mouth. 
 
 Action. — Especially to elevate the angle of the mouth, and to 
 assist in drawing these angles inward, decreasing the size of the 
 buccal orifice. 
 
 Zygomaticus Major. — This muscle, the companion of which 
 has been described in connection with the muscles of the lips, 
 belongs to the first facial layer. It is composed of a long, fleshy 
 band of muscular fibers, which run direct from their point of 
 origin to their point of insertion. 
 
 Origin. — From the malar bone, in close proximity to the 
 zygomatic suture. 
 
28 ANATOMY. 
 
 Insertion. — From its origin it passes obliquely downward to 
 the angle of the mouth, and blends into the fibers of the orbicu- 
 laris oris and depressor anguli oris. 
 
 Relations. — Superficially, with the skin and subcutaneous fat; 
 deeply, with the malar bone, the masseter and buccinator mus- 
 cles, the facial and transverse facial arteries, the facial vein, and 
 branches of the facial nerve. 
 
 Action. — To draw upward and outward the angles of the 
 mouth, as in smiling or laughing. By contracting, it throws into 
 prominence the cheek tissues in front of the malar bone, and 
 forces the lower eyelid upward. When acting simultaneously 
 with its fellow of the opposite side, the buccal aperture is 
 widened, and the upper lip is elevated, exposing the superior 
 teeth. 
 
 Risorius. — One of the superficial set of facial muscles, re- 
 ceiving its name from its supposed action in laughter [ridere, to 
 laugh). It is flat and ribbon-shaped, and is frequently very 
 small and poorly developed. 
 
 Origin. — From the deep fascia covering the masseter muscle 
 and parotid gland, some of its fibers occasionally arising from 
 the mastoid process of the temporal bone. 
 
 Insertion. — Passing transversely forward and inward to the 
 angle of the mouth, its fibers blend with those of the orbicularis 
 oris, and the depressor anguli oris. 
 
 Relations. — Superficially, with the integument and subcuta- 
 neous fat ; deeply, with the masseter and buccinator muscles, the 
 facial artery and vein, and branches of the facial nerve. 
 
 Action. — To draw the angles of the mouth directly outward, 
 thereby increasing the width of the buccal orifice. 
 
 Depressor Anguli Oris. — Also one of the superficial layer 
 of facial muscles, deriving its name in accordance with its action 
 upon the angle of the mouth. It is a triangular-shaped muscle 
 with its base below, becoming narrow as it ascends. 
 
 Origin. — From the lower border of the inferior maxilla, and 
 from its external oblique line below the cuspid, bicuspid, and 
 first molar teeth. 
 
 Insertion. — Passing upward and inward it is inserted into the 
 integument at the angle of the mouth, its fibers blending into 
 
THE LATERAL WALLS OF THE MOUTH. 29 
 
 those of the muscles previously described as coming together at 
 this point. 
 
 Relations. — Externally, with the integument ; deeply or inter- 
 nally, with the depressor labii inferioris, the buccinator, and the 
 inferior coronary artery. 
 
 Action. — To draw down the angle of the mouth and to slightly 
 extend it. 
 
 Blood-supply to the Cheeks. 
 
 The blood-supply to the cheeks is principally through the 
 facial artery and its direct branches, the superior and inferior 
 coronary, the transverse facial and branches from the internal 
 maxillary. 
 
 The Facial Artery and Branches. — The facial artery, also 
 called the external maxillary, enters the cheek after passing 
 over the body of the inferior maxilla at the anterior edge of the 
 masseter muscle. It courses obliquely forward and upward 
 through the substance of the cheek, until it reaches the inner 
 angle or canthus of the eye, where it joins the nasal branch of 
 the ophthalmic artery, and is called the angular artery. Near 
 the center of the cheek the iiiferior labial artery is given off, 
 which passes forward and downward to the lower lip, but sup- 
 plies a portion of the cheek in so doing. Midway between the 
 center of the cheek and the angle of the mouth the sjcperior and 
 inferior coronary arteries are given off, supplying that part ot 
 the cheek immediately adjacent to the angle of the mouth, alter 
 which they pass on to supply the upper and lower lips. The 
 masseteric branch is given off in the immediate center of the 
 cheek, at a point immediately below the inferior labial, passes 
 directly upward over the masseter muscle, and anastomoses with 
 branches of the internal maxillary and transverse facial. There 
 are also given off from the main trunk near the center of the 
 cheek the buccal branches, which pass upward over the bucci- 
 nator muscle, and also anastomose with branches of the internal 
 maxillary and transverse facial arteries. 
 
 The Transverse Facial Artery. — This is the largest branch 
 of the temporal arter)'. It is at first deeply-seated in the sub- 
 stance of the parotid gland, after leaving which it courses trans- 
 
versely over and supplies the masseter muscle, sends off small 
 branches which supply the integument of the cheek, and anas- 
 tomoses with the buccal, infra-orbital, and the facial arteries. 
 Besides the arteries already named, the deeper portions of the 
 cheek receive blood from two branches of the internal maxillary 
 artery, the masseteric branch and the buccal branch. The 
 former supplies the masseter muscle and anastomoses with the 
 masseteric branch of the facial, while the latter supplies the 
 buccinator muscle and anastomoses with the buccal branches 
 of the facial. 
 
 Course of the Blood From the Heart to the Cheeks. — 
 From the heart to the aorta, to the common carotid, to the 
 external carotid, to the facial and its direct branches, or from the 
 external carotid to the temporal, to the transverse facial and 
 branches. 
 
 From the cheeks the blood is returned to the heart jarinci- 
 pally through the facial vein, a division of the anterior super- 
 ficial vein. It enters the cheek at a point midway between the 
 lower eyelid and the wing of the nose, passes obliquely down- 
 ward, being in close contact with the anterior edge of the mas- 
 seter muscle over the body of the lower jaw, joining the inter- 
 nal jugular vein in the neck. The transverse facial vein which 
 follows the course of the transverse facial artery, and the supe- 
 rior and inferior coronary veins also collect and convey a por- 
 tion of the blood from the cheeks to the larger veins and thence 
 to the heart. 
 
 Nerves of the Cheeks. 
 
 The nerve-supply to the cheeks is principally from the 
 seventh o'c facial nerve and its branches, the buccal branch sup- 
 plying a greater part of their substance. There are also a few 
 fibers of the infra-orbital branch of the seventh nerve distributed 
 to the labiobuccal region. The btucal branch of the lower 
 division of the facial, also the buccal branch of the inferior max- 
 illary division of the fifth nerve, supplies the buccinator muscle. 
 The infra-orbital branch of the upper division of the facial nerve 
 supplies the zygomaticus major and the levator anguli oris ; the 
 buccal branch supplies the risorius, and the snpramaxillary 
 
THE INTERIOR OF THE MOUTH. 31 
 
 branch of the lower division of the facial nerve supplies the 
 depressor anguU oris. 
 
 THE INTERIOR OF THE MOUTH. 
 
 For convenience of description the mouth may be divided 
 into two parts — a superior portion and an inferior portion. In dis- 
 section this division may be accomplished by an incision begin- 
 ning at the angles of the mouth and carried backward and 
 slightly upward through the substance of the cheeks until the 
 temporomaxillary articulation is reached. After disarticulating 
 this joint another incision is made, beginning at the joint on 
 either side, carried downward and forward, then obliquely across 
 the throat, until the two come together at the median line. This 
 latter incision must be deep enough to completely sever the tis- 
 sues of the throat. 
 
 The superior portion of the mouth contains the Jiard palate, 
 or roof of the mouth, the soft palate, and the sixteen tipper teeth, 
 firmly set in the bone and surrounded by a dense fibrous tissue 
 — the gums. The inferior portion contains the tongue and its 
 attached muscles, forming- the floor of the mouth, the sixteen 
 loiver teeth and the gums surrounding them. 
 
 THE SUPERIOR PORTION OF THE MOUTH (Fig. 2). 
 
 The osseous framework, or base upon which this half of the 
 mouth is constructed, is composed of a part of four bones — 
 the two superior maxillary, or upper jaw bones, and the two 
 palate bones (see Bones of the Mouth, p. 51). 
 
 The Hard Palate, or Roof of the Mouth (Fig. 2). 
 
 This is formed by the union of the palatal processes of the 
 superior maxillary bones and the horizontal plates of the two 
 palate bones at the median line. It is limited in front and later- 
 ally by the margins of the alveolar process, or that portion of 
 the bone which gives support to the teeth, and ends posteriorly 
 in an irregular border, to which is attached a muscular, mem- 
 brane-like curtain — the soft palate. The hard palate is covered 
 throughout by a thick and firm mucous membrane, seldom so 
 
highly colored as the membrane lining the lips and cheeks. 
 The mucous membrane is closely adherent to the bone through 
 its covering, the periosteum. In the center of the hard palate 
 is a ridge or fold of mucous membrane, which follows the 
 median line from before backward ; this is called the palatal 
 
 Fig. 2. — The Superior Portion or Roof of the Mouth. 
 
 raphe. Anteriorly, the raphe ends in a small papilla, Avhich 
 marks the opening of a canal in the bone — the anterior palatal 
 canal. Posteriorly, the raphe usually diminishes, but occasion- 
 ally is well marked through the whole extent of the hard palate. 
 Near the center of the hard palate it frequently separates into 
 
THE INTERIOR OF THE MOUTH. 33 
 
 two or more smaller ridges, which are proportionately dimin- 
 ished in size, and are continued backward side by side. On 
 either side of this central ridge, anteriorly, the mucous mem- 
 brane presents a number of fantastically arranged folds, the 
 palatal rjt.g(E (wrinkles). These folds are usually quite 
 numerous and prominent, but are occasionally almost absent. 
 The nature of these wrinkles is strongly indicative of the char- 
 acter or temperament of the individual ; thus, in the four basal 
 temperaments they may be divided as follows : in the bilious, 
 heavy and strong, composed of angles rather than curves ; in 
 the nervous, few in number, close together, not prominent, and 
 composed of long curves; in the sanguine, quite numerous, 
 fairly prominent, well rounded and graceful in outline; in the 
 lymphatic, few in number, flat, widely separated, and but little 
 curved. Accompanying these varying conditions in the rugse 
 will be found a corresponding variation in the raphe. The an- 
 terior and lateral margins of the mucous membrane covering 
 the hard palate form the palatal portion of the gums, known as 
 the gingiva (the gum) or gingival border. 
 
 In figure 3 the hard palate is shown with its membranous 
 covering removed. It will be observed that the bony plates are 
 perforated by numerous small foramina, through which the body 
 of the bone receives its nourishment, broken by depressions for 
 the accommodation of the various mucous glands, and traversed 
 by longitudinal grooves which give lodgment to blood-vessels 
 and nerves. 
 
 The arch formed by the hard palate from side to side varies 
 greatly in form, imparting much knowledge in regard to the 
 temperament of the individual, and in a measure controlling the 
 quality of the voice. Thus, in the sanguine temperament the 
 roof of the mouth presents almost a perfect oval. In the bilious 
 type it is comparatively high and flat, extending from the base 
 of one alveolar process to another, from which point it descends 
 abruptly to the necks of the teeth. In the nervous type the 
 roof is high and semi-elliptical or parabolic in shape, and in the 
 lymphatic it is low and segmental in form. 
 
 In the same illustration the union or suture between the two 
 bones may be observed at the median line. Near the anterior 
 
third of this central suture is the opening of the incisive or 
 anterior palatal canal, the anterior palatal foramen, the location 
 of which has been referred to in the description of the mucous 
 membrane. Near the posterior border, and situated within the 
 suture which unites the superior maxillary bones with the palate 
 bones (the palatomaxillary suture), are two other foramina, the 
 posterior palatal ; and immediately behind these, and separated by 
 a thin ridge of bone, are the accessory palatal foramina, these 
 being in the tuberosity of the palate bones. (For further descrip- 
 
 FiG. 3. — The Hard Palate, or Roof of the Mouth, with its Membranous 
 Covering Removed. 
 
 tion oi these foramina, see Bones of the Mouth, p. 51.) By the 
 vessels and nerves which enter the hard palate through these 
 various foramina, the mucous membrane and glands receive their 
 blood- and nerve-supply. 
 
 Blood-supply to the Hard Palate. — This is principally 
 derived from the posterior or descending palatal branch of the 
 internal maxillary or deep facial artery, which passes downward 
 in the posterior palatal canal and emerges through the posterior 
 palatal foramen. Immediately on reaching the palate it divides 
 into an anterior and a posterior branch, the former passing for- 
 
THE INTERIOR OF THE MOUTH. 35 
 
 ward in a groove provided for it to tlie anterior palatal foramen, 
 where it anastomoses with the nasopalatal artery. The groove 
 in which the artery lies in its passage forward is usually at the 
 base of the alveolar process, and in some instances is converted 
 into a canal for a part of its length. The posterior branches 
 pass backward and downward to supply the soft palate. In 
 connection with supplying the hard palate proper, this artery 
 carries blood to the palatal alveolar walls, to the mucous glands, 
 the mucous membrane, and the gums. 
 
 Course of the Blood from the Heart to the Hard 
 Palate. — From the heart to the aorta, to the common carotid, to 
 the external carotid, to the internal maxillary, to the posterior or 
 descending palatal branch of the latter. From the hard palate 
 the blood is returned to the heart by the superior palatal and 
 inferior or descending palatal veins, the former following the 
 course of the superior palatal artery, while the latter originates 
 at a point near the junction of the hard and soft palates, passes 
 downward, and joins the facial vein below the body of the inferior 
 maxilla. 
 
 Nerves of the Hard Palate. — The nerves of the hard 
 palate are the anterior or large palatal and branches from 
 the nasopalatal, both of which are branches of the spheno- 
 palatal (Meckel's) ganglion. The anterior palatal nerve 
 arises from the inferior angle of the ganglion, passes down- 
 ward, accompanied by the descending palatal artery, through 
 the posterior palatal canal, from which it emerges at the pos- 
 terior palatal foramen. From this point it passes forward in a 
 groove of the hard palate, and joins the nasopalatal nerve as 
 it emerges from the anterior palatal foramen. Accompanying 
 this nerve in its course through the posterior palatal canal are 
 other branches of the sphenopalatal ganglion, which pass to 
 the soft palate, and will be described in that connection. The 
 nerves of the hard palate are all sensory, and filaments are dis- 
 tributed to the mucous membrane and glands and to the palatal 
 portion of the gums. 
 
THE SOFT PALATE (Fig. 2). 
 
 The soft palate is attached to the posterior border of the hard 
 palate, from which it is continued as a backward prolongation. 
 Hanging downward, with its free borders inclining backward, it 
 may be considered as forming a part of the posterior boundary 
 of the mouth. It partially separates the mouth from the nasal 
 cavity and from the pharynx. It is attached laterally to the walls 
 of the pharynx, while its lower border is free. The substance of 
 the soft palate is composed of a number of thin, but dense, mus- 
 cular fibers, blood-vessels, nerves, and mucous glands, the latter 
 being similar to those of the hard palate. The anterior surface 
 of this muscular curtain is concave, directed forward and down- 
 ward, and is traversed by a median raphe. The posterior sur- 
 face is conve.x, directed backward and upward, and is continuous 
 with the nasal cavity. Suspended from the center of its free 
 border is a small rounded or conic membranous appendix, the 
 uvula, and passing outward from the base of this at each side 
 are two curved folds of mucous membrane, which extend out- 
 ward and downward, and are known as the pillars of the fauces. 
 From the position which these folds occupy they are divided into 
 the antenor and the posterior pillars of the fauces. The anterior 
 pillar is formed from muscular fibers which extend from the soft 
 palate to the side and base of the tongue (palatoglossus muscle), 
 and is somewhat prominent as it passes downward, outward, 
 and forward. The posterior pillar approaches more closely to 
 its fellow of the opposite side than does the anterior. It is 
 formed of muscular fibers which extend from the soft palate 
 above to the pharynx below (palatopharyngeus muscle). It is 
 somewhat concave in its downward and backward course, and 
 while closely united to the anterior pillar above, is separated 
 from it below, leaving a triangular interval or niche in which is 
 lodged a small, almond-shaped body, the tonsil, the space being 
 known as the tonsillar recess. The intervening space — bounded 
 by the margins of the soft palate above, the root of the tongue 
 below, and the pillars laterally — is called the isthmus of the fauces, 
 and establishes the communication between the mouth and the 
 pharynx. The free margins of the soft palate, assisted by the 
 
THE INTERIOR OF THE MOUTH. 37 
 
 pillars of the fauces, mark the posterior boundary of the vumth. 
 The entire surface of the soft palate and its prolongations, the 
 pillars of the fauces, is covered with mucous membrane, being 
 continuous with that of the mouth on its anterior surface, and 
 with that of the nasal cavity on its posterior surface. 
 
 Muscles of the Soft Palate. 
 
 On each side the muscles of the soft palate are the palato- 
 glossus, palatopharymgeus, levator palati, and tensor palati, to- 
 gether with the azygos uvulce. 
 
 Palatoglossus. — A small fasciculus of fibers, somewhat 
 cylindric in form, expanding at either end into a thin sheet. It 
 is named from its attachment to the soft palate and to the 
 tongue. It is the prominence of this muscle, together with its 
 covering of mucous membrane, that forms the anterior pillar of 
 the fauces. 
 
 Origin. — By a thin muscular sheet from the under surface of 
 the aponeurosis of the soft palate near the median line, its fibers 
 uniting with those of the opposite side. It passes downward in 
 front of the tonsil and against the pharyngeal wall. 
 
 Insertion. — Into the side and base of the tongue. 
 
 Relations. — Superficially, It is covered by the mucous mem- 
 brane of the soft palate and tongue ; deeply, in contact with the 
 aponeurosis of the soft palate, the superior constrictor muscle 
 of the pharynx, and one of the muscles of the tongue — the hyo- 
 glossus. 
 
 Action. — The lateral walls of the soft palate are drawn down, 
 and the sides of the tongue are drawn upward and slightly 
 backward. Acting in conjunction with the palatopharyngeus, 
 the opening of the fauces is constricted. 
 
 Palatopharyngeus. — This muscle — also named from its 
 attachments — is broad above, where it forms the greater part 
 of the lower half of the soft palate. Near the median line a few 
 of its fibers blend with those of its fellow of the opposite side. 
 
 Origin. — By two heads from a point near the raphe or median 
 line of the soft palate, passing downward and slighdy backward, 
 forming, with its covering of mucous membrane, the posterior 
 pillar of the fauces. 
 
3$ ANATOMY. 
 
 I'dsertion. — Into the posterior border of the thyroid cartilage, 
 and to the inner surface of the lower part of the pharynx. 
 
 Relations. — In the soft palate, superficially, with the mucous 
 membrane, both anteriorly and posteriorly; above, with the leva- 
 tor palati; and beneath, by the mucous glands. In the posterior 
 pillar it is surrounded with mucous membrane, and in the 
 pharynx by the constrictor muscles of the pharynx and the 
 mucous membrane. 
 
 Action. — To constrict the opening of the fauces, by bringing 
 together the posterior pillars, thus depressing the soft palate 
 and elevating the pharynx. It controls the position of the soft 
 palate during respiration, and elevates the pharynx during 
 deglutition. 
 
 Levator Palati. — This is a moderately thick muscle, and 
 derives its name from its action upon the soft palate. 
 
 Origin. — By a short tendon from the under surface of the 
 petrous portion of the temporal bone, and from the posterior 
 and inferior aspect of the cartilage of the Eustachian tube. 
 
 Insertion. — After passing downward by the side of the poste- 
 rior nares it is inserted into the median line of the soft palate, 
 where its fibers unite with those of its fellow of the opposite 
 side. 
 
 Relations. — Externally, with the tensor palati and superior 
 constrictor muscles ; internally and posteriorly, with the mucous 
 membrane. 
 
 Action. — To raise the soft palate, bringing it against the pos- 
 terior wall of the pharynx. 
 
 Tensor Palati. — This is a slender and flattened muscular 
 sheet, and receives its name from its action upon the soft 
 palate. 
 
 Ojngin. — From the scaphoid fossa at the base of the internal 
 pterygoid plate and the spinous process of the sphenoid bone ; 
 also from the outer side of the anterior aspect of the Eustachian 
 tube. 
 
 Insertion. — After descending between the internal pterygoid 
 muscle and the internal pterj'goid plate, and winding around the 
 hamular process of the latter, it is inserted into the transverse 
 ridge on the horizontal portion of the palate bone, and at the 
 
THE INTERIOR OF THE MOUTH. 39 
 
 median line of the soft palate, where it is continuous with the 
 aponeurosis of the opposite side. 
 
 Action. — To tighten or spread the soft palate laterally, form- 
 ing a septum between the posterior nares and the pharynx. It 
 also opens the Eustachian tube during deglutition. 
 
 The azygos uvulae (so named because it was at one time 
 supposed to be a single muscle) is composed of a pair of small 
 muscles which oidgmate from the aponeurosis of the soft palate 
 and the nasal spine of the palate bone. They pass downward 
 and form or are insej'ted into the uvula. 
 
 Relations. — Anteriorly, with the levator palati, palatoglossi, 
 and a part of the palatopharyngei ; posteriorly, to the mucous 
 membrane. 
 
 Action. — To shorten or draw up the uvula. 
 
 Blood-supply to the Soft Palate. 
 
 The poste^Hor or descending palatal bt'ancli of the deep facial 
 artery, after emerging from the posterior palatal canal, sends its 
 posterior division backward and downward to the soft palate, in 
 the substance of which they anastomose with the ascending palatal 
 artery. After passing over the superior border of the pharynx, 
 the ascendijig pharyngeal artery sends off branches which are 
 distributed to the soft palate. A few branches of the superior 
 palatal branch of the internal maxillary and a few twigs from 
 the lingual artery also convey blood to the parts. 
 
 Course of the Blood from the Heart to the Soft 
 Palate. — From the heart to the aorta, to the common carotid, 
 to the external carotid, to the facial or lingual, to the various 
 branches named above, to the soft palate. The return of the 
 blood to the heart is principally through the superior and infe- 
 rior or descending palatal veins, both of which closely follow 
 the course of the arteries of the same name. 
 
 Nerves of the Soft Palate. — The small, or posterior, pala- 
 tal, the external palatal (both of which are branches of Meckel's 
 ganglion), branches of the glosso-pharyngeal nerve, and the 
 following nerves which supply the various muscles : filaments 
 from the pharyngeal plexus to the palatoglossus and palato- 
 pharyngeus, branches of the Vidian to the levator palati and 
 
azygos uvulae, and from the mandibular division of the fifth 
 nerve to the tensor palati.'^' 
 
 THE INFERIOR PORTION OR FLOOR OF THE MOUTH (Fig. 4). 
 
 This half of the cavity of the mouth contains the tongue and 
 
 its attached muscles, the sixteen lower teeth firmly implanted 
 
 Fig. 4. — The Inferior Portion or Floor of the Mouth. 
 
 in the jaw, and the gums covering- the alveolar walls. The base 
 or osseous framework upon which this portion of the mouth is 
 constructed is principally made up of a single bone, the inferior 
 maxillary, mandible, or lower jaw bone (see Bones of the Mouth, 
 p. 51). The hyoid bone, situated in the median line at the upper 
 
 * A description of the upper teeth will be found in another chapler. 
 
THE INTERIOR OF THE MOUTH. 41 
 
 part of the neck, and at the base of the tongue, giving attach- 
 ment to many of the muscles about the Hoor of the mouth, may 
 also be considered in this connection. The floor of the mouth 
 is bounded anteriorly by the lower lip, laterally by the cheeks, 
 and below by the muscles attached to the external and internal 
 oblique lines of the mandible. 
 
 THE TONGUE (Fig. 5). 
 
 The tongue is a freely movable, highly sensitive, muscular 
 
 True Vocal Cord Posteiior Wall of Ihe Pharynx Corniculum Laryng 
 
 Fungiform Papilla; Circumvallale Papillae 
 Fig. 5. — Superior Aperture of Larynx. — [Deava:) 
 
 organ. It assists in the function of speech, participating, also. 
 
in the special sense of taste, and in mastication and deglutition. 
 The organ is attached posteriorly to a U-shaped bone, the hyoid 
 bone, which of itself is movable, and is placed in the neck be- 
 tween the angles of the lower jaw and the thyroid cartilage. 
 
 The tongue is suspended and kept in its position in the mouth 
 by numerous muscles, some of which are attached to the base 
 of the skull, and others to the lower jaw and hyoid bone. 
 
 The size of the tongue bears little or no relation to the 
 size of the individual, but is proportioned to the capacity of the 
 alveolar arch, which space it completely fills when at rest. The 
 shape of the tongue is controlled by the shape of the alveolar 
 arch ; thus, when the arch is contracted, narrow, and pointed, the 
 margins of the tongue, when at rest, will assume that form [a, 
 
 Fig. 6) ; but when the arch is 
 broad and rounded anteriorly, 
 the margins of the tongue will 
 also be broad and rounded 
 (b, Fig. 6). 
 
 The substance of the tongue 
 is chiefly composed of muscular 
 fibers, which are arranged in a 
 complicated manner, crossing 
 one another at various angles, 
 "' Y\G d " ^'\y\'s, making the movements of 
 
 the organ exceedingly varied 
 and extensive. Fibrous, areolar, and fatty tissues enter into its 
 structure, and it is freely supplied with blood-vessels and nerves. 
 Its free surface is covered by sensitive mucous membrane, and 
 over its entire surface are numerous mucous follicles and glands. 
 Before continuing the description of the tongue, it will be 
 necessary to name its parts. The upper surface, or that facing 
 the roof of the mouth, is the dorsum; those portions directed 
 toward the cheeks are known as the sides of the tongue ; while 
 the hem which unites these two borders at the median line, and 
 extending a short distance backward on either side, is the tip. 
 That portion between the frenum and extending back to the 
 pillars of the fauces is the base, while that part of the dorsum 
 immediately posterior to the tip is the post-tip, that region which 
 
THE INTERIOR OF THE MOUTH. 43 
 
 lies between the post-tip and the base being \h<t prebase. The 
 dorsum, sides, and tip are free, while the base is attached by 
 muscles to the lower jaw and hyoid bone. 
 
 From the base to the epiglottis is a fold which serves to limit 
 the movement of the latter organ, and from the sides of the 
 base the pillars of the fauces are given off. Under the anterior 
 free extremity in the median line is a fibrous muscular lamina 
 or ligament, the fre^ium, which connects this part of the organ 
 with the lower jaw and marks the anterior border of the base of 
 the tongue. The tongue is divided through its anterior two- 
 thirds by a slight longitudinal furrow, the median raphe, which 
 ends posteriorly near a small foramen, not constant in the adult 
 tongue, but plainly observed in the fetus or infant, the foramen 
 ccBCiim. This foramen represents the upper termination of the 
 thyreoglossus duct. 
 
 Papillae of the Tongue. — Over the anterior two-thirds ot 
 the dorsum and the sides and tip of the tongue are a number 
 of small, soft, conic eminences, which are known as the papillae 
 of the tongue. These are most numerous over the anterior part 
 of the dorsum, and at the back they are covered and partly 
 hidden by an epithelial coating. In general, the papillae are 
 quite similar to those of the integument, not being compound 
 organs in their vascular and nervous supply. In consequence 
 of their variation in form, the papillae are variously named. The 
 largest papillae, being arranged like the letter V, are called the 
 circunivallate or calciform ; those of medium size, \h& fungiform^ 
 are so named from their resemblance to a young mushroom ; 
 and the smallest and most numerous are known as the conic 
 or filiform papillae. Each papilla presents a broad, free end, 
 and is attached by a constricted base, which rests in a small, cup- 
 like concavity, about the margins of which is a well-formed 
 circular rim. Beneath the thick epithelium of these parts are 
 numerous secondary papillae, and about the base of each papilla 
 are the openings of one or more glands. 
 
 The circuvrjallate or calciform papillae (Fig. 5) form a V-shaped 
 line at the posterior boundary of the dorsum. They are few in 
 number (varying from six to twelve), but are largest in size, 
 not infrequently measuring y^ of an inch in diameter. These 
 
papillae are generally regarded as being gustatory, or directly 
 interested in the sense of taste. Each papilla is capped with a 
 small secondary papilla. 
 
 'X\\it fungiform papilla; (Fig. 5), of medium size, varying from 
 2V to Jq of an inch in diameter, are scattered over the dorsum, 
 sides, and tip of the tongue at irregular intervals, and are much 
 more highly colored than the smaller papillae which surround them. 
 They vary greatly in number, and being principally gustatory, 
 account in a great measure for the diversity in the acuteness 
 of the sense of taste in different individuals. These papillae, 
 like the circumvallate, are capped with smaller secondary papillae. 
 
 The conic or filiform papillae (Fig. 5) are the smallest and 
 most numerous, and are thickly scattered over the entire surface 
 of the dorsum in front of the circumvallate as well as over the 
 sides and tip of the tongue. They are placed closely together, 
 and with such regularity that they fairly ridge the tongue with 
 delicate lines, which run parallel with the circumvallate in that 
 region, but as the tip is approached they become transversely 
 inclined. These papillae are generally regarded as being tactile 
 or directly interested in the sense of touch, and are concerned in 
 directing the movements of the food during mastication. They 
 also possess secondary papillae upon their surfaces. 
 
 Immediately posterior to the circumvallate papillae are two 
 shallow grooves which follow the V-shaped line of the papillae 
 and unite at the foramen caecum. These grooves serve to indi- 
 cate the line of junction between the anterior and posterior 
 portions of the tongue. The latter not being within the cavity 
 of the mouth will not be described. 
 
 Muscles of the Tongue (Fig. 7). 
 
 The muscles of the tongue are both c xtrinsic-oiitward or e.x- 
 ternal, and intrinsic-inherent, inward, or special. 
 
 The extrinsic muscles include those which have their origin 
 from the base of the skull, the hyoid bone, or the mandible, and 
 are the Jiyoglossus, geniohyogiossus, styloglossus, palatoglossus, 
 and a few fibers of the superior constrictor of the pharynx. 
 The intrinsic muscles which make up the bulk of the tongue are 
 two in number, the superior lingualis and inferior bngualis. 
 
THE INTERIOR OF THE MOUTH. 45 
 
 Hyoglossus. — As its name implies, this muscle extends from 
 the hyoid bone to the tongue. Its fibers are so arranged that 
 they form a thin square sheet. 
 
 Origin. — It arises from the whole length of the upper border 
 of the great cornu, from the body, and by a few fibers from the 
 
 DORSUM OF TONGUE 
 
 Genio-hyo-gl 
 Genio hvoid 
 
 GREATER CORNU OF HYOID BONE 
 
 STYLOID PROCESS 
 Stylo-hyoid 
 
 Stylo-pharyngeus 
 
 CARTILAGO TRITICEA 
 
 THYROID CARTILAGE 
 
 Median portion of 
 crico-thyroid 
 membrane 
 
 CRICOID CARTILAGE 
 
 FIRST RING OF TRACHEA 
 
 Fig. 7. — Side View of the Tongue, with its Muscles. — [Morris.) 
 
 lesser cornu of the hyoid bone. At their point of origin the 
 fibers are in the form of a thin sheet, and ascend toward the 
 tongue almost parallel to one another, but before reaching the 
 tongue the anterior fibers pass slightly forward, and at the upper 
 margin of the side of the tongue bend inward and join the fibers 
 of the superior lingualis. In their distribution to this part of 
 
46 ANATOMY. 
 
 the tongue they form a kind of submucous covering to the 
 organ. 
 
 Insertion. — Into the posterior half of the side of the tongue, 
 between the styloglossus and superior lingualls muscles. 
 
 Relations. — Externally, with the digastricus, styloglossus, 
 stylohyoid, and mylohyoid muscles, the lingual and hypoglossal 
 nerves, Wharton's duct, and the sublingual gland. Internally, 
 with the lingualis, geniohyoglossus, and middle constrictor of 
 the pharynx muscles, the lingual artery, and the glossopharyn- 
 geal nerve. 
 
 Action. — To extend the tongue and to draw it backward, also 
 to draw downward the sides of the tongue, making its dorsum 
 more convex transversely. 
 
 Geniohyoglossus (Fig. 7). — This muscle also receives its 
 name from its three points of attachment, the chin internally, the 
 hyold bone, and the tongue. It is a triangular-shaped muscle, 
 narrow and pointed at its attachment to the mandible, and broad 
 and fan-shaped on approaching the tongue. Being near the 
 median line, it is separated from its fellow of the opposite side 
 by a thin layer of connective tissue, the septum of the tongue. 
 
 Origin. — It arises by a short tendon from the upper genial 
 tubercle of the lower jaw, from which point its fleshy fibers 
 diverge fan-like to its extensive insertion. 
 
 Insertion. — To the whole length of the tongue from base to 
 apex immediately external to the median line, into the body of 
 the hyoid bone, and by a few fibers into the side of the pharynx. 
 
 Relations. — By its inner surface, with the septum of the tongue 
 and its fellow of the opposite side; by its outer surface, with the 
 hyoglossus, mylohyoides, styloglossus, and lingualis muscles, 
 sublingual gland, lingual artery, and hypoglossal nerve. Su- 
 periorly, with the mucous membrane of the floor of the mouth ; 
 inferiorly, with the geniohyoid muscle. 
 
 Action. — Its anterior fibers assist in drawing back the tip of 
 the tongue, its posterior fibers throwing forward and protruding 
 the tongue. This muscle also depresses the center of the dor- 
 sum longitudinally, making it concave transversely, and some of 
 the lower fibers which are attached to the hyoid bone elevate 
 the bone and assist in raising the tongue. 
 
THE INTERIOR OF THE MOUTH. 47 
 
 Styloglossus. — Also named from its attachment, is a long 
 fan-shaped muscle, somewhat compressed laterally. 
 
 Origin. — From its point of origin at the tip of the styloid 
 process of the temporal bone, and from a portion of the stylo- 
 maxillary ligament, it passes with a long curve, forward, slightly 
 downward, then upward and inward to its place of insertion at 
 the side of the tonojue. 
 
 Vena Conies ^ 
 
 1 Ranine Arteries \'eiia Comes 
 
 Intrinsic Muscular Fibers 
 
 Fig. 8. — Transverse Section of One-half of Tongue. — {Denver.) 
 
 Insertion. — Upon reaching the side of the tongue it divides 
 into two portions, the fibers of one portion passing transversely 
 inward, while the others pass longitudinally along the side of 
 the tongue. 
 
 Relations. — Externally, with the internal pterygoid muscle, 
 parotid and sublingual glands, lineal nerve, and the mucous 
 
48 ANATOMY. 
 
 membrane of the mouth ; internally, with the superior con- 
 strictor and hyoglossus muscles, and with the tonsil. 
 
 Action. — To draw the tongue backward and to produce a 
 transverse concavity to its upper surface by elevating its sides. 
 
 Superior Lingualis. — This is one of the intrinsic muscles, 
 and is situated immediately beneath the mucous membrane, ex- 
 tending from the base to the tip of the organ. 
 
 FR/ENUM LIN3'J,€ 
 
 Lingualis inferior 
 
 Mylo-hyoid, reflected 
 
 Steruo-hyoid — ' — ^ 
 
 Fig. 9. — Under Surface of the Tongue with Muscles. — [Morris.' 
 
 Inferior Lingualis (Fig. 9). — This muscle is placed near the 
 under surface of the tongue, and is composed of two bands which 
 extend from base to apex, some of its fibers being attached pos- 
 teriorly to the hyoid bone, and in passing forward are placed 
 between the hyoglossus and geniohyoglossus. Anteriorly, its 
 fibers blend with those of the styloglossus. 
 
 Many of the fibers of this muscle run transversely and are 
 
THE INTERIOR OF THE MOUTH. 49 
 
 placed between the two former intrinsic muscles. These, to- 
 gether with some fatty tissue, compose the greater part of the 
 substance of the tongue. The fibers are attached at the median 
 line to the fibrocartilaginous septum of the tongue, and laterally 
 to the mucous membrane. In connection with the transverse 
 fibers there are a few placed vertically, which pass by long curves 
 from the dorsum to the under surface of the tongue. 
 
 Blood-vessels of the Tongue (Fig. lo). 
 
 This organ receives its blood principally through the lingzial, 
 facial, and ascending pharyngeal arteries. The lingual artery 
 
 -Descending palaiijie A . 
 
 -Anferior br, of descending palatine A . 
 ,. Styto-ylossusM. 
 
 yPatafo -(^iossusAf. 
 
 ^ Tonsillar br.dorsalis linguae A . 
 
 Posterior br. of 
 descending palatine A 
 
 Palatine br. of 
 a-s cen dinqphaijn'qeal 
 
 Ascending phan.'nqealA'- 
 
 AscendJnq palatine hr 
 'of facial A 
 Tonsillar br — 
 of fcLcial A 
 Stylo-phaiynqeus M.- 
 
 Facial A. 
 
 Middle conslHcforM .- 
 Dorsalis linguae A 
 
 Lingual A- 
 ExleiTtal carotid A 
 
 Superior ihyroid 
 
 infra- iiyoid br oj skp.tliyroid 
 
 ^"P''%l'yiZguaiA. Sty-lo-hyoidM. ^Sublingual a: 
 
 Fig. 10. — Arteries of Tongue and Tonsil. — [Dearer.) 
 
 arises from the front of the external carotid near the facial, and 
 often as a common trunk with it. From its point of origin to 
 the tongue it is divided into three portions, the first or oblique, 
 the second or horizontal, and the third or ascending, and it is 
 this latter portion which directly supplies the tongue. Ascending 
 tortuously beneath the hyoglossus muscle, it reaches the under 
 surface of the tongue, and, lying between the lingualis and hyo- 
 4 
 
50 ANATOMY. 
 
 glossus muscles, it is continued to the under surface of the tip of 
 the tongue, at which point it is called the ranine artery. At a 
 point about corresponding with the posterior margin of the hyo- 
 glossus muscle a branch is given off (the dorsalis liiigiics), which 
 passes almost directly upward, and, after dividing into two or 
 more small branches, supplies the back part of the dorsum of 
 the tongue and the mucous membrane about the circumvallate 
 papillae. At the anterior border of the hyoglossus muscle 
 another branch is given off (the sublingual artery) supplying 
 the anterior muscular structure of the floor of the mouth. The 
 facial artery by one of its muscular branches supplies the stylo- 
 glossus muscle. 
 
 Course of the Blood From the Heart to the Tongue. — 
 From the heart to the aorta, to the common carotid, to the ex- 
 ternal carotid, to the lingual artery, and its smaller branches to 
 the tongue. From the tongue the blood is returned to the 
 heart principally through the lingual vein, which begins at the 
 ranine vein beneath the tip of the tongue, passes backward under 
 cover of the mucous membrane, following the course of the 
 lingual artery until the hyoglossus muscle is reached, beyond 
 which point the fibers of the muscle separate the artery from 
 the vein. After receiving the sublingual and dorsalis linguae 
 veins, the course of which corresponds to the arteries of the 
 same name, the vein passes backward and downward and 
 empties into the internal jugular. 
 
 Nerves of the Tongue. 
 
 The mandibular division of the fifth nerve by its lingual 
 branch supplies the papillae of the anterior portion and sides of 
 the tongue, while the lingual branch of the glossopharyngeal 
 supplies the circumvallate papillae, the base, and posterior sides. 
 A few branches of the superior laryngeal are distributed to the 
 back part of the root of the organ. The motor nerve of the 
 tongue is the hypoglossal or nintli, supph'ing both the extrinsic 
 and intrinsic muscles.'^' 
 
 ■* A description of die lower teelli will be found in another chapter. 
 
CHAPTER II. 
 
 THE BONES OF THE MOUTH: THE SUPERIOR MAXILL/E, THE PALATE 
 BONES, THE INFERIOR MAXILLA OR MANDIBLE. 
 
 SUPERIOR MAXILLARY BONES. 
 
 The superior maxillary bones, two in number, one on each 
 side of the median hne or center of the face, are irregular in 
 shape, and may be classed as the largest bones of the face, with 
 the probable exception of the mandible or inferior maxilla. 
 From the central position which they occupy they contribute 
 largely to the bony framework of this portion of the skull. They 
 are not only instrumental in forming the major portion of the 
 roof of the mouth or hard palate, but assist in the formation of 
 the floor of the orbit, and the sides and base of the nasal cham- 
 ber. They furnish a solid and firm foundation for the sixteen 
 upper teeth, and by their variety in form contribute much to 
 the character and quality of the voice. The outer or facial 
 surface of these bones provides attachment for numerous mus- 
 cles. Each superior maxillary bone presents for examination a 
 body, four surfaces, and four processes. The body may be 
 described as forming an irregular triangle, its general contour 
 depending much upon the temperament of the subject and con- 
 sequent character of the teeth. Within the body of the bone is 
 an irregular cavity, the maxillary sinus or antrum of Highmore. 
 
 The four surfaces of the body of the bone are the superior or 
 orbital, the lateral or facial, the proximal or nasal, and the pos- 
 terior or zygomatic. 
 
 The Superior or Orbital Surface, which assists in forming 
 the greater portion of the floor of the orbit, is slighdy concave 
 over its anterior two-thirds, and somewhat convex over the re- 
 maining or posterior third. The three borders of this surface 
 form almost an equilateral triangle, and are named, as indicated 
 by their location, the anterior, the posterior, and the mesial or 
 proximal. The anterior border is convex from before backward 
 
 51 
 
and slightly concave throughout its length. That portion which 
 forms a part of the lower border of the completed orbit is smooth, 
 while the remaining portion is roughened to form an articulation 
 with the malar bone. The posterior'' border extends from the 
 center of the malar process backward and inward to the orbital 
 process of the palate bone, which articulates with the superior 
 maxillary at this point. A portion of this border, together M'ith 
 the orbital process of the palate bone, is instrumental in forming 
 the anterior boundary of the sphenomaxillary fissure. 
 
 The mesial or proximal border is marked by an irregular 
 thin edge, which articulates with a portion of two bones, the 
 lacrymal anteriorly, and the os planum of the ethmoid bone 
 posteriorly. Only the posterior two-thirds of this border pre- 
 sents an articulating edge, the remaining or anterior third being 
 smooth and forming the commencement of the lacrymal groove, 
 which in the articulated skull becomes a canal, passing down- 
 ward and backward to communicate with the inferior meatus 
 of the nose. Beginning at the posterior border of this sur- 
 face and running forward will be found a deep groove — the 
 infra-orbital groove. When near the center of the surface, this 
 groove dips down and is covered by a layer of bone, from which 
 point it passes forward as a canal, — the infra-orbital canal, — 
 making its exit at a point about yi of an inch below the border 
 of the orbit, near the center of the facial surface of the bone, 
 the foramen thus formed being the infra-orbital foramen. Near 
 the root of the nasal process, and immediately within the ante- 
 rior border of this surface, is a small depression which marks 
 the origin of the inferior oblique muscle of the eyeball. 
 
 The Lateral or Facial Surface (Fig. ii). — This surface is 
 made up of the anterior part of the bone ; it is irregularly con- 
 cave, and presents a greater variety in form than any other part 
 of the bone, with the single exception of the palatal process. It 
 is bounded above by the infra-orbital ridge, and the roughened 
 surface of the malar process which articulates with the malar 
 bone ; below, by the border of the alveolar process ; anteriorly, 
 by the frail concave border of the opening into the nasal cavity, 
 the anterior nasal spine, and the perpendicular margins of the 
 bone beneath. Posteriorly, this surface is separated from the 
 
SUPERIOR MAXILLARY BONES. 
 
 S3 
 
 posterior or zygomatic surface by a strong projecting eminence, 
 the malar process. 
 
 The canine fossa is a deep depression, situated almost in the 
 center of this surface, the bone at this point being extremely 
 thin and closely related to the floor of the antrum. The concave 
 floor of this fossa is frequently traversed by one or two smaller 
 convex ridges, corresponding to the roots of the bicuspid teeth. 
 
 The canine eminence is a prominent ridge running vertical to 
 
 Nasal Process 
 
 Orbital Surface 
 
 Malar Process 
 
 Tuberosity 
 
 Fig. It. — Left Superior Maxilla, Outer or Facial Surface. 
 
 the body of the bone immediately anterior to the canine fossa, 
 and corresponding in position to the root of the cuspid tooth, 
 the size and type of the tooth having much to do with its extent 
 and prominence. This ridge gives origin to one of the depressor 
 muscles of the upper lip, and also to one of the depressor 
 muscles of the wing of the nose. The incisive or viyrtiform 
 fossa is a depression found between the canine eminence and the 
 inner margin of the bone. The depth of this tossa is in a meas- 
 
54 ANATOMY. 
 
 lire controlled by the position and size of the teeth, and by the 
 amount of prominence in the canine eminence. 
 
 The infra-orbital forameji, which transmits the infra-orbital 
 nerves and blood-vessels, is immediately below the center of the 
 infra-orbital ridge, and near the upper margin of the canine 
 fossa. It is oval in form and faces almost directly toward the 
 median line. Between this foramen and the infra-orbital ridge 
 is the point of origin for the principal levator muscle of the upper 
 lip, the levator labii superioris proprius. The whole extent of 
 the facial surface may present a number of vertical ridges, or 
 the same space may be regular and smooth, the condition being 
 controlled by the size and shape of the tooth-roots and the 
 thickness of the bone covering them. One of the levator 
 muscles of the angle of the mouth, the levator anguli oris, is 
 attached to this surface near the upper border of the canine 
 fossa. 
 
 The Proximal or Nasal Surface (Fig. 12). — Above, this 
 surface presents a large, irregular opening into the maxillary 
 sinus, this opening being nearly closed in the articulated skull 
 by neighboring bones. In front of the opening into the sinus, 
 and standing perpendicular from the body of the bone, is the 
 strong ascending plate of the nasal process, marked near its 
 lower extremity by a rough, horizontal ridge, the inferior tur- 
 binated crest, which gives attachment to the inferior turbinated 
 bone. The smooth, concave surface immediately above this 
 ridge corresponds to the middle meatus of the nose, and forms 
 the external wall of that passage. Below the opening into the 
 sinus and the nasal process, and occupying the anterior two- 
 thirds of the middle of this surface, is a large semicircular space, 
 forming the outer wall of the inferior meatus of the nose. 
 Below this space, and projecting inward from the body of the 
 bone, is the palatal process, which articulates with the correspond- 
 ing process of the opposite bone. At the anterior superior 
 angle of the nasal surface, and passing downward just behind 
 the nasal process, is the lacrymal groove. In the articulated 
 skull this groove becomes a canal, the lacrymal canal the 
 ethmoid and the inferior turbinated bones assisting in its forma- 
 tion. The canal passes downward and slightly backward, and 
 
SUPERIOR MAXILLARY BONES. 55 
 
 opens into the inferior meatus of the nose. It is aioout ^4 of an 
 inch in length, and gives passage to the lacrymonasal duct. 
 
 T/ie lacrymal tubercle is a small prominence of bone formed 
 at the junction of the anterior border of this surface, with the 
 external surface of the nasal spine. The extended portion of 
 the lacrymal duct, the lacrymal sac, finds lodgment at this point. 
 
 Tlie posterior palatine or palatomaxillary canal commences 
 
 Inferior Meat 
 
 Palale Process 
 
 Nasal Process 
 
 Middle Meatus 
 
 Tlni7i plate of 
 hone over Lac- 
 rymal Groove 
 
 Fig. 12. — Left Superior Maxilla, Internal, Proximal, or Nasal Surface. 
 
 near the middle of the posterior border of this surface, appear- 
 ing in the disarticulated bone as a groove, and, passing downward 
 and forward, gives passage to the posterior palatine vessels and 
 anterior palatine nerves. The canal is made complete by the 
 articulation of the superior maxillary with the vertical plate of 
 the palate bone. On the posterior portion of the nasal surface, 
 extending from the irregular opening into the antrum downward 
 
S6 ANATOMY. 
 
 to a point opposite the palatal process, is a roughened surface 
 about i^ of an inch in width, which marks the extent of articu- 
 lation with the palate bone. 
 
 The proximal or 7iasal sicrf ace presents four borders — superior, 
 inferior, anterior, and posterior. The superior border is irregular, 
 and articulates with the lacrymal and ethmoid bones. The inferior 
 border projects inward, and forms a strong horizontal plate — the 
 palatal process. This process defines the border from before 
 backward to the posterior third, at which point it is marked by 
 the lower border of the roughened surface which articulates with 
 the palate bone. The anterior border is sharp, frail, and irreg- 
 ular in outline, and forms the free margin of the opening into 
 the nasal cavity. The posterior border is marked by the inner 
 margin of the zygomatic surface, being smooth upon its upper 
 half, and roughened upon its lower half, at which point it articu- 
 lates with the palate bone. 
 
 The Posterior or Zygomatic Surface (Fig. 1 1 ). — This sur- 
 face is partly convex and partly concave, and is bounded above 
 by a well-defined margin, which serves as the dividing-line be-i 
 tvveen this and the superior or orbital surface. This border is 
 also marked by a roughened margin on the posterior portion of 
 the malar process, the orbital pordon of the palate bone articu- 
 lating at this point. The major portion of this border is smooth 
 and rounded, forming the lower border of the sphenomaxillary 
 fissure, and marked by a notch, the commencement of the infra- 
 orbital groove. The outer border of the surface is formed by 
 the malar process, and by a line drawn from this point directly 
 downward to the alveolar process. The inner border is smooth 
 and somewhat irregular above, while below it is roughened for 
 articulation with the palate bone. 
 
 The htberosity, which also forms a portion of the inferior 
 border of this surface, is a roughened and rounded eminence ot 
 bone, and is penetrated by a number of nutrient vessels, which 
 enter the many small foramina at this point. Between the 
 tuberosity and the body of the zygomatic surface are several 
 large apertures leading into canals, which pass into, and give 
 nourishment to, the substance of the bone. These canals trans- 
 mit the posterior dental blood-vessels and nerves, one of which, 
 
SUPERIOR MAXILLARY BONES. 57 
 
 after passing over the outer wall of the maxillary sinus, unites 
 with the anterior dental canal. The tuberosity is posterior to, 
 and above, the third molar tooth, in some instances extending 
 directly backward from this tooth for the distance of half an inch 
 or more, but usually the tooth penetrates the base of the tuber- 
 osity, leaving but a thin layer of bone posterior to it. 
 
 The inferior border ol the posterior or zygomatic surface is 
 formed by that portion of the alveolar process which supports 
 the second and third molar teeth. 
 
 The bone presents four processes for examination — the nasal, 
 the malar, the palatal, and the alveolar. 
 
 The nasal process is a strong, irregular piece of bone, stand- 
 ing vertically above the body of the bone proper, and forming the 
 lateral boundary of the nose. This process is greatly increased 
 in. strength by the infra-orbital ridge joining it at or near its 
 base, and ascending its external anterior surface to some extent. 
 That portion of the process posterior to its junction with the 
 infra-orbital ridge assists in forming the inner wall of the orbit. 
 
 The external or ante7-ior surface of the nasal process is marked 
 by a number of shallow grooves, traces of the development of 
 the bone. Scattered over this surface are a number of small 
 foramina, the entrances to minute canals transmitting nutrient 
 vessels to the body of the bone. This surface gives origin to 
 one of the lip muscles, the levator labii superioris alaeque nasi. 
 
 Tlie ijiternal surface of the nasal process is usually described 
 as including all that portion between the superior border and 
 the floor of the anterior nares. The surface is marked by two 
 concave portions and two ridges. The two ridges divide the 
 surface into three parts — the superior meatus, the middle meatus, 
 and the inferior meatus of the nose. The supenor meatus is the 
 smallest of the three, and occupies the slightly concave space 
 above the superior ridge. The middle meatus, partly concave, 
 and partly convex, includes the space between the superior and 
 the inferior ridges, and extends from the free margin of the 
 bone in front to the lacrymal groove behind. The inferior 
 meattcs, which is much the largest, occupies all that concave 
 surface between the inferior ridge above and the palatal process 
 below, and extends from the anterior margin of the bone back- 
 
58 ANATOMY. 
 
 ward to the point of articulation with the palate bone. The two 
 ridges previously referred to are known as the supeinor tur- 
 binated C7'est, which articulates with the middle turbinated bone> 
 and the inferior turbinated crest, which articulates with the 
 inferior turbinated bone. 
 
 The malar process is a large, irregular portion of bone 
 situated at the angle of separation between the facial and zygo- 
 matic surfaces, and presents a triangular, roughened surface for 
 articulation with the malar bone. The superior boundary of 
 this process is formed by the orbital surface and the outer end 
 of the infra-orbital ridge ; the inferior boundary may be marked 
 by an irregular imaginary line running from the upper margin 
 of the canine fossa to a point between the first and second 
 molar teeth, while the posterior inferior boundary may be traced 
 from the outer superior angle of the zygomatic surface down- 
 ward and forward to the point above referred to. This process, 
 as well as the nasal process, is subject to much variety in form 
 and general outline. The malar process, assisting as it does in 
 forming what is commonly called the cheek bone, is particularly 
 variable in size, and in certain types and races it is so prominent 
 as to become a controlling feature in the facial form. One of 
 the muscles of mastication — the masseter — has a portion of its 
 origin from the malar process. 
 
 The palatal process is more directly interested In the forma- 
 tion of the cavity of the mouth than any other portion of the 
 superior maxillary bone. By articulating with its fellow of the 
 opposite side, It forms about three-fourths of the hard palate or 
 roof of the mouth, the remaining fourth being formed by a por- 
 tion of the palate bones. It Is thick and strong, and projects 
 horizontally Inward from the Inner surface of the body of the 
 bone. It presents two surfaces for examination, — a superior or 
 nasal surface, and an Inferior or oral surface. 'Wi^ superior or 
 nasal surface Is smooth and more or less concave, and forms the 
 floor of the nares. The inferior or oral S7irfacc is also concave, 
 but Is much roughened by numerous small projections, between 
 which are lodged the mucous glands. Upon the anterior por- 
 tion of this surface are a number of small foramina, which mark 
 the entrance to numerous small canals giving passage to nutrient 
 
SUPERIOR MAXILLARY BONES. 59 
 
 vessels to supply the body of the bone. Near the center of the 
 posterior third are the anteroposterior grooves, which accommo- 
 date the posterior palatine nerves and blood-vessels. This 
 process also presents for examination three borders and various 
 other points of interest. The three borders are the anterior, 
 posterior, and mesial. The anterior border is thick and some- 
 what irregular ; the posterior border is thin and frail, and articu- 
 lates with a portion of the palate bone. The mesial border 
 presents a wide articulating surface in front, behind it is narrow, 
 the whole extent of this border articulating with the correspond- 
 ing process of the opposite bone. 
 
 The Nasal Spine. — At the anterior superior angle of the 
 palatal process is a well-defined spine, — the nasal spine, — being 
 formed by a prolongation of the process beyond the level of the 
 facial surface of the bone. This process, when articulated with 
 its fellow of the opposite side, forms the base of the nose. 
 
 The Nasal Crest. — Beginning at the base of the nasal spine, 
 and extending backward along the median border of the bone, 
 is a sharp, irregular ledge of bone, the nasal crest. This portion 
 of the process articulates with the vomer. 
 
 The incisor crest is a continuation of the nasal crest anteriorly, 
 projecting beyond the nasal spine in the form of a sharp, spear- 
 like point. 
 
 The iiicisive foramen, ox foramen of Stenson, is situated imme- 
 diately back of the incisor crest, and leads downward and for- 
 ward from the nasal chamber toward the mouth, entering that 
 cavity just back of the central incisor tooth. This passage in 
 the single bone is a simple groove, but in the articulated skull 
 it becomes the anterior palatine canal, which, after passing down- 
 ward, opens on the nasal surface of the palatal process by four 
 foramina — the incisive foramina, and the foramina of Scarpa, or 
 the naso-palatine foramina. These foramina transmit the naso- 
 palatine nerves. 
 
 The palatal process of the superior maxilla is subject to a 
 greater variety in form than any other portion of the bone, 
 this variation in the articulated skull being the cause of the 
 many different curves assumed by the roof or dome of the 
 mouth. 
 
The Alveolar Process. — This process forms the lower 
 margin of the bone, and extends from the base of the tuberosity 
 behind to the median Hne in front, at which point it articulates 
 with the same process of the opposite bone. It has an outer 
 and an inner margin corresponding to the buccal and palatal 
 surfaces of the roots of the teeth, which are firmly imbedded in 
 it. Its general form from before backward is that of a gradual 
 curve, somewhat variable in different bones, the extent of this 
 variation depending on the type or race to which the bone 
 belongs. The body of the process is made up of an outer and an 
 inner plate, which are connected by numerous septa of cancel- 
 lated bone. The outer plate of the process is continuous with 
 the facial and zygomatic surface of the body of the bone, and 
 assists in forming these surfaces. It is quite thin and frail, and 
 the position of the alveoli beneath are well shown by the 
 numerous vertical ridges upon it. The inferior margin of the 
 outer plate is reinforced by an additional thickness of bone, 
 forming the border of the alveolar sockets. That portion of 
 the plate supporting the molar teeth is heavier in general, and 
 the position of the sockets are not so plainly outlined. The 
 inner plate of the alveolar process is much heavier and stronger 
 than the outer plate, and extends from the margins of the 
 alveoli below to the palatal process above. The inferior margin 
 of this plate is not reinforced except in the region of the 
 molars. The construction of the inner plate is, to a great 
 degree, controlled by the shape and position of the palatal pro- 
 cess. In the lymphatic temperament this process, when articu- 
 lated with its fellow, forms a flat or shallow dome to the oral 
 cavity, and in so doing gradually curves into the alveolar pro- 
 cess, giving it additional thickness. The depth of the process 
 in this type is not great, and the roots of the teeth are short and 
 heavy in proportion. In the bilious temperament the inner alveo- 
 lar plate is deep and abrupt, extending from the inferior margin 
 upward in almost a perpendicular direction to the palatal process, 
 which joins it almost at right angles. The alveolar process gives 
 origin to one of the cheek muscles, — the buccinator, — which is at- 
 tached to the outer plate near its upper margin, and direcdy over 
 the space occupied by the second bicuspid and first molar teeth. 
 
SUPERIOR MAXILLARY BONES. 6i 
 
 The Alveoli orTooth Sockets. — These cavities,which are variable 
 in number, are formed by the outer and inner plate of the 
 alveolar process, and by numerous connecting septa of bone 
 placed between the two plates. The shape and depth of these 
 cavities is regulated by the form and length of the roots of the 
 teeth which they support. The first socket, or that next to the 
 mesial surface of the bone, gives support to the central incisor 
 tooth. It forms almost a perfect cone, and has an average depth 
 of half an inch. Its lower border is circular, and the anterior or 
 labial portion describes a larger circle than the posterior or palatal 
 half. The mesial and distal walls are somewhat flattened. The 
 second cavity, proceeding backward from the median line, sup- 
 ports the lateral incisor tooth. It is also conic, but much 
 smaller than the preceding. It is seldom over y^ to y^ of an 
 inch in depth. It is much flattened on its mesial and distal walls, 
 giving the appearance of an oblong, rather than a round, cavity. 
 This socket, as well as that for the central incisor, occupies 
 an almost vertical position in the process. Very frequently the 
 socket for the lateral incisor presents a slight distal curve at its 
 upper extremity. The third socket, or that giving support to 
 the cuspid tooth, is much larger and deeper than either of those 
 previously described. It extends upward, inward, and backward 
 to the average depth of fg to ^ of an inch. 
 
 In transverse section, its labial wall presents a much larger 
 circle than its palatal margin. The labial and distal walls are 
 much flattened and somewhat convex. The general direction 
 of this socket is slightly to the distal. The socket which sup- 
 ports the first bicuspid is usually divided from mesial to distal 
 by a thin septum of bone, thus forming an outer or buccal 
 socket, and an inner or palatal socket. This division seldom 
 exists to the full depth of the cavity, but usually begins about 
 midway of its length. The lower margin of this socket is 
 oblong or egg-shaped, its outer or buccal portion forming 
 a larger curve than its palatal. The lateral walls are slightly 
 concave or flattened, until the point of separation is reached, 
 when they become more circular, the alveoli above this point 
 becoming cone-shaped. It is not uncommon for this socket 
 to be a single cavity, and when thus formed it resembles a 
 
flattened cone, with the buccal and palatal margins rounded. 
 The next socket gives support to the second bicuspid tooth, in 
 most instances being a single cavity, but in rare instances it is 
 divided near its upper extremity. In general outline it re- 
 sembles the socket for the first bicuspid. 
 
 The socket for the first molar is much larger than any of 
 those previously described ; its inferior margin presents a cir- 
 cular outline on its buccal and palatal portions, the former curve 
 being larger than the latter. The mesial and distal walls are 
 flattened and slightly concave. The upper three-fourths of this 
 socket is divided into three separate compartments, being so 
 arranged that two are upon the buccal and one upon the palatal 
 side. The septa separating the two buccal cavities from the 
 palatal cavity are heavy and strong, while that placed between 
 the two buccal sockets is thin and frail. The two buccal cavities 
 are usually flattened upon their mesial and distal sides. The 
 palatal socket is larger and somewhat deeper than the buccal, 
 the average depth of all being about ^/^ of an inch. The 
 socket for the second molar is similar in most respects to 
 that for the first molar, except that it is somewhat smaller. 
 The same description might answer for the third molar socket, 
 which in general is similar to the alveoli for the other molars. 
 It is smaller than the second molar socket, and may be a 
 single cavity, or it may be divided into three or more compart- 
 ments. 
 
 Articulations. — The superior maxillary bone articulates with 
 its fellow of the opposite side, with the frontal, lacrymal, ethmoid, 
 palate, vomer, malar, and inferior turbinated bones. Occasion- 
 ally it articulates with the sphenoid bone. 
 
 Attachment of Muscles. — The muscles attached to this 
 bone are eleven in number, and are as follows : 
 
 Compressor nares, Internal pterygoid, 
 
 Orbicularis oris, Orbicularis palpebrarum, 
 
 Levator labii superioris alaeque Levator labii superioris proprius, 
 
 nasi, Inferior oblique, 
 
 Levator anguli oris, Buccinator, 
 
 Depressor alje nasi, Masseter. 
 
SUPERIOR MAXILLARY BONES. 
 
 63 
 
 Blood-supply. — The maxilla receives its vascular supply 
 from numerous large arteries. They are derived from the 
 alveolar, infra-orbital, nasopalatal, descending palatal, eth- 
 moidal, nasal, frontal, and facial branches. 
 
 Development. — The superior maxilla arises from four points 
 of ossification, which are .deposited in membrane. These four 
 centers make their appearance as early as the eighth fetal week, 
 this early beginning making it somewhat difficult to accurately 
 follow its growth. The four centers are named, as located, pre- 
 
 FiG. 13.— Left Superior Maxillary, about the Third Year, Enlarged. 
 
 maxillary, maxillary, malar, and prepalatal. The premaxillary 
 nucleus gives rise to the incisive portion of the bone, or that 
 part supporting the incisor teeth. During early life this division 
 of the bone is separated from the body of the bone, and is 
 known as the premaxillary portion (Fig. 13). Union between the 
 premaxillary portion and the maxilla proper takes place about 
 birth, and the suture thus formed is visible on the facial surface 
 until the sixth or seventh year, and on the palatine surface until 
 
64 ANATOMY. 
 
 the adult period. The palatal suture extends as far back as 
 the posterior border of the anterior palatal canal. This nucleus 
 also sends a narrow process upward which forms part of the 
 outer boundary of the anterior narial aperture. On the palatal 
 aspect it furnishes a speculum which surrounds the anterior and 
 mesial walls of Stenson's canal. The posterior limit of the 
 premaxillary portion is indicated by the suture on the palatal 
 surface. The maxillary nucleus forms the greater portion of 
 the body of the true maxilla and the nasal process. The malar 
 center gives origin to the malar process, and all that portion 
 
 Fig. 14. — Developing Maxillary Bones about the Fifth Month after Birth. 
 
 external to the infra-orbital groove. The prepalatine center 
 gives rise to the nasal surface of the bone and that portion of 
 the palatal process posterior to Stenson's canal. 
 
 Developine7it of the Alveolai- Process. — This process is rep- 
 resented at birth by the walls of a deep groove, in which are 
 lodged the partly calcified, deciduous teeth and the germs of 
 most of the permanent teeth (see Development of the Teeth). 
 
 The growth of the process continues with the growth of the 
 teeth until, finally, at about the seventh month after birth, the 
 dental organs are completely encased within its walls. With the 
 
SUPERIOR MAXILLARY BONES. 65 
 
 decalcification of the roots of the deciduous teeth comes the loss 
 of the process surrounding them, and, as the permanent teeth 
 advance to take their place in the arch, the process is again built 
 up about their roots. 
 
 The Maxillary Sinus, or Antrum of Highmore* (Fig. 
 12). — This is a large cavity situated within the body of the 
 maxilla. Its general shape is that of a pyramid, with its base 
 directed toward the median line, or nasal surface, its apex 
 pointing toward and extending into the malar process, and, in 
 some instances, penetrating the malar bone. The size of the 
 cavity varies in different subjects and in the opposite bone of 
 the same subject. The average capacity is about three fluid- 
 rams, but this may be increased to six or eight fluidrams. 
 The size of the bone and the prominence of the malar process 
 control, in a measure, the size of the cavity ; but not infrequently 
 the largest bone will present the smallest sinus. Sex also 
 appears to exert a controlling influence over the capacity of the 
 cavity, it being greater in the male than in the female. In youth 
 the cavity is quite small, the walls being much thicker propor- 
 tionately than in the adult. The walls of the sinus in the 
 matured subject are quite thin and frail, and are four in number. 
 The superior wall is formed by a thin plate of bone, the floor of 
 the orbit. This surface is almost flat, and serves as a roof to 
 the cavity. Near the anterior margin of this surface is a thick 
 rib of bone which marks the course, and forms one of the walls 
 of the infra-orbital canal. 
 
 The inner wall, or that looking toward the nasal surface, is 
 formed by the thin bony layer separating this cavity from that 
 of the nares. The outer or lateral surface, formed by the facial 
 and zygomatic surfaces of the bone, is smooth, and convex from 
 before backward. Near the center of this surface the cavity 
 may penetrate the malar process, and in the disarticulated skull 
 would present an opening at this point. The inferior wall is 
 formed by the alveolar process, and is marked by a number of 
 irregular eminences corresponding to the roots of the neighbor- 
 ing teeth. The teeth referred to are generally the first and 
 
 * Described separately, in preference to including in general description of the bone. 
 S . 
 
second molars, and occasionally the second bicuspid. It is not 
 unusual for the roots of one or more of these teeth to penetrate 
 the floor of the sinus, in consequence of which the lining mem- 
 brane of the cavity may suffer disease generated in the teeth. 
 
 The inferior wall is much the strongest of the four, and, besides 
 the unevenness of the surface produced by the tooth-roots, it 
 frequently supports a number of thin, bony partitions, which 
 may completely or pardy divide the floor of the cavity into 
 numerous small compartments. 
 
 The posterior portion of the lateral wall is marked by the 
 posterior dental canals, which give passage to the posterior 
 nerves and blood-vessels. In like manner the anterior portion 
 of the lateral wall is grooved for the reception of the anterior 
 dental nerves and blood-vessels. Upon the inner wall, or that 
 forming the base of the pyramid, is an opening which communi- 
 cates with the middle meatus of the nose. In the articulated 
 skull this opening is quite small, being from y^ to j^ of an inch 
 in diameter. The correct idea of this opening can not be 
 obtained by studying the individual bone, as the numerous per- 
 forations then to be observed are closed or partly closed by 
 articulation with adjacent bones. The mucous membrane lining 
 the nasal cavity enters the sinus through the small aperture above 
 referred to, and forms a continuous lining over its entire sur- 
 face. Cryer has thrown much light upon the relations of the 
 maxillary sinus to the mouth and teeth, and he has demonstrated 
 beyond a doubt that the relationship existing between the parts 
 is susceptible to extensive variation. He has shown that in 
 some instances the cavity upon one side will be large, with its 
 floor broken by the tooth-roots, while that upon the opposite 
 side will be extremely small and far removed from the root 
 apices. In fact, these researches have so revolutionized the 
 subject under consideration that the foregoing descripdon is 
 only reliable in so far as it treats of the conditions most fre- 
 quently met with. 
 
THE PALATE BONE. 67 
 
 THE PALATE BONE. 
 
 T\\& palate bones (Fig. 15), two in number, are situated imme- 
 diately posterior to the two maxillae, and with them complete 
 the hard palate. They also assist in forming the boundaries 
 of the orbital and nasal cavities, the sphenomaxillary, the 
 sphenopalatine, and the pterygoid fossa, the sphenomaxillary 
 fissure, the posterior ethmoidal cells, and the maxillary sinus. 
 When in position in the skull, these bones are wedged between 
 the maxillae and the sphenoid bone. They are rectangular in 
 outline, and each bone presents for examination a horizontal and 
 
 PTERVGOLD FOSSA 
 
 Fig. 15. — The Two Palate Bones in their Natural Position, 
 Dorsal View. — (Testut.) 
 
 a vertical plate, a tuberosity, and two processes, the orbital and 
 the sphenoid. 
 
 The horizontal plate, smaller than the vertical, assists in 
 forming the hard palate, and corresponds to the palatal process 
 of the maxilla. In entering into the construction of the hard 
 palate the form of this plate varies to the same degree as the 
 palatal plate of the maxilla. In general, it is described as quad- 
 rilateral in shape, having two surfaces and four borders. The 
 superior surface, which is concave from side to side, forms the 
 posterior floor of the nasal chamber. The inferior surface com- 
 pletes the hard palate posteriorly, and presents, near its posterior 
 border, a transverse ridge for the attachment of one of the mus- 
 
cles of the soft palate (the tensor palati) ; the anterior border is 
 serrated for articulation with the palatal process of the maxilla. 
 The posterior border is free, curved, and sharp, and marks the 
 posterior boundary of the hard palate. At the median line this 
 border terminates in a sharp point, which, when articulated with 
 the corresponding bone of the opposite side, forms the posterior 
 nasal spine ; to this point the azygos uvulae muscle is attached. 
 The external border is situated just below the junction of the 
 horizontal and vertical plates. In this portion is a groove which 
 assists in forming a portion of the posterior palatal canal. 
 The internal border is broad and serrated for articulation with 
 its fellow of the opposite side. When the palate bones are in 
 position in the skull, these borders form a ridge, continuing the 
 crest formed by the palatal process of the maxilla, this crest 
 receiving the inferior border of the vomer. 
 
 The vertical plate is thin and frail and extends from the 
 floor of the nasal chamber below to the upper extremity of the 
 sphenopalatine notch above. It has two surfaces and four 
 borders. 
 
 The external stirface is roughened for articulation with the 
 maxilla, excepting a small triangular surface near the upper 
 extremity, which forms a portion of the sphenomaxillary fossa, 
 and a small portion near the middle of the surface close to the 
 anterior border, which forms a portion of the wall of the maxil- 
 lary sinus. Near the posterior boundary of this surface is a 
 vertical groove, which forms, when articulated with the maxilla, 
 the posterior palatal canal, transmitting the descending palatal 
 nerves and vessels. 
 
 Tlie internal stir/ace is divided into three shallow depressions 
 by two transverse ridges — the superior and inferior turbinated 
 crests. The lower depression thus formed assists in the con- 
 struction of a portion of the interior meatus of the nose. The 
 crest immediately above this depression articulates with the infe- 
 rior turbinated bone. The central depression, the largest of the 
 three, forms a portion of the middle meatus of the nose, the 
 crest above articulating with the middle turbinated bone. The 
 superior depression — much smaller but deeper than either of 
 those previously described — forms a large part of the superior 
 
THE PALATE BONE. 69 
 
 meatus. The anterior border of the vertical plate is thin and 
 sharp, the inferior turbinated crest protruding near the center 
 of the border, and forming the maxillary process. This process 
 assists in closing the ma.xillary sinus by being received into the 
 maxillary fissure of the maxilla. At the upper extremity of this 
 border is the orbital process, which presents for examination 
 five surfaces, three of which are articular. The anterior or 
 maxillary surface is directed outward, upward, and downward. 
 It is oblong in form and articulates with the posterior superior 
 angle of the inner surface of the maxilla. The posterior or 
 sphenoidal surface is directed backward, upward, and inward, 
 and articulates with the vertical plate of the ethmoid bone. The 
 superior or orbital surface is triangular in form, extending 
 upward and outward, forming the posterior angle of the floor 
 of the orbit. The external or zygomatic surface is smooth, 
 oblong, and directed outward, backward, and downward, forming 
 a portion of the sphenomaxillary fossa. 
 
 The posterior border of the vertical plate is irregular and 
 serrated, and comes into relation with the internal pterygoid 
 process, terminating below in a prominent tuberosity. This 
 presents three grooves or flutes. The inner receives the in- 
 ternal pterygoid, the outer the external pterygoid process, while 
 the middle groove completes the pterygoid fossa, and gives 
 attachment to a portion of the internal pterygoid muscle. This 
 process also gives rise to the superior constrictor of the pha- 
 rynx. Passing through the tuberosity are a number of small 
 canals, those on the nasal side being the accessory palatal 
 canals. Near the junction of the tuberosity with the horizontal 
 plate is the opening of the posterior palatal canal, and beyond 
 this the small external palatal canals. 
 
 The sphenoidal process is at the superior end of the posterior 
 border. It is variable in shape and curves upward, backward, 
 and inward. It presents a superior, an external and an internal 
 surface, and two borders — an anterior and a posterior. 
 
 The superior surface, the smallest of the three, is marked by 
 a groove, which assists in forming the sphenopalatine canal. 
 This surface articulates with the horizontal portion of the 
 sphenoidal turbinated bone. The external surface assisis in 
 
forming the sphenomaxillary fossa by its anterior portion, while 
 the posterior portion is rough for articulation with the pterygoid 
 plate of the ethmoid bone. The internal surface is instrumental 
 in forming a portion of the outer wall of the posterior nares, 
 and for this purpose is smooth and concave. The anterior 
 border forms the posterior margin of the sphenopalatine notch. 
 The posterior border is serrated, and articulates with the inner 
 surface of the pterygoid process. 
 
 The superior border of the vertical plate is divided by a deep 
 notch or foramen, which divides the orbital from the sphenoidal 
 process. This opening is the sphenopalatine notch or foramen, 
 and transmits the sphenopalatine vessels and nerves from the 
 sphenopalatine fossa to the nasal chamber. 
 
 The inferior border of the vertical plate joins the external 
 border of the horizontal plate. Extending downward and back- 
 ward from the inferior and posterior borders is the pyramidal 
 process, the borders of which are serrated for articulation with 
 both pterygoid plates of the sphenoid bone. 
 
 Articulations. — The palate bone articulates with the sphe- 
 noid, superior maxilla, sphenoidal turbinated, inferior turbinated, 
 ethmoid, and with its fellow of the opposite side. 
 
 Attachment of Muscles. — The following muscles are at- 
 tached to the palate bone : 
 
 Tensor palati, Internal pterygoid, 
 
 Azygos uvulae, Superior constrictor of pharynx. 
 
 Blood-supply. — The arteries which supply this bone are 
 derived from branches of the descending palatine, the spheno- 
 palatine, and pterygopalatine. 
 
 Development. — The palate bone is developed from a single 
 center deposited in membrane. This center makes its appear- 
 ance about the eighth or ninth fetal week, near the line of junc- 
 tion between the horizontal and vertical plates. At birth these 
 plates are about the same length, but soon after this period, 
 w^hen the nasal sinuses Increase in height, the vertical plate 
 begins to lengthen, and continues to do so until it becomes 
 nearly double the length of the horizontal plate. 
 
INFERIOR MAXILLARY BONE. 71 
 
 INFERIOR MAXILLARY BONE. 
 
 The Inferior Maxillary, JMandible, or Lozver Jazv Bone (Fig. 
 16). — This bone, having no osseous union with the skull proper, 
 may be considered as one of its appendicular elements. It is 
 the heaviest and strongest bone of the head, gives support to 
 the sixteen lower teeth, and serves as a framework for the 
 
 Fig. 16. — The Mandible or Inferior Maxilla. Right Side, External or Facial 
 
 Surface. 
 
 lower half or floor of the mouth. It is situated at the lower 
 extremity of the face, and immediately below the superior 
 maxillary and malar bones, while its posterior extremity rests 
 against the glenoid fossa of the temporal bone, forming a mov- 
 able articulation with this cavity. In general, the bone is 
 symmetric in outline, and presents for examination a horizontal 
 portion, or body, and two vertical portions, or ravti, which in the 
 
adult are almost perpendicular to, or at right angles with, the 
 body of the bone. 
 
 The body, or horizontal portion, consists of two identical 
 halves, which meet at the median line and form a slight vertical 
 ridge, the symphysis. This line indicates the point of union 
 between the two lateral halves, which at birth are usually sepa- 
 rated, but soon after this period become firmly united. Each 
 lateral half of the body presents two surfaces — an external and 
 an internal ; and two borders — a superior and an inferior. 
 
 The external or facial surface (Fig. i6) is smooth and 
 convex, and furnishes a number of points for examination. 
 Beginning at the median line, the symphysis ends inferiorly in a 
 prominent triangular surface — the mental protuberance, or chin. 
 
 The Incisive Fossa. — Passing backward from the symphysis, 
 and immediately above the triangular ridge which forms the 
 mental process, is a decided but shallow depression — the incisive 
 fossa. This fossa gives origin to one of the elevator muscles of 
 the chin — the levator menti. Slightly posterior to and below 
 this fossa, on a line corresponding to the position of the cuspid 
 tooth, is an oblong depression for the origin of the depressor 
 muscle of the lower lip — depressor labii inferioris. 
 
 The External Oblique Line. — Extending obliquely across the 
 facial surface from the mental process to the base of the vertical 
 portion of the bone, and continuous with its anterior margin, is a 
 well-defined ridge — the external oblique line. Near the center 
 of this ridge, or below the position occupied by the bicuspid and 
 first molar teeth, is the point of attachment of the depressor 
 muscle of the angle of the mouth — the depressor anguli oris. 
 Somewhat anterior to and above this point is the origin of the 
 depressor muscle of the lower lip — the depressor labii inferioris. 
 Between the line of origin of the depressor anguli oris and the 
 inferior border of the bone is a roughened surface for the attach- 
 ment of the platysma myoides muscle. This roughened surface 
 divides the body of the bone into an upper and a lower portion. 
 That portion above is known as the alveolar or mucous portion, 
 while that below is called the basilar or non-mucous portion. 
 The attachment of the platysma myoides muscle at this point 
 marks the lower boundary or floor of the mouth. The superior 
 
INFERIOR MAXILLARY BONE. 
 
 or alveolar portion of the bone is within the cavity of the mouth, 
 and is covered with mucous membrane and mucoperiosteum ; 
 while the inferior or basilar portion is outside and below the 
 cavity, and is covered with periosteum similar to other bones. 
 
 The Mental, or Anterior De7ital Formnen. — Midway between 
 the superior and inferior border of the body, and usually below 
 the second bicuspid tooth, is a large foramen, — the mental or 
 anterior dental foramen, — giving passage to the mental branches 
 of the inferior dental nerve and accompanying blood-vessels. 
 The position of this foramen is not constant, but, as previously 
 stated, it is usually below the second bicuspid, or between this 
 point and the first bicuspid. The buccinator muscle, which 
 forms a large portion of the lateral wall of the mouth, has its 
 origin from the facial surface of the mandible, being attached to 
 the alveolar portion immediately below the molar teeth. 
 
 The Internal Surface of the Body of the Bone (Fig. 17). 
 — The median line is marked by a slight vertical depression, 
 representing the line of union, and corresponding to the sym- 
 physis externally. 
 
 The Mylohyoid, or Internal Oblique Ridge. — The internal 
 surface is divided into two portions by a well-defined ridge — the 
 mylohyoid, or internal oblique ridge. It occupies a position closely 
 corresponding to the external oblique ridge on the facial sur- 
 face. Beginning near the base of the bone at the median line, it 
 passes backward and upward, increasing in prominence until the 
 base of the vertical portion of the bone is reached, into which it 
 gradually disappears. This ridge gives origin to the mylohyoid 
 muscle, which forms the central portion of the floor of the mouth. 
 In correspondence to the facial surface of the bone, the attach- 
 ment of the mylohyoideus muscle forms the dividing line between 
 the mucous membrane and mucoperiosteum covering the upper 
 portion of the body of the bone, and the periosteum covering 
 the inferior portion. 
 
 TJie Gejiial Tubercles. — Near the lower third, at the median 
 line, is a roughened eminence — the genial tubercles. Taken 
 collectively, these are in two pairs — a superior and an inferior. 
 The superior pair (usually the largest) give origin to the genio- 
 hyoglossus muscle, and the lower pair to the geniohyoid muscle. 
 
74 , ANATOMY. 
 
 The Subling2ial Fossa. — By the side of the genial tubercles, 
 and above the mylohyoid ridge, is a shallow, smooth depression 
 — the sublingual fossa. One of the salivary glands — the sub- 
 lingual — is partially supported in this fossa. 
 
 The Digastric Fossa. — Below the mylohyoid ridge, and near 
 the median line, is a slight depression, — the digastric fossa, — 
 which affords attachment for the dieastric muscle. 
 
 Coronoid Sigmoid 
 
 Internal Oblique Line 
 
 Fig. 17. — The M.^ndibi.e or Inferior Maxilla. Right Side, Internal Surface. 
 
 The Siibmaxillary Fossa. — In the center of the internal sur- 
 face, extending from before backward, between the mylohyoid 
 ridge and the lower border of the bone, is an oblong depression 
 — the submaxillary fossa. In this fossa rests another of the 
 salivary glands — the maxillary. 
 
 The Superior or Alveolar Border. — This border extends 
 from the junction of the body, with the vertical plate on one side, 
 to the corresponding point on the other. The construction of 
 this border is similar to the alveolar border of the superior 
 
INFERIOR MAXILLARY BONE. 75 
 
 maxilla. At the anterior portion it is narrow, but gradually 
 increases in width as it proceeds backward — in some instances 
 following the line of the body of the bone ; in others, inclining 
 inward, or to the lingual. Each lateral half is marked by eight 
 sockets, for the accommodation of the sixteen lower teeth. 
 They are smaller in proportion than the alveolar sockets in the 
 superior maxilla. The socket nearest the median line receives 
 the central incisor tooth, and is the smallest of the number. It 
 has an average depth of Yn of an inch, is conic from above 
 downward, oblong in transverse section, with its lateral walls 
 flattened. The second socket gives support to the lateral 
 incisor tooth ; it is a trifle larger than the central incisor 
 socket, but in other respects is quite similar. The socket for the 
 cuspid tooth is situated at the anterior angle of this border, and 
 is much larger and deeper than either of the incisor sockets. It 
 has an average depth of fV of ^^ '"ch ; its lateral walls are 
 compressed, and sometimes slightly concave. In transverse 
 section the labial wall forms a larger curve than the internal or 
 lingual wall. Passing backward, the next two sockets are for 
 the support of the bicuspids ; they are circular in outline, with 
 an average depth of }4 of an inch. The cavity for the first 
 bicuspid is usually a little larger than that for the second. In 
 rare instances one or the other of these sockets will be divided 
 for the accommodation of two roots. The sockets for the first 
 and second molars present a circular outline upon their free 
 margins, but below they divide into two flattened, cone-shaped 
 cavities — one anterior and one posterior. The flattened sides 
 of these cavities are concave in the center, and at their lower 
 third curve backward. The average depth of these sockets is 
 j4 of an inch. The socket for the third molar, like its superior 
 fellow, is variable both in form and position, frequently being 
 crowded inside or outside of the tooth-line. In some instances 
 it is divided into two or more compartments. The average 
 depth is not over 3s of an inch. 
 
 The alveolar process, which composes the superior border of 
 the body of the mandible, differs from the same process in the 
 superior maxilla in one very important particular: instead of 
 the outer plate being thin and frail, it is equally as heavy as the 
 
76 ANATOMY. 
 
 inner or lingual plate. When the tooth-line is inclined inward 
 from the body of the bone, the posterior outer wall is much 
 heavier than the interior. 
 
 The Infejdor Border of the Body of the Bone. — This border 
 extends from a slight depression, to be observed at the point of 
 union between the body and ramus, to the corresponding point 
 upon the opposite side. It is strong, rounded, and compact, 
 and gives to the bone the greatest portion of its strength. 
 Near its junction with the ramus is the facial notch, so named 
 from the facial artery passing over this point. 
 
 The Ramus, or Vertical Portion of the Bone. — This 
 vertical plate is quadrilateral in outline, and presents two sur- 
 faces — external and internal ; four borders — superior, inferior, 
 anterior, and posterior ; and two processes — the condyloid and 
 the coronoid. 
 
 The external surface is flat and smooth. Near the center it 
 is slightly concave and roughened for the attachment of one of 
 the muscles of mastication — the masseter. 
 
 TJie internal surface presents near the center an oblong open- 
 ing — the itferior dental or mandibular foramen — leading into 
 the inferior dental or mandibular canal. Surrounding this fora- 
 men, on its posterior internal margin, is the mandibular spine, to 
 which is attached the sphenomandibular ligament. Running 
 obliquely downward from the base of the foramen, and beneath 
 the spine, is a decided groove, — the mylohyoid groove, — which 
 accommodates the mylohyoid nerve, artery, and vein, which pass 
 forward to supply the floor of the mouth. Below and behind 
 this groove the surface is roughened for the attachment of an- 
 other muscle of mastication — the internal pterygoid. 
 
 Tlie hferior Dental or Mandibular Canal. — Beginning at the 
 foramen of the same name, this canal enters the body of the 
 bone, passes downward and forward horizontally, until it finds 
 an exit at the mental foramen. This canal lies immediately 
 below the alveolar sockets, and from it are given off smaller 
 canals which open into the tooth-sockets through minute fora- 
 mina. Near the mental foramen the canal divides into a num- 
 ber of smaller ones, which pass forward through the substance 
 of the bone to the sockets of the cuspid and incisor teeth. 
 
INFERIOR MAXILLARY BONE. 77 
 
 The Superior Border of the Ramus. — This border is crescent- 
 shaped, and is otherwise known as the sigmoid notch. Arising 
 from its anterior portion is a flattened, cone-shaped process — the 
 coronoid process. On its posterior portion is a rounded or 
 oblong eminence — the condyloid process. The concave or cres- 
 cent-shaped margin of this border is thin and smooth in front, 
 becoming wider and heavier as it approaches the condyle. 
 
 Tlie Coronoid Process. — The anterior margin of this process, 
 being a continuation of the external oblique line, is heavier at 
 the base than at the apex. The outer surface is smooth, and 
 affords attachment to the masseter, and a few fibers of the tem- 
 poral muscle. The internal surface is marked by a vertical 
 ridge, which passes downward, increasing in size, and finally 
 joining the internal oblique line at a point posterior to the third 
 molar. The surface anterior to this ridge is grooved, and gives 
 attachment to a part of the temporal muscle above, and the 
 buccinator muscle below. The surface posterior to this ridge 
 affords attachment for the greater part of the temporal muscle. 
 The posterior border of this surface is thin, and forms the ante- 
 rior margin of the sigmoid notch. 
 
 The Condyloid Process. — This may be described as the ex- 
 panded extremity of the posterior border of the ramus, and is 
 quite variable in form (see Occlusion of the Teeth). It is 
 divided into a superior or articular portion, and an inferior 
 portion, or neck. 
 
 The articular portion of the condyle is more or less oblong, 
 and is convex above, fitting into the glenoid fossa of the temporal 
 bone, and forming, with the interarticular cartilage which lies 
 between the two surfaces, the temporomaxillary articulation. 
 
 The neck is that constricted portion immediately below the 
 articular surface. It is flattened in front and presents a pit, — 
 the pterygoid fossa, — to which a portion of the pterygoid muscle 
 is attached. Immediately below the point of junction between 
 the neck and the articular surface externally is the condyloid 
 tubercle, to which is attached the external lateral ligament. 
 
 The Inferior Border of the Ramus. — This border is thick, 
 rounded, and continuous with the lower border of the body of 
 the bone. At the point of junction between this and the pos- 
 
78 ANATOMY. 
 
 terior border is the angle of the jaw. The angle has a slight 
 outward inclination, and is roughened for the attachment of a 
 part of the superficial portion of the masseter muscle. 
 
 The anterior border has been described in connection with the 
 coronoid process. 
 
 The posterior border is smooth and rounded on its upper half, 
 the lower half being roughened for the attachment of the stylo- 
 maxillary ligament. 
 
 Attachment of Muscles. — The following muscles are 
 attached to the mandible: 
 
 Buccinator, Superior constrictor of pharynx, 
 
 Depressor labii inferioris, Masseter, 
 
 Depressor anguli inferioris, Orbicularis oris, 
 
 Levator menti, Internal and external pterj'goid, 
 
 Geniohyoglossus, Geniohyoid, 
 
 Platysma myoides, Mylohyoid, 
 
 Digastric, Temporal. 
 
 Development.* — On account of its early functional activity, 
 the mandible is among the first bones to ossify. Develop- 
 ment takes place from six centers for each lateral half, the 
 nuclei being deposited as early as the sixth or eighth fetal 
 week, and after their establishment the developmental process 
 takes place very rapidly. The six centers of ossification are 
 principally named according to their position. The early 
 preparation for the development of the bone is found in the 
 appearance of what is known as the mandibular plates, which are 
 thrown out from the sides of the cranial base, and finally unite at 
 the median line. Not long after this period a cartilaginous band 
 — Meckel's cartilage — is developed in the substance of the man- 
 dibular plates, and it is about this cartilaginous framework that 
 ossification first takes place. The various centers are distributed 
 along the line of Meckel's cartilage, and are named as follows : 
 Mental, dentinary, coronoid, condyloid, angular, and splenic. 
 The mental center provides for the development of that portion 
 of the bone between the median line and the mental foramen. 
 The dentinary center forms the lower border and outer plate, 
 
 * See " Development of the Teeth." 
 
INFERIOR MAXILLARY IJONE. 79 
 
 and provides for die establishment of the crypts inclosing the 
 developing tooth-follicles. 
 
 The coronoid and condyloid centers are both instrumental in 
 constructing these processes, and the angular center provides 
 for the angle of the bone. The splenic center is somewhat later 
 in making its appearance, and from it the inner plate of the 
 
 Fig. iS. — Chart Showing the Evolution and Degeneracy of the Mandible. 
 
 mandible is formed, the line ot union between it and the den- 
 tinary center being indicated by the mylohyoid groove. While, 
 as above stated, most of the centers of development are along 
 or near the line of Meckel's cartilage, the condyloid and coro- 
 noid processes are developed from other cartilage. Soon after 
 
So ANATOMY. 
 
 birth the two lateral halves of the mandible begin to coalesce at 
 the median line, this union taking place from below upward ; and 
 by the eighth or tenth month union is complete and the indi- 
 vidual bone is established. The inferior maxilla is subject to a 
 continuous change in form, not only in regard to its general 
 contour, but also accommodating itself to the movements and 
 growth of the teeth, the former taking place at or about the 
 angle,, while the latter occurs in the alveolar portion of the 
 bone. 
 
 Figure i8 represents the changes which take place in the angle 
 of the mandible from youth to old age. It will be observed that 
 the angle formed in the adult bone, with the teeth in position, is 
 almost a right angle ; and that in youth, with the deciduous teeth 
 in the alveoli, the angle is much more obtuse, which condition is 
 again approached in old age. 
 
 THE HYOID BONE. 
 
 This is a U-shaped bone placed in the upper part of the neck 
 at the median line near the base of the tongue. It has no bony 
 connection with other bones ; it is classed as a floating bone. 
 It is made up of a body and four processes. 
 
 The body, or central portion, is quadrilateral in outline, some- 
 what oblong from side to side, with its anterior aspect convex, 
 and presents a longitudinal ridge which divides it into a supe- 
 rior and an interior portion. It is also usually divided at the 
 median line by a slight vertical ridge. At the point of junction 
 between the longitudinal and vertical ridges a slight tubercle is 
 formed. The anterior surface is given up to the attachment of 
 muscles. The posterior surface of the body of the bone is con- 
 cave and smooth, and is directed backward and downward. The 
 superior border gives attachment to the thyrohyoid membrane, 
 while the inferior border, which is somewhat thicker, gives 
 attachment to the sternohyoid and thyrohyoid muscles. 
 
 The processes known as the greater and lesser cornua are 
 four in number, one of each kind on either side. 
 
 The greater cornua project backward and upward, and their 
 lower borders and anterior surfaces are occupied with muscles. 
 
THE HYOID BONE. 8l 
 
 The thyrohyoid ligament is attached to the posterior terminal 
 corner. 
 
 The lessei^ cornua are short conical pieces of bone, and project 
 upward and backward from the extremities of the body of the 
 bone. They give attachment to the stylohyoid ligaments. 
 
 Development. — Ossification takes place from five centers, 
 one for the body of the bone and one for each cornua. 
 
 Attachment of Muscles. — 
 
 Geniohyoglossus, Sternohyoid, 
 
 Geniohyoid, Lingualis, 
 
 Thyrohyoid, Omohyoid, 
 
 Mylohyoid, Digastric, 
 
 Hyoglossus, Middle constrictor. 
 
 The thyrohyoid ligament, as well as the stylohyoid, and the 
 thyrohyoid membrane are also attached to this bone. 
 
CHAPTER III 
 
 THE TEMPOROMANDIBULAR ARTICULATION. — THE MUSCLES OF 
 MASTICATION. 
 
 TEMPOROMANDIBULAR ARTICULATION. 
 
 Although external to the cavity of the mouth, this articula- 
 tion is so closely associated with the masticatory function that 
 it seems important that a brief description of its construction 
 
 Fig. 19. — Temporomandibular Articulation. 
 
 and action should be given. It receives its name from the two 
 bones which enter into its formation — the temporal and the man- 
 dible, or inferior maxillary. 
 
 This joint is the seat of motion in the mandible, and entering 
 into its construction are bones, ligaments, cartilage, and synovial 
 membrane, these being the tissues essential to all diarthrodial 
 
% 
 
 TEMPOROMANDIBULAR ARTICULATION. 83 
 
 or movable articulations. The various movable joints of the 
 body are classified according to the nature of the movement, 
 and correspond to the mechanical actions known as hinge joint, 
 ball-and-socket joint, gliding joint, pulley joint, etc. The tem- 
 poromandibular joint is of the diarthrodial class, and the move- 
 ments which it possesses are a combination of the gliding 
 movement (arthrodia) and of the hinge movement (ginglymus). 
 The osseous parts entering into the formation of the joint are 
 the anterior portion of the glenoid fossa of the temporal bone 
 and the condyloid process of the mandible (Fig. 19). 
 
 The glenoid fossa may be described as an oblong cavity, 
 with its base directed upward, being bounded anteriorly by a 
 heavy bony ridge (the anterior root of the zygoma), posteriorly 
 by an irregular, flattened portion of the bone (the tympanic plate 
 of the petrous portion). Internally by a union of the anterior 
 and posterior boundaries, and externally by the middle root of 
 the zygoma. The floor of the fossa is traversed by a well- 
 marked fissure — the glenoid fissure (fissure of Glaserius) — which 
 divides the fossa into two portions, an anterior and a posterior. 
 The anterior half is deeper and more concave than the posterior, 
 and is die_ articulatin g portion, being occupied by the condyle, 
 while the posterior half gives lodgment to the parotid gland. 
 
 The condyloid process of the mandible having been de- 
 scribed with that bone, in this connection reference will be made 
 to the variety of forms which it presents, and the influence 
 which it exerts over the nature of the tooth occlusion. This 
 process, when narrow and oblong (Fig. 19), closel)' resembles 
 the ginglymus, or hinge joint, and will be accompanied by teeth 
 presenting deep, penetrating cusps, forming a positive and well- 
 locked occlusion (Fig. 20, B), with little or no lateral motion. If 
 the condyle presents the appearance shown in figure 21, which 
 resembles the enarthrodia, or ball-and-socket joint (although it 
 can not be considered as such), the teeth associated with such a 
 formation will be provided with short, rounding cusps, and the 
 occlusion will be loose and wandering (Fig. 20, A). This differ- 
 ence in the form of the condyle will be accompanied by a corre- 
 sponding variation in the concavity of the glenoid fossa. Not 
 only does the osseous structure in the joint partake of individual 
 
characteristics, but likewise the muscles and ligaments ; their 
 functions being to operate the articulation, they are developed 
 in accordance with the action required of them, which action is. 
 
 in a measure, dependent upon the conditions existing in the 
 mouth. 
 
 Both the condyle and the glenoid fossa are covered with ar- 
 
TEMPOROMANDIBULAR ARTICULATION. 85 
 
 ticLilar cartilage. In the latter this membrane extends over its 
 anterior border, to facilitate the play of the joint. The condyle 
 is held in position in the fossa by three ligaments — the cap- 
 sular, the sphenomaxillary, and stylomaxillary. The caps^dar 
 liga7nentis divided into four portions — anterior and posterior, ex- 
 ternal and internal. The anterior portion consists of a few fibers 
 
 styloid Process Capsular Lij 
 
 Internal Lateral Li; 
 
 Stylohyoid Ligament 
 
 Stylomaxillary Ligament 
 Fig. 22. — Temporomaxillary Articulation — Internal View. — {Deaver.) 
 
 connected with the anterior margin of the fibrocartilage, at- 
 tached below to the anterior margin of the condyle and above 
 to the front of the glenoid ridge. The posterior portion is 
 attached above just in front of the glenoid fissure, and is in- 
 serted into the posterior margin of the ramus of the maxilla 
 just below the neck of the condyle. The external portion. 
 
otherwise known as the external Hgament, is the strongest por- 
 tion of the capsular ligament. It has a broad attachment above 
 to the zygoma, from which point it passes downward and back- 
 ward, and is inserted into the outer side of the neck of the 
 condyle. The internal portion, or short internal lateral ligament, 
 is composed of well-defined fibers, having a broad attachment 
 
 External Lateral Ligament 
 
 Styloid Process 
 Stylohyoid Ligament 
 Stylomaxillary Ligament 
 
 Fig. 23. — Temporomaxillary Articulation — External View. — [Deaver.) 
 
 above to the inner edge of the glenoid fossa and to the alar 
 spine of the sphenoid bone ; below it is inserted into the inner 
 side of the neck of the condyle. 
 
 The sphenomaxillaT-y ^ or long internal lateral ligament, is a 
 thin, loose band, situated some distance from the joint proper. 
 
TEMPOROMANDIBULAR ARTICULATION. 87 
 
 and, as its name implies, has its attachment above to the alar 
 spine of the sphenoid bone, and also to that portion of the tem- 
 poral bone contiguous to it. It passes downward and forward, 
 and is inserted into the mandibular spine of the maxilla. 
 
 The stylomaxillary ligament extends, from the styloid process 
 of the temporal bone, downward and forward, to be inserted 
 into the posterior border of the ramus of the inferior maxilla, at 
 a point between the masseter and internal pterygoid muscles. 
 
 The interM'ticidar Jibrocartilage is an oval sheet placed be- 
 tween the two articulating- surfaces. It is thinnest at the center 
 
 Fig. 24. — Showing Variation in the Shape of the Condyles. 
 
 and becomes thicker as the margins of the fossa are approached, 
 at which point it is connected with the fibers of the capsular 
 ligament. Being placed immediately between the two articular 
 surfaces it divides the joint into two separate synovial cavities. 
 Each of these synovial cavities is occupied by a synovial mem- 
 brane, that occupying the upper compartment being the largest, 
 and passes from the margins of the glenoid fossa above to the 
 upper surface of the interarticular cartilage below. The mem- 
 brane which occupies the lower cavity is smaller, and passes 
 from the under surface of the interarticular cartilage above to 
 the margins of the condyle below. The blood-siipply to this 
 
articulation is derived from the temporal, middle meningeal, and 
 ascending pharyngeal arteries. 
 
 The nerves are derived from the masseteric and auriculo- 
 temporal. 
 
 The movements of this articulation present as great a range 
 
 Temporal Muscle 
 
 Superficial Temporal 
 
 Artery 
 Facial Ne 
 
 Buccinator Muscl 
 
 Masseteric Nerve / 
 Masseteric Artery 
 
 Fig. 25. — Temporal Muscle. — [Deaver.) 
 
 as any other joint in the human body. While the chief move- 
 ment is of the ginglymoid or hinge character, brought into play 
 in simple depression and elevation of the mandible, it also has 
 the power of extension and retraction, may be rotated from side 
 to side, together with all the motions intermediate between 
 
TEMPOROMANDIBULAR ARTICULATION. 89 
 
 these. When the mandible is depressed, the condyle moves on 
 the fibrocartilage, and at the same time glides forward and 
 slightly downward until it rests on the anterior border of the 
 glenoid fossa ;^this movement does not extend sufficiently to 
 allow the condyle to rest upon the extreme summit of the 
 border, except in cases of excessive movement, as in yawning, 
 when the condyle may glide over the summit and the joint 
 become disarticulated. When the mandible is elevated, the 
 condyle slides backward and upward, and at the same time the 
 fibrocartilage, which has extended with it, also retracts until the 
 condyle is settled in the fossa. The movement of extension and 
 retraction is by a horizontal gliding action, by which the mandible 
 is thrust forward and drawn back again. In this movement, as 
 well as in the one previously described, both condyles are sim- 
 ilarly and simultaneously engaged. The lateral or triturating 
 movement is made in an oblique direction. This consists in a 
 rotation of the condyles within the fossae, the cartilage gliding 
 obliquely forward and outward on one side, and backward and 
 inward on the other, this action taking place alternately. This 
 movement is more or less developed in accordance with the 
 nature of the occlusion, being favored by those teeth possessing 
 but little cusp formation, with a consequent loose and wandering 
 occlusion ; while in that type of tooth associated with a long 
 overbite and deep penetrating cusps, forming a firm and well- 
 locked occlusion, this movement will be but little developed. If 
 this movement be employed to throw the symphysis to one side 
 and back again, and not from side to side, the condyle of that 
 side rotates in the glenoid fossa, while the condyle of the oppo- 
 site side is drawn forward and inward. 
 
 The Muscles of Mastication. 
 
 Occupying the back part of the side of the face, and forming 
 an independent group, are four muscles, usually classed as the 
 muscles of mastication. While this is true to a great degree, 
 they are not the only muscles brought into action during this 
 process. They are the masseter, temporal, internal pterygoid, 
 and external pterygoid. The masseter, temporal, and internal 
 pterygoid lift or close the lower jaw, the principal function of 
 
go ANATOMY. 
 
 the external pterygoid being to extend the lower jaw so that the 
 lower teeth pass beyond the upper. The muscles which open 
 the jaws, such as happens when the head is thrown backward, 
 are the muscles of the neck. 
 
 The masseter muscle is made up of a strong quadrate 
 sheet, consisting of two distinct layers extending from the 
 zygomatic arch to the mandible. The layers of which the muscle 
 
 Interarticular flbro-cartilage 
 
 External pterygoid 
 
 Internal pterygoid 
 
 Fig. 20. — The Pterygoid Muscles. — [Morris.) 
 
 is composed differ somewhat in size as well as in the directions 
 which they take. 
 
 Origin. — The superficial layer, much the stronger and larger 
 of the two, arises from the lower border of the malar bone, and 
 from the anterior two-thirds of the zygomatic arch. The deep 
 layer arises from the posterior third of the lower border and 
 from nearly all the internal surface of the zygomatic arch. 
 
 Insertion. — After passing downward and backward it is in- 
 serted into the outer surface of the ramus of the mandible. 
 The deep layer, passing downward and slightly forward, mingles 
 
TEMPOROMANDIBULAR ARTICULATION. 91 
 
 with some of the fibers of the superficial portion, and is finally 
 inserted into the upper half of the ramus of the mandible. 
 
 Action. — To draw slighdy forward, and by its superficial layer 
 to close the jaw. " In closing the jaw it acts with less mechan- 
 ical disadvantage than is usual with muscles. When the pres- 
 sure to be overcome is exerted upon the back teeth, the arm of 
 the lever upon which the power acts is almost as long as that 
 which intervenes between these teeth and the fulcrum. This 
 fulcrum is not at the temporomaxillary joint, but at a point below 
 the neck of the mandible, corresponding very nearly to the 
 lower attachment of the internal lateral ligament. Moreover, 
 the resultant force of the muscle acting, as it does, upward and 
 forward, is perpendicular to the lever, which may roughly be 
 described as a bar extending downward and forward from the 
 neck of the mandible to the point of the chin." (Morris.) 
 
 Relations. — It is covered superficially by the skin and fascia 
 of the platysma myoides, by the risorius and the masseter fascia, 
 by the parotid gland and ducts, facial veins, and portions of the 
 facial nerve. Deeply, the muscle lies in contact with the ramus 
 of the jaw and the buccinator muscle, being separated from the 
 latter by a layer of fat. A small portion of the temporal mus- 
 cle also comes in relation to the deeper lying portion. 
 
 The temporal muscle is covered by a strong membrane, 
 the temporal fascia, which arises from the temporal ridge, and 
 is inserted into both the inner and outer portions of the upper 
 border of the zygomatic arch. Near this point it divides into 
 two distinct layers, one passing to the inner, the other to the 
 outer margins of the zygoma. Below the fascia is continuous 
 with the masseteric fascia. Passing downward from this to the 
 inferior borders of the ramus of the jaw, it envelopes the mas- 
 seter muscle. The muscle itself is radiating and fan-shaped in 
 form, located in the temporal fossa, from which point it descends 
 to the coronoid process of the mandible. 
 
 Origin. — From nearly the entire surface of the temporal 
 fossa, from the temporal ridge, from the entire surface of the 
 temporal fascia, down to its lower attachment to the zygomatic 
 process. 
 
 Insertion. — Into the coronoid process ot the mandible. 
 
Action. — To close the lower jaw, some of its fibers drawing 
 the jaw backward after the other muscles have protruded it. 
 
 Relations. — Its superficial portion is covered by the temporal 
 fascia which separates it from some of the auricular muscles ; 
 branches of the facial nerve, the auriculotemporal nerve, and a 
 portion of the epicranial aponeurosis. The temporal fossa 
 and the external pterygoid muscles are in relation with it 
 deeply. 
 
 The internal pterygoid muscle is a thick, quadrilateral, 
 sheet-like muscle, and receives its name from its origin and rela- 
 tive position. 
 
 Origin. — From the inner surface of the external pterygoid 
 plate; the tuberosity of the palate bone and a small portion of 
 the maxilla. 
 
 Insertion. — Into the internal surface of the ramus of the man- 
 dible at its lower and posterior borders and extending as high 
 as the mandibular foramen and mylohyoid. 
 
 Action. — To close the jaw and at the same time draw it back- 
 ward and throw it toward the opposite side. " The same re- 
 marks which were made with respect to the very small loss ol 
 mechanical advantage in the masseter miiscle apply to this 
 muscle. When closed it will draw the jaw forward ; and also 
 it will help the external pterygoid in drawing the ramus of 
 its own side toward the middle line." (Morris.) 
 
 Relations. — Superficially the internal maxillary vessels, the 
 external pterygoid muscle, the internal lateral ligament, the 
 inferior dental and hngual nerves. Deeply, the submaxillary 
 glands ; the tensor palati and superior constrictor of the 
 pharynx, as well as the stylohyoid and posterior border of the 
 digastric muscles. 
 
 The external pterygoid muscle is composed of two trian- 
 gular sheets, one passing in a horizontal and the other in a 
 vertical direction. It receives its name from its attachment to 
 the pterygoid process of the sphenoid bone as well as its rela- 
 tion to its companion muscle, the internal pterygoid. 
 
 Origin. — It is composed of two distinct heads, an upper and 
 a lower. The upper head arises from the greater wing of the 
 sphenoid bone, from the internal pterygoid ridge, and external 
 
TEMPOROMANDIBULAR ARTICULATION. 93 
 
 to the foramen ovale and foramen spinosum. The lower head 
 arises from the outer surface of the external pterygoid plate. 
 
 Insertion. — The upper head is inserted into the inter-articular 
 fibrocartilage, into the capsule of the joint as well as the neck 
 of the condyle. The lower head is inserted into the neck of the 
 condyle. 
 
 Action. — To draw the condyle and inter-articular fibrocartilage 
 forward and inward. " The combination of these two move- 
 ments produces the oblique movement of the lower molar teeth 
 of one side, forwards and inwards with respect to the upper 
 molars which are their opponents. It should be observed also 
 that this inward movement of one side is the agent by which the 
 ramus of the opposite side is moved outwards. To assist 
 in opening the mouth by depression of the lower jaw. As the 
 transverse axis of this movement passes through the mandible 
 at two points situated below the necks of the rami, it follows 
 that a forward movement of the condyles and necks will assist in 
 the backward movement of the angles and body which accom- 
 panies the depression of the mandible." (Morris.) 
 
 Relations. — Superficially, some of the fibers of the internal 
 pterygoid, the temporal, and part of the masseter muscle. 
 Deeply, the internal pterygoid muscle, the middle meningeal 
 and inferior dental vessels, internal maxillary vessels, and mas- 
 seteric and posterior deep temporal nerves passing behind or 
 through the attachment to the upper head ; the inferior dental 
 and lingual gustatory nerves beneath the lower head. 
 
CHAPTER IV. 
 
 A GENERAL DESCRIPTION OF THE TEETH.-THE PERMANENT TEETH : 
 CLASSIFICATION, SURFACES, ETC.-THE ROOTS OF THE TEETH. 
 —THE DENTAL ARCH. 
 
 A GENERAL DESCRIPTION OF THE TEETH. 
 A Tooth (Fig. 27). — One of the thirty-two speciahzed organs 
 for the seizure and mastication of food, placed at the entrance 
 to the alimentary canal (the mouth). The typical form of a 
 
 tooth is a modified cone or combi- 
 nation of cones, and is composed of 
 two fundamental parts — the crown 
 and the 7'oot or roots. The crown is 
 that part which projects beyond the 
 gum and is visible in the mouth ; 
 while the root is that part which is 
 implanted in the bone and covered 
 by the gum. Intervening between 
 ..^ these two extremities, and usually 
 occupying a portion of each, is a 
 third division — the neck. 
 
 Completely covering the crown of 
 a tooth is a hard, vitreous-like sub- 
 stance, enamel ; * the root Is covered 
 by a hard, bone-like substance, ce^n- 
 jTiQ 27. entum ;* while the interior or body 
 
 of the organ is composed of a hard 
 substance closely resembling bone, the dentin.* The neck of 
 a tooth, which serves to unite the crown to the root, and which 
 is usually formed at the expense of each, is covered partly by 
 enamel and partly by cementum. This brief description in the 
 singular number can best be continued in the plural. Teeth are 
 
 * See Tissues of the Teeth, part II. 
 94 
 
A GENERAL DESCRIPTION OF THE TEETH. 95 
 
 classified according to their form, which is always in accordance 
 with their function, into swiple and complex. In the simple class 
 (Fig. 27) the single modified cone is the predominating form, the 
 free extremity of the crown serving as the base of the cone, while 
 the apex is formed by the free end of the root. Included in this 
 same classification are those teeth which are made up of a double 
 cone, or a simple cone and an inverted cone attached to each 
 other at a common base. The purposes for which such teeth 
 are adapted are those of grasping, incising, and tearing, and 
 they are usually so arranged that the free extremities of their 
 crowns interlock or overhang each other. 
 
 In the complex class (Fig. 28) the external form of the tooth 
 is produced by a combination of cones, some of which are simple, 
 others inverted, but all uniting at a com- 
 mon base — the neck of the tooth. In this 
 class the simple cones form the roots of 
 the teeth, while the crowns are made up 
 of a number of smaller cones, much modi- 
 fied. These teeth are adapted to crush- 
 ing and grinding, and are less inclined to 
 interlock during active service. 
 
 The teeth are divided into two grand 
 divisions — those of infancy and child- 
 hood, called deciduotis or temporary 
 teeth, and those of the adult period, 
 known as permanent teeth. The latter 
 class being most important, will first receive consideration. 
 
 The Permanent Teeth (Fig. 29). — The permanent teeth, 
 thirty-two in number, are divided into those of the superior 
 portion of the mouth, tipper, and those of the inferior portion, 
 lower. In number they are equally divided, each jaw giving 
 support to sixteen. They are firmly imbedded in the alveolar 
 sockets of three of the bones of the mouth, the upper sixteen 
 being attached to the two superior maxillary or upper jaw-bones, 
 and the lower sixteen to the mandible, inferior maxillary, or 
 lower jaw-bone. As above referred to, the attachment of the 
 teeth to the bones is by implantation in sockets, the alveoli (see 
 description, "Bones of the Mouth"). In this attachment there 
 
96 ANATOMY. 
 
 is a special development of bone, closely modeled to the roots of 
 the teeth, and which is subservient to the ever-varying changes 
 which take place during the development of the organs. The 
 joint thus formed between the roots of the teeth and the alveoli 
 is of the immovable or synarthrodial class, and is styled gom- 
 pliosis. Intervening between the roots of the teeth and the walls 
 of the alveoli is a delicate membrane — the alveolodental mem- 
 brane. 
 
 Before continuing the description of the teeth, a further clas- 
 sification, which refers alike to the upper and lower organs, 
 
 Lingual Surfaces 
 
 Labial and Buccal Surfac 
 
 I Surfaces Labial ! 
 
 Fig. 29. — The Permanent Teeth. 
 
 must be presented. This classification is derived from the 
 function and form of the teeth. Figure 29 shows the thirty-two 
 teeth removed from the jaws and placed side by side in two 
 straight lines. In the center is a perpendicular line, which 
 corresponds to the median line or center of the mouth, the teeth 
 at either extremity being those which occupy the back part of 
 the mouth. Without confining the description to either the 
 upper or lower teeth, it will be observed that the first two 
 teeth upon either side of the median line are similarly formed, 
 and all four are called incisors {incidere, to cut); the two largest 
 
A GENERAL DESCRIPTION OF THE TEETH. 97 
 
 incisors, being nearest the median line or center, are called 
 central incisors ; while the two smallest, being placed at the side 
 of the centrals, are known as lateral incisors {lateralis, the side). 
 The third tooth from the median line upon either side is the 
 cuspid (cuspis, a point), so named from possessing a single cusp 
 or point. Passing to the right or left on the chart, or backward 
 in the mouth, the fourth and fifth teeth from the median line are 
 the bicuspids {bi, two ; ciispis, a point), having two points or 
 cusps. The bicuspid nearest the median line is th.& first bicuspid ; 
 that most distant from the median line is the second biacspid. 
 The sixth, seventh, and eighth teeth from the median line upon 
 either side are those of another class, the molars (mola, a mill- 
 stone), being named according to their function, that of crushing 
 or grinding the food. Proceeding from before backward, the 
 molars are denominated first molar, second molar, and tJiird 
 molar. To sum up, the names and number of the permanent 
 teeth may be given by the dental formula, as follows : 
 
 Incisors, f Bicuspids, I 
 
 Cuspids, 1 Molars, \ 
 
 The Surfaces of the Teeth. — The crown of each tooth pre- 
 sents five surfaces, which are variously named, in accordance 
 with the duty which they are called upon to perform or suggest- 
 ive of their location. The outer surface of the incisors and 
 cuspids, or that contiguous to the lips (labia), is called the labial 
 surface ; the corresponding surface of the bicuspids and molars, 
 or that contiguous to the cheeks (buccae), is the buccal surface. 
 That surface of both upper and lower teeth which faces the 
 palate or tongue is characterized as the lingual surface. 
 
 The proximate surfaces of the teeth are named with regard 
 to their relation to the median line, those surfaces nearest to 
 this point being called mesial, those most distant, distal. In 
 addition to these four surfaces, which represent what might be 
 termed the sides of the teeth, a fifth surface is present, that 
 which occludes with the teeth of the opposite jaw, and called 
 the occlusal surface. 
 
 In the incisors and cuspids this surface is formed by the con- 
 verging of the labial and lingual surfaces, forming an edge to the 
 7 
 
free extremity of the crown, named, from its action in mastica- 
 tion, the incisive or ciitting-edge. In the bicuspids and molars 
 the various sides of the crowns remain nearly parallel to each 
 other throughout their extent, thus providing a surface nearly 
 equal to, or greater than, any of the others, and one well adapted 
 to the purposes for which it is intended — that of grinding or 
 crushing the food. 
 
 The Roots of the Teeth. — The upper incisors and cuspids 
 are each provided with one root ; the upper first bicuspid may 
 have one or two roots, most frequently the latter ; while in the 
 second bicuspid a single root is usually present. The upper 
 first and second molars are each supported in the jaw by three 
 roots, and while in the upper third molar three roots are most 
 common, the number is quite variable, ranging from a single 
 cone-shaped root to three, four, five, or even six smaller branches 
 given off from a common base. 
 
 In the lower incisors, cuspids, and bicuspids, a single root is 
 most frequently met with, although the latter class, in rare in- 
 stances, may be provided with two. The lower first and second 
 molars are each provided with two roots, but in the third molar, 
 like its superior fellow, the number may be diminished or in- 
 creased. In the upper molars, two of the three roots are placed 
 above the buccal half of the crown, and are called buccal roots ; 
 the remaining root is placed above the lingual half of the crown, 
 and is designated as the lingual root. In the lower molars, one 
 of the two roots is placed below the anterior or mesial half of 
 the crown, and is named the mesial root, and the other below 
 the posterior or distal half, and is known as the distal root. In 
 those teeth with a complicated root formation, it would seem to 
 be a question whether they are possessed of a single root, with 
 two or more branches, or separate and distinct roots throughout. 
 To determine this, some account must be taken of the point at 
 which the bifurcation or trifurcation takes place. If this separa- 
 tion be in close proximity to the crown, the tooth should be 
 considered as having more than one root (Fig. 30, A) ; but, on 
 the other hand, if the point of separation be some distance from 
 the crown, with a solid mass of root substance intervening, the 
 tooth may be said to possess a single root, with two or more 
 
A GENERAL DESCRIPTION OF THE TEETH. 
 
 branches (Fig. 30, B). In the latter instance, that part of the 
 tooth between the point of separation and the crown is called 
 the root or root base ; while the prolongations beyond the point 
 of separation are known as the branches of the root. 
 
 The roots of the teeth are not only variable in number, but 
 are also subject to much variety in form. In the antei-ior teeth 
 (the incisors and cuspids) the roots are inclined to the form of 
 the simple cone, which form, however, is frequently more or less 
 broken by a slight curvature 
 near their extremities, or by 
 a slight compression of their 
 lateral walls. In the poste- 
 rior teeth (the bicuspids and 
 molars) the roots, root 
 bases, or root branches are 
 all inclined to the conical 
 form, but do not approach 
 so nearly the perfect cone 
 as those of the anterior 
 teeth. These roots are also 
 more or less crooked and " p,^ , -^ 
 
 ric. jO. 
 
 flattened laterally. The free 
 
 extremity of the roots of the teeth, forming- as they do the apex 
 of these cone-like prolongations of the crowns, are known as 
 the apices or apical extremities. 
 
 The extent of the enamel covering to the crowns of the teeth 
 is marked by a well-defined line, which completely encircles the 
 neck of the tooth, the cervical line. 
 
 The Dental Arch (Fig. 31). — The teeth are arranged in the 
 jaws in the form of two parabolic curves, the superior arch de- 
 scribing the segment of a larger circle than the inferior, as a result 
 of which the upper teeth slightly overhang the lower. Figure 
 31 represents the sixteen upper teeth in position in the bone, 
 presenting their occlusal surfaces, a part of their lingual sur- 
 faces also being visible. Viewed in this direction, the gradual 
 change in the crowns of the teeth from the simple incisors to 
 the complex molars may be observed. An examination of the 
 central incisors will show how perfectly they are adapted to the 
 
process of cutting or incising the food, the cutting-edge being 
 sharp and the lingual surface comparatively smooth and 
 unbroken. In the lateral incisors the cutting feature predomi- 
 nates, but the lingual surface is broken near the neck of the 
 tooth by a slight depression, surmounted by a more or less pro- 
 nounced fold of enamel, in many instances resembling a small 
 cusp. The crown of the cuspid tooth furnishes the intermediate 
 form between the simple and the complex. This tooth, instead 
 of being provided with a straight cutting-edge, is surmounted 
 
 Fig. 31. — The Dental Arch. 
 
 at the center of its occlusal surface with a well-defined point or 
 cusp, descending from the summit of which are two cutting- 
 edges, one passing to the mesial and one to the distal. The 
 lingual surface of this tooth presents a marked contrast to the 
 corresponding surface of the incisors, being broad and full, and 
 frequently provided with a prominent ridge of enamel in the 
 region of the neck, showing a rapid approach to the complex 
 form. In the bicuspids the buccal half of the crown is quite 
 similar to the crown of the cuspid, but in the lingual half a com- 
 plete revolution has taken place. The enamel fold — but slightly 
 
A GENERAL DESCRIPTION OF THE TEETH. loi 
 
 apparent in the incisors, and somewhat increased in the cuspids — 
 has now become a fully developed cusp, resulting in the produc- 
 tion of an occlusal surface adapted to crushing or grinding, 
 instead of incising or tearing. In the molars, the increase in 
 the size of the tooth-crown is accompanied with an occlusal 
 surface much more complex than any of the teeth previously 
 described, and one well adapted to its function — that of crushing 
 and grinding the food. 
 
 Arrangements of the Teeth in the Dental Arch (Fig. 31). — 
 Beginning with the upper teeth, the central incisors are found 
 occupying the center of the arch, and are, therefore, slightly in 
 advance of the laterals. These teeth are so implanted in the 
 alveoli that their crowns are not perpendicular, the cutting edge 
 being slightly more prominent than the neck of the tooth. The 
 roots are also somewhat inclined from the median line, and as a 
 result the crowns have a slight mesial inclination, the mesial 
 surfaces approximating each other at or near the cutting-edge, 
 with a slight space intervening at the necks. In certain typal 
 forms, — the bilious, for example, — when the front of the arch is 
 flat, the labial surfaces of these teeth form nearly a direct line 
 from side to side ; while in those types in which the arch is well 
 rounded anteriorly, notably in the sanguine temperament, the 
 labial surfaces of these two teeth form a small segment of the 
 arch, so that the mesial extremity of the cutttng-edge of each 
 tooth-crown is somewhat in advance of the distal. The lateral 
 incisors are similarly implanted in the alveoli, causing their cut- 
 ting-edges to project. The roots of the lateral incisors usually 
 have a stronger distal inclination than those of the centrals, and 
 the crowns show a more marked mesial inclination. The mesial 
 surfaces approximate the distal surfaces of the central incisors at 
 or near the cutting-edge. When the front of the arch is flattened, 
 these teeth are but little less prominent than the central incisors, 
 but when the arch is well rounded they continue the segment be- 
 gun by the centrals, and are necessarily less prominent. While 
 the occlusal surfaces of the teeth are usually considered as form- 
 ing a perfect plane (see Occlusion of the Teeth), the lateral inci- 
 sors are generally a trifle shorter than the centrals. The cuspids 
 may be considered as occupying the corners or turning-points 
 
of the arch. They are more prominently placed than the 
 adjoining teeth, this feature being increased by the bulging or 
 general convexity of their labial surfaces. The extremity of the 
 occlusal surface of the cuspids—/', e., the point of the cusp — is 
 a trifle below the cutting edge of the laterals and about on a 
 line with that of the centrals. While the apical extremities of 
 the roots of the cuspid teeth are directed away from the 
 median line, the crowns assume almost a perpendicular, this 
 condition resulting from a bend in the tooth at the neck. 
 Although the perpendicular position is most commonly assumed 
 by the crown, it is not unusual to find either a mesial or distal 
 inclination present. Reference has been made to the cuspid 
 teeth occupying a position which might be termed the turning- 
 points or corners of the arch, and in most instances it may be 
 thus considered ; but in certain typal forms — the sanguine, for 
 example — the tooth-line is unbroken and passes over the cutting- 
 edges of the incisors, the summit of the cusps of the cuspids, 
 and is continued backward over the buccal cusps of the posterior 
 teeth. The bicuspids are placed nearly perpendicular in the 
 arch, but occasionally deviate from this by a slight mesial or 
 buccal inclination. The length usually corresponds to that of 
 the central incisors, and their buccal surfaces are slightly less 
 prominent than the corresponding surfaces of the cuspid teeth. 
 The increase in the buccolingual diameter of the crowns of the 
 bicuspids over that of the incisors and cuspids results in break- 
 ing the lingual line of the occlusal surfaces. In the bilious and 
 kindred types, the tooth-line is carried directly backward from 
 the cuspid to the first molar, making the buccal face of the 
 bicuspids equally prominent, but when the arch is well rounded 
 the second bicuspid is slightly more prominent than the first. 
 The first and second molars usually assume a perpendicular 
 position, but are occasionally inclined to the distal and buccal. 
 The relative prominence of the buccal as well as the lingual 
 surfaces of these teeth is also controlled by the form of the arch. 
 The occlusal surfaces are about on a level with those of the 
 bicuspids and central incisors, but generally the lack of devel- 
 opment in the distal half of the crown of the second molar 
 results in the production of a slight upward curve to the tooth- 
 
A GENERAL DESCRIPTION OF THE TEETH. 103 
 
 line level at this point (see Occlusion of the Teeth). On account 
 of the limited accommodations afforded it, the position of the 
 upper third molar is quite variable. It may be either to the 
 buccal or to the lingual of the tooth-line, and is usually strongly 
 inclined to the distal. In those cases in which there is a decided 
 dip to the arch (see Occlusion of the Teeth), this tooth is rela- 
 tively shorter than those anterior to it, but when the tooth-line 
 level is a perfect plane, the length of this tooth corresponds to 
 the other molars and bicuspids. 
 
 The lower incisors are placed more nearly in a perpendicular 
 
 Fig. 32. — The Tooth-ltne in the Lower Jaw. 
 
 position than the upper, and a reverse condition exists, in the 
 lateral incisors being a trifle larger than the centrals. The 
 lower cuspids are probably more constant in their position than 
 any class of teeth in the mouth, in nearly all instances assuming 
 a direct perpendicular. Like the upper cuspids, they may be 
 said to establish the corners or turning-points of the inferior 
 arch, and are somewhat more prominent in the tooth-line than 
 neighboring teeth. All of the six anterior lower teeth may be 
 slightly inclined to the mesial. The lower bicuspids and molars, 
 instead of having the buccal inclination possessed by the corre- 
 sponding upper teeth, are inclined to the lingual. The first 
 
ANATOMY. 
 
 molar seldom deviates either to the mesial or the distal, the 
 second molar is generally inclined to the mesial, while the third 
 molar is strongly inclined to the mesial. In the inferior arch 
 the curve formed by the incisors and cuspids is the segment of 
 a smaller circle than the corresponding curve in the superior 
 arch. This curve may be continued over the buccal cusps of 
 the bicuspids and molars, or it may be broken at the cuspid 
 tooth and continued backward in a direct line (Fig. 32). The 
 teeth in the inferior arch are placed directly over the body of 
 the bone as far back as the second bicuspids, while the molars 
 
 Fig. 33. — The Tooth-line in the Lower Jaw. 
 
 frequently overhang the body of the bone by an extension of 
 the alveoli inward (Fig. 33). 
 
 The curve described by the dental arch is quite variable, and 
 this variation is generally referred to in connection with the 
 temperament. Thus, in the sanguine temperament (Fig. 34), the 
 arch is well rounded anteriorly, the circle being continued back- 
 ward to the region of the molars, where the line is broken by 
 slightly inclining to the lingual. In this arch the distance in a 
 straight line from the center of the second molar, on one side, 
 to the center of the corresponding tooth on the other, is about 
 equal to the distance from either of these points to the median 
 line between the central incisors, forming a right-angle triangle. 
 
A GENERAL DESCRIPTION OF THE TEETH. 105 
 
 In the bilious temperament (Fig. 35) the arch presents a broad 
 front from cuspid to cuspid, with but little curve ; at these points 
 it turns abruptly backward, being continued almost in a direct 
 
 
 
 _ Inff^y |J. ' ' : -..^ 
 
 i 
 
 's 
 
 I 
 
 m€ik 
 
 Ij 
 
 H^^P' 
 
 ■-^ 
 
 Fig. 34. — Sanguine. 
 
 line to its extremity. In this arch the side of the triangle (repre- 
 sented by the line from molar to molar) is much reduced in length. 
 In the nervous temperament (Fig. 36) the arch is Gothic in form, 
 
 Fig. 35. — Bilious. 
 
 the segment formed by the anterior teeth being that of a much 
 smaller circle than either of the types previously referred to. 
 The distance from molar to molar is much less than the distance 
 
from molar to median line. In the lymphatic temperament 
 (Fig. 37) the arch is well rounded and broad, the segment being 
 
 
 
 fe. 
 
 
 .^^ -^ ^^ir'' ' 
 
 'B^fS^v/ifck 
 
 
 ,^0IS\4^ ^^K V : 
 
 
 i 
 
 M'iW^'''^ 
 
 r^^f^y<;^B^ 
 
 
 ^ffir v^JW^ 
 
 ^W^ 
 
 Fig. 36. — Nervous. 
 
 that of a much larger circle than any of the above, the side of 
 the triangle formed by the line from molar to molar being of 
 the greatest length. 
 
 Fig. 37. — Lymphatic. 
 
 Interproximate Spaces. — In the mesiodistal direction the 
 crowns of the teeth, as a class, are broader at their occlusal 
 surfaces or cutting-edges than at their necks (Fig. 38). This 
 
A GENERAL DESCRIPl'ION OF THE TEETH. 107 
 
 bell-shaped form of the tooth-crowns causes their proximate 
 surfaces to touch at a point representing their greatest mesio- 
 distal diameter, which is usually near the cutting-edge or occlusal 
 surface. Between this point of contact and the cervical line 
 there exists a V-shaped space, called the interproximate space. 
 These spaces are largest in that class of teeth found in the ner- 
 vous and bilious types, where the necks of the teeth are much 
 constricted, and the bell-shaped crown strongly outlined. In 
 
 Fig. 38. — Section of the Superior Maxilla Showing Interpkoximate Spaces. 
 
 teeth of this class the point of contact is slight, and the inter- 
 proximate spaces are only partially occupied by the gum tissue, 
 leaving a free passage between the point of contact and the gin- 
 gival margins. In the sanguine and lymphatic temperaments 
 the proximate surfaces of the teeth are nearer parallel with 
 one another, thus making the point of contact cover a greater 
 extent of surface, and reducing the size of the interproximate 
 spaces. 
 
CHAPTER V. 
 OCCLUSION OF THE TEETH. 
 
 Fig. 39. — The Teeth in Occlusion. 
 
 As Stated elsewhere, the teeth are arranged in the mouth in 
 the form of two parabohc curves, one of which occupies the 
 upper half and the other the lower half of the cavity. To prop- 
 erly perform their function it is necessary for the upper and 
 lower teeth to come in contact, which they are enabled to do 
 by the movement of the lower jaw, and it is the relation exist- 
 ing between the two when thus brought together that consti- 
 tutes the occlusion of the teeth. During mastication the teeth do 
 not only occlude, and remain stationary at a given point until 
 the lower jaw is again depressed, but, through the combined 
 movements of the mandible, the lower teeth are made to move 
 from side to side, thus grinding or crushing any substance placed 
 between the occlusal surfaces of the bicuspids and molars. This 
 
OCCLUSION OF THE TEETH. 109 
 
 gliding antagonism of the teeth is commonly termed the articula- 
 tion, and it is important that a distinction be made between the 
 terms "occlusion" and "articulation," the former referring to 
 the relations existing between the upper and lower teeth when 
 brought together normally and held firmly in that position, 
 while the latter relates to the various movements of the teeth 
 after being brought together in occlusion. In the majority 
 of instances the segment described by the superior arch is some- 
 what larger than that formed by the inferior, and the upper 
 teeth project over and are pardy outside of those in the inferior 
 arch. Figure 39 presents a labial and buccal view of the teeth in 
 position in the alveoli, and also in occlusion. It will be observed 
 that the upper teeth are not directly antagonistic to those of 
 the same name in the inferior arch. There are two reasons for 
 the presence of this condition : First, the mesiodistal diameter 
 of the upper central incisors is much greater than that of the 
 corresponding lower teeth ; second, the larger circle present 
 in the superior arch. This arrangement provides that each 
 tooth, instead of being antagonized by a single tooth of the 
 opposite jaw, is met in occlusion by a portion of two teeth. 
 The upper central incisor is met in occlusion by the entire 
 cutting-edge of the lower central incisor and the mesial third 
 of the cutting-edge of the lower lateral incisor. The upper 
 lateral incisor is met in occlusion by the distal two-thirds of the 
 cutting-edge of the lower lateral incisor and by the mesial 
 cutting-edge of the lower cuspid. The upper cuspid is met 
 in occlusion by the distal cutting-edge of the lower cuspid 
 and by the mesial two-thirds of the buccal cusp of the lower 
 first bicuspid. The upper first bicuspid is met in occlusion 
 by the remaining or distal third of the lower first bicuspid and 
 by the mesial two-thirds of the buccal cusp of the lower second 
 bicuspid. The upper second bicuspid is met in occlusion by 
 the remaining or distal third of the buccal cusp of the lower 
 second bicuspid, and by the mesial incline of the mesiobuccal 
 cusp of the lower first molar. The upper first molar is met 
 in occlusion by the distal incline of the mesiobuccal cusp of the 
 lower first molar, by the entire distal cusp of the same tooth, 
 and by the mesial incline of the mesiobuccal cusp of the lower 
 
ANATOMY. 
 
 second molar. The upper second molar is met in occlusion 
 by the distal incline of the mesiobuccal cusp of the lower 
 second molar, by the entire distobuccal cusp of the same tooth, 
 and by the mesial incline of the mesiobuccal cusp of the lower 
 third molar. The upper third molar is met in occlusion by 
 the distal incline of the mesiobuccal cusp of the lower third 
 molar and by the entire distobuccal cusp of the same tooth, 
 thus being the only tooth in the superior arch with but a 
 single opponent. Likewise each lower tooth is met in occlu- 
 sion by two in the superior arch, with the single exception 
 of the central incisor, which occludes with the upper central 
 
 Fig. 40. — The Mandible at the Adult Period, showing the Equilateral Triangle 
 
 DESCRIBED BY THE DeNTAL ArCH. 
 
 alone. There are many variations from this so-called typical 
 occlusion, as above described, and any slight difference one way 
 or another should not be considered abnormal. In certain types 
 the segmental form of the superior arch is but little greater than 
 that of the inferior, and the cutting-edges of the upper incisors 
 occlude almost directly upon the cutting-edges of the lower 
 incisors. As a result, all of the upper teeth are forced to the 
 distal, and the relationship between the upper and lower organs 
 is much altered. When the upper teeth overhang the lower, the 
 lingual cusps of the upper bicuspids and molars penetrate the 
 fossae or sulci of the corresponding lower teeth, when in occlu- 
 
OCCLUSION OF THE TEETH. iii 
 
 sion, and the buccal cusps of the lower bicuspids and molars 
 rest in the fossse of their upper opponents. 
 
 To assist in the study of the occlusion of the teeth, some ref- 
 erence must be made to the tooth-line level, or plane of oc- 
 clusion. For this purpose the lines forming the facial angle 
 are of value. These lines are as follows : A fixed line repre- 
 senting the base of the angle may be drawn from the center of 
 the glenoid fossa, passing forward through the anterior nasal 
 spine or base of the nose (a, Fig. 41), the angle being com- 
 pleted by a perpendicular line resting upon the labial surface of 
 the upper incisors, passing upward and touching the most 
 
 / 
 
 
 ""'X^ 
 
 / 
 
 
 ■^ 
 
 /fe^ 
 
 1 
 
 ^^ipr 
 
 / 
 
 - 
 
 
 Fig. 41. — Lines showing Facial Angle, Caucasian or White Race. 
 
 prominent part of the forehead (b. Fig. 41). The tooth-line 
 level is approximately horizontal to this basal line, but instead of 
 a perfect plane we usually find the superior arch dipping down- 
 ward, while the inferior arch will be provided with a correspond- 
 ing depression. This dip to the arch is greatest in the region 
 of the bicuspids, and the extent to \vhich it may exist varies with 
 the type of tooth and the consequent nature of the occlusion. 
 
 Thus far no reference has been made to what is commonly 
 termed the overbite, and the cusp forms in the teeth. As 
 these two factors exert a dominating influence over the char- 
 acter of the occlusion, the effects which they produce will 
 be briefly described. The overbite is so named from the upper 
 
incisors and cuspids projecting beyond, or overhanging and 
 partly covering, the labial surfaces of the corresponding lower 
 teeth. This may be a pronounced feature in the tooth-occlu- 
 sion, or it may exist to a very slight degree. Although the 
 overbite is usually referred to as existing in the incisive region 
 alone, it is not confined to these teeth, but is also present in the 
 bicuspids and molars by the buccal cusps of the upper teeth 
 overhanging those of the lower. The extent of the over- 
 bite is gradually diminished from before backward, the central 
 incisors presenting the greatest amount of overhanging surface, 
 
 Fig. 42. — Lines showing Facial Angle, Negro or Mixed Races. 
 
 which condition is slightly decreased in the laterals, and a cor- 
 responding reduction is continued until the third molars are 
 reached, at which point the overbite is scarcely observed. 
 Where the overbite is extensive, as shown in figure 39, the 
 upper incisors overhanging and hiding from view about one- 
 third of the labial surfaces of the lower incisors, the cusps of 
 the bicuspids and molars will be correspondingly long and pene- 
 trating, the buccal cusps of the upper teeth extending well 
 down over the buccal cusps of the corresponding lower teeth. 
 In an occlusion of this class, which is usually found in the ner- 
 vous and bilious types, the dip to the arch will be a prominent 
 
OCCLUSION OF THE TEETH. 
 
 feature, the occlusion will be firm and well locked, and the lateral 
 articular movements will be slight during mastication. In the 
 lymphatic and sanguine temperaments the occlusion is loose and 
 
 Fig. 43. — Lymphatic. 
 
 Fig. 44. — Sanguine. 
 
 f « f f 
 
 Fig. 45. — Bilious. 
 
 wandering, greater freedom of movement being permitted by 
 the short overbite and the corresponding lack of cusp-formation. 
 Figure 43 represents such an occlusion ; the superior arch is 
 
but little greater in its segmental outline than the inferior. The 
 cutting-edges of the upper incisors are somewhat more prom- 
 inent than those of the lower, but the former do not overlap 
 the labial surfaces of the latter. In an occlusion of this charac- 
 ter the dip to the arch is not so pronounced, and the articular 
 movements are much more extensive. 
 
CHAPTER VI. 
 THE BLOOD- AND NERVE-SUPPLY TO THE TEETH. 
 
 THE BLOOD-SUPPLY TO THE TEETH. 
 
 Briefly stated, the course of the blood from the heart to the 
 teeth is as follows : From the heart to the aorta, to the common 
 carotid artery, to the external carotid artery, to the internal 
 maxillary artery, from the various branches of which the teeth 
 are supplied. 
 
 The Internal Maxillary Artery (Fig. 47). — This artery, 
 otherwise known as the deep facial, is the larger of the two ter- 
 minal branches of the external carotid. In addition to supply- 
 ing the teeth, it is distributed to the roof and floor of the mouth, 
 to the maxillary sinus, and to other parts of the face and head. 
 It has its origin from the external carotid artery opposite the 
 condyle of the mandible within the substance of the parotid 
 gland, passes forward between the condyle of the jaw and the 
 sphenomaxillary ligament, from which point it passes obliquely 
 upward and forward between the external and internal ptery- 
 goid muscles until it reaches the sphenomaxillary fossa, where 
 its terminal branches are given off. It is divided into three por- 
 tions — the first or maxillary, the second or pterygoid, and the 
 third or sphenomaxillary. The teeth are supplied from branches 
 of the first and third divisions, the upper teeth receiving their 
 blood-supply from the alveolar or superior maxillary and the 
 infra-orbital branches of the third division, while the lower teeth 
 are supplied by the inferior dental branch of the first division. 
 
 The alveolar or superior maxillary branch arises, in 
 common with the intra-orbital branch, from the internal maxillary 
 as it passes into the sphenomaxillary fossa. It passes down- 
 ward, in a tortuous manner, in a groove provided for it in the 
 back of the maxilla. In its downward course it gives oft the 
 following bi-anches : The antral, to supply the antrum; the 
 dental (known as the posterior dental arteries), which pass into 
 
Fig. 46. — Dissection Showing Blood-supply to the Teeth. 
 
THE BLOOD-SUPPLY TO THE TEETH. 117 
 
 the substance of the bone through the posterior dental canals 
 to supply the molar and bicuspid teeth; the alveolar or gingival, 
 to supply the gums ; and the buccal, to the lateral walls of the 
 mouth. The an-terior upper teeth are supplied through the 
 infra-orbilal branch of the internal maxillary. This branch arises 
 from the internal maxillary artery, generally, in common with the 
 posterior dental. It passes forward in company with the maxil- 
 
 Inf aorbi al aitny and nene 
 
 Spheno-palahne branch 
 
 Posterior 01 descending palatine branch 
 ^aso-patatme blanch 
 
 Vidian branch 
 
 Antei cor deep temporal artery 
 
 Ezlemal pterygoid branch 
 
 Orbital branch 
 
 Nasal branch 
 
 Anterior 
 
 dental branch 
 
 Labial branch 
 
 Posterior dental 
 
 branch 
 
 , I / Posterior deep temporal artery 
 
 \\ I'/ ' / / ^ Small 1 
 
 Submental branch 
 
 Bvecal branch : 
 portion 0/ buccal nervt 
 Mylo-hyoidean branch 
 
 Internal pterygoid branch 
 
 Fig. 47. — Scheme of Internal Maxillary Artery. 
 
 lary division of the fifth nerve — first along the groove and then 
 in the canal on the orbital plate of the maxilla, and finally makes 
 its exit upon the face through the infra-orbital foramen. Besides 
 giving off branches to the orbital and nasal cavities, it supplies 
 the incisor and cuspid teeth through its anterior dental branch, 
 which passes downward through a groove in the anterior wall 
 of the maxilla. 
 
Fig. 48.— Dissection Showing Nerve-supply to the Teeth. 
 
THE BLOOD-SUPPLV TO THE TEETH. 119 
 
 The Inferior Dental Artery (Fig. 47). — The lower teeth 
 receive their blood-supply through the inferior dental or 
 mandibular artery. This artery arises from the under part of 
 the internal maxillary as it passes downward and forward 
 between the sphenomaxillary ligament and the neck of the jaw 
 and enters the inferior dental canal through the inferior dental 
 foramen. It passes forward in the canal accompanied by the 
 inferior dental nerve, and in so doing sends off twigs to supply 
 the molar and bicuspid teeth. When the mental foramen is 
 reached, it divides into two brandies, the incisive branch and the 
 mental branch. 
 
 The incisive branch continues its course within the cancellated 
 structure of the bone, sending off minute branches which supply 
 the anterior teeth, the terminal branches anastomosing with the 
 artery of the opposite side. 
 
 The mental branch passes out through the mental foramen 
 accompanied by the mental branches of the inferior dental nerve, 
 and supplies the tissues of the chin and lower lip. 
 
 The Veins. — The blood, in returning from the teeth to the 
 heart, is first taken up by the posterior dental and inferior dental 
 veins, which in their course follow closely that of their cor- 
 responding arteries. These veins, in conjunction with others 
 which accompany branches of the internal maxillary arterj^ 
 form the pterygoid plexus. At the posterior confluence of this 
 plexus the returning blood empties into the internal maxillary 
 vein. Accompanied by the internal maxillary artery it passes 
 backward and outward, enters the parotid gland, and finally 
 empties into the temporomaxillary vein midway between the 
 zygoma and the angle of the jaw. After leaving the substance 
 of the parotid gland, the temporomaxillary vein passes down- 
 ward until near the angle of the jaw, where it divides into two 
 branches, one of which passes downward and slightly forward, 
 uniting with the facial to form the common facial vein, and the 
 other, after passing downward and backward, empties into the 
 external jugular vein. The external jugular vein returns the 
 principal portion of the blood from the teeth, and from its point 
 of beginning it passes almost perpendicularly downward and 
 empties into the subclavian vein, which, by joining with the in- 
 
ternal jugular vein, forms the innominate vein, which, in turn, 
 empties into the superior vena cava, thus communicating with 
 the heart. 
 
 THE NERVE-SUPPLY TO THE TEETH. 
 
 The nerves supplying the teeth are derived from branches 
 of the fifth cranial nerve, otherwise known as the trifacial or 
 trigeminal nerve. The fifth nerve is the largest of the cranial 
 nerves, and consists of two parts, a large root (sensory) and 
 a small root (motor). The larger portion passes into a ganglion 
 (the Gasserian ganglion), frequently compared to the ganglion 
 on the posterior root of the spinal nerve. It arises, or makes 
 its appearance, at the surface of the brain, on the anterior part 
 of the side of the pons Varolii. The sensory root, which, 
 through its branches, supplies the teeth, is composed of from 
 80 to 100 filaments, each inclosed in a neurilemma, the entire 
 bundle being bound together in a single nerve. 
 
 The fifth nerve is divided into three divisions : First, or opJi- 
 tJialmic ; second, or supejHor maxillary ; and third, or inferior 
 maxillary (mandibular). The branches which supply the teeth 
 are included in the second and third divisions, the upper teeth 
 being supplied by branches from the superior maxillary nerve, 
 and the lower teeth by branches from the inferior maxillary 
 nerve. 
 
 The Second Division, or Superior Maxillary Nerve (Fig. 
 49). — This nerve, composed entirely of sensory fibers, is inter- 
 mediate in size between the inferior maxillary and the ophthal- 
 mic divisions. It passes forward from the Gasserian ganglion 
 and leaves the cranium through the foramen rotundum. It 
 traverses the upper part of the sphenomaxillary fossa, and 
 passes into the orbit through the sphenomaxillary fissure ; then 
 passes forward along the infra-orbital groove, and enters the 
 infra-orbital canal, where it receives the name of the infra-orbital 
 nerve. Passing through this canal, it emerges upon the face 
 through the infra-orbital foramen. The superior maxillary 
 nerve, beside supplying the teeth, sends ofif branches to the dura 
 mater, to the orbit, and terminal branches in three groups — 
 labial, nasal, and palpebral. The branches given off" to the 
 
THE NERVE-SUPPLY TO THE TEETH. 121 
 
 teeth are the posterior superior denial, the middle superior dental, 
 and the anterior superior dental. 
 
 The posterior superior dental arises from the second division 
 of the fifth nerve, by one or two roots, just before it passes into 
 the infra-orbital canal. It is divided into a superior and an infe- 
 rior set ; the former passes forward and terminates in the canine 
 fossa, while the latter, usually the larger, enters the posterior 
 dental canals, and, following the line of the alveolar process 
 through minute canals in the bone, sends off twigs to the molar 
 teeth, ending in a plexiform manner by communicating with the 
 
 AyiERIOR DENIAL MAXILLARY NEEVB ORBITAL URAACH 
 
 MAXILLARY KEEVE 
 
 MECKEL'S GANGLION 
 
 POSTERIOR DENTAL 
 
 LOOP FORMED BY MIDDLE AND ANTERIOR DENTAL NERVES 
 
 Fig. 49. — The Maxillary Nerve, Seen from Without. — {Morris, afia- Beaunis.) 
 
 middle superior dental nerve. This nerve is also distributed to 
 the gums and adjacent buccal mucous membrane. 
 
 Middle Siiperior Dental Nerve. — The infra-orbital nerve, soon 
 after entering its canal, gives off this branch, which passes out- 
 ward, downward, and forward over the outer wall of the maxil- 
 lary sinus, and, after forming plexuses with the posterior dental 
 branches, gives off filaments to supply the bicuspid teeth. 
 
 Tlie anteHor superior dental nerve, which is the largest of the 
 dental set, is given off from the infra-orbital nerve, enters a 
 
canal close to the infra-orbital foramen, passes over the anterior 
 wall of the maxillary sinus, and, after communicating with the 
 middle and posterior dental nerves, divides into ascending and 
 descending branches, the latter being distributed to the incisor 
 and cuspid teeth. 
 
 The Third Division, or Inferior Maxillary Nerve (Fig. 
 50). — This is the largest of the three divisions of the fifth nerve. 
 
 Temporal Bone 
 
 Fig. 50.— Dissection showing Mandibular (Third) Division of Fifth Nerve. 
 
 and is both motor and sensory in its function. Besides being 
 distributed to the lower teeth, it sends filaments to the lower 
 portion of the face, the muscles of mastication, the tongue, and 
 mandible. It arises from the Gasserian ganglion, passes down- 
 ward, and emerges from the skull through the foramen ovale, 
 after which it divides into a small anterior (motor) branch and 
 a large posterior (sensory) branch. 
 
 The Inferior Dental Nerve. — This is the largest branch of the 
 
THE NERVE-SUPPLY TO THE TEETH. 123 
 
 inferior maxillary nerve. From its point of origin it passes 
 downward internally to the external pterygoid muscle, and, upon 
 reaching a point between the ramus of the mandible and the 
 sphenomandibular ligament, it enters the inferior dental canal 
 through the posterior or inferior dental foramen. Before enter- 
 ing the foramen, two branches are given off, a lingual and a mylo- 
 hyoid branch. The nerve is accompanied through the inferior 
 dental canal by the inferior dental artery, and, when the mental 
 foramen is reached, it terminates by dividing into an incisive and a 
 mental branch. Between the posterior dental foramen and the 
 mental foramen the nerve gives off a series of twigs to the bicuspid 
 and molar teeth, and these, by communicating with one another 
 within the substance of the bone, form a fine plexus. 
 
 The incisive branch follows the incisive arteries through the 
 substance of that part of the bone between the mental foramen 
 and the symphysis, and supplies the incisor and bicuspid teeth, 
 while the mental branch passes forward to supply the chin and 
 lower lip. 
 
CHAPTER VII. 
 
 OTHER STRUCTURES WITHIN THE MOUTH.— THE GUMS.— THE 
 
 MUCOUS MEMBRANE.— THE ALVEOLODENTAL MEMBRANE.— 
 
 GLANDS, DUCTS, ETC. 
 
 Fig. 51. — Section through Gum and Alveolus. 
 
 The Gums {Gingivce). — The gums are formed by a layer of 
 tough fibrous vascular tissue, covering the alveoli, closely attached 
 to their periosteum, and provided with a free margin (gingival 
 margin), which is closely molded to the necks of the teeth. 
 They are covered on both aspects by the general mucous mem- 
 brane of the mouth, that overlying the labial and buccal surfaces 
 being reflected from the lips and cheeks, the palatal surface being 
 continuous with that of the hard palate, and the lingual surface 
 reflected from the under surface of the tongue and floor of the 
 
 124 
 
THE GUMS. 125 
 
 mouth. In the immediate region of the neclvs of the teeth the 
 gums are especially thin and hard, being- closely adherent to the 
 periosteum and alveolodental membrane in this region. In pass- 
 ing toward the base of the alveolar walls the tissue becomes less 
 firmly attached to the underlying structure, and, when finally 
 passing into the mucous membrane of the cheeks and lips, is 
 quite loose and flabby. This condition also prevails on the 
 lingual aspect, but the palatal surface remains firm throughout, 
 the entire mucous membrane overlying the roof of the mouth 
 being similar in structure and attachment to that portion imme- 
 diately surrounding the necks of the teeth. In various situations 
 about the labial, buccal, and lingual surfaces of the gums small 
 slender folds of mucous membrane are found extending to the 
 surrounding tissues. These folds, which act as a bridle or curb 
 to the adjacent movable parts, are known as the frena of the 
 mouth. The principal frena are found at the median line, and 
 are three in number — the frenum labium superioris, frenum 
 labium inferioris, and the frenum linguae. The two former 
 extend from the inner surface of the lips to the gums, to which 
 their extent of attachment is somewhat variable. The frenum 
 labium superioris is usually much larger than the frenum labium 
 inferioris, and its attachment to the gum frequently extends 
 almost to the gingival border. The frenum linguae extends from 
 the under surface of the tip of the tongue to the lingual surface 
 of the inferior gums. This is a much stronger fold than 
 those connected with the lips. Similar bridles are found in 
 the buccal region, usually near the bicuspid teeth, but they are 
 much smaller than those at the median line. The gingival 
 margins, or that portion of the gums embracing the necks of the 
 teeth, present much variety in outline. Instead of encircling 
 the neck of the tooth in a direct line, the margins are made 
 up of a series of semicircles. Using the incisive region for 
 reference, the labial and palatal margins are concave rootward, 
 while the interproximate spaces are partly or completely 
 filled by gum tissue, having the outline reversed or convex 
 in the direction of the crowns of the teeth. The gingival 
 margin is also termed the "free margin of the gum," this name 
 better describing" its extent. As previously stated, the gums are 
 
attached to the periosteum and peridental membrane, but in 
 most instances, and particularly before the adult period, the 
 margins of the gums extend beyond the alveolodental membrane, 
 the limit of which is formed by the cervical line. That portion 
 of the gum margin beyond the cervical line is in close contact 
 with the neck of the tooth, but is not adherent to it, the connect- 
 ing medium, the alveolodental membrane, not being present to 
 form the attachment. The curvature of the gingival margins, 
 and the nature of the tissues which enter into their construction, 
 are usually considered as strongly indicative of the temperament 
 of the indivadual. Thus, in the bilious temperament the mar- 
 gins are inclined to angularity and the tissues rather thick and 
 firm. In the sanguine type the outline formed is almost a per- 
 fect semicircle, and the tissues are of moderate thickness and 
 firmness. In the nervous type the curvature is strongly par- 
 abolic, and the tissues firm and delicate. In the lymphatic the 
 tissues are loose and thick, and the curvature is long and poorly 
 defined. In some instances the interproximate spaces are com- 
 pletely filled by the gingivae ; in others the space is only partly 
 occupied by these tissues. The former condition is present when 
 the proximate surfaces of the teeth are nearly or quite parallel 
 with each other, thus reducing the capacity of the space. The 
 latter condition is present when the crowns of the teeth are 
 bell-shaped and the interproximate spaces extensive. The labial 
 and buccal surfaces of the gums are more or less broken by 
 numerous prominences and depressions, all of which accord 
 with the variations upon the surface of the bone beneath. 
 
 Mucous Membrane of the Mouth. — The term "membrane"' 
 in a general sense is one applied to thin layers of tissue, some- 
 what elastic and of a whitish or reddish color. Such tissues 
 are found lining either closed cavities or canals which open 
 externally, absorbing or secreting fluids, and enveloping various 
 organs. The simple membranes are of three varieties, being 
 either mucous, serous, or fibrous. The mucous membranes are 
 so called from the clear viscid fluid (mucus) which they secrete. 
 They line the various cavities or tracts of the body which com- 
 municate with the exterior. The three grand divisions of 
 mucous membrane are those lining the digestive, respiratory, 
 
MUCOUS MEMBRANE OF THE MOUTH. 127 
 
 and genito-urinary passages. Lining the entire cavity of tlie 
 mouth we find the beginning of the digestive tract, being con- 
 tinuous with the skin on the exterior and performing many 
 similar functions within. It is soft, smooth, and velvety, of a 
 bright red color, and quite vascular ; it is covered on the ex- 
 terior by a layer of epithelial cells overlying the vascular parts. 
 Immediately beneath this is a network of fibrous connective 
 tissue forming the proper mucous membrane, and still deeper 
 is a third layer, somewhat loose in texture, but composed of 
 fibrous connective tissue, the submucous membrane. The oral 
 mucous membrane, at its point of beginning on the contiguous 
 surfaces of the lips, is endowed with keen sensibility ; it is dry, 
 bright red in color, and plentifully supplied with vascular papillae, 
 in many of which are sensory nerve terminals. Distributed 
 along the line of junction between the integument and the 
 mucous membrane are numerous sebaceous follicles, which, 
 however, are devoid of hair-bulbs. The characteristic dryness 
 of this surface gradually becomes changed to a mucus-secreting 
 one, as that part of the membrane lining the interior of the lips 
 is approached. Distributed over the surface of the labial 
 mucous membrane are a number of minute openings, the 
 mouths of the labial glands, which lie immediately beneath 
 the membrane. The buccal mucous membrane, or that lining 
 the cheeks, is similar to that covering the internal surface of 
 the lips. It is penetrated at various points by the mouths 
 of the buccal glands, which, in general, are smaller and less 
 numerous than the labial glands. In the region of the second 
 molar teeth the membrane is broken by four or five openings 
 of larger size, which communicate with the molar glands. The 
 mucous membrane covering the hard palate is thick and firm, 
 less brilliant in color than that covering the cheeks and lips, 
 and firmly bound down to the periosteum. Running from 
 before backward at the median line, the membrane is formed 
 into a slight fold, the median raphe, while near the anterior 
 portion of the palate are a number of fantastically arranged 
 folds, the rug(g (see General Description of the Mouth). 
 The thin but rather dense fibrous' aponeurosis forming the 
 soft palate is covered anteriorly by the oral mucous membrane. 
 
Suspended from the center of the free margin of the soft 
 palate is the uvula, which is likewise covered by mucous mem- 
 brane, and from the base of this, on either side, are two folds 
 of the membrane, which extend outward and downward, form- 
 ing the anterior and posterior pillars of the fauces. The 
 mucous membrane covering the tongue has already been de- 
 scribed in connection with that organ (see p. 41). From the 
 mouth the digestive mucous membrane passes through the 
 fauces, pharynx, and esophagus to the stomach, and is so 
 continued throughout the whole digestive tract. Other pro- 
 longations also pass into the ducts of the salivary glands.* 
 
 The Alveolodental or Root Membrane. 
 
 This membrane invests the roots of the teeth, and at the same 
 time lines the wall of the alveoli. Being reflected from the peri- 
 osteum covering the outer alveolar walls, it enters the alveolar 
 sockets as a single membrane, affording nourishment to the bone 
 on one side and to the cementum of the tooth on the other. 
 It is a connective tissue of moderate density, and is rich in its 
 nerve- and blood-supply. The general direction of its fibers 
 is transverse, being attached at one extremity to the alveolar 
 wall and at the other to the cementum of the root. The con- 
 nective-tissue fibers are not merely attached to the surface of 
 the calcified structure, but the strength of this attachment is 
 greatly increased by the passage of the fibers into the sub- 
 stance of the bone at one extremity and into the lamellse ot 
 the cementum at the other. In general, the membrane is more 
 closely adherent to the cementum than to the bone, usually 
 clinging to the former when removed from its socket. The nature 
 of the articulation between the tooth-root and the alveolar socket, 
 to the production of which this membrane so largely contributes, 
 is one peculiar to itself While there is no marked mobility, 
 there is, nevertheless, sufficient elasticity in the intervening mem- 
 brane to provide against the severe concussions and lateral 
 strains incident to mastication, the former being provided for by 
 the general elasticity, while the latter is cared for by specially 
 
 * For a minute description of the mucous membrane of the mouth see Part ii. 
 
THE ALVEOLODENTAL PERIOSTEUM OR ROOT MEMBRANE. 
 
 distributed fibers, which serve to return the tooth to its normal 
 position when sHghtly rotated or laterally displaced. This elas- 
 ticity is greatest in youth and up to the meridian of life, after 
 which time it gradually becomes less pronounced. The membrane 
 is thickest about the apical ends of the roots and in the cervical 
 region, and the distribution of the fibers at these points is some- 
 what different from those about the body of the root. In the 
 former location they are 
 spread out fan-like from the 
 apical root surface to meet 
 the surrounding alveolar 
 wall, while in the latter they 
 pass longitudinally over the 
 alveolar margins to unite 
 with the periosteum of the 
 parts. In conjunction with 
 the functions already men- 
 tioned, the peridental mem- 
 brane is the medium by 
 which all forces applied to 
 the tooth-surface are taken 
 up and conveyed to the 
 brain. A tooth in a normal 
 condition may be said to 
 possess no sense of touch, 
 unless it be so severely ap- 
 plied as to make its influ- 
 ence felt by the pulp, in 
 which case the sensation 
 becomes one of pain. The 
 nerves of the membrane act 
 in precisely the same man- 
 ner as do other sensory-nerve terminals, being influenced by 
 the slightest touch applied to the surface of the tooth-crown.* 
 In certain conditions of defective hearing the alveolodental 
 membrane may be made to assist this function by the use 
 
 Fig. 52. — Root and Membrane of Tooth. 
 p., /, Peridental membrane ; ap^ apical space ; 
 a, artery ; al, al, alveolar process ; /, /, dental 
 ligament. 
 
 ■■ This membrane is more fully described in Part ii. 
 
I30 ANATOMY. 
 
 of an instrument made for the purpose known as a denti- 
 phone. 
 
 Blood-supply to the Alveolodental Membrane. — A very 
 clear Idea of the blood-supply to this membrane may be obtained 
 from figure 52. 
 
 Entering the alveolar socket as a single arterial branch, the 
 thickest portion of the membrane is gained where a number 
 of smaller twigs are given off, one or more of which enter the 
 pulp-canal of the tooth-root through the apical foramina supply- 
 ing the pulp, which in turn supplies the tooth-structure within, 
 while the others ramify through the substance of the alveolodental 
 membrane, through its capillaries, supplying the cementum 
 from without; while passing through the membranous structure, 
 further minute branches are given off which penetrate the walls 
 of the alveolus and anastomose with the arteries which supply 
 the oral mucous membrane, in this manner providing a gen- 
 erous blood-supply to the parts. Further on we shall see that 
 the tooth-pulp and the alveolodental membrane spring from the 
 same source (see Development of the Teeth), and the blood- 
 supply to the parts during the saccular stage of development 
 is alike distributed to the base of the pulp and to the follicular 
 walls. After the completion of the developmental process this 
 distribution is but little changed, the blood-vessels accommo- 
 dating themselves to the alterations incident to the generation 
 of the parts. 
 
 The Nerve-supply to the Alveolodental Membrane. — 
 The nerve-supply to this membrane is distributed in a manner 
 similar to the blood-supply, being derived from a single filament 
 given off from the dental nerve and entering the tooth-socket 
 by the side of the blood-vessels, and by numerous filaments 
 which reach the structure by passing through the many minute 
 canals in the substance of the alveolar walls and the intervening 
 septa. 
 
 GLANDS OF THE MOUTH. 
 
 The glands of the mouth are of two kinds, being either serous 
 or mucous, and, as they differ in the character of their secretions, 
 so they differ in structure. The mucous glands are the most 
 
GLANDS OF THE MOUTH. 131 
 
 numerous, and are found beneath the mucous membrane of the 
 lips, in the same membrane lining the cheeks, the hard and soft 
 palate, the tonsils, and at the back of the tongue. These glands 
 are quite variable in size, but are all of macroscopical propor- 
 tions, appearing when examined in this manner as minute 
 whitish bodies. The secretions from the glands are poured into 
 the mouth through small ducts which pass in various directions 
 through the substance of the mucous membrane. Beginning 
 as a single duct for each gland, they pass to the submucous 
 tissue, here branching into two or more smaller ducts termi- 
 nating in alveoli, the number and size of these depending 
 upon the size of the gland with which they are connected. 
 The glands are variously named according to their location, 
 those occupying the lips being known as labial glands ; those 
 of the cheeks, the buccal glands ; those of the palate, the pal- 
 atal glands, etc. The mucous glands, although differing in size, 
 are similar when histologically considered. 
 
 The Labial Glands. — These are among the largest mucous 
 glands of the mouth, and are more numerous in the upper than 
 in the lower lip. The form, size, and location of the labial glands 
 may best be studied by dissection, which may readily be accom- 
 plished by first removing the integument and muscular tissues 
 from the parts, when they will be brought into view. The glands 
 are irregularly arranged, and are most numerous near the 
 median line. The body of each gland is rounded and held in 
 position by connective tissue, as well as by the duct connecting 
 it with the interior of the mouth. 
 
 Besides the mucous glands of the lips, there are present 
 numerous sebaceous glands. These are somewhat smaller, and 
 are situated beneath the mucous membrane covering the contigu- 
 ous surfaces of the lips, the numerous ducts leading from them 
 opening upon these parts. 
 
 The Buccal Glands. — The glands of the cheek, otherwise 
 known as buccal glands, are similar to, but smaller than those of 
 the lips, and are placed between the submucous tissue and the 
 buccinator muscle. These glands also pour their secretions 
 into the mouth through numerous ducts which pass through the 
 buccal mucous membrane. 
 
In the region of the third molar teeth another set of mucous 
 glands open into the mouth, known as the molar glands. They 
 are placed between the buccinator and masseter muscles, are 
 similar in construction, and secrete a like fluid to those pre- 
 viously described, being larger than the buccal and smaller 
 than the labial glands. 
 
 Palatal Glands. — Situated between the mucous membrane 
 of the hard palate and the periosteum are numerous mucous 
 glands similar to those previously described. Provision is made 
 for the accommodation of these glands by many small depressions 
 in the bony plates (see Fig. 3). They are irregularly distributed 
 over the surface of each lateral half of the hard palate, but are 
 absent at the median raphe and immediately beneath the rugse. 
 The mucous membrane of the hard palate is tense and hard, in 
 consequence of which it is not so thick as the buccal and lingual 
 membranes, and the ducts from the numerous glands are there- 
 fore not so long. The glands of the soft palate, uvulae, and 
 fauces are situated beneath the deep layer of mucous membrane 
 covering these parts, in the former structure opening on both 
 the oral and nasal surfaces. 
 
 Lfingual Glands. — The glands of the tongue are of two 
 kinds — mucous and serous. The former are chiefly found at the 
 back part of the tongue, but a few of smaller size are present 
 near the tip. The serous variety are to be found only at the 
 back of the organ, and are closely associated with the taste 
 organs in this region. These glands are assisted in performing 
 their function by being placed between bundles of striped mus- 
 cular tissue, the activity of which forces the secretions to the 
 surface by compressing the glands. While the majority of the 
 lingual glands are present in the circumvallate region, a number 
 are found distributed beneath the mucous membrane of the 
 borders and tip of the organ. 
 
 The Salivary Glands (Fig. 53). — These glands, while 
 outside the mouth, are so closely associated with its functions 
 that a brief description will be presented. The chief salivary 
 glands are six in number, three on each side. They are named 
 parotid, submaxillary, and sublingual ; the former, secreting true, 
 thin, watery saliva, is a true salivary gland, while the latter two 
 
GLANDS OF THE MOUTH. 
 
 133 
 
 are known as mixed, or mucosalivary glands, secreting both 
 mucus and saliva. 
 
 The Parotid Gland. — This gland is the largest of the three, 
 and is placed a little below and in front of the ear, having the 
 following boundaries : Anteriorly, by the ramus of the mandible ; 
 posteriorly, by the styloid and mastoid processes of the temporal 
 bone ; above, by the root of the zygoma, and below, by a line 
 drawn backward from the angle of the jaw. While the extent 
 
 SOOIA TAROTIDIG 
 
 DUOT OF PAROTID 
 
 Freenum llaguee 
 DUCT OF RIVINUS 
 
 SUBLINGUAL GLAND 
 
 PAROTID GLAND 
 
 MaBBeter muscle 
 
 Mylo-hyoid muBCle 
 
 '/ Posterior belly of 
 
 digastric muscle 
 
 Loop of fascia 
 
 DEEP PORTION OF SUBMAXILLARY BLAND 
 
 Fig. 53. — The Salivary Glands. — (Moi-ris.) 
 
 and outline of the gland is somewhat variable, its position is 
 approximately that oudined in figure 53. Its superficial surface, 
 somewhat lobulated, is in close reladon to the skin and fascia, 
 while deeply it penetrates well into the neck by two processes, 
 one of which passes behind the styloid process and beneath the 
 mastoid process of the temporal bone and the sternomastoid 
 muscle, while the other passes in front of the styloid process. 
 Given off from the body of the gland and extending in various 
 directions are a number of processes or lobes, one extending 
 
134 ANATOMY. 
 
 forward between the two pterygoid muscles, and known as the 
 pterygoid lobe ; another passing into the glenoid cavity, the 
 glenoid lobe ; while a third passes deeply between the carotid 
 vessels, and is called the carotid lobe. In many instances there 
 is an additional lobe, which is detached from the body of the 
 gland, known as the socia parotidis. When present, this lobe is 
 placed over the parotid duct and empties into it. Passing 
 through the substance of the gland are a number of arteries and 
 veins, principal among which are the external carotid, transverse 
 facial, and internal maxillary, the gland receiving its blood- 
 supply by branches from these. The internal carotid artery 
 and internal jugular vein lie close to its internal surface. The 
 facial nerve and its branches and the great auricular nerve pass 
 through the gland from before backward, and supply its sub- 
 stance with nerve-force. The weight of this gland is from one- 
 half to one ounce. 
 
 The Parotid Duct. — Leading from the gland to the mouth 
 is the parotid or Stenson's duct. After passing through the fat 
 of the cheek and the fibers of the buccinator muscle, the duct 
 comes in contact with the deep layer of the oral mucous mem- 
 brane. After passing between this structure and the cheek 
 tissues for a short distance it enters the mouth opposite the 
 crown of the upper second molar tooth, the orifice of the 
 duct appearing on the surface of the mucous membrane in the 
 form of a small papilla, which may be readily observed with the 
 naked eye. When first given off from the gland a number of 
 small ducts are present, but these soon unite and form a single 
 canal. The parotid duct is quite dense, of considerable thick- 
 ness, and is lined by a reflexion of the buccal mucous mem- 
 brane. 
 
 The Submaxillary Gland. — This gland, which receives its 
 name from occupying a position below the maxillary bone, is 
 somewhat smaller than the parotid. It is situated beneath the 
 mylohyoid ridge, and occupies the anterior part of the sub- 
 maxillary triangle, extending upAvard to occupy the submaxillary 
 fossa on the lower border of the maxilla. Superficially, it is 
 covered by the skin and a few muscular fibers and the deep 
 fascia. The facial vein and branches of the facial nerve pass 
 
GLANDS OF THE MOUTH. 135 
 
 over its superficial surface. Deeply, it is in relation with the 
 mylohyoid and hyoglossus muscles, and also with the mylohyoid 
 artery and nerve. The gland receives its blood- and nerve- 
 supply from the arteries and nerves which penetrate it. This 
 gland is separated from the sublingual gland by the mylohyoid 
 muscle, and weighs about two drams. 
 
 The Submaxillary Duct. — The submaxillary duct, other- 
 wise known as Wharton's duct, passes forward and inward, 
 opening into the cavity of the mouth on the summit of a small 
 papilla near the frenum linguae. The duct, which is nearly two 
 inches in length, first passes through the adjacent muscular tis- 
 sue, and finally beneath the oral mucous membrane to its outlet. 
 Like the parotid duct, it is lined by a reflexion of the oral 
 mucous membrane. 
 
 The Sublingual Gland. — This is the smallest of the salivary 
 glands, and is also named from its location beneath the tongue. 
 Its position is beneath the tip of the tongue and the mucous 
 membrane covering this part of the floor of the mouth. It rests 
 in the submaxillary fossa of the maxilla, meeting with its fellow 
 at the median line, and extending as far back as the mylohyoid 
 muscle, which separates it from the submaxillary gland. The 
 gland is supplied with blood from the sublingual and submental 
 arteries, and with nerves from the gustatory. The weight of 
 this gland is about one dram. 
 
 The Sublingual Ducts. — This gland communicates with the 
 mouth by one large duct — the duct of Rivini — which springs from 
 the main portion of the gland, and by a number of smaller ducts, 
 eight to twenty in number, which open on the floor of the mouth. 
 The duct of Rivini follows the submaxillary duct, and opens 
 with it at the same papilla. The smaller ducts are given ofi" 
 from a number of litde lobes which cluster about the fore part 
 of the sfland. 
 
CHAPTER VIII. 
 
 DESCRIPTION OF THE UPPER TEETH IN DETAIL.— CALCIFICA- 
 TION, ERUPTION, AND AVERAGE MEASUREMENTS.— THEIR SUR- 
 FACES, RIDGES, FOSSAE, GROOVES, SULCI, ETC. 
 
 UPPER CENTRAL INCISOR. 
 
 7th 
 
 8th 
 year 
 
 Fig. 54. 
 
 9th 
 year 
 
 Calcification begins, from three centers, first year after birth. 
 Calcification completed, tenth to eleventh year. 
 Erupted, seventh to eighth year. 
 Average length of crown, .39.* 
 
 Average length of root, .49. 
 
 Average length over all, .88. 
 
 During the first year after birth this tooth begins to calcify, 
 this primitive process taking place along the future cutting-edge 
 of the tooth in three distinct lobes or plates, which afterward 
 unite and form three eminences or tubercles, the lines of this 
 union being indicated upon the completed crown by two more 
 or less defined grooves — developmental grooves. By the end 
 of the third year the deposit of lime-salts has carried the 
 process of calcification to a point about midway between the 
 cutting-edge and the cervical line. By a continuation of this 
 formative action the calcification of the crown is completed 
 
 "^The measurements given are in fractions of an inch, and are taken from Black's " Dental 
 Anatomy." 
 
 136 
 
UPPER CENTRAL INCISOR. 137 
 
 between the fifth and sixth year. At the beginning of the 
 seventh year calcification has progressed to such an extent that 
 the neck of the tooth and base of the root are fully outlined. 
 Between the seventh and eighth year the cutting-edge of the 
 tooth begins to make its appearance through the gum at a point 
 either to the right or left of the median line, and, by a gradual 
 separation of the gum tissue, eruption takes place. During 
 the following year about one-eighth of an inch has been added 
 to the length of the root. At the end of the eighth year the 
 root has become calcified to about one-half of its completed 
 length. During the ninth year, owing to a reduction in the 
 diameter of the root, the extent of growth in an apical direction 
 has almost doubled that of the previous year, and a decided 
 narrowing of the free root margins is to be observed. At the 
 eleventh year calcification is completed in the outer root walls, 
 and the apical foramen has been established (Fig. 54). 
 
 The Crown of the Upper Central Incisor presents for 
 examination four surfaces — labial, lingual, mesial, and distal ; two 
 angles — a mesial and a distal ; and a cutting-edge. The general 
 form of the crown is that of a double Inclined plane, or wedge- 
 shape, the cutting-edge representing the junction of the two 
 sides of the incline, one of which looks anteriorly (labial) and 
 the other posteriorly (lingual). The labial side of the incline is 
 convex, while the lingual is concave from the cutting-edge 
 toward the root ; but, upon reaching its upper or cervical third, 
 it presents a slight general convexity. The base of the wedge Is 
 directed upward and partakes of the contour of the neck of the 
 tooth. 
 
 The Labial Surface of the Crown (Fig. 55).— In general 
 outline this surface resembles an imperfect quadrilateral. The 
 margins of the surface are the mesial, the distal, the cervical, 
 and the incisive. The mesial margin begins at the lower border 
 or cutting-edge and passes upward, usually with a slight distal 
 Inclination, gradually uniting with the cervical margin. The 
 distal margin begins at the cutting-edge and passes upward with 
 a slight mesial inclination, also joining the cervical margin. Both 
 of these margins possess more or less general convexity, and, 
 at their junction with the cutting-edge, form the mesial and 
 
138 ANATOMY. 
 
 distal angles of the crown. The cervical margin is rounded and 
 gradually passes into the two lateral margins just described^' 
 The incisive margin is marked by the cutting-edge, and extends 
 from the mesial angle on one side to the distal angle on the 
 other. These four margins, which assist in giving to the tooth 
 its typal form, are quite variable. This difference is particularly 
 marked on the mesial and distal margins, where, in some cases, 
 
 there is a decided convergence 
 in the direction of the root, form- 
 ing what is commonly termed 
 the bell-shaped crown, while in 
 others the same margins will be 
 nearly parallel with each other, 
 making the width of the crown 
 almost as great at the cervical 
 margin as at the cutting-edge. 
 Y\ ^H '^^H ]The mesial angle is usually 
 
 pointed and square, while the 
 distal is much rounded. This 
 surface of the crown is slightly 
 Edge Grooves convex irom above downward, 
 
 ^'" "-l?bL\' lr.lc\'. ''""°^' as well as from side to side, and 
 
 in the majority of instances is of 
 greater vertical than transverse extent/^] Beginning at the inci- 
 sive margin are two slight longitudinal depressions or grooves — 
 the labial grooves — which are resultant from the developmental 
 lobes previously composing the primitive cutting-edge, and, for 
 this reason, are otherwise known as developmental grooves. In 
 many instances one or more transverse ridges are found upon 
 the cervical portion, but these are supplemental. 
 
 The Lingual Surface of the Crown (Fig. 56). — This surface 
 has its borders formed by three marginal ridges and the cutting- 
 ■~f- edge. The marginal ridges are pronounced'elevations of enamel, 
 and surround the surface upon three sides, the intervening space 
 in many instances being a decided concavity or fossa — the lin- 
 gual fossa. , The mesial marginal ridge begins at the mesial angle 
 of the crown, passes upward, inward and backward, following the 
 curvature of the mesial border. . The distal mar ginal ridgeh&gm?, 
 
UPPER CENTRAL INCISOR. 
 
 at the distal angle of the crown in a somewhat less pronounced 
 form, passes upward, backward, and inward, following the cur- 
 vature of the distal surface. Upon reaching the cervical portion 
 of the crown these two margins unite and form the cervicoinar- 
 ginal ridge. This ridge may be bold and prominent, or it may 
 be but slightly developed. Near its center it is frequently broken 
 by a depression or pit — the lingual pit. In some instances this 
 pit is deeply penetrating; in others it assumes the form of a 
 fissure, and may completely sever 
 the ridge. This border is some- 
 times elevated into a slightly de- 
 veloped tubercle or cusp — the 
 cuspule. When this is present 
 it has the appearance of being 
 produced by a fold of enamel, 
 and encircling it is a well-marked 
 fissure. The lingual fossa is 
 usually traversed by two longi- 
 tudinal grooves, which corres- 
 pond to the developmental 
 grooves of the labial surface. 
 When a cuspule is present, the 
 fissure which surrounds it fre- 
 quently passes into the fossa, or the fossa may be partly cov- 
 ered by the cuspule overhanging its cervical portion. When 
 the cervicolingual fissure exists, it is not unusual for it to 
 bifurcate and throw a branch along the inner border of each 
 marginal ridge, or it may penetrate the fossa proper and 
 divide it into two parts. The lingual surface is somewhat 
 less in extent than the labial surface, this reduction being 
 principally in a mediodistal direction, the length of the two 
 surfaces from the -cutting-edge to the cervical margin being 
 about equal. 
 
 The Mesial Surface of the Crown (Fig. 57). — The outline 
 of this surface resembles an inverted cone or triangle, the lines 
 of which are more or less broken, the apex of the cone terminat- 
 ing at the cutting-edge and the base directed toward the root of 
 the tooth. The base of the cone is made concave by the enamel 
 
 Fig. 56. — Upper Central Incisor, 
 Lingual Surface. 
 
margin or cervical line. The margins of the mesial surface are 
 % the labial, the lingual, and the cervical. ' The labial margin is 
 convex and rounded throughout its entire extent, from the 
 cutting-edge to the cervical line. The contour of this margin 
 varies with the typal form of the crown, in some presenting a 
 decided and well-marked convexity, in others being but slightly 
 curved. i^The lingual margin is concave and rounded, but the 
 line is much broken. Beginning at the cutting-edge, it is decided 
 
 and square, this feature usually 
 including the lower third. As 
 it passes upward and the center 
 is approached, the line is more 
 concave and rounded in a mesio- 
 lingual direction, this latter fea- 
 ture increasing upon approach- 
 \ ingthe cervical line. The cer- 
 ige vical margin is that formed by 
 the cervical line. It is usually 
 ,, . , . , well-defined, beine concave or 
 
 Mesial Angle o 
 
 V-shaped, with the point of the 
 V more or less rounded, and 
 
 Fig. 57. — Upper Central Incisor, . , . ^ , . . 
 
 Mesial Surface. With its tree ends pointing one 
 
 in a labial and one in a lingual 
 direction, the former being a trifle longer than the latter.^ The 
 surface between the borders presents a slight general convexity, 
 but with an inclination to flatness near the cervical portion, 
 which is occasionally developed into a slight concavity. What- 
 ever deviations may be present in the borders of this surface, 
 from those assumed in the description just given, their union at 
 the cutting-edge will always be in a direct line with the long 
 axis of the tooth. 
 
 The Distal Surface of the Crown (Fig. 58). — In a general 
 way, this surface resembles the mesial surface just described. 
 There are, however, one or two minor points of distinction : the 
 borders are all more rounded, the labial border presenting a 
 greater convexity, and the lingual a more perfectly formed con- 
 cavity. The surface is quite full in the center, from which it slopes 
 away in all directions, thus producing a decided general convexity. 
 
UPPER CENTRAL INCISOR. 
 
 141 
 
 Ridge 
 
 Lingual 
 Ridge 
 
 Fig. 58. — Upper Central Incisor, 
 Distal Surface. 
 
 The cervical margin of the surface is almost identical with the 
 cervical margin of the mesial surface. The distance in a direct 
 line from the cervical border to 
 the cutting-edge is a trifle less 
 than the corresponding meas- 
 urement on the mesial surface. 
 The distal angle is equally con- 
 stant in its position, and, being 
 connected with the mesial an- 
 gle in a direct line by the cut- 
 ting-edge, finds this latter cor- 
 onal margin always in the labio- 
 lingual center of the crown. 
 
 The Ctitting-edge of the 
 Central Incisor. — The cutting 
 or incisive edge receives its 
 name from its function, that of 
 cutting or incising the food. It is formed by the junction of the 
 labial and lingual surfaces of the crown, and extends almost in a 
 direct line from the mesial to the distal 
 surface ; at its union with the mesial sur- 
 face it assists in forming the mesial angle 
 of the crown, and serves the same purpose 
 by its union with the distal surface. In the 
 majority of instances it is an unbroken 
 line. In passing from the mesial to the 
 distal angle it converges slightly in the 
 direction of the root, thus making the 
 crown a trifle shorter on the mesial than 
 on the distal side. In the recently erupted 
 tooth (Fig. 59) the line is broken by the 
 developmental grooves ; these usually 
 disappear by wear, but occasionally traces 
 of their existence remain, and thus per- 
 manently break the positive line that 
 would otherwise be present. As the cut- 
 ting-edge approaches the distal angle of the crown it is inclined 
 to slope away, producing a less positive angle than the corre- 
 
 FiG. 59. — A Young Upper 
 Central Incisor, Labial 
 Surface, showing Develop- 
 mental Grooves — a. 
 
spending mesial angle. In some instances the cutting-edge is 
 quite thin and inclined to sharpness, in others it is blunt and 
 dull, the former condition being present when there is a decided 
 overbite in occlusion, the latter occurring when this feature is 
 less pronounced. The cutting-edge is frequently referred to 
 as the occlusal surface, this term being employed to make the 
 description more uniform with the bicuspids and molars, and 
 for this reason is permissible ; but it is only in rare instances 
 that the surfaces occlude directly with the opposing teeth, the 
 condition being most frequent in teeth of the lymphatic type, 
 and in cases of malocclusion. 
 
 The Cervical Margin. — This margin, which is distinctly 
 outlined by the free extremity of the enamel covering of the 
 crown, also marks the extent of the membrane covering the 
 root of the tooth. The margins formed by this line are those 
 of a double concavity and a double convexity. On the labial 
 and lingual portions it is concave rootward, while on the 
 mesial and distal sides it is convex in this direction. If a 
 line be drawn around the tooth at the extreme upper point 
 of the enamel covering, it will be found to touch only the labial 
 and lingual prolongations, while a space will exist between the 
 line thus drawn and the cervical margins of the proximate sur- 
 faces. The character of the cervical curvature varies with the 
 type of the tooth, being more or less pronounced as the case 
 may be. In a typical central incisor the cervical line of the labial 
 surface will usually form the segment of a larger circle than that 
 of the lingual, and, while the mesial convexity may be gracefully 
 curved, the distal may incline to angularity. 
 
 The Neck of the Tooth. — The neck of this tooth partakes 
 of a form between that of the crown and root which it joins. It 
 is principally formed by a sudden sloping of the enamel margin 
 to meet the root. It is broader on the labial than on the lingual 
 surface, and is somewhat flattened laterally, with an occasional 
 depression or concavity on its mesial portion. The neck of this 
 tooth is seldom a decided anatomic feature, being less pro- 
 nounced than upon any other tooth. In the bicuspids and 
 molars both the crowns and the roots assist in forming the neck 
 
UPPER CENTRAL INCISOR. I43 
 
 by a constriction of their adjacent parts, while in this tooth the 
 crown alone is instrumental in this direction. 
 
 The Root of the Upper Central Incisor. — The root of 
 this tooth is conic in form, its base directed downward, its apex 
 upward. ''"Viewed in transverse sections its outline is that of a 
 rounded triangle, one side of which faces in a labial, one in a 
 mesiolingual, and one in a distolingual direcdon. The labial 
 side is the most flattened, while the two remaining sides are of 
 equal length and oval in form. This triangular oudine usually 
 condnues throughout the entire length of the root, but in some 
 instances, near the apical end, may have a decided or slight distal 
 curve, included in which will be a more circular form. ^ The taper 
 of the root from the base to the apex is very gradual upon the 
 labial and lingual surfaces, until the apical third is reached, when 
 the two sides converge more rapidly. The mesial and distal 
 surfaces are somewhat flattened and taper very gradually from 
 the base to the apex. In a majority of instances the root is 
 much longer than the crown, but in rare cases its length is 
 barely equal to, or less than, that of the crown. 
 
 Bilious Type. — The crown of the upper central incisor in 
 this type is of greater longitudinal than transverse extent ; large 
 in size, abounding in angles rather than curves. It possesses 
 neither brilliancy nor transparency of surface, but is slightly in- 
 clined to translucency. The labial surface is flat, with more or 
 less decided transverse ridges in the cervical portion. The 
 labial grooves are generally present in the form of well-defined 
 depressions. On account of the angular nature of the tooth, 
 this surface approaches closely to the quadrilateral form. The 
 mesial and distal surfaces are flat, with their margins bold and 
 well defined. The lingual surface also shows the angular nature 
 of the crown in having its marginal ridges squarely set and its 
 developmental grooves definitely outlined. The cutting-edge 
 is rather thin, square, and sharp, the line frequently being im- 
 perfectly formed. The mesial and distal angles are both well 
 produced, and the cervical margin, in keeping with the rest of 
 the parts, is Inclined to angularity. 
 
 Nervous Type. — The central incisor common to this tem- 
 perament is delicate and graceful in outline. The crown is of 
 
144 ANATOMY. 
 
 medium size, witli tlie length predominating over breadth. The 
 enamel is inclined to transparency, and is of a blue or bluish- 
 gray color, presenting much brilliancy. The labial surface is 
 fairly well rounded, and the labial grooves are present as slightly 
 rounded depressions, which frequently extend well toward the 
 cervical margin, where they gradually disappear. In general 
 outline this surface partakes of the triangular form, the crown 
 of the tooth being broad at the cutting-edge and much con- 
 stricted at the neck. The mesial and distal surfaces show a 
 convexity in every direction, and the nature of the occlusion is 
 manifest from the decided wedge-shape appearance of the crown 
 providing for a long overbite. Upon the lingual surface but 
 little in the way of detail is to be observed, the entire surface 
 from the cutting-edge to the cervical ridge being smooth and 
 concave. The cuspule previously referred to is occasionally 
 present in this type, breaking the general smoothness of the 
 surface with its prominence. The marginal ridges are poorly 
 defined ; the cutting-edge is a sharp, unbroken line ; the mesial 
 and distal angles are present in the form of long, graceful 
 curves, rather than definite angles, this being particularly true 
 of the distal angle. The cervical line is decidedly curved, the 
 labial and lingual portions being deeply concave rootward, while 
 the mesial and distal are decidedly convex. 
 
 Sanguineous Type. — The crown of the central incisor is 
 usually above the average in size, but is well proportioned, 
 abounding in curves and rounded outlines. The enamel is 
 inclined to translucency, particularly near the cutting-edge. 
 The labial surface is smooth and rounded ; the depressions 
 formed by the labial grooves are slightly observable, and ex- 
 tend but a short distance from the cutting-edge. The surface 
 is somewhat greater in longitudinal than in transverse extent, 
 and approaches much nearer to a circular form than the corre- 
 sponding tooth of other types. The mesial and distal surfaces 
 are well rounded, making the point of contact with approxi- 
 mating teeth near the center of the surface. The lingual sur- 
 face abounds in heavy rounded lines ; the marginal and cervical 
 ridges are particularly prominent, diminishing the extent of the 
 lingual fossa. A cuspule is frequently present in the form of a 
 
UPPER CENTRAL INCISOR. 145 
 
 well-rounded prominence. The cutting-edge is of moderate thick- 
 ness and slopes away from the center in either direction to assist 
 in forming the rounded mesial and distal angles. The cervical 
 curvature on the labial and lingual surfaces is an unbroken semi- 
 circle, while that of the mesial and distal surfaces is less uniform. 
 
 Lymphatic Type. — In the central incisor of this typal form 
 the crown is large, but not shapely, and the breadth is equal 
 to, or exceeds, the length. The enamel coloring is muddy or 
 brownish-yellow, and the surface is lacking in brilliancy. The 
 labial surface is flat and smooth, with a faint sign of the labial 
 grooves. The general outline of this surface is that of a circular 
 cone, with the cutting-edge for the base, and the apex formed 
 on the cervical margin. The mesial and distal aspects present 
 a striking contrast to the types previously described, by having 
 a labiolingual diameter greater than that represented between 
 the cervical line and the cutting-edge. These two surfaces are 
 convex in a labiolingual direction only, making the point of 
 contact with approximating teeth an extended surface rather 
 than a single point. 
 
 The lingual surface is heavy and bulky, frequently to such a 
 degree as to produce a general convexity rather than a concav- 
 ity, as found in most typal forms. This surface is frequently 
 broken by one or more longitudinal grooves, but is seldom 
 crossed by transverse lines of any kind. The cutting-edge is 
 barely deserving of the name. Although formed by the free 
 borders of the labial and lingual surfaces, these two planes are 
 so far separated at their incisive margins that the space between 
 them, instead of being an edge, becomes a more or less broad- 
 ened surface, and one upon which the lower incisors frequently 
 occlude. The line thus formed is straight and direct from the 
 mesial to the distal angle of the crown, both of which are well 
 produced. The cervical curvature is represented by the segment 
 of a much larger circle than that found upon teeth of other 
 types, and the neck of the tooth is heavy and bulky, showing 
 but little constriction at this point. 
 
146 
 
 UPPER LATERAL INCISOR. 
 
 4th 5th 
 
 year year 
 
 Fig. 60. 
 
 Calcification begins, from three centers, first year after birth. 
 Calcification completed, tenth to eleventh year. 
 Erupted, seventh to eighth year. 
 Average length of crown, .34. 
 
 Average length of root, .51. 
 
 Average length over all, .85. 
 
 Like the central incisor, calcification in this tooth begins during 
 the first year after birth, the process taking place in the same 
 manner, firom three centers, along the future cutting-edge, and 
 gradually extending in the direction of the root. By the expi- 
 ration of the third year the cutting-edge and the angles of 
 the crown are fully formed ; the fourth year finds the crown 
 calcified to nearly one-half its completed length ; by the fifth 
 year the cervical ridge is reached ; while the sixth year usually 
 completes the process of coronal calcification. At the close of 
 the seventh year the base of the root is fully outlined, and 
 during the following year about one-eighth of an inch is added 
 to its length, and still greater progress is made during the ninth 
 year, by which time fully three-fourths of the root length has 
 become calcified. During the tenth year the apical end of the 
 root begins to form by a sudden doubling-over of the free cal- 
 cifying margins, and by the eleventh year the apical foramen is 
 established (Fig. 60). By the above description it will be 
 observed that at the time of eruption the root of this tooth is 
 only calcified to about one-half of its completed length, and the 
 same may be said of the central incisor ; but so much time 
 
UPPER LATERAL INCISOR. 
 
 elapses between the beginning of the eruptive stage and the 
 period at which this phenomenon is completed that the apical 
 foramen is usually established by the time the tooth assumes its 
 permanent position in the jaw. 
 
 The crown of the upper lateral incisor, like that of 
 the upper central incisor, presents for examination four sur- 
 faces, — labial, lingual, mesial, and distal, — a cervical margin, a 
 cutting-edge, and a mesial and distal angle. The general con- 
 tour of the crown closely resembles that of the upper central 
 incisor, except that it measures about one-third less from mesial 
 to distal, and is a trifle shorter from the cutting-edge to the cer- 
 vical line. As in the central incisor, the labial and distal surfaces 
 form a double incline plane, and 
 unite below to form the cutting- 
 edge. The labial side of the in- 
 cline is convex, while the lingual 
 is concave, but seldom so marked 
 as that found upon the central 
 incisor. The base of the wedge, 
 or double incline, formed by the 
 cervical margin, is correspond- 
 ingly smaller than that of the 
 crown of the central incisor. 
 
 The Labial Surface of the 
 Crown (Fig. 61). — This surface 
 of the crown of the upper lat- 
 eral incisor is more irregular in 
 outline than the corresponding 
 surface of the central incisor. The 
 
 margins of the surface are the mesial, distal, cervical, and incisive. 
 The mesial margin begins at the mesial angle and passes upward 
 with a decided distal inclination to meet the cervical margin. 
 The distal margin is shorter and decidedly more convex than 
 the mesial margin, this variation in outline being still more 
 marked when compared with the corresponding margin of the 
 central incisor. At the cutting-edge these two margins assist 
 in forming the mesial and distal angles of the crown, and by 
 their continuation and union above form the cervical margin. 
 
 labial 
 Ridge 
 
 Labial Grooves 
 
 Fig. 61. — Upper Lateral Incisor, 
 Labial Surface. 
 
I4S 
 
 ANATOMY. 
 
 The incisive margin is formed by the cutting-edge. Like the 
 central incisor, the four margins of this surface vary greatly in 
 the different types ; this is particularly true of the two lateral 
 margins, which at times are found to be in the form of a direct 
 line, or even slightly concave, while in others they are both 
 decidedly convex. This surface of the crown shows a greater 
 general convexity than the labial surface of the central incisor, 
 the cervical portion presenting a curve much more decided than 
 that near the cutting-edge. The labial grooves are in all 
 respects similar to those described in connection with the central 
 incisor, and extend from the cutting-edge toward the center of 
 
 the surface, where they grad- 
 ually disappear. Transverse 
 ridges are occasionally found 
 near the cervical portion of the 
 surface. 
 
 The Lingual Surface of 
 the Crown (Fig. 62). — This 
 surface of the upper lateral in- 
 cisor is subject to much varia- 
 tion in form, but presents the 
 same points for examination as 
 the corresponding surface of the 
 central incisor. These consist 
 of the marginal ridges, which 
 are usually more pronounced 
 than those of the central, mak- 
 ing the concavity or fossa between them small and deep. 
 In some instances the surface will be smooth and flat, with 
 an entire absence of ridges or fossae. The distal marginal 
 ridge is shorter and more bowed than the mesial, and the 
 cervical ridge is well marked and proportionately broader and 
 stronger than in the central incisor. In some instances the 
 marginal ridges are but slighdy developed, with their cer- 
 vical ends broadened and separated by a deep fissure, giving 
 the appearance of a terminal fold in the enamel. The cervical 
 ridge is frequently broken by a cuspule, which is usually 
 more pronounced than when found upon the central incisor. 
 
 ginal Ridge 
 
 Fig. 62. — Upper Lateral Incisor, 
 Lingual Surface. 
 
UPPER LATERAL INCISOR. 
 
 Fig. 63. — Upper 
 Lateral Incisor, 
 Mesial Surface. 
 
 The lingjial fossa may be present as a smooth, unbroken con- 
 cavity, or it may be subdivided by a longitudinal ridge, which 
 often exists to such an extent as to force the remaining portions 
 of the fossa well against the marginal ridges, 
 where they will be observed as slight depres- 
 sions rather than marked concavities. 
 
 The Mesial Surface of the Crown (Fig. 
 63). — Viewing the crown from this aspect, 
 the outline is that of an inverted cone or 
 triangle. The lingual margin of the surface 
 is well defined, and the angle formed by the 
 union of this surface with the lingual surface 
 is moderately acute. The labial margiti is 
 well rounded, and passes into the labial sur- 
 face without a decided line of demarcation. 
 The surface on its upper or cervical third is 
 usually flattened and occasionally concave. 
 At the center, and condnuing toward the 
 cutting-edge, it is decidedly convex in every 
 direction, thus producing a prominent point of contact with the 
 distal surface of the central incisor. 
 
 The Distal Surface of the Crown (Fig. 64). — This surface 
 also shows the characterisdc wedge-shape ot 
 the crown, and is principally different from the 
 mesial surface in being convex throughout. 
 Near the center it is well rounded and full, pro- 
 viding a point of contact for the mesial surface 
 of the cuspid. The lingual margin, while being 
 more decidedly outlined than the labial, is much 
 more rounded than the lingual margin of the 
 mesial surface. From the most prominent point 
 near its center the surface slopes away in every 
 direction, the convexity being most marked 
 near the cutting-edge. 
 
 The Cutting-edge of the Lateral Incisor. — In 
 the young tooth the cutting-edge presents the 
 three litde tubercles common to all incisors, the 
 grooves which divide them passing up over the labial and lin- 
 
 FiG. 64. — Upper 
 Lateral Incisor, 
 Distal Surface. 
 
glial surfaces and forming the labial and lingual grooves. These 
 soon disappear by wear, usually leaving the cutting-edge in the 
 form of a direct line and connecting the two angles of the crown. 
 Like the central incisor, this margin of the crown may be thin 
 and sharp, or it may be thick and dull. 
 
 The Cervical Margin, — The line of demarcation between the 
 crown and the root of the tooth resembles so closely that de- 
 scribed in connection with the central incisor that it will only be 
 necessary to mention one or two characteristic differences. 
 The lingual side of the line presents a much smaller curve pro- 
 portionately, and usually extends a little higher in the direction 
 of the root than that represented upon the labial portion. The 
 mesial and distal portions of the line dip well down, decreasing 
 the length of the crown on these surfaces ; the margin on the 
 former surface is usually angular and V-shaped, while on the 
 latter it is circular in form. 
 
 The Angles of the Crozuii. — The angles of the crown are the 
 mesial and the distal, and are formed in the same manner as the 
 same angles of the central incisor. The mesial angle is generally 
 well produced, in most instances being slightly acute ; but when 
 the cutting-edge is thin and frail, the angle is frequently much 
 obliterated by wear. That portion of the crown of the upper 
 lateral incisor which is usually referred to as the distal angle is 
 scarcely worthy of the name. It is usually present as a long 
 curve, which begins near the center of the cutting-edge and ex- 
 tends well up on the distal surface. This characteristic outline is 
 sometimes so pronounced as to completely destroy the cutting- 
 edge, the distal surface being carried forward by a long curve 
 ending in the mesial angle. 
 
 The Neck of the Tooth. — In this tooth the neck is usually 
 marked by a constriction much more pronounced than that 
 found in the central incisor. On the labial and lingual sur- 
 faces it is principally formed by a sudden sloping of the enamel 
 surface rootward, but on the two lateral surfaces it is formed 
 by a flattening or slight concavity of both the crown and the 
 root. 
 
 The Root of the Upper Lateral Incisor. — The root 
 of this tooth is conic in form, and is much more flattened from 
 
UPPER LATERAL INCISOR. 151 
 
 mesial to distal than the root of the central incisor. At its 
 junction with the crown it is circular in form, the labial portion 
 forming the segment of a larger circle than the lingual, this feature 
 being observed throughout its entire length. The flattening of 
 the mesial and distal sides begins immediately above the neck, 
 and gradually increases as the center of the root-length is ap- 
 proached, where it often develops into a slight longitudinal de- 
 pression. As the apical end of the root is reached, this longi- 
 tudinal depression gradually disappears, and the root again 
 becomes circular in form. The thickness of the root is about 
 one-third greater from labial to lingual than from mesial to 
 distal, and, while it is generally classed as a straight root, it is 
 frequently provided with a pronounced distal curve near the 
 apical extremity. In some instances it is found with a double 
 mesiodistal curve. 
 
 Bilious Type. — In this type the lateral incisor is frequently 
 poorly developed, the cutting-edge and distal angle are want- 
 ing, the crown being in the form of a single conic cusp, the 
 distal surface meeting the mesial at a point near the mesial 
 angle. This form of crown might be classed as one of malfor- 
 mation, but the fact that it most frequently occurs in this tem- 
 perament would appear to indicate a normal condition. When 
 the crown takes the form common to incisors, it is of greater 
 longitudinal than transverse extent, the angles are well pro- 
 duced, and the mesial and distal surfaces are flat and almost par- 
 allel with each other. The labial surface is flat and is frequently 
 broken by transverse ridges near the cervical portion. The 
 lingual surface presents well-marked outlines and margins, a cus- 
 pule is seldom present, and the lingual fossa is well marked, but 
 not deep. The cutting-edge is thin and sharp, to provide for 
 the overbite, which is rather long. The cervical border is square 
 and angular. 
 
 Nervous Type. — In this typal form the neck of the tooth 
 is a pronounced feature. The crown is long and narrow, the 
 constriction forming the neck beginning well down on the crown 
 and extending over the cervical line to the surface of the root. 
 The labial surface is convex in every direction and the labial 
 grooves fairly well defined. The mesial surface is convex near 
 
152 ANATOMY. 
 
 the center and cutting-edge, but often shows a sHght concavity 
 on its cervical portion. The distal surface is rounded and smooth. 
 The lingual surface presents a general concavity, a cuspule 
 being more frequently present than in other types. The lingual 
 fossa is deep, and often extends beneath the cervicomarginal 
 ridge in the form of a circular fissure. The cutting-edge is 
 thin and sharp, providing for a long overbite ; the mesial angle 
 is pointed and well formed, while the distal is usually much 
 rounded. The cervical line is well arched, forming the segment 
 of a much smaller circle than that seen on the same tooth of 
 other temperaments. 
 
 Sanguineous Type. — The crown is well proportioned, with 
 the length slighdy predominating over breadth, all the surfaces 
 being more or less rounded and smooth, showing the crown 
 to be made up of curves rather than angles. The labial surface 
 presents a graceful convexity throughout ; the mesial and distal 
 surfaces are both convex, with their margins poorly defined. 
 The lingual surface shows the rounded nature of the crown in 
 having its fossa and marginal ridges oval and blending one into 
 the other. The cutting-edge is moderately heavy and dull, in 
 keeping with the overbite, which is short. The cervical line is 
 made up of curves rather than angles. 
 
 Lymphatic Type. — In this type the crown is generally of 
 greater transverse than longitudinal extent. The neck is poorly 
 produced, the crown and root uniting without any marked con- 
 striction of the parts. The labial surface is much flattened from 
 mesial to distal, and but slightly convex in the direction of the 
 long axis of the tooth. The mesial and distal surfaces are but 
 little rounded and are nearly parallel with each other, so that the 
 contact with adjoining teeth becomes an extent of surface rather 
 than a single point. The lingual surface is convex above, but 
 as the cutting-edge is approached it becomes flat, but seldom 
 concave. The marginal ridges are not well shown and the 
 lingual fossa is but a slight depression. The angles of the 
 crown are well produced and the cutting-edge thick and blunt, 
 this marginal surface frequently occluding directly upon the 
 opposing lower teeth. The curvature of the cervical line is 
 that of a long circle. 
 
UPPER CUSPID. 
 
 153 
 
 UPPER CUSPID. 
 
 ^ IPf f 
 
 Fig. 65. 
 
 Calcification Begins, from Three Centers, Third Year after Birth. 
 Calcification Completed, Twelfth to Thirteenth Year. 
 Erupted, Twelfth to Thirteenth Year. 
 Average Length of Crown, .37. 
 
 Average Length of Root, .68. 
 
 Average Length over All, 1.05. 
 
 About the third year after birth calcification begins in the 
 central lobe, which is gradually extended laterally, until, at the 
 fourth year it is met by the two lateral lobes, which are some- 
 what later in beginning, and by the fifth year the three are 
 united, the former eventually establishing the single cusp of the 
 tooth and the latter two the mesial and distal angles. About 
 the sixth year two-thirds of the crown is formed, and by the 
 seventh year the constriction which marks the beginning of the 
 neck of the tooth commences to make its appearance. Between 
 the seventh and eighth year calcification in the crown is com- 
 pleted and the cervical line established, during the following year 
 nearly one-quarter of an inch is added to the length of the root, 
 and by the beginning of the tenth year the root is formed for fully 
 two-thirds of its entire length. Between the twelfth and thirteenth 
 years or at the time of eruption, calcification is completed in the 
 root and the apical foramen established (Fig. 65). In this latter 
 particular the cuspid tooth differs from most of the others in 
 
154 ANATOMY. 
 
 being completely calcified previous to, or about the time of, 
 its eruption, the eruptive process in this tooth, therefore, 
 differs from that of the other teeth, being fully calcified about 
 the time it makes its appearance through the gum tissue. 
 To reach its final position in the arch the tooth moves bodily 
 downward, the bone filling in behind ; while in the incisors, bi- 
 cuspids, and molars the free calcifying root-extremities remain 
 nearly stationary, the crowns being forced downward as the lime 
 salts are deposited. 
 
 The crown of the upper cuspid presents for examination 
 four surfaces, — labial, lingual, mesial, and distal, — two margins, — 
 the cervical margin and the cutting-edge, — and a mesial and a 
 distal angle. In general outline it is of the simplest form, re- 
 sembling the primitive cone-shaped teeth of many fishes. When 
 viewed by looking directly upon the mesial or distal surface, the 
 wedge-shape common to the incisors is observed. The base of 
 the double incline is, however, much broader proportionately 
 than the corresponding measurement of the incisors. Looking 
 at the crown from a labial or lingual direction, its function, 
 as both a penetrating and incising organ, may be observed 
 in the single cusp from which it derives its name. The cusp, 
 which is formed at the expense of the cutting-edge, divides this 
 latter margin into two distinct portions — the mesial cutting-edge 
 and the distal cuttitig-edge . 
 
 The Labial Surface of the Crown (Fig. 66). — The contour 
 of this surface is that of a broken circle more or less perfectly 
 drawn. It is bounded by five margins — mesial, distal, cervical, 
 mesial-incisive, and distal-incisive. The mesial margin is rounded 
 from labial to mesial, and slightly convex from the cutting-edge 
 to the cervical line. The distal margin is also rounded from 
 labial to distal, presents a greater convexity, and is somewhat 
 shorter from the cutdng-edge to the cervical line than the mesial 
 margin. By a continuation and final union of these two lateral 
 margins the cervical margin of the surface is formed, while by 
 their union with the cutting-edges the mesial and distal angles 
 of the crown are established. The mesial-incisive margin is usu- 
 ally slightly concave near its center, although in some instances 
 it is convex. The distal incisive margin responds to the same 
 
UPPER CUSPID. 
 
 155 
 
 description, although the concavity, when present, is nearest the 
 point of the cusp. t^From the summit of the cusp these two 
 margins slope away to join the mesial and distal angles, the_ 
 distal incline being about one-fourth longer than the mesial._ 
 This surface is generally of greater longitudinal than transverse 
 extent, its greatest mesiodistal diameter being from angle to 
 angle, or at a point immediately above them. The surface 
 is convex in every direction, and is marked by a central lon- 
 gitudinal ridge, usually well defined — the labial ridge. Begin- 
 ning at the summit of the 
 cusp, this ridge is more or less 
 contracted laterally, but as it 
 passes over the surface in the 
 direction of the rootit becomes 
 broadened and flattened, and 
 gradually disappears in the 
 cervical portion. Upon either 
 side of this ridge are the 
 labial grooves, well defined 
 at their beginning, but which 
 gradually blend into the sur- 
 face of the crown as they 
 pass rootward. In some in- 
 stances these grooves are so 
 strongly defined as to form a 
 decided ridge upon the mesial 
 
 and distal margins of the surface ; — these are the labial marginal 
 ridges. 
 
 The labial ridge and the two labial grooves mark the develop- 
 mental lines of the crown, the former resulting from the middle 
 lobe, which in this tooth is much the largest of the three, while 
 the latter denotes the line of junction between the middle and 
 the lateral lobes. 
 
 The Lingual Surface of the Crown (Fig. 67). — This sur- 
 face presents nearly the same general outlines as the labial, 
 with the exception of the cervical portion, which is more con- 
 stricted, tending to produce an oblong or egg-shape. It usually 
 abounds in well-defined ridges and depressions, giving to the 
 
 Cervical ^S 
 Ridge ^H 
 
 ■ 
 
 Line 
 
 Mesial ^V 
 Angle ^m 
 
 M 
 
 
 Mesial Cut- ^^L 
 ting-edge ^^^^ 
 
 i 
 
 Distal 
 Angle 
 Distal Cut- 
 ting-edge 
 
 Labial Ridge 
 
 
 Fig. 66. — Upper Cus 
 
 piD, Labial 
 
 Surface. 
 
156 
 
 ANATOMY. 
 
 tooth a rugged and strong appearance. There is but little gen- 
 eral concavity to the surface in passing from the point of the 
 cusp to the root, while it may be flat, concave, or convex. 
 As in the incisors, the margins of this surface are formed by 
 three marginal ridges and by the cutting-edge. The mesio- 
 niarginal ridge is commonly a well-defined fold of enamel, be- 
 ginning at the mesial angle and passing upward in the direction 
 of the root, where it unites with the cervicomarginal ridge. It 
 is sometimes quite narrow and rather sharply outlined ; at others, 
 
 it extends well toward the 
 center of the surface in the 
 form of a well-rounded fold. 
 The distomarginal ridge, 
 which is somewhat shorter 
 than the mesial, begins at the 
 distal angle and passes root- 
 ward to meet the cervical 
 ridge. It is well rounded in 
 every direction, but seldom 
 so well produced as the me- 
 sial. The cervicomarginal 
 ridge, which is formed by a 
 continuation or union of the 
 two former, nearly always 
 partakes of their nature, ex- 
 cept when broken by the 
 presence of a cuspule, which 
 is frequendy found upon this tooth (Fig. 70). This small cusp of 
 enamel may be bounded on one or both sides by a fissure, which 
 often extends well under the cervicomarginal ridge, and some- 
 times completely separates it from the two lateral ridges. Pass- 
 ing through the center of the surface from the summit of the 
 cusp to the base of the cervicomarginal ridge is the lingual 
 ridge, which corresponds to the labial ridge of the labial surface. 
 This ridge is usually well produced at or near the point of the 
 cusp, and may continue so throughout, but most frequently 
 becomes reduced in size near the center of the surface. Be- 
 
 FlG. 67. 
 
 Lingual Ridge 
 -Upper Cuspid, Lingual Surface. 
 
UPPER CUSPID. 
 
 157 
 
 tween this ridge and the mesio- and disto-marginal ridges are 
 two longitudinal depressions — the lingual grooves. 
 
 Mesial Surface of the Crown (Fig. 68). — In general out- 
 line this surface resembles that of the central incisor, excepting 
 that the wedge shape which it describes is more heavily set and 
 blunt, with the surface extending beyond the base of the cone, 
 in the direction of the root, to the extent of about one-third of 
 its entire length. In some cases the base of the cone will be 
 on a line with the cervical margin. The lower two-thirds of 
 the surface, or that nearest the mesial angle, is convex in every 
 direction ; this convexity grad- 
 ually disappears as the center 
 is approached, beyond which 
 point it is much flattened, usu- 
 ally ending in a slight con- 
 cavity at the cervical margin. 
 When looking directly upon 
 this surface, its margins will be 
 found within the profile lines, 
 these being represented by the 
 labial ridge anteriorly, and by 
 the lingual and cervical ridges 
 posteriorly. The margins, 
 three in number, are the labial, 
 which is well rounded and 
 poorly defined ; the lingual, 
 more or less distinctly out- 
 lined and somewhat irregular ; and the cervical, which is 
 represented by the extent of the enamel covering of the 
 crown ; this latter margin being concave in the direction of the 
 root. The most prominent point of this surface serves as a 
 point of contact for the distal surface of the lateral incisor, the 
 extent of contact being much influenced by the type of tooth, 
 but in the cuspid this is usually a single point rather than an 
 extent of surface. 
 
 The Distal Surface of the Crown (Fig. 69). — This surface 
 in many respects is similar to the mesial, particularly in its gen- 
 eral outline. The extent of surface is somewhat less and the 
 
 Fig. 68.- 
 
 -Right Upper Cuspid, Mesial 
 Surface. 
 
iS8 
 
 ANATOMY. 
 
 convexity much more marked than that of the mesial surface. 
 The position of the distal angle, which is the lower boundary 
 of the surface, being much nearer the cervical line, makes this 
 surface about one-third shorter than the mesial surface. The 
 lateral margins of the surface, which are also within the profile 
 lines, differ from those of the mesial in being more clearly de- 
 fined. The cervical margin differs from that of the mesial sur- 
 face by having a concavity with much less depth. As stated 
 above, the surface is decidedly more convex than the mesial, 
 the point of contact for the mesial surface of the first bicus- 
 pid being almost in the 
 center. Near the cervi- 
 cal margin the surface is 
 inclined to flatness, and 
 frequently concave. 
 
 The Ctitting-edge, or 
 Cusp. — As inferred in the 
 beginning of this descrip- 
 tion, the cuspid tooth is 
 both an incisingand a pene- 
 trating organ, the latter 
 function being provided for 
 by the presence of the sin- 
 gle cusp, which divides the 
 cutting-edge into an ante- 
 rior or mesial portion and a 
 posterior or distal portion. 
 The mesial cutting-edge 
 begins at the summit of the cusp and slopes away to meet 
 the mesial angle, which it assists in forming. The outline of 
 this edge is usually gracefully curved and unbroken unless 
 permanently crossed by the labial groove. The distal cut- 
 ting-edge is generally somewhat longer than the mesial. 
 Immediately after leaving the summit of the cusp it may be 
 slightly concave ; but beyond this point it is well rounded, until 
 it reaches the distal angle, into which it gradually disappears. 
 This edge is also frequently broken by the labial groove. In 
 its entirety the cutting-edge is subject to the same variations as 
 
 Fig. 69. — Left Upper Cuspid, Distal 
 Surface. 
 
UPPER CUSPID. 
 
 those of the incisors — /. e., it may be thin and sharp, or it may 
 be thick and blunt. 
 
 The Cusp. — The single cusp from which this tooth derives its 
 name is formed by the union of the labial ridge, the lingual 
 ridge, and the mesial and distal cutting-edges. The summit of 
 the cusp is constant in its position, always being in a direct line 
 with the long axis of the tooth, whether it be viewed from a 
 mesial or a lingual direction. 
 
 The Cervical Line. — To describe this fully would be to repeat 
 what has already been said in connection with the incisor teeth. 
 This enamel margin differs in one particular only from that of 
 the incisors, and that variation is 
 not a constant one — the lingual 
 portion is frequently extended in 
 the direction of the root, produc- 
 ing a short, positive curve at that 
 point. 
 
 Tlie Angles of the Crow7i. — 
 Owing to the rounded nature of 
 the majority of cuspid crowns, the 
 term angle, as applied to its free 
 extremities, is almost a misnomer, 
 and can only be considered as 
 assisting in description. The 
 mesial angle, which is formed by 
 the union of the marginal ridges 
 of the labial and lingual surfaces 
 with the mesial cutting-edge, is 
 
 seldom a well-produced angle, usually being rounded in every 
 direction. The distal angle, which is formed in a manner similar 
 to the mesial, is somewhat more deserving of the name, both the 
 labio- and linguo-marginal ridges frequently presenting angu- 
 larity. The position of the distal angle is usually well toward the 
 center of the crown, and occasionally above this point, and, al- 
 though it may descend, it is seldom found on a line with the 
 mesial angle. 
 
 The Neck of the Upper Cuspid. — This may or may not 
 be a distinctive feature of the cuspid tooth, although when viewed 
 
 Marginal Ridges 
 
 Fig. 70. — Upper Cuspid, Lingual 
 Surface, Strongly Developed. 
 
ANATOMY. 
 
 from a labial aspect, the lateral flare or bulging of the crown gives 
 the appearance of a decided constriction between the crown and 
 the root ; but, when examined from the mesial surface, this con- 
 stricted appearance is absent, the contour of the crown passing 
 into that of the root, with the cervical line alone marking the extent 
 of each. The tooth at this point is well rounded anteriorly, flat- 
 tened laterally, and again rounded posteriorly, the latter forming 
 the segment of a smaller circle than that of the labial surface. 
 
 The Root. — This tooth possesses the largest and longest root 
 of any of the teeth, in the latter respect usually exceeding the 
 central incisor by about one-third, and the lateral incisor by one- 
 fourth or more. Like the base of the crown, 
 it is rounded on the labial and lingual sur- 
 faces, and is flattened laterally, this form 
 usually being continued throughout its en- 
 tire length. It gradually diminishes in size 
 from the neck to the apex, and in its 
 entirety forms a perfect cone. On the 
 mesial and distal sides it is not only much 
 flattened, but is frequently provided with a 
 longitudinal depression, which is most 
 marked near the center of its length. In 
 some instances this root is possessed of a 
 slight distal curve, which may be gradual 
 from the base to the apex, or it may exist 
 in a more positive way by a sudden distal 
 curve near its apical extremity. 
 Bilious Type (Fig. 71). — The rounded outlines common 
 to the cuspid tooth are less pronounced in this type than in any 
 other, and instead of curves, angles are present. The crown is 
 above the average size, length predominating over breadth, the 
 cusp well formed, and the angles strong. The labial surface 
 is often crossed by a number of transverse ridges near the cer- 
 vical portion, the labial ridge is bold, as are also the labio- 
 marginal ridges. The mesial and distal surfaces possess no dis- 
 tinguishing features, but the lingual, like the labial, shows the 
 angular nature of the crown in having its margins and ridges 
 squarely set. 
 
 Fig. 71. — Bilious Type, 
 Distal Surface. 
 
UPPER CUSPID. 
 
 A cuspule is more frequently found in this type than any 
 other, and sometimes reaches down to a point corresponding 
 to the transverse center of the crown. The neck is moder- 
 ately well produced, and the cervical line decidedly V-shaped on 
 its lateral portions, while on the labial and lingual it takes the 
 form of a broken circle. The cutting-edges are rather heavy 
 and square, and are nearly of equal length. In this tempera- 
 ment the cuspid tooth often partakes of the form described in 
 connection with the lateral incisor of the same type — /. e., the 
 absence of the cutting-edge and one or both 
 angles, making the crown a perfect cone. 
 
 Nervous Type (Fig. 72). — The crown 
 is of much greater longitudinal than trans- 
 verse extent, the outlines oval and gracefully 
 formed, and the neck is much constricted from 
 mesial to distal, being made so by the lateral 
 flare of the body of the crown, which is a 
 distinctive feature of this type. The labial 
 ridge is well formed near the summit of the 
 cusp, but usually disappears near the center 
 of the surface. The labiomarginal ridges 
 are seldom present, and the surface in general 
 is convex and smooth. The mesial and distal 
 surfaces show a pronounced convexity near 
 the angles, and often a slight concavity be- 
 tween this point and the cervical line. The lingual surface, while 
 generally showing all the descriptive lines, may be considered 
 smooth ; it is convex from mesial to distal, and slightly concave 
 in the direction of the long axis of the tooth. The cusp is long 
 and penetrating, the distal cutting-edge is much longer than the 
 mesial, and both are inclined to sharpness. The cervical line on 
 the labial and lingual surfaces is deeply arched, frequently giving 
 to the gingival margin a receded appearance. 
 
 Sanguineous Type (Fig. ']t^. — The crown in this type 
 abounds in long curves, the longitudinal and transverse extents 
 are nearly equal, the angles, owing to their circular form, are 
 barely deserving the name, while the cusp and cutting-edges 
 are outlined by one long, oval sweep. The labial surface is 
 
 Fig. 72. — Nervous 
 Type, Labial- Sur- 
 face. 
 
prominent and convex, and the developmental grooves are fairly 
 well shown. The mesial and distal surfaces show a moderate 
 general convexity, while the lingual abounds in well-rounded 
 ridges and borders. The constriction forming the neck of the 
 tooth is moderate. The cervical line is in the form of perfectly 
 arched curves, forming on the labial sur- 
 face the segment of a circle correspond- 
 ing to the circumference of the crown 
 of the tooth. 
 
 Lymphatic Type. — In this type the 
 crown is usually greater in its transverse 
 than in its longitudinal measurement; it is 
 lacking in graceful outline, and may best 
 be described as being short, thick, and 
 heavy set. None of the surfaces abound 
 in descriptive lines, although transverse 
 ridges are sometimes present on the 
 labial surface near the cervix. Both the 
 labial and lingual surfaces are convex 
 in every direction, while the mesial and 
 distal are inclined to flatness. The cusp 
 is heavy and blunt, and the cutting-edges, 
 which are nearly of equal length, are 
 thick and dull. The mesial and distal 
 angles are well produced. The cervical line is almost a direct 
 line encircling the neck of the tooth, the segmental form on the 
 labial surface being that of a much larger circle than any of 
 those previously described. The neck is thick and heavy, and 
 the roots generally short. 
 
 Fig. 73. — Sanguineous 
 Type, Distal Surface. 
 
UPPER FIRST BICUSPID. 
 
 163 
 
 UPPER FIRST BICUSPID. 
 
 Calcification Begins, from Four centers, about the Fourth Year. 
 Calcification Completed, Eleventh to Twelfth Year. 
 Erupted, Tenth to Eleventh Year. 
 AvER.\GE Length of Crown, .32. 
 
 Average Length of Root, .48. 
 
 Average Length over All, .So. 
 
 This tooth, although presenting a crown of vastly different 
 contour, is developed by a process almost identical with that of 
 the incisors and cuspids. As the name implies, it is made up 
 of two cusps, one forming the buccal and the other the lingual 
 half of the crown. Calcification in the buccal cusp is from three 
 centers and begins about the fourth year, the central lobe first 
 receiving the lime salts. During the following year the two 
 lateral lobes begin to calcify, soon followed by a union of the 
 three, thus completing the margins and summit of the cusp. 
 Unlike the incisors, but corresponding to the cuspid, the middle 
 lobe is much the largest of the three, frequently forcing the 
 developmental (buccal) grooves well toward the angles of the 
 crown. The development of the lingual cusp corresponds to 
 the development of the cervical ridge on the incisors and cus- 
 pids, except that it has a separate center of calcification, and 
 a cusp almost as large as the buccal results. Between the 
 fifth and sixth year union between the two cusps takes place, 
 the line of confluence being permanently recorded by a well- 
 
1 64 ANATOMY. 
 
 defined groove, which traverses the crown from mesial to distal. 
 This groove, although forced to occupy a different position, cor- 
 responds with the lingual groove of the incisors and cuspids. 
 After the union of the cusps the process of calcification is con- 
 tinued into the body of the crown, and by the seventh year it is 
 more than half completed. The eighth year usually finds the 
 crown fully formed and the base of the root or roots outlined. 
 As this tooth is generally provided with two roots, the first indi- 
 cation of bifurcation will be observed between the eighth and 
 ninth year by a filling-in near the center of the mesial and distal 
 walls, which finally become united by a thin septum of dentine or 
 cementum. After this period the roots calcify separately, and by 
 the middle of the ninth year about one-third of their length is 
 
 established. During the follow- 
 Buccai Triangular Ridge iug year, or at about the time 
 
 of eruption, the development of 
 the roots has extended to about 
 three-fourths of their com- 
 pleted length, and between the 
 eleventh and twelfth year, or 
 at a time corresponding to that 
 of the crown assuming its final 
 
 Lingual Cusp ... . 
 
 ,,,,,„„ -D position in the arch, calcifica- 
 
 FiG. 75. — Upper First Bicuspid, r ' 
 
 Occlusal Surface. tion is completed and the apical 
 
 foramen formed (Fig. 74). 
 
 The Crown of the Upper First Bicuspid presents for 
 examination five surfaces — buccal, lingual, mesial, distal, and 
 occlusal. In general, the contour of the crown is irregularly 
 quadrilateral, being about one-third greater in its buccolingual 
 measurement than from mesial to distal. It is somewhat flat- 
 tened from mesial to distal, but rounded on its buccal and 
 lingual surfaces. 
 
 The Occlusal Surface of the Crown (Fig. 75). — The 
 contour of the crown is best observed by a view of this surface, 
 which may be described as trapezoidal or irregularly quadri- 
 lateral in form. The four margins of the surface are those 
 which represent the four lateral surfaces, — the buccal, lingual, 
 mesial, and distal, — the latter two being in the form of well- 
 
UPPER FIRST BICUSPID. 165 
 
 defined ridges — the mesio- and disto-marginal ridges. The 
 buccal margin is formed by the mesial and distal inclines of the 
 buccal cusp ; it has a slight buccal convexity, and at its union 
 with the proximate surfaces assists in forming the mesial and 
 distal angles of the crown. The distal half of this margin is 
 usually somewhat longer than the mesial, and the distal angle 
 is less pronounced than the mesial. The lingual margin presents 
 a much greater convexity than the buccal, but the curve formed 
 is the segment of a much smaller circle. As in the buccal mar- 
 gin, the distal half of this margin is the longest, but unlike the 
 former, its free extremities pass into the mesial and distal mar- 
 gins without producing angles. The mesio- and disto-marginal 
 ridges are strong folds of enamel which arise from the mesial 
 and distal angles and converge slightly as they pass to the lin- 
 gual, where they are gradually lost in the lingual margin. 
 
 The Cusps (Fig. 75). — These are two in number, and are 
 named, in accordance with their location, buccal and lingual. 
 The buccal cusp is the larger and longer of the two. From 
 the summit of this cusp four ridges descend — one in a mesial 
 direction, forming the mesial cutting-edge of the crown ; one in a 
 distal direction, forming the distal cutting-edge ; one to the buc- 
 cal surface, the buccal ridge ; and a fourth, the btucai triangidar 
 ridge, descends the central incline. The mesial and distal ridges 
 enter into the formation of the mesial and distal angles at their 
 extremities ; the latter is slightly longer than the former, and both 
 are frequently broken near the center by the grooves of devel- 
 opment — the buccal grooves. The buccal ridge may be well 
 developed and extend almost to the cervical line, or it may be 
 slight and disappear near the center of the surface. The buccal 
 triangular ridge usually ends somewhat abruptly in the central 
 groove, but in some instances it is continued and joins a similar 
 ridge from the lingual cusp, this union forming the transverse 
 ridge. The triangular ridge often bifurcates near the center of 
 its incline, and is continued in two distinct but smaller ridges. 
 The lingual cusp is much less angular than the buccal ; the apex 
 is usually rounded, while the descending ridges are generally 
 three in number instead of four. The mesial and distal ridges 
 are nearly of the same length, and pass without interruption into 
 
1 66 ANATOMY. 
 
 the mesio- and disto-marginal ridges. The triangular ridge is 
 less clearly defined than its fellow of the buccal cusp, and it is 
 not unusual for it to be entirely wanting. The lingual aspect of 
 the cusp is smooth and rounded, presenting nothing in the form 
 of a ridge in correspondence with the buccal ridge of the buccal 
 cusp. Like the incisors and cuspids, the summits of these cusps 
 are usually in a direct line with the long axis of the tooth. 
 
 The developmental grooves, all of which are observed upon 
 the occlusal surface, are the central, mesial, distal, two trian- 
 gular, and two buccal. The central groove is the most marked, 
 is deeply sulcate, and extends through the center of the sur- 
 face from mesial to distal, ending just within the two marginal 
 ridges in two irregularly formed depressions or pits — the mesial 
 and distal pits. This groove marks the line of union between 
 the buccal and lingual lobes. The mesial and distal grooves 
 are not always well defined, but may usually be observed as 
 fine lines passing over the central portion of the mesio- and 
 disto-marginal ridges. The mesio- and disto-triangular grooves 
 begin in the mesial and distal pits, and pass in the direction of the 
 mesial and distal angles, where they are either lost, or may be 
 traced as slight depressions passing over the buccal ridges 
 near the angles, and they may further continue over the buccal 
 surface in the direction of the root. These two grooves, together 
 with the mesial and distal above referred to, form the outlines 
 of the mesiobuccal and distobuccal developmental lobes. The 
 buccal grooves will be described in connection with the buccal 
 surface. Supplemental grooves are seldom found in connection 
 with the buccal half of the occlusal surface, but are occasionally 
 present on the central incline of the lingual cusp. 
 
 The Buccal Surface of the Crown (Fig. 76). — In many 
 respects this surface resembles the corresponding or labial sur- 
 face of the cuspid tooth. It is bounded by four margins — occlu- 
 sal, mesial, distal, and cervical. The occlusal half of the sur- 
 face is formed of the buccal cusp, and is cone-shaped, while the 
 cervical half is irregularly quadrilateral in form. The extent of 
 surface from the cervical line to the point of the cusp is usually 
 about one-third greater than the greatest mesiodistal diameter, 
 which is represented by a line drawn from the mesial to the dis- 
 
UPPER FIRST BICUSPID. 
 
 167 
 
 Ridge 
 
 tal angle. The form shown is that of a general convexity, the 
 summit of which is surmounted by a longitudinal ridge — the 
 bticcal ridge. This ridge, which is 
 formed from the central develop- 
 mental lobe, is most pronounced 
 near the occlusal margin, and grad- 
 ually disappears near the center 
 of the surface. Upon either side 
 of the buccal ridge are two grooves 
 — the buccal grooves — which denote 
 the line of union between the central 
 and the two lateral lobes, and be- 
 yond these are the angles of the ■^"s'*' 
 crown. The buccal ridge springs 
 
 from the buccal cusp, the summit of 
 
 , . , . 11 • 1- 1- Fig. 76. — Upper First Bicuspid, 
 
 which IS generally m a direct line Buccal Surface. 
 
 with the long axis of the tooth ; 
 
 when there is a deviation from this the summit is usually 
 
 thrown a little to the mesial, resulting in a reduction of 
 
 the length of the mesial cutting- 
 edge. 
 
 As previously stated, the great- 
 est mesiodistal diameter of the 
 surface is on a line with the angles 
 of the crown ; this measurement 
 is much reduced at the cervical 
 line, so that the point of contact 
 with adjoining teeth is thrown 
 near the occlusal margins of the 
 crown. This variation in the 
 transverse measurement also re- 
 sults in what is commonly referred 
 to as the "bell shape" of the 
 crown. The cervical margin of 
 the surface is fairly well arched, 
 
 but seldom to such a degree as the corresponding margin upon 
 
 the incisors and cuspids. 
 
 The Lingual Surface of the Crown (Fig. ']•]). — This surface 
 
 Summit of Lingual Cusp 
 
 Fig. 77. — Upper First Bicuspid, 
 Lingual Surface. 
 
is smooth and decidedly convex, the absence of strongly devel- 
 oped grooves and ridges contributing to the former fact. Like 
 the buccal surface, its greatest transverse measurement is at the 
 base of the cusp in which it terminates. The extent of the sur- 
 face is about one-third less than that of the buccal, and its occlud- 
 ing and cervical margins are alone well defined, the mesiodistal 
 convexity passing so gradually into these respective surfaces 
 that a positive line of distinction can scarcely be recognized. 
 In passing from the cervical line to the occlusal margin, the 
 surface is rapidly carried toward the center of the crown. 
 
 The cervical margin of this 
 surface is usually in the form 
 of a direct line encircling the 
 neck, but occasionally pre- 
 sents a slight concavity in 
 the direction of the root. 
 
 The Mesial Surface of 
 the Crown (Fig. 78). — This 
 surface of the crown has 
 three of its borders well de- 
 fined ; these are the buccal, 
 the occlusal, and the cervi- 
 cal, the remaining or lingual 
 margin passing so gradually 
 into the lingual surface that 
 no positive line of demarcation can be given. The buccal margin 
 extends from the mesial angle to the cervical line, and invariably 
 presents a slight buccal inclination, thus Increasing the width ot 
 the surface^on its cervical portion. The occlusal margin is formed 
 by the mesiomarginal ridge, and by a portion of the ridge 
 descending from the lingual cusp. It is irregularly V-shaped, 
 and in many instances is broken in the center by the mesial 
 groove. The cervical margin differs from those of the incisors 
 and cuspids, nearly always being in the form of a straight line 
 from buccal to lingual. The surface in general is flattened, but 
 shows a slight general convexity near the occlusal margin, 
 and frequently a slight concavity immediately below the cervical 
 line, this form placing the point of contact with the distal surface 
 
 ginal Ridge 
 
 Fig. 78. — Upper First Bicuspid, Mesial 
 Surface. 
 
UPPER FIRST BICUSPID. 
 
 169 
 
 of the cuspid near the occlusal margin. The surface is occa- 
 sionally divided into a buccal and a lingual portion by the mesial 
 groove, which may extend to the cervical line, but which gener- 
 ally disappears near the center of the surface. The buccal half 
 of the surface which is formed from the mesial developmental 
 lobe is inclined to angularity, while the lingual half is decidedly 
 rounded, particularly in the direction of the occlusal margin. 
 
 The Distal Surface of the Crown (Fig. 79). — In general, 
 this surface resembles the mesial, being flattened and bounded 
 by three more or less distinct 
 margins. The slight bucco- 
 lingual convexity is not con- 
 fined to the occlusal portion 
 of the surface, but is inclined 
 to extend to the cervical mar- 
 gin, in this particular being at 
 variance with the mesial sur- 
 face. This surface passes 
 into the lingual by a much 
 longer curve than that shown 
 on the mesial surface. 
 
 The Angles of the 
 Crown. — These are two in 
 number and, as in the teeth 
 previously described, are 
 named, according to their 
 location, mesial and distal. 
 
 Occlusal Surface 
 
 79. — Upper First Bicuspid, Distal 
 Surface. 
 
 The 
 
 mesial angle is formed by 
 ridore and mesial cuttingr- 
 
 the union of the mesiomarginal _ ^ 
 
 edge. It is primarily the product of the mesial developmental 
 lobe, and is usually well produced. The distal angle, which is 
 formed in a like manner, is inclined to be more rounded. 
 
 The Neck of the Tooth. — In most typal forms the neck 
 of the upper first bicuspid is well defined, particularly upon 
 the mesial and distal surfaces. Viewing the tooth from a buccal 
 aspect, the neck is a distinctive feature, but when studied from 
 the mesial or distal sides, the constriction is scarcely observed, 
 this being particularly the case if the tooth has but a single root. 
 In general, the neck partakes of the contour of the crown, being 
 
170 ANATOMY. 
 
 convex on the buccal and lingual, and flattened and frequently 
 slightly concave on the mesial and distal. 
 
 The Roots of the Upper First Bicuspid. — This tooth 
 is usually developed with two roots, sometimes with only one, 
 and in rare instances it may have three. When two roots are 
 present, one is above the buccal and the other above the lingual 
 half of the crown, and are named, according to their location, 
 as buccal and lingual. In general form the two roots are quite 
 similar, but the buccal is usually a trifle longer than the lin- 
 gual. They taper off to a slender apex, and are inclined to 
 curve in various directions near their extremities. The point of 
 
 Fig. 8o. — Types of Bicuspids. 
 
 bifurcation is frequently some distance above the neck, so that 
 the tooth may be said to possess a single root with two 
 branches. Below the bifurcation the root assumes the form of 
 the neck or cervical portion of the crown, but as the bifurcation 
 is approached, the mesial and distal sides present a longitudinal 
 groove, which gradually increases in depth until the single root 
 becomes separated. The curves of the root-branches above 
 referred to are, in the buccal branch, first to the buccal and 
 then to the lingual ; while the lingual branch first shows a slight 
 lingual inclination immediately above the point of separation, fol- 
 
UPPER FIRST BICUSPID. 
 
 lowed by a gentle buccal curve as the apical end is reached. In 
 some cases the bifurcation begins immediately above the neck of 
 the tooth ; in others it may occur in the apical third ; while a third 
 class is represented by the two roots being united throughout 
 their entire length by a thin septum of dentine and cementum, or, 
 as occasionally happens, by a layer of cementum alone. In this 
 latter instance each root is provided with a distinct canal and 
 foramen. When the tooth has but a single root, it is much flat- 
 tened from mesial to distal, the flatness being slightly broken 
 by an inclination to convexity. The four surfaces usually con- 
 verge toward the apical end, which is oblong from buccal to 
 lingual, and generally provided 
 with a slight distal curve. The 
 presence of three roots is so 
 rare that the condition might be 
 classed as a malformation ; but 
 when they do exist, two are 
 usually attached to the buccal 
 and one to the lingual half of 
 the crown, with the point of 
 separation near the neck of the 
 tooth. 
 
 Bilious Type (Fig. 8i).— 
 The upper first bicuspid of this 
 temperamental type is marked 
 by a crown of moderate length, 
 
 the neck well pronounced, and the cusps and angles marked 
 by angular outlines. The buccal ridge is strongly defined, and 
 the buccal grooves, which extend well up on the buccal surface, 
 cross the mesial and distal cutting-edges, separating them into 
 two distinct parts. The cusps are long and penetrating, and 
 are nearly of equal length, assisting to form the firm and well- 
 locked occlusion common to this type. The mesial and distal 
 surfaces are nearly parallel with each other ; they are seldom 
 convex, so that the approximating teeth are in contact over an 
 extent of surface rather than a single point. The cervical line 
 is but little curved. 
 
 Nervous Type (Fig. 82). — In this temperament the bell- 
 
 Si. — Bilious Type, Distal 
 Surface. 
 
shaped crown Is strongly observed, die crown being long and the 
 tooth much constricted at its neck. The extreme length of the 
 buccal cusp, and the marked cervical constricdon, produce an 
 appearance in the buccal surface resembling the labial surface of 
 the cuspid tooth. The developmental grooves are finely outlined, 
 and the cusps long and penetrating, usually being more pro- 
 nounced than in any other class. The cutdng-edges are sharp 
 and inclined to angularity ; the mesial and distal surfaces are 
 convex near their occlusal margins, but near the cervical 
 line a pronounced concavity is observed, which is continued 
 upon the corresponding root-surfaces. This formation forces 
 the point of contact with adjoining teeth well 
 toward the occlusal surface, and results in an 
 extensive V-shaped interproximate space. The 
 cervical line is sharply and gracefully formed, 
 the curvature being well arched. 
 
 Sanguineous Type. — The typical upper 
 first bicuspid of this class is provided with 
 a crown well proportioned, its length being 
 somewhat greater than its breadth, but about 
 equal to its buccolingual measurement. The 
 buccal surface is seldom broken by the 
 buccal grooves, and is strongly convex in 
 every direction. The lingual surface is much 
 more rounded than the same surface of other 
 types. The mesial and distal surfaces are 
 usually smoothly convex, with an occasional slight concavity 
 immediately below the cervical line. Upon the occlusal surface 
 the grooves are rounded and obscure, rather than sharp and well 
 defined, and the cusps, much less pronounced than in either of the 
 types previously described, are rounded and smooth ; this latter 
 fact is particularly true of the lingual cusp, which is usually much 
 smaller than the buccal. The cutting-edges of the buccal cusp 
 are scarcely deserving of the name, being broad and rounded 
 throughout. The form of the mesial and distal surfaces above 
 described provides for a point of contact near the center of 
 each surface, leaving a slight interproximate space both above 
 and below this point. 
 
 Fig. 82. — Nerv- 
 ous Type, Buccal 
 Surface. 
 
UPPER FIRST BICUSPID. 173 
 
 Lymphatic Type. — An examination of the upper first bi- 
 cuspid of the lymphatic type results in finding a tooth vastly 
 different from any of those previously described. The length 
 of the crown from the cervical line to the point of the cusp is 
 less than either the mesiodistal or buccolingual measurements. 
 In general appearance it is lacking in symmetry, or poorly pro- 
 portioned. The buccal surface presents a gradual convexity 
 from mesial to distal, and seldom has the buccal ridge well de- 
 veloped. The lingual surface is smoothly convex and passes 
 off into the lingual root without the interposition of a decided 
 neck. The mesial and distal surfaces are flattened and spar- 
 ingly conve.x, and are nearly parallel with each other, so that 
 the contact with adjoining teeth is inclined to be distributed 
 over the entire surface, leaving little or no interproximate space. 
 The cusps are short, flat, and rounded, and the occlusal sur- 
 face much flattened in general, corresponding with the 
 nature of the occlusion, which is loose and wandering. The 
 developmental grooves and ridges are fairly well shown, while 
 the cutting-edges and angles of the crown are smooth and 
 rounded. The neck is less pronounced in this type than in any 
 other, the curvature of the cervical line is very slight, the root 
 is short and heavy set, frequently passing well up toward the 
 apex before bifurcating. 
 
UPPER SECOND BICUSPID. 
 
 9 § a 
 
 Calcification Begins, from four Centers, about the Fifth Year. 
 Calcification Completed, Eleventh to Twelfth Year. 
 Erupted, Eleventh to Twelfth Year. 
 Average Length of Crown, .29. 
 
 Average Length of Root, .55. 
 
 Average Length Over All, .84. 
 
 The process of development in this tooth is identical with 
 that of the first bicuspid, calcification in the buccal half of the 
 crown taking place in one central and two lateral lobes, while 
 the lingual half is developed from a single center. The calcify- 
 ing process is about one year later than that in the first bicuspid, 
 the summit of the buccal cusp receiving its lime salts about 
 the beginning of the fifth year. During the following six 
 months calcification begins in the lateral lobes, and also in the 
 lingual lobe. By the sixth year the occlusal surface and a por- 
 tion of the crown are completed by a union of the various lobes, 
 and at seven years the crown is calcified for more than two- 
 thirds of its completed length. Between the eighth and ninth 
 year the contour of the crown is established, and the neck of 
 the tooth and outline of the root-base formed. At the tenth 
 year about one-third of the root-length is formed, and during 
 the following year about ^ of an inch is added to it. By 
 the eleventh or twelfth year calcification is completed and the 
 apical foramen established (Fig. 83). 
 
UPPER SECOND BICUSPID. 
 
 I7S 
 
 fI3 
 1^ 
 
 Fig. 84 
 
 — Second Upper Bicuspid, 
 Occlusal Surface. 
 
 This tooth so closely resembles the first bicuspid that a de- 
 scription in detail will be unnecessary ; there are, however, a few 
 minor points which are at variance and must be described in 
 order to distinguish one from the other. In general, the tooth 
 is a trifle smaller than the first bicuspid, the cusps are somewhat 
 shorter, and the various ridges less 
 distinct. A distinguishing feature ce.urai 
 
 of the occlusal surface is found in 
 the diminished length of the central 
 groove (Fig. 84). This groove, as 
 observed in the first bicuspid, ex- 
 tends from mesial to distal for fully 
 three-fourths of the entire width of 
 the surface ; but in the second bicus- 
 pid it is diminished by one-third, be- 
 ing thus reduced by the broadened 
 
 marginal ridges, which force the mesial and distal pits well 
 toward the center. It is not uncommon to find the triangular 
 grooves joining the central groove direcdy in the center of the 
 
 surface, forming a central pit 
 from which may radiate numer- 
 oussmall supplemental grooves 
 and ridges. The summits of 
 both the buccal and lingual 
 cusps are nearer to the mesial 
 than to the distal surface, thus 
 increasing the length of the 
 ridges which descend from them 
 in a distal direction, and de- 
 creasing those which pass to the 
 mesial. The buccal surface 
 presents a greater convexity 
 than that of the first bicuspid ; 
 the buccal grooves are usually 
 shallow depressions and are fre- 
 quently entirely wanting, thus giving the buccal ridge the appear- 
 ance of extending its margins to the angles of the crown. Unlike 
 the first bicuspid, the mesiodistal diameter of the mesial surface 
 
 Fig. 85. — Upper Second Bicuspid, Me- 
 sial Surface. Most common form. 
 
176 
 
 is but little more than the same measurements on the lingual 
 surface. The neck of the tooth is not quite so pronounced as 
 that of the first bicuspid, thus giving less of the bell shape to 
 the crown. One very important difference between this tooth 
 and the first bicuspid is in the root-formation. We have seen 
 that the first bicuspid is generally provided with two roots, while 
 in the second bicuspid a single root is usually present. Like the 
 first bicuspid, there are exceptions to this, the tooth sometimes 
 being provided with two, and in rare in- 
 stances with three, roots. When the single 
 root is present, it partakes of the form of 
 the crown at its base, being well rounded 
 on the buccal and lingual portions and much 
 flattened on the mesial and distal. The 
 mesiodistal diameter of the root at its base 
 is only about one-third that of the bucco- 
 lingual measurement, this proportionate 
 size continuing throughout its entire length. 
 In passing from the base to the apex the 
 root is gradually diminished in size, finally 
 ending somewhat abruptly in an oblong 
 extremity. In some instances the apical 
 end is round and pointed, resembling the 
 apex of the incisors and cuspids, but 
 when thus formed the root is usually 
 curved near its apical third and somewhat extended in length. 
 The mesial and distal surfaces are provided with a well-defined 
 longitudinal concavity, extending from the cervical margin to the 
 apex and dividing the root into a buccal and a lingual portion. 
 This depression is often so decided that the contour of the single 
 root is almost lost, and in its place the appearance is that of two 
 roots similar to those described in the first bicuspid. The length 
 of the root is usually a little greater than that of the first bicus- 
 pid, but the crown being a trifle shorter, results in producing a 
 tooth the entire length of which is about equal to that of the first 
 bicuspid. 
 
 Fig. 86.— Young Up- 
 per Second Bicuspid, 
 Lingual Surface. 
 
UPPER FIRST MOLAR. 
 
 UPPER FIRST MOLAR. 
 
 €^ m i9 II K 
 
 2d year 3d year 
 
 5tli year 6th year ylh ye 
 
 Fig. 87. 
 
 Calcification Begins, from Four Centers, about One Month Before Birth. 
 Calcification Completed, Ninth to Tenth Year. 
 Erupted, Sixth to Seventh Year. 
 Average LengtIi of Crown, .30. 
 
 Average Length of Root, .51. 
 
 Average Length over All, .81 
 
 This tooth being the first of the permanent organs to erupt, 
 it precedes all others in the process of calcification, beginning 
 to receive its lime salts as early as the eighth fetal month. 
 The form of the crown being so entirely different from those 
 previously described, embodies a developmental process which 
 is also different, four distinct lobes being present, one for, each 
 cusp, these making their appearance during the first year after 
 birth, closely followed by a completion of the occlusal surface 
 by the union of the free calcifying margins, these lines of 
 union being finally represented by the developmental grooves 
 of the occlusal surface. After the completion of this surface, 
 calcification proceeds in the direction of the base of the crown, 
 and at the beginning of the third year about two-thirds of the 
 crown is formed. During the fifth year the contour of the 
 crown is completed, and at the beginning of the eruptive 
 period, or about the si.\th year, the developmental process has 
 extended to the base of the roots, and an effort at trifurcation 
 begun. At seven years the three roots with which the tooth is 
 provided are branching out, each into its own socket, subsequent 
 
178 ANATOMY. 
 
 development in each being continued as a separate and distinct 
 process. The tenth year more than half completes the calcifying 
 process in the roots, and at the beginning of the eleventh year 
 the apical foramina are established (Fig. 87). Like the first bi- 
 cuspid, the crown of this tooth presents for examination five sur- 
 faces — occlusal, buccal, lingual, mesial, and distal. In general 
 contour it is irregularly quadrilateral, with the angles of the 
 crown more or less rounded, two of its sides convex and 
 two flattened or slightly concave. The length of the crown 
 from the cervical line to the summits of the cusps is about equal 
 to, or slightly less than, its mesiodistal diameter, while the bucco- 
 lingual measurement is usually a trifle greater than the mesio- 
 distal. 
 
 Central Fossa ^S 't^S^ |fc"^M Distobuccal 
 
 Oblique Ridge ■ ^- ^Jf H DistaTFossa 
 
 MesioIi.,gual Cusp M^ ^^ ■ gi'.^a? R?dge 
 
 The Fifth Cusp 
 
 Fig. 88. — Upper First Molar, Occlusal Surface. 
 
 The Occlusal Surface of the Crown (Fig. 88).— The 
 coronal outline of this tooth is best studied when looking 
 directly upon this surface, which shows the two convex sides 
 above referred to, represented by the buccal and lingual mar- 
 gins, with the mesial and distal margins more or less flat- 
 tened. The surface is bounded by these four margins, which 
 are nearly of equal length, the angles formed by their union 
 being more or less rounded, two of which, the mesiobuccal 
 and the distolingual, are acute angles, while the mesiolingual 
 and distobuccal are obtuse angles. The surface is divided 
 into four developmental portions — the mesiobuccal, disto- 
 buccal, mesiolingual, and distolingual. Each one of these 
 parts is surmounted by a well-defined point or cusp, which 
 likewise is named in accordance with its location. These 
 
UPPER FIRST MOLAR. 179 
 
 various parts are separated from one another by four develop- 
 mental grooves — the mesial, the buccal, the distal, and the disto- 
 lingual. In the center of the triangle formed by the central 
 incline of the mesiobuccal, distobuccal, and mesiolingual cusps 
 is a deep depression, — the central fossa, — while near the distal 
 margin is a somewhat similar depression — the distal fossa. 
 Traversing the surface in various directions are a number of 
 ridges and supplemental grooves, each of which will be de- 
 scribed in turn. 
 
 The Marginal Ridges of the Occlusal Surface. — These are 
 four in number — the mesial, distal, buccal, and lingual. The 
 mesiomarginal ridge is a well-pronounced elevation of enamel 
 which passes from the mesiobuccal angle to the mesiolingual 
 angle. It is slightly concave in the direction of the root, and is 
 broken near the center of its concavity by the mesial groove, 
 upon either side of which are frequently found one or two small 
 points or tubercles, which are formed either by a division of the 
 mesial developmental groove, or by one or more supplemental 
 grooves. These grooves pass over the ridge and are continued 
 for a short distance on the mesial surface. Descending from 
 the mesiobuccal cusp, the ridge passes in a lingual direction to 
 meet the mesiolingual cusp, and in so doing has a slight distal 
 inclination until the mesial groove is reached, after passing 
 which it makes a sweeping distal curve and is lost in the lingual 
 margin. This ridge marks the line of junction between the 
 occlusal surface and the mesial surface. The distomarginal 
 ridge in some respects resembles the mesial just described, 
 being concave and ascending in a buccal and lingual direction, 
 with a somewhat rounded outline, to the summits of the disto- 
 buccal and distolingual cusps. The depth of the concavity is 
 usually greater than that of the mesial margin, and is fre- 
 quently crossed near the center by the distolingual groove, 
 frequently so marked as to produce a V-shape to the center of 
 the margin. There are occasionally found upon either side of 
 this central groove one or more small tubercles, corresponding 
 to those of the mesial ridge, but they are less frequent and less 
 pronounced. This ridge forms the line of demarcation between 
 the occlusal surface and the distal surface. The bnccomar spinal 
 
ridge begins at the mesiobuccal angle, and gradually ascends to 
 the summit of the mesiobuccal cusp, from which it afterward 
 descends in a distal direction to the buccal groove ; continuing, 
 it again ascends the distobuccal cusp, after descending from 
 which it ends in the distobuccal angle. The nature of this ridge 
 is a series of cutting-edges, giving to the cusps their angular 
 nature. Besides the buccal groove, which makes a decided 
 break in the center of its course, the ridge is frequently crossed 
 by numerous small supplemental grooves occurring in various 
 locations and forming a series of minute tubercles ; this latter 
 condition is most frequently present in young teeth, and is soon 
 obliterated by wear. The course of this ridge is not that of a 
 direct line from mesial to distal, but in its ascent of the mesio- 
 buccal cusp it is inclined to the buccal ; in its descent it pre- 
 sents a corresponding return to the lingual, and the same 
 variations are observed in passing over the distal cusp. 
 The linguomarginal ridge begins at the mesiohngual angle 
 of the crown and passes distally to the distolingual angle, 
 differing from the three previously described by being heavy 
 and rounded in its nature, more irregular in outline, and 
 divided nearest to its distal extremity instead of in the center 
 of its length. From the point of beginning it makes a curved 
 ascent to the summit of the mesiolingual cusp ; descending 
 from this in a distobuccal direction, it divides, one portion 
 passing to join the triangular ridge of the distobuccal cusp, 
 the two uniting to form the oblique ridge, the other portion 
 continuing in the direction of the distolingual cusp, before 
 reaching the base of which it is broken by the distolingual 
 o-roove. From this groove the ridge makes a sudden and direct 
 ascent to the summit of the distolingual cusp, after passing 
 which it gradually descends in a long curve to join the disto- 
 marginal ridge. Like the buccal ridge, it is frequently crossed 
 by numerous supplemental grooves. The ridge forms the lin- 
 gual margin of the occlusal surface, and gives to the cusps their 
 angularity. 
 
 The Cusps (Fig. 88). — These are four in number (see 
 also Fig. 89) — the mesiobuccal, distobuccal, mesiolingual, and 
 distolingual. 
 
UPPER FIRST MOLAR. l8l 
 
 The Mesiobuccal Cusp (Fig. 88). — In extent of surface this 
 is usually the largest cusp, although it is sometimes exceeded 
 by the mesiolingual. From the summit of the cusp three ridges 
 descend — the biucal ridge to the buccal surface, the buccomar- 
 ginal ridge making a double descent, and the mesiobuccal tri- 
 angular ridge, the latter descending the central incline and 
 ending in the central fossa. The mesial base of the cusp is fre- 
 quently crossed by one or more supplemental grooves, which 
 begin at the mesial margin and pass in the direction of the 
 central fossa. The central slope of the cusp contributes to the 
 formation of the central fossa, its extent in this direction being 
 controlled by the mesial and buccal grooves, which together 
 form the mesiobuccal triangular groove. 
 
 The DistobiLccal Cusp (Fig. 88). — This cusp is frequently the 
 smallest in extent of surface, but is usually longer and more 
 pointed than the others. Like the mesiobuccal cusp, three 
 ridges descend from it — the buccal ridge to the buccal surface 
 two which spring from the buccomarginal ridge, and the disto- 
 buccal triangular ridge, which descends obliquely toward the 
 distal center of the surface and joins a similar ridge (previously 
 described) from the mesiolingual cusp, the two forming the 
 oblique ridge. The mesial portion of the base of this cusp 
 assists in forming the central fossa, while a portion of the distal 
 contributes to the formation of the distal fossa. The inner 
 boundary of the cusp is formed by the buccal groove, the distal 
 groove, and by a portion of the distolingual groove. 
 
 The Mesiolingual Cusp (Fig. 88). — As above stated, this 
 cusp is frequently the largest in extent of surface, and is some- 
 what rounded, with its summit poorly defined. The ridges 
 which descend from it correspond in name and number to those 
 of the buccal cusps, the linguomarginal ridge making a double 
 descent, the mesiolingual ridge descending to the lingual sur- 
 face, while the central incline is marked by the mesiolingual 
 triangular ridge, which ends in the central fossa. Toward the 
 mesial portion of the cusp one or more small ridges are fre- 
 quendy present, extending from the marginal ridge to the 
 mesial groove. The distal descent of the marginal ridge is 
 bifurcated, one portion making a sweeping curve and joining 
 
the transverse ridge from the buccal cusp, forming the obhque 
 ridge previously referred to, the other portion passing in a distal 
 direction and ending at the distolingual groove. The central 
 incline of this cusp forms the lingual side of the central fossa, 
 and its boundaries are outlined by the mesial, distal, and disto- 
 lingual grooves. 
 
 The Distolingual Cusp (Fig. 88). — This cusp is usually the 
 smallest of the four; it is triangular in outline, with the summit 
 nearest the mesiolingual portion. The ridges which descend 
 from this cusp are only two in number, one passing in a mesial 
 direction and forming a portion of the linguomarginal ridge, 
 the other passing to the distal, with a gradual buccal curve, to 
 join the distomarginal ridge. Of the two remaining inclines, 
 one looks in a distolingual direction, presenting a surface which 
 is smooth and rounded ; the other, sloping by a broad expanse 
 in a mesiobuccal direction, ending in the distolingual groove, 
 and also assisting to form the distal fossa. This latter incline 
 is often crossed by small supplemental grooves, which take a 
 winding course from the base to the summit of the incline. The 
 inner margin or outline of the cusp is formed by the disto- 
 lingual groove. 
 
 The Fifth Cusp (Fig. 89). — Although usually referred to as 
 possessing but four cusps, this tooth is frequently developed 
 with five, the additional lobe being situated on the lingual side 
 of the mesiolingual cusp, about midway between its summit and 
 the neck of the tooth. When present, it is distinctly separate 
 from the main cusp by a well-developed groove — the mesio- 
 ling2ial groove. Both the cusp and the groove may be more or 
 less developed, the former in some instances assuming dimen- 
 sions corresponding to that of the distolingual cusp, and the 
 latter sometimes being as well marked as the distolingual 
 groove. When thus pronounced, the groove begins near the 
 center of the mesial surface, and passes obliquely toward the 
 summit of the mesiolingual cusp, before reaching which it makes 
 an abrupt turn rootward, and joins the lingual terminal of the 
 distolingual groove, this union frequently resulting in a well- 
 defined pit — the lingual pit. This cusp, as usually found, is small 
 and apparently without function. When occurring on the tooth 
 
UPPER FIRST MOLAR. 183 
 
 of one side, it is usually present on the corresponding tooth of 
 the opposite side. It is seldom present on any but the upper 
 first molar. 
 
 The Fossae and Grooves of the Occlusal Surface (Figs. 
 88 and 89). — The fosste are two in number — central and distal. 
 The central fossa occupies a position near the center of the sur- 
 face, and is formed by the central incline of the mesiobuccal, 
 distobuccal, and mesiolingual cusp, which usually give it a 
 three-sided form. Connecting the three sides of the fossa, and 
 in a measure assisting in its construction, is the mesiomarginal 
 ridge and the oblique ridge. The depth of this fossa, as well as 
 that of the distal, is of course regulated by the length of the 
 
 
 Buccal Groove 
 
 Mesiobuccal 
 
 Cusp 
 Central Fossa 
 Mesiomar- 
 ginal Ridge 
 
 The Fifth 
 Cusp 
 
 E 
 
 1 
 
 Distobucc, 
 Cusp 
 
 Distolingt 
 Cusp 
 
 Mesiolingual Oblique 
 Cusp Ridge 
 
 Fig. 89.— Upper First Molar, Occlusai, Surface, Strongly Developed, showing 
 Presence of Fifth Cusp. 
 
 cusps, which in turn is much influenced by the temperamental 
 type of the tooth. The bottom of the fossa is deeply marked 
 by two of the grooves of development — the mesial groove and 
 the buccal groove. The former begins on the mesial surface 
 passes over the mesiomarginal ridge, and continues in an irreg- 
 ular line to the bottom of the fossa ; the latter, beginning near 
 the center of the buccal surface, enters the fossa by crossing the 
 buccomarginal ridge near the center of its length, and also 
 ends in the central pit of the central fossa. i\s previously 
 referred to, the union of these two grooves forms the mesio- 
 bnccal triangular groove. From the central pit of this fossa 
 another groove is given off — the distal groove. It is usually well 
 
i84 ANATOMY. 
 
 defined at its beginning, but as it passes over the oblique ridge 
 it is generally partly obliterated, although occasionally being so 
 marked as to divide this ridge. The distal fossa is much 
 smaller than the central, and is of an entirely different form. 
 Its walls are principally formed by the distolingual incline of the 
 oblique ridge, and the mesiobuccal incline of the distolingual cusp ; 
 a portion of the distomarginal ridge and the distal incline of the 
 distobuccal cusp also assist in its formation. Like the central 
 fossa, its sides are more or less irregular, from the presence of 
 various grooves and ridges in its vicinity. The greatest length 
 
 of the fossa is in a disto- 
 lingual direction, and it is 
 traversed by a deep de- 
 velopmental groove — the 
 1 Root distolingual groove. When 
 the distal groove crosses 
 the oblique ridge, it usu- 
 ally extends to the bottom 
 of this fossa. 
 
 The Buccal Surface 
 of the Crown (Fig. 90). 
 — This surface, which is 
 the result of a union be- 
 tween the mesial and dis- 
 Buccai Groove tal developmental lobes. 
 
 Fig. go.— Upper First Molar, Buccal may be divided into a 
 
 Surface. . , , ,. , ,^ 
 
 mesial and a distal halt. 
 
 These two portions are 
 quite similar in outline, and are separated from each other 
 by the buccal groove, which usually ends near the center or 
 about half-way to the cervical line in a decided pit — the 
 buccal pit. In some instances this groove is continued to 
 the cervical line, or even beyond this to the bifurcation of 
 the roots. Both the mesial and distal half are provided with 
 a longitudinal ridge (the buccal ridges) — one the mesiobuccal 
 ridge and the other the distobuccal ridge. These are similarly 
 formed and descend from the summits of the respective cusps, at 
 which point they are usually well defined, but gradually disappear 
 
UPPER FIRST MOLAR. 
 
 185 
 
 as they pass toward the cervical hne. The location of the buccal 
 groove being a little to the distal of the center of thesurface, gives 
 to the mesial portion a somewhat greater extent than the distal. 
 The margins of the surface, which form an irregular quadri- 
 lateral, are the mesial, distal, occlusal, and cervical. The mesial 
 and distal margins are rounded, and gradually converge as they 
 pass rootward, making the average diameter of the surface 
 about one-fourth less at the cervical line than at the base of the 
 cusps. In some instances these margins are slightly concave 
 over their cervical portion, and convex on approaching the occlu- 
 sal margins ; or the mesial may be concave and the distal con- 
 vex throughout their en- 
 tire length ; in some types 
 they appear as straight 
 lines and are parallel with 
 each other. The occlu- 
 sal margin is formed by 
 the marginal ridges as 
 they pass over the two 
 buccal cusps, being in the 
 form of the letter W. The 
 cervical margin is usually 
 a direct line drawn around 
 the circumference of the 
 tooth, but in some in- 
 stances deviating slightly 
 from this. Immediately 
 
 below the cervical line, and conforming to its general direction, 
 is a rounded fold of enamel — the cervical ridge. 
 
 Lingual Surface of the Crown''= (Fig. 91). — In correspond- 
 ence with the buccal surface, this surface is developed from two 
 lobes, — the mesio- and disto-lingual lobes, — the line of union be- 
 tween the two being recorded by a well-defined groove — the lin- 
 gjial groove. This groove, which is a continuation of the distolin- 
 gual groove of the occlusal surface, usually ends near the center 
 of the lingual surface in a well-defined pit — the lingual pit — or it 
 
 *When the fifth cusp is present, the anatomy of the mesial half of this surface is somewhat 
 more complex. 
 
 Lingual Lingual Ridge 
 Groove Mesiolingual Cusp 
 
 Fig. 91. — Upper First Molar, Lingual 
 Surface. 
 
may continue rootward and gradually disappear. It Is located 
 a little to the distal of the center of the surface, thus making the 
 mesial a trifle larger than the distal portion. The mesial half 
 of the surface is smooth and conve.x ; the lingual incline of the 
 mesiolingual cusp is seldom provided with a well-defined ridge, 
 although usually referred to as the mesiolingiMl ridge. The 
 distal half of the surface is also smooth and rounded, with the 
 mesiodistal convexity much more marked than that of the mesial 
 lobe. The cervical ridge is seldom so pronounced as that of the 
 buccal surface, but the enamel frequently makes a sudden dip at 
 this point to meet the cementum of the root. That portion of 
 the surface immediately below the cervical ridge is smooth and 
 
 unbroken, slightly convex 
 in the direction of the long 
 axis of the tooth, and 
 flattened or slightly con- 
 vex from mesial to distal. 
 The margins of the sur- 
 face are the mesial, distal, 
 occlusal, and cervical. The 
 surface passes so gradu- 
 ally into the mesial and 
 distal that it is somewhat 
 difficult to define these 
 margins. In general, the 
 margins converge slightly 
 in the direction of the 
 root. Both the occlusal and cervical margins are similar to the 
 corresponding margins of the buccal surface. 
 
 The Mesial Surface of the Crown (Fig. 92). — This sur- 
 face is almost an unbroken plane, being smooth and flat. In 
 some instances it is crossed near the center of its occlusal margin 
 by a continuation of the mesial groove, but this is seldom so pro- 
 nounced as to divide the surface. The occlusal third of the 
 surface is inclined to a slight general convexity, providing a 
 point of contact for the distal surface of the second bicuspid, 
 but between this and the cervical line there is often a slight con- 
 cavity. The margins of the surface are the occlusal, buccal. 
 
 IlG. 92 
 
 -Upper First Molak, Mesial 
 Surface. 
 
UPPER FIRST MOLAR. 
 
 187 
 
 Mesiobuc- 
 cal Root 
 
 Distobuc- 
 cal Root 
 
 lingual, and cervical. The first named is formed by the mesio- 
 marginal ridge of the occlusal surface, and is concave in the 
 direction of the root. The buccal and lingual margins are 
 rounded, and, unlike the lateral margins of the buccal and 
 lingual surfaces, diverge in the direction of the roots. The 
 cervical margin is slightly concave in the direction of the occlusal 
 surface, and its length is much greater than that of any other 
 margin of the crown. This surface is more extensive than 
 either the buccal, lingual, or distal, and is about equal to that of 
 the occlusal. When the fifth cusp is present it alters the form 
 of the lingual margin of this surface by crossing it near the 
 center, and extending for 
 some little distance on the 
 face of the surface. 
 
 The Distal Surface of 
 the Crown (Fig. 93). — 
 Taken in its entirety, this 
 surface usually presents a 
 general convexity. The lin- 
 gual half of the surface is 
 usually somewhat more pro- 
 minent than the buccal, the 
 latter being flattened and 
 frequently slightly concave, 
 particularly near the cervi- 
 cal portion. In some in- 
 stances the surface is trav- 
 ersed by a continuation of the distolingual groove, which, after 
 passing over the distomarginal ridge, is continued in a longi- 
 tudinal direction, dividing the surface into two equal parts. Not 
 infrequently this groove, instead of existing as such, is repre- 
 sented as a shallow depression, often extending to the bifurcation 
 of the roots. The margins of the surface are four in number; 
 the occlusal, which closely resembles the corresponding margin 
 of the mesial surface ; the buccal, which is not well defined ; the 
 lingual, somewhat angular ; and the cervical, formed by the 
 cervical line. 
 
 The Neck of the Tooth. — When looking upon the buccal 
 
 Lingual 
 Root 
 
 Disto- 
 
 liMKual 
 Cusp 
 
 B 
 
 Fig. 93. — Upper First Molar, Distal 
 Surface. 
 
i88 ANATOMY. 
 
 surface of this tooth, the constricted portion forming the neck 
 is greatest at a point immediately above the cervical line. 
 Viewed in this direction the crown is usually bell-shaped, and 
 both the crown and the base of the roots assist in producing 
 the neck. Viewed from a lingual direction, the neck is a 
 distinctive feature, but is seldom so marked as when examined 
 from the opposite side. When studied from either a mesial or 
 a distal aspect, the neck appears above the cervical line, the 
 prominent fold of enamel immediately adjacent to this line 
 forcing the neck rootward. 
 
 The Roots of the Upper First Molar. — The roots of this 
 tooth are three in number, two of which are on the buccal side, 
 and are, therefore, called mesiobuccal and distobuccal roots, and 
 one on the lingual side, known as the lingual root. These three 
 roots are given off from a common base, which is sometimes 
 referred to as the root, while those parts above the point of 
 trifurcation are considered as root-branches. The number, 
 location, and form of the roots of this tooth are, perhaps, more 
 constant than those found in connection with any other cuspidate 
 tooth. The common base from which the roots are given off is 
 similar in contour to the crown of the tooth, excepting in those 
 cases in which the form of the root is carried over this base to 
 meet the neck of the tooth. 
 
 The mesiobuccal root (Fig. 90) is flattened from mesial to 
 distal, broad at its base from buccal to lingual, from which point 
 it gradually tapers to the apex. At the base the mesiodistal 
 measurement is less than one-third that of the buccolingual. 
 In its course it is first inclined to the mesial, but after reaching 
 the center of its length it makes a decided distal curve, which 
 looks almost directly to the distal. The mesial side of this root 
 is decidedly flattened at its base, but as the center of the surface 
 is reached a shallow longitudinal grobve is present, which is 
 continued to the region of the apex. The distal side is also 
 possessed of a similar groove, which extends throughout its 
 entire length. Both the buccal and lingual sides of the root are 
 smoothly convex, the latter being only about half the width ot 
 the former. 
 
 The distobuccal root (Fig. 90) is much the smallest of the 
 
UPPER FIRST MOLAR. 189 
 
 three, and, while inclined to flatness on its mesial and distal sides, 
 it is much more rounded than the mesial root. The mesial side 
 is provided with a slight longitudinal groove, and in rare 
 instances a similar groove exists on the distal side. The buccal 
 and lingual sides are similar to those of the mesial root. The root 
 is generally straight, and tapers gradually from base to apex, 
 ending in a rounded point. 
 
 The lingtial root (Fig. 91) is usually the largest and longest of 
 the three, and is more rounded in form than either of the buccal 
 roots. The lingual surface is inclined to flatness near its base, 
 and is provided with a well-defined longitudinal groove, which is 
 sometimes independently formed, while at others it is present as 
 a continuation of the lingual groove. This root being the only 
 one given off from the lingual side of the tooth, is constructed 
 with a mesiodistal measurement about equal to that of the base 
 of the crown at this point. From its place of beginning it passes 
 first in a lingual and then in a buccal direction, forming a long 
 curve and ending in a sharp-pointed apex. 
 
 Bilious Type. — The upper first molar of this temperament 
 is manifest by a crown with angles well produced, the marginal 
 ridges and cutting-edges of the cusps bold and well marked. 
 The cusps are of medium length, with summits angular and 
 pointed. The developmental grooves are deep and often 
 sulcate, and numerous supplemental grooves are found upon 
 the occlusal surface. The longitudinal and transverse meas- 
 urements of the crown are about equal, and when viewed upon 
 the occlusal surface, the angular nature of its anatomy is noted 
 as a distinctive feature. The neck is fairly well developed, 
 giving a slight bell-shape to the crown. The cervical line is 
 made up of angles rather than curves, and the roots are long 
 and straight. 
 
 Nervous Type. — Like the teeth previously described under 
 this class, the crown of this tooth is of greater longitudinal than 
 transverse extent ; the neck is especially well formed, producing 
 a decided bell-shape to the crown. The cusps are long and 
 penetrating, the marginal ridges sharply defined, as are also 
 those ridges upon the central incline of the cusps. The grooves 
 of development are decided and frequently sulcate. The buccal 
 
surface is rounded and smooth, with the buccal groove extending 
 well toward the cervical line. The lingual surface also presents 
 a general convexity, and is usually divided by the lingual groove. 
 The mesial surface is convex over its cervical third, and the 
 occlusal margin is a decided convex ridge, serving as a point of 
 contact for the adjoining tooth, and thus forming the character- 
 istic V-shape common to this temperament. It is in this type 
 that the fifth cusp is most frequently present. The cervical line 
 is much curved, and the roots are slim and frail. 
 
 Sanguineous Type. — The crown of the upper first molar 
 of this type usually presents a slightly greater longitudinal than 
 transverse extent. The angles of the crown are poorly formed, 
 being rounded and smooth. The cusps are of moderate length, 
 and are rounded in their nature ; the marginal ridges, as well as 
 those ridges of the central incline of the cusps, are less distinct 
 than either of the forms previously described. The buccal and 
 lingual surfaces are convex and seldom broken by grooves ; the 
 mesial and distal surfaces are convex in every direction, throw- 
 ing the point of contact with adjoining teeth near the center of 
 the surface. The roots are inclined to be large and oval in form, 
 while the cervical line is a series of long curves. 
 
 Lymphatic Type. — In this temperament the crown is much 
 less in its longitudinal than transverse measurement. The neck 
 of the tooth is poorly defined, the crown passing into the root- 
 base without a marked constriction. The mesial and distal 
 surfaces are flattened and nearly parallel with each other, 
 providing a broad contact surface. The buccal and lingual 
 surfaces each present a marked general convexity, the latter 
 being frequently broken by the distolingual groove. The tooth 
 is provided with cusps which are short and heavy-set ; the 
 marginal ridges, as well as all the ridges common to the occlusal 
 surface, are poorly defined. The developmental grooves are 
 shallow and terminate abruptly. There is but little curvature 
 to the cervical line, and the roots are short, heavy-set, and 
 inclined to cluster together. 
 
UPPER SECOND MOLAR. 
 
 191 
 
 UPPER SECOND MOLAR. 
 
 7th year Sth year 9th year 
 
 loth year 
 Fig. 94. 
 
 Calcification Begins kkom Four Centers About the Fifth Year. 
 Calcification Completed, Sixteenth to Eighteenth Year. 
 Erupted, Twelfth to Fourteenth Year. 
 Average Length of Crdwn, .28. 
 
 Average Length of Root, .51. 
 
 Average Length Over All, .79. 
 
 Calcification in this tooth takes plact in precisely the same 
 manner as that of the first molar, but the formative process is 
 much later in beginning, the lime-salts commencing to accumulate 
 in the four separate lobes about the fifth year. At the beginning 
 of the si.xth year the formation of the cusps is completed, soon 
 after which they coalesce and the occlusal surface of the crown 
 is established. At the beginning of the eighth year fully two- 
 thirds of the crown is calcified, and the following year the crown 
 and neck are completed and the root-base outlined. By the tenth 
 year the beginning of separate root-development is observed ; 
 at the twelfth year, or at the time of eruption, the roots are 
 formed to about one-half of their completed length, the process 
 continuing until the sixteenth or seventeenth year, when calcifi- 
 cation is completed and the apical foramina established (Fig. 
 94). In many respects this tooth closely resembles the first 
 molar previously described, the crown presenting the same 
 number of surfaces similarly named, and also being provided 
 with the same number of roots. Notwithstanding this fact, 
 there are a number of ways in which they are at variance. 
 The crown of the second molar is smaller than that of the 
 
first, and the quadrilateral outline common to the first molar 
 is much compressed and broken in the second. The distal 
 cusps are much smaller proportionately than the mesial cusps, 
 this being particularly true of the distoling-ual cusp. This 
 reduction in size of the distal cusps gives to that portion of the 
 occlusal surface a slight distal incline. 
 
 Occlusal Surface of the Crown (Fig. 95). — The general 
 contour of the crown is best studied by viewing it directly upon 
 the occlusal surface ; this aspect also shows to best advantage 
 the difference in form between this and the first molar tooth, as 
 shown in figure 87. The mesial and lingual outlines closely 
 resemble the corresponding outlines on the first molar, but the 
 
 Buccal Groove 
 
 M< 
 Tria 
 
 ^siobuccal 
 ngular Ridge 
 
 Mesi 
 
 al Gro( 
 
 Dve 
 
 Mesi 
 
 iomarg 
 
 iiial Ridge 
 
 Mesi 
 
 oliiigu; 
 
 al Cusp 
 
 Distobuccal Cusp 
 
 Distal Fossa 
 Distolingual Groove 
 
 Central Dislal Incline of 
 Fossa Mesiolingual Cusp 
 
 Fig. 95. — Upper Second Molar, Occlusal Surface. 
 
 buccal and distal are much at variance, the former passing into 
 the latter without a distinct line of demarcation existing between 
 the two, this gradual blending of one into the other being at the 
 expense of the distobucsal angle of the crown, which is poorly 
 developed. The crown is much compressed in a distobuccal- 
 mesiolingual direction, making this measurement of the occlusal 
 surface about one-third less than the mesiobuccal-distolingual 
 measurement. The cusps are much inclined to cluster toward 
 the center of the surface, this being especially true of those on 
 the lineual half 
 
UPPER SECOND MOLAR. 193 
 
 Maj'ginal Ridges of the Occlusal Surface (Fig. 94). — Like the 
 occlusal surface of the upper first molar, this surface of the 
 second molar is bounded by four marginal ridges — the mesial, 
 distal, buccal, and lingual. They are usually less marked than 
 those found on the first molar, and are much more variable 
 in their individual anatomy. 'Yht mesiomarginal ridge extends 
 from the summit of the mesiobuccal cusp to the summit of the 
 mesiolingual cusp. It is concave in the direction of the body of 
 the crown, and is broken near its central portion by the mesial 
 groove. In some instances one or more small supplemental 
 grooves are found to cross it. Compared with the mesiomar- 
 ginal ridge of the first molar, its length is much less and the 
 convexity not so pronounced. The distomarginal 7'idge, owing 
 to the variation in form and size of the distal cusps, is difficult to 
 describe definitely ; suffice it to say that it extends from the 
 summit of the distobuccal to the summit of the distolingual 
 cusp. The concavity is V-shaped, and is usually crossed near 
 the center by the distolingual groove. In some instances the 
 distolingual cusp is almost wanting, in others the distobuccal is 
 but litde developed ; when either of these conditions are present, 
 the marginal ridge is extended either to the buccal or to the 
 lingual, in a measure taking the place of the missing cusp. 
 The mesial half of the buccomarginal ridge closely resembles 
 the corresponding margin of the first molar ; beginning at 
 the mesiobuccal angle it ascends to the summit of the mesio- 
 buccal cusp, after which it descends by a longer incline to 
 the buccal groove. The distal half of the ridge, unlike that 
 of the first molar, presents much variety, its form being con- 
 trolled by the character and position of the distobuccal cusp; 
 usually small. As most frequently observed, it ascends to the 
 summit of the cusp, and in so doing it presents a decided 
 lingual inclination. In passing down the distal incline the 
 lingual inclination is increased and gradually passes into the 
 distomarginal ridge. Branching off from the mesiomarginal 
 ridge, the liiiguoniarginal ridge ascends to the summit of the 
 mesiolingual cusp and descends by a much shorter incline to the 
 distolingual groove. This portion of the margin is thrown well 
 toward the center of the surface, the location of the cusp carry- 
 13 
 
194- ANATOMY. 
 
 ing it to that point. Like tlie distal half of the buccal margin, 
 the outline of the distal half of this margin is controlled by the 
 position and form of the distolingual cusp. In the majority of 
 cases, when the cusp is moderately strong, the ascent from 
 the distobuccal groove to the summit of the cusp is short and 
 abrupt, the descent being somewhat more gradual, and with 
 a decided buccal inclination it passes into the distomarginal 
 ridge, or ends abruptly at the distal end of the distolingual 
 groove. 
 
 The Cusps and Ridges (Fig. 95). — This tooth is provided 
 with four lobes or cusps, two of which are located on the buccal, 
 and two on the lingual side. They are usually smaller and less 
 angular than the cusps of the first molar. This is particularly 
 true of both the distal cusps, and especially of the distolingual 
 cusp, which is often quite diminutive and occasionally entirely 
 wanting. When this latter condition exists, the lingual half of 
 the surface is for the most part occupied by what would other- 
 wise be the mesiolingual cusp, the absence of the distal cusp 
 permitting the distolingual groove to occupy a position near the 
 extreme distolingual angle, that portion of the surface which is 
 distal to the groove being a portion of the distomarginal 
 ridge. 
 
 The Mesiobuccal Cusp (Fig. 95). — Like the corresponding 
 cusp of the first molar, this cusp is usually the longest of the 
 four, and in many instances covers a greater extent of surface 
 than any of the others. Its base is outlined by the buccal and 
 mesial grooves, the two together forming the mesiobuccal 
 triangular groove. Descending from its summit to the buccal 
 surface is the mesiobuccal ridge ; the marginal ridge makes a 
 double descent, one in a mesial and one in a distal direction, 
 while sloping toward the central fossa is the mesiobuccal tri- 
 angular ridge. The cusp is seldom traversed by supplemental 
 grooves such as are found on the corresponding cusp of the 
 first molar. 
 
 The DistobiLccal Cusp (Fig. 95). — As previously stated, this 
 cusp is not constant in its form ; in some instances it is bold and 
 well produced, corresponding closely to the mesiobuccal cusp 
 just described. When thus pronounced it is possessed of ridges, 
 
UPPER SECOND MOLAR. 195 
 
 and bounded by grooves which are similar to those described in 
 connection with the first molar. More frequently the cusp is 
 much rounded, its summit being carried well toward the center 
 of the surface. When this formation exists, the buccal ridge is 
 absent, the marginal ridges short and rounded ; the distobuccal 
 triangular ridge which descends from it toward the center of 
 the crown is short and heavy set. 
 
 The Mesioliiignal Cusp (Fig. 95). — In the majority of instances 
 this is the largest cusp, particularly when there is a degenerate 
 tendency in the distolingual cusp. Descending from its summit 
 are a number of ridges, the marginal ridges being given off as 
 already described, the mesiolingual triangular ridge descending 
 the central incline to the central fossa, and when the cusp has 
 an additional mesiodistal extent by the presence of a diminutive 
 distal cusp, other ridges descend in the same direction. The 
 lingual descent of the cusp is smooth and more rounded than 
 the corresponding surface of the first molar, and is seldom 
 elevated in the form of a definite ridge. The central outline of 
 this cusp is marked by the mesial, the distal, and the distolingual 
 grooves. 
 
 The Distolingual Cusp (Fig. 95). — In no other cusp do we 
 find such a diversity of form as in the distolingual cusp of the 
 upper second molar. In some instances it is fully as promi- 
 nent as its neighbor just described, in others appearing as a 
 mere fold of enamel, and it is not uncommon to find it entirely 
 wanting, the distomarginal ridge extending to occupy a portion 
 of the space which it should claim. Deductions might be drawn 
 from an average between these two extremes, wherein the e.\- 
 isting cusp would be much smaller than any of the others, the 
 summit rounded rather than sharp, but with a decided inclination 
 to occupy the extreme distolingual angle of the surface, in this 
 latter respect differing from the distobuccal cusp. The mesial 
 and buccal outlines of the cusp are formed by the distolingual 
 groove, and its mesiolingual incline contributes to the formation 
 of the distal fossa. 
 
 The Fossae and Grooves of the Occlusal Surface (Fig. 
 95). — These in name, number, and general form are similar to 
 those of the first molar. The central fossa is never, strictly speak- 
 
196 
 
 ing, in the center of the surface, and is formed by tlie central in- 
 cHne of the mesiobuccal, distobuccal, and mesioHngual cusps. It 
 is seldom so deep as the central fossa of the first molar. The 
 distal fossa is more or less pronounced, its size and position being 
 controlled by the extent of development in the distolingual cusp. 
 The distolingual groove, which usually crosses the lingual surface 
 of the first molar near its center, is not constant in its location on 
 this tooth, in some cases being near the center, in others near 
 the distolingual angle of the crown. The buccal groove is never 
 constant in its location, usually crossing the buccomarginal 
 ridge and passing over the buccal surface near its mesiodistal 
 center, but it is not uncommon to find it 
 forced to the distal by a diminution in the 
 size of the distal cusp. 
 
 Buccal Surface of the Crown (Fig. 
 96). — The most constant dilTerence be- 
 tween this and the corresponding surface 
 of the upper first molar is the wandering 
 location of the buccal groove. While in 
 the majority of instances it may be found 
 near the mesiodistal center of the surface, 
 it is not uncommon to find it passing over 
 the distal third, or even as far posterior as 
 the distobuccal angle. In general, the sur- 
 face is somewhat more convex and neces- 
 sarily less extensive than the buccal surface 
 The buccal ridges which descend from the 
 summit of the two buccal cusps are seldom so marked as those 
 on the first molar, and in many instances the distal ridge is 
 wanting. The distal half of the surface frequently passes into 
 the distal surface, by a long gradual sweep, there being no line 
 of demarcation between the two. 
 
 The Lingual Surface of the Crown (Fig. 97). — In keeping 
 with the other surfaces just described, the lingual surface differs 
 from the corresponding surface of the first molar in that it pre- 
 sents a greater general convexity. This is particularly true in 
 passing from the cervical line to the occlusal surface. The 
 lineual eroove is also less constant in its location. In most 
 
 Fig. 96. — Upper 
 Second Molar, Buc- 
 cal Surface. 
 
 of the first molar. 
 
UPPER SECOND MOLAR. 
 
 197 
 
 ! Ridge 
 
 Fig. 97. — Upper Second Molar, Lingual 
 Surface. 
 
 instances it is to be found a little to the distal of the center, in 
 others being- as far posterior as the e.xtreme distal third of the 
 surface, and in rare instances it is entirely wanting. The 
 general character of this 
 surface, which is smooth 
 and convex, is seldom 
 broken by the presence 
 of well- defined ridges, 
 such as are usually found 
 descending from the lin- 
 gual cusps of the first 
 molar. As previously re- 
 ferred to, the mesial, dis- 
 tal, and buccal surfaces, as 
 well as the surface under 
 consideration, are propor- 
 tionately smaller than 
 those of the first molar, 
 
 and, while this refers to both the transverse and longitudinal 
 measurements, it is particularly applicable to the latter. 
 
 The Mesial Surface of the Crown (Fig. 98). — Aside from 
 
 this surface being of less 
 extent than the corres- 
 ponding surface of the first 
 molar, there are no other 
 differences of importance. 
 In many instances, how- 
 ever, there is a decided 
 tendency for the surface 
 to be concave from buccal 
 to lingual, the convex dis- 
 tal surface of the first 
 molar closely fitting into 
 this concavity. Another 
 variation which is fre- 
 quently observed is that 
 of the longer and more gradual sweep which it takes in passing 
 into the lino-ual surface. 
 
 Fig. 98. — Upper Second Molar, Mksiai, 
 Surface. 
 
The Distal Surface of the Crown (Fig. 98). — This differs 
 from the distal surface of the first molar principally in its more 
 pronounced convexity. Its general form is also much influenced 
 by the nature of the two distal cusps. If one or the other of these 
 is sparingly developed, either the buccal or lingual half of the 
 surface, as the case may be, is quickly rounded off to pass into 
 the deficient lobe. 
 
 The Angles of the Crown. — The increased inclination for 
 the crown of this tooth to general convexity dispels, in a meas- 
 ure, the presence of angles, as such, in correspondence with the 
 
 four corners of the first 
 molar. In some instances 
 the crown is represented 
 as a fairly well-formed qua- 
 drilateral, in which case 
 the angles are well de- 
 fined, but usually this 
 outline is so much broken 
 by a mesiodistal compres- 
 sion that the angular form 
 of the crown is entirely 
 abolished. But, whatever 
 the form of the crown 
 may be, it is well to ad- 
 here to the commonly 
 accepted term, and speak of that point at which the sides of the 
 crown unite as the angles, each being named in accordance with 
 its location. 
 
 The Neck of the Tooth. — The principal variation between 
 the neck of this tooth and that of the first molar, is that pro- 
 duced by the greater general convexity of the crown, which 
 contributes to the production of a neck much more constricted. 
 There is also a greater variety in the contour of the neck, inci- 
 dent to the variation in the general outline of the crown. 
 
 The Roots of the Upper Second Molar. — These are 
 the same in name and number as those of the first molar — 
 two buccal and one lingual. In many respects they differ 
 from the roots of the first molar. They are much smaller, fre- 
 
 FiG. 99. — Upper Second Molar, Distal 
 Surface. 
 
UPPER SECOND MOLAR. 199 
 
 quently inclined to cluster together, and are often fused, in some 
 instances, all three being united, in others the union existing 
 between but two. When isolated, each root usually presents a 
 decided distal curve near its apical third. When the crown is 
 flattened from mesial to distal, as before described, the disto- 
 buccal root is forced to occupy a position much more to the 
 lingual than that assumed by the mesiobuccal root. The 
 lingual groove seldom passes over the lingual root, as ob- 
 served on the first molar. 
 
UPPER THIRD MOLAR. 
 
 m 
 
 lolh j-ear nth year 12th year uih year :Sth year 
 
 Fig. 100. 
 
 Calcification Begins, Ninth Year. 
 
 Calcification Completed, Eighteenth to Twentieth Year. 
 Erupted, Seventeenth to Twentieth Year. 
 Average Length of Crown, .24. 
 
 Average Length of Root, .44. 
 
 Average Length over All, .6S. 
 
 Calcification of this tooth takes place in precisely the same 
 manner as that in the first and second molar, with the excep- 
 tion of the number of lobes, which are sometimes three and 
 sometimes four. The lime-salts begin to accumulate between 
 the eighth and ninth year, and continue with somewhat more 
 activity than that of the first or second molar. Between 
 the ninth and tenth year the three or four cusps, of which the 
 future tooth is to be composed, have coalesced, and by the 
 eleventh year calcification in the crown of the tooth is completed ; 
 at the end of the following year the roots, which are variable in 
 number, have made considerable progress ; at the fourteenth 
 year they are calcified to about half their length, w^hile at a 
 period between the eighteenth and nineteenth year the forma- 
 tive process is completed (Fig. lOo). This tooth, like the cuspid, 
 is usually fully formed before eruption takes place. 
 
 This tooth is subject to a greater variety of form than any 
 other ; in rare instances it is similar in general outline and 
 cusp formation to the first molar, but in a vast majority of 
 cases it is dissimilar, the most constant deviation being its 
 
UPPER THIRD MOLAR. 201 
 
 size, which on the average is about one-third less. In the 
 accompanying illustration (Fig. loi) the iorms most frequently 
 met with are shown. It will be observed that the contour 
 of the tooth in general is much more rounded than either 
 the first or second molar. The buccal angles of the crown 
 are alone well marked, the mesial and distal surfaces passing 
 into the lingual surface by a long, gradual sweep, and thus 
 obliterating the lingual angles. In the vast majority of instances 
 the tooth is tritubercular, and is usually made so by the 
 absence or diminutive size of the distolingual cusp. Just as 
 
 Fig. ioi. — Various Types of Upper Third Molar. 
 
 this cusp was inclined to degenerate in the second molar, so 
 we find this retrograde developmental tendency increased in 
 the third molar. With this change in the construction of the 
 occlusal surface, there is a corresponding variation in the 
 grooves, ridges, and fossas. 
 
 Mesial Surface of the Crown (Fig. 102). — In many particu- 
 lars this surface corresponds in form and outline to the mesial 
 surface of the first molar ; it is, however, usually much more 
 convex, seldom presenting a concavity or even a positive flatness. 
 The surface is not only rounded from buccal to liuQ-ual, but also 
 
cal Cusp 
 
 Fig. 102. — Upper Third Molar, Mesial 
 Surface. 
 
 from the cervical line to its occlusal margin. Thus formed, a 
 point of contact is provided near the center of the surface. The 
 
 occlusal margin, the buccal 
 margin, and the cervical 
 margin are almost identical 
 to those of the first molar, 
 but in most instances the 
 lingual margin is vv^anting, 
 the surface gradually pass- 
 ing into the lingual without 
 a decided line of demarca- 
 tion. 
 
 Distal Surface of the 
 Crown (Fig. 103). — This 
 surface is much less exten- 
 sive in comparison to the 
 size. of the crown than the 
 corresponding surface of either the first or second molars. It is 
 decidedly rounded in every direction and is frequently crossed by 
 the distal developmental groove, and sometimes by one or more 
 supplemental grooves. The 
 general form of the surface 
 is much influenced by the 
 presence or absence of the 
 distolingual cusp ; with the 
 former, the surface is more 
 extensive, presenting less 
 convexity and resembling 
 more closely the distal sur- 
 face of the first and second 
 molars ; with the latter, the 
 extent of the surface is de- 
 creased and the convexity 
 increased. 
 
 Buccal Surface of the Crown (F'ig. 104). — The mesial por- 
 tion of this surface is in no way at variance with the mesial por- 
 tion of the buccal surface of the first or second molar, but much 
 variety of form exists in the distal portion. The buccal groove 
 
 Fig. 103.- 
 
 -Upper Third Molar, Distal 
 Surface. 
 
UPPER THIRD MOLAR. 
 
 Lingual Root 
 
 -Upper Third Molar, 
 Surface. 
 
 which serves to separate these two portions is located well 
 toward the distal third of the surface, thus reducing the size of 
 the distal portion to about one-third that of the mesial por- 
 tion. In general, the surface is but little more convex than 
 the corresponding sur- 
 face of the first and second 
 molar. Its mesial border 
 is definitely outlined, as 
 are also the cervical and 
 occlusal margins, but the 
 distal margin can not be 
 definitely located, the sur- 
 face tending to pass grad- 
 ually into the distal sur- 
 face. Like the distal, the 
 extent of this surface is 
 much regulated by the 
 size and shape of the dis- 
 
 tobuccal cusp, which, like the distolingual cusp, is inclined to de- 
 generate. 
 
 Lingual Surface of the Crown (Fig. 105). — Like the distal 
 surface previously described, the form of 
 this surface is much influenced by the pres- 
 ence or absence of the distolingual cusp. 
 When this cusp is wanting or but little de- 
 veloped, the surface presented is decidedly 
 convex and smooth ; in many instances the 
 mesiodistal curvature described is almost a 
 perfect semicircle, and in passing from the 
 cervical line to the occlusal margin the sur- 
 face is carried well toward the center of 
 the crown by a long gradual sweep toward 
 the lingual. The lingual groove is usually 
 absent. The change in form produced by 
 the presence of the distolingual cusp is 
 principally noticeable in a less pronounced convexity and the 
 presence of the lingual groove, which may be noticed as a slight 
 depression or as a well-defined groove. This groove, when pres- 
 
 FiG. 105. — Upper 
 Third Molar, Lingual 
 Surface. 
 
ent, is always located near what would represent the distolingual 
 angle of the crown ; the distolingual cusp seldom if ever being of 
 sufficient size to force its location near the center of the surface 
 as in the first molar. In some instances this groove is shown 
 upon the lingual surface when the cusp is not present ; in this 
 case the distomarginal ridge represents in a manner the cusp 
 by its bold, heavy development. 
 
 Occlusal Surface of the Crown (Fig. io6). — When looking 
 directly upon this surface, an opportunity is presented to study 
 the general contour of the crown ; the most noticeable difference 
 in this respect between this tooth and the first molar being ob- 
 served in its smaller size, and the absence of well-marked 
 
 angles. It will be noted 
 that the mesial and buc- 
 cal outlines in a meas- 
 ure resemble the corres- 
 ponding outlines of the 
 first and second molars, 
 but there is scarcely any 
 similarity existing when 
 comparing the distal and 
 lingual outlines. In some 
 instances the crown is 
 triangular (Fig. loi); in 
 others the mesiobuccal 
 and buccomarginal outlines form an obtuse angle, the free ends 
 of which are joined together by a long semicircle, the latter 
 constituting the distal and lingual outlines (Fig. loi). Again, 
 almost the reverse of this last-mentioned form is seen, the 
 buccal and distal outlines constructing the angle, while the semi- 
 circular connection between the two is made up of the mesial 
 and lingual outlines. 
 
 The Marginal Ridges. — The viesioinarginal ridge is usu- 
 ally well defined, and in most instances is crossed near its 
 center by the mesial groove, and frequently by two or more 
 supplemental grooves. This marginal ridge is probably the 
 most constant in form, the numerous variations to which the 
 surface is liable seldom making any material alteration in it. 
 
 FiF. io6. — Upper Third Molar, Occlusal 
 Surface. 
 
UPPER THIRD MOLAR. 205 
 
 Unlike the ridge above described, the dislomaroiual ridge 
 is most variable in its construction, nearly all of the forms 
 characteristic of the occlusal surface exerting a controlling- 
 influence over it. In rare instances the ridge resembles that 
 of the first and second molars, but this form is most frequently 
 interfered with by the absence or diminutive size of the disto- 
 lingual cusp, the ridge itself frequently supplying the place of 
 the cusp. In many cases the ridge is elevated near its central 
 part by being reinforced by a portion of the oblique ridge. 
 When the distolingual cusp is wanting, this ridge not infre- 
 quently descends from the summit of the distobuccal cusp to 
 the distal groove and from this point ascends obliquely to the 
 summit of the lingual cusp. The bucco- 
 viarginal ridge may be described as 
 similar in most respects to the correspond- 
 ing margin on the first and second molars, 
 the principal variation being in the distal 
 half, which is much shorter and less pro- 
 nounced. In the linguomarginal ridge, 
 again, much variety in outline is noticeable. 
 In nearly all instances the ridee is thrown ^ ,, ^ 
 
 -' " Fig. 107. — Upper Third 
 
 much nearer the center of the body of the Molar, Occlusal sur- 
 
 , , , .... • 1 • FACE, WITH Distolingual 
 
 crown, and, when the tooth is bicuspid in Cus? and Distal Fossa 
 
 form, it simply makes a mesial ascent of ^"''^''^ ^^^^^^^. 
 the lingual cusp, followed by a gradual 
 
 incline, and passes into the distal ridge, as above noted. When 
 the distolingual cusp is present, the ridge is similar to that 
 upon the first and second molars, with the exception of the 
 distal portion, which is less clearly marked. 
 
 The Cusps (Fig. io6). — As previously stated, the form 
 most frequently met with is tritubercular, two of the cusps 
 being upon the buccal and one upon the lingual half of the 
 surface. 
 
 The Jllesiobuccal Cusp (Fig. 106). — This cusp corresponds in 
 nearly every particular to the mesiobuccal cusp of the first and 
 second molars ; it is the most constant in size and form of the 
 three. Its summit is usually angular, and the numerous ridges 
 
which descend from it are well defined and similar in name 
 and number to those of the first molar. 
 
 Distobjucal Cusp (Fig. io6). — The constant inclination to 
 degeneracy in the distal portion of the crown of the tooth is 
 noticeable in this cusp, which is much smaller than the mesio- 
 buccal and scarcely half as large as the corresponding cusp of 
 the first and second molars. In some instances, however, it is 
 inferior only in size, retaining its angularity, being possessed 
 of small but well-defined ridges. 
 
 The Lingual Cusp (Fig. io6). — When the three cusps alone 
 are present, this one is much the largest, the extent of the sur- 
 face covered being all of the lingual half of the crown. The 
 summit of the cusp, which is thrown well toward the center of 
 the body of the crown, is prominent, but seldom angular. Only 
 in rare instances will there be found a lingual ridge descending 
 therefrom, but the central incline is usually marked by a number 
 of wrinkles or folds of enamel resembling minute ridges. The 
 central boundary of this cusp Is marked by the mesial and distal 
 developmental grooves. 
 
 The Distolingiial Cusp (Fig. io6). — It Is the presence or 
 absence of this cusp that contributes most to the variations 
 present In the crown. When present, It is usually diminutive in 
 size, and Is without definite form. In many Instances nature 
 is apparently attempting to cast it off in precisely the same 
 manner In which she is attempting to add to the first molar by a 
 development of the "fifth cusp," the distobuccal cusp appearing 
 to hang to the distollngual angle of the crown in a manner 
 very similar to the " fifth cusp." When thus situated. It Is sepa- 
 rated from the body of the crown by a groove, which cannot be 
 considered as being upon the occlusal surface. When located 
 In Its normal position, it has for its Inner boundary the disto- 
 llngual groove. 
 
 The Fossae and Grooves of the Occlusal Surface. — The 
 great variety andy^rw common to this surface exerts a con- 
 trolling Influence over the size, number, and position of the 
 grooves and fossae. In the tritubercular class the central fossa 
 alone is present. The developmental grooves, wdth the excep- 
 tion of the buccal, are not definitely outlined, but, descending 
 
UI'PER THIRD MOLAR. 207 
 
 toward the fossae from the central incHne, are numerous small 
 ridges divided from each other by a like number of diminutive 
 supplemental grooves. The distal groove is sometimes well 
 defined, and crosses over the oblique ridge, which in this type 
 becomes the distomarginal ridge. When the distolingual cusp 
 is present, all of the ridges and grooves are more pronounced. 
 In this case the central fossa corresponds more closely to the 
 central fossa of the other molar teeth, this resemblance increas- 
 ing just in proportion as the size of the distolingual cusp in- 
 creases. The distal fossa, in a vast majority of instances, is 
 present as a mere pit ; the size of this fossa is likewise much 
 controlled by the extent of development in the distolingual cusp. 
 Where the distomarginal ridge is supplementary to the disto- 
 lingual cusp, the distolingual groove lies between the former and 
 the oblique ridge. Another peculiarity found only upon the occlu- 
 sal surface of this tooth is, what appears to be an effort upon the 
 part of the cusps to cluster toward the center. This is common 
 only to those teeth possessing three cusps, and accompanying this 
 form the central fossa shows a number of fantastically arranged 
 grooves and ridges which ascend the cusps, passing over the 
 marginal ridges and breaking them into a number of small 
 tubercles. 
 
 Temperamental Types. — The third molar tooth is probably 
 less influenced by the character and habits of the individual than 
 any other tooth in the mouth. The inclination to a general de- 
 generacy is no doubt favored by civilization. With a constant 
 decline in the functional activity, brought about by the pres- 
 ent culinary methods common to civilization, this tooth in a 
 measure becomes useless, and nature is gradually making an 
 effort to cast it off While there are undoubtedly many indi- 
 viduals possessed of the highest mental attainments with the 
 third molar as fully developed as either the first or the second, 
 this condition is usually confined to those possessed of little in- 
 tellectuality. If in general, the temperament of the subject be 
 taken into consideration, the cusp-formation on this tooth will 
 correspond in a relative degree to that on the bicuspids and 
 molars. 
 
CHAPTER IX. 
 
 A DESCRIPTION OF THE LOWER TEETH IN DETAIL.-CALCIFICA- 
 TION, ERUPTION, AND AVERAGE MEASUREMENTS.-THEIR SUR- 
 FACES, RIDGES, FOSS/C, GROOVES, SULCI, ETC. 
 
 THE LOWER TEETH. 
 
 In most respects the lower teeth correspond to the upper, 
 but in each class we find a slight variation existing between 
 the two sets. As compared to the upper incisors, the crowns 
 of the lower incisors are more slender and somewhat mare 
 angular in outline. The roots are more slender, proportionately 
 longer, more flattened laterally, and seldom crooked. The 
 crowns of the lower incisors are probably more constant in 
 form than those of any other teeth in the mouth, seldom vary- 
 ing except in size. The mesiodistal measurement of the crown 
 of the lateral incisor is a trifle greater than that of the central, 
 a condition exactly the reverse to that of the upper incisors. 
 The labial and the lingual surfaces of these teeth are smooth, 
 and, with the exception of young teeth, show but little trace of 
 the developmental process by the presence of grooves, fissures, 
 etc. The outline of the lower cuspids is almost identical to 
 that of the corresponding teeth in the superior arch, excepting 
 that they are in every way more slender. The bicuspids are 
 proportionately smaller in every direction, have their cusps 
 much less developed than their upper antagonists, and are 
 seldom found with more than one root. The crowns of the 
 lower molars are somewhat larger than those of the upper, 
 and are provided with five cusps instead of four,* and they are 
 attached to the alveolus with two, instead of three, roots. In the 
 incisors, cuspids, and bicuspids the process of development is 
 the same as in the corresponding upper teeth, calcification 
 taking place from the same number of centers along the coronal 
 
 *The lower firat mo'ar his five cusps in ninety per cent, of cases, while, in the second, 
 five cusps are present in about fifty per cent. 
 
 208 
 
LOWER CENTRAL INCLSOR. 209 
 
 extremities. In the molars, however, development may proceed 
 from five centers instead of four, as in the upper molars. The 
 manner of development, and the period at which this action 
 takes place, so nearly corresponds with that of the upper 
 teeth that the process will not be repeated. 
 
 LOWER CENTRAL INCISOR. 
 
 Calcification Begins, First Year after Birth. 
 
 Calcification Completed, about the Tenth Year. 
 Erupted, Seventh to Eighth Year. 
 Average Length of Crown, .34. 
 
 Average Length of Root, .47. 
 
 Average Length Over All, .81. 
 
 Like the upper central incisor, this tooth presents for ex- 
 amination four surfaces, a cutting-edge, and various angles, 
 margins, etc. By the union of the labial and lingual surfaces 
 at the cutting-edge the incisive feature is established and the 
 double incline plane common to in- 
 cisors produced. 
 
 The Labial Surface of the 
 Crown (Fig. io8). — This surface is 
 smooth and convex, its general out- 
 line resembling an inverted cone, the 
 base of which is formed by the cut- 
 ting-edge and the apex by the cervical 
 line. The margins of the surface are, 
 with the exception of the cutting-edge, 
 not so well defined as those of the 
 upper central. Near the cutting- 
 edge the mesial and distal margins 
 pass somewhat abruptly into the re- 
 spective lateral surfaces, but as the 
 neck of the tooth is approached, they 
 are much rounded. The incisive mar- 
 gin is squarely cut, and is nearly at right angles with the long axis 
 of the tooth. The cervical margin is fairly well defined, and is 
 deeply concave in the direction of the root. Except in very 
 
 H 
 
 Fig. 108. — Lower Incisor, Right 
 Side, Labial Surface. 
 
young teeth, this surface is seldom much broken by the labial 
 grooves ; but in certain types one or more transverse ridges 
 may be found occupying the cervical third. The mesiodistal 
 diameter at the cutting-edge is about one-third greater than at 
 the cervical line, and, while these measurements are likely to 
 vary in accordance with the temjoerament of the subject, this 
 variation is not so pronounced as in the upper incisor. The 
 surface is frequently inclined to flatness near the incisive 
 margin, the general convexity becoming more marked as the 
 cervical line is approached. 
 
 The Lingual Surface of the Crown (Fig. 109). — In general 
 outline this surface resembles the labial, with the exception of 
 
 the cervical margin, the lines of 
 Lingual Grooves whicli are somewhat more acute. 
 
 The surface presents a marked 
 concavity from the cutting-edge 
 to the cervical ridge, and also a 
 slight transverse concavity near 
 the incisive margin. All of the 
 margins are more definite than 
 those of the labial surface. The 
 mesial and distal margins are 
 formed by the marginal ridges 
 common to these borders, but 
 these ridges are not so well de- 
 fined as those of the upper 
 incisors. The cervicomarginal 
 ridge is present as a well-rounded band of enamel, but is never 
 a well-defined cingulum, or cuspule. The depression between 
 these marginal ridges is so slight that it can scarcely be referred 
 to as a fossa, although usually characterized as the lingual fossa. 
 The lingual grooves are generally more pronounced than the 
 corresponding developmental grooves of the labial surface, but 
 end more or less abruptly before reaching the cervical ridge. 
 The mesiodistal measurements of the surface are a trifle less 
 than the corresponding measurements of the labial surface. 
 
 The Mesial Surface of the Crown (Fig. no). — The out- 
 line of this surface is exactly the reverse of the labial and 
 
 Fig. 109. — Lower Incisor, Right 
 Side, Lingual Surface, Strongly 
 Developed. 
 
LOWER CENTRAL INCISOR. 
 
 no. — Lower 
 Incisor, Mesial Sur- 
 face. 
 
 lingual just described, being a cone, with its base directed 
 downward or in the direction of the root, while its apex is 
 formed by the mesial extremity of the cutting-edge. The cer- 
 vical margin of the surface, or that 
 represented by the base of the cone, 
 is concave ; the labial and lingual 
 margins are rounded over the cer- 
 vical third and inclined to angularity 
 near the cutting-edge. There is a 
 slight convexity over the entire sur- 
 face, which is most marked near the 
 center. The lingual half of the cer- 
 vical portion slopes away to the dis- 
 tal, passing gradually into the lingual 
 surface. By the union of this surface 
 with the cutting-edge and the labial 
 and lingual surfaces, the mesial angle 
 of the crown is formed. This angle 
 is well outlined and reaches out to- 
 ward the median line, giving to this portion of the crown a 
 prominent appearance. Near the cutting-edge the surface pre- 
 sents a slightly rounded promi- 
 nence, which provides a point of 
 contact with the corresponding 
 tooth of the opposite side. 
 
 The Distal Surface of the 
 Crown (Fig. iii). — In a general 
 way this surface closely resembles 
 that of the opposite or mesial side 
 of the crown. Near the cutting- 
 edge the surface is usually more 
 prominent and presents a more 
 marked convexity, and near the 
 cervical margin it is flattened and 
 sometimes slightly concave. The 
 union of this surface with the cut- 
 ting-edge and the labial and lingual surfaces forms the distal angle 
 of the crown, which, like the mesial angle, is square and well 
 
 -Lower Incisor, Distal 
 Surface. 
 
defined. The margins of the surface are in no way different 
 from those of the mesial surface. 
 
 The Cutting-edge. — In the young tooth this incisive margin 
 is thin and generally divided into three distinct parts (Fig. 112) 
 by the developmental grooves, but these disappear so early that 
 they can scarcely be considered in connection with a description 
 of the fully developed tooth ; in fact, the cutting-edge of this, 
 as well as that of all the lower incisors, is so susceptible to 
 change by mechanical abrasion that a normal condition is of 
 but short duration. After the disappearance of the primitive 
 cusps, and before further abrasion has taken 
 Developmental Grooves placc, the edgc IS fairly sharp and placed 
 
 B nearly at right angles with the crown. As 
 in the upper incisors, the cutting-edge is in 
 a line with the long axis of the tooth. The 
 labial margin of the edge is slightly convex, 
 while the lingual is irregularly concave to 
 the same extent. 
 The Cervical Margin. — This marginal 
 line, which is marked by the extent of the 
 enamel cap, corresponds closely to that of the 
 upper incisors, dipping down with a grace- 
 ful concavity on the labial and lingual sur- 
 faces, with a corresponding convexity on the 
 mesial and distal surfaces. The prominence 
 of this enamel margin, together with the 
 nature of the curvature, is much influenced 
 by the tooth type. 
 The Neck of the Tooth. — A distinctive feature of this 
 tooth is found in the convergence of its mesial and distal sur- 
 faces in passing from the cutting-edge rootward, thus produc- 
 ing a neck much constricted from mesial to distal. When ex- 
 amined from either the mesial or distal surface, this feature is 
 scarcely noted, the crown passing into the root with little more 
 than the cervical line as a mark of separation. The labial and 
 lingual portions of the neck are rounded and narrow, while the 
 two lateral sides are flat and broad. 
 
 The Root. — The root of this tooth is usually smaller than 
 
 Fig. 112. — Young 
 Lower Incisor, with 
 Cutting - edge, show- 
 ing THE Lines of De- 
 velopment. 
 
LOWER LATERAL INCISOR. 213 
 
 that of any other tooth in the mouth. It is much flattened from 
 mesial to distal, while the labial and lingual aspects are rounded 
 and narrow. Besides being flattened and broad, the mesial and 
 distal sides are usually found with a longitudinal depression ex- 
 tending from a point near the base of the root almost to its 
 apex. These surfaces gradually taper from the base to the 
 apex, while the labial and lingual first widen from the base and 
 then gradually taper to the apex. The contour of the root-base 
 is generally reduced at the apical extremity, although in some 
 instances the latter is a rounded point. While the root of the 
 tooth is usually straight, there is sometimes a tendency for the 
 apical third to have a slight distal inclination. 
 
 LOWER LATERAL INCISOR. 
 
 Calcification Begins, First Year after Birth. 
 
 Calcification Completed, Tenth to Eleventh Year. 
 Erupts, Eighth to Ninth Year. 
 Average Length of Crown, .35. 
 
 Average Length of Root, .50. 
 
 Average Length over All, .85. 
 
 The crown of this tooth differs from the central incisor in 
 being broader from mesial to distal at the cutting-edge, resulting 
 in a crown more strongly bell-shaped. The cutting-edge, instead 
 of being at right angles to the long axis of the tooth, slopes 
 to the distal at the expense of the distal angle, which is much 
 rounded, while the mesial angle closely resembles the corre- 
 sponding angle of the central incisors. The labial and mesial 
 surfaces do not differ materially from the corresponding surfaces 
 of the central incisor, excepting that the lingual more frequently 
 shows the lines of development, and the distal is at variance in 
 having that portion which contributes to the formation of the 
 distal angle extended and prominent. The marginal ridges of 
 the lingual surface are probably more definitely outlined than 
 those of the central incisor, and the crown in general presents a 
 stronger appearance. The neck of the tooth is similar to the 
 neck of the central incisor, as is also the root, with the excep- 
 tion of a slio'ht addition to its lenoth. 
 
LOWER CUSPID. 
 
 calcifrcation begins, third year after birth. 
 
 Calcification Completed, Twelfth to Thirteenth Year. 
 Erupts, Twelfth to Thirteenth Year. 
 Average Length of Crown, .40. 
 
 Average Length of Root, .60. 
 
 Average Length over All, i.oo. 
 
 There is probably a greater similarity existing between the 
 upper and lower cuspid teeth than in any other class ot 
 teeth in the mouth. Occupying as they do a prominent 
 position in the dental arch, and being called upon to perform 
 
 the double function of incis- 
 Labiai Grooves |p,g ^pj teaHug the food, their 
 
 crowns are strong and heavy- 
 set, and their roots long and 
 firmly anchored in the alveoli. 
 Like the upper cuspid, the 
 crown of the lower is sur- 
 mounted by a single cusp, 
 from the summit of which de- 
 scend a mesial and a distal 
 cutting-edge. There is also a 
 labial, lingual, mesial, and dis- 
 tal surface presented for ex- 
 amination. 
 
 The Labial Surface of 
 the Crown (Fig. 113). — The 
 crown of the tooth, being a 
 little longer than that of the upper cuspid, gives to this 
 surface the appearance of being more slender, when in 
 reality there is but little difference in the width of the two 
 teeth. This surface is smooth and convex, and, while the labial 
 grooves are usually present, they are not so marked as those 
 found upon the corresponding upper tooth. A pronounced 
 feature of the surface is the labial ridge, which extends from the 
 summit of the cusp to the cervical line, providing additional 
 strength to the crown. Aside from this ridge and the labial 
 
 Fig. 113. 
 
 -Lower Cuspid, 
 face. 
 
 Ladial Sur- 
 
LOWER CUSPID. 
 
 215 
 
 Lingual Grooves 
 
 grooves, the surface is occasionally broken by one or more 
 transverse ridges over the cervical portion. The margins of the 
 surface closely resemble those of the upper cuspid, the incisive 
 and mesial being definite in character, while the distal is made 
 equally indefinite by the passing of the labial into the distal 
 surface by a gentle curve. 
 
 The Lingual Surface of the Crown (Fig. 114). — The 
 ridges and grooves of this surface are far less bold in their 
 character than those of the upper cuspid. The lingual ridge, 
 which divides the surface into two equal parts, extends from the 
 summit of the cusp to the base of the cervical ridge, while the 
 marginal ridges pass root- 
 ward from the angles of the 
 crown, and, uniting, form the 
 cervical ridge. The slight 
 depressions between the lin- 
 gual ridge and the marginal 
 ridges correspond to the pal- 
 atal grooves of the upper 
 cuspid, but in this tooth par- 
 take more of the nature of 
 fossae. 
 
 The Mesial Surface of 
 the Crown (Fig. 115). — A 
 peculiarity found in connec- 
 tion with this surface is the 
 general plane existing be- 
 tween the crown and root- 
 surface. In all other teeth the mesial and distal surfaces are 
 found to bulge somewhat beyond the corresponding surface of 
 the root, but this surface of the lower cuspid is not only usually 
 in a direct line with the mesial surface of the root, but is occa- 
 sionally inclined to the distal, resulting in a crooked or bent 
 appearance to the tooth. In addition to this individual pecu- 
 liarity, the surface is flat and passes by a long curve to meet the 
 lingual surface. 
 
 The Distal Surface of the Crown (Fig. 1 1 6). — This surface 
 is somewhat less in extent than the mesial surface, and, in place 
 
 114. — Lower Cuspid, Lingual 
 Surface. 
 
Cervica 
 Ridge 
 
 -Lower Cuspid, Mesial 
 Surface. 
 
 of being flat and in line with the root-surface, that portion near 
 the angle of the crown presents a marked convexity, while that 
 
 near the cervical line is fre- 
 quently slightly concave. This 
 general form of the surface fur- 
 ther assists in producing the 
 distal crook previously referred 
 to. The lingual margin is well 
 defined and somewhat angu- 
 lar, while the surface passes 
 so gradually into the labial 
 that a positive line of demarca- 
 tion can scarcely be said to 
 exist. 
 
 The Cusp and Cutting- 
 edges. — In most respects these 
 are similar to the correspond- 
 ing parts of the upper cuspid. 
 The length of the mesial cutting-edge is usually somewhat less 
 than that of the distal, but this difference is seldom so marked as 
 that found in the upper cuspid. The mesial and distal angles of 
 the crown are equally as pro- 
 nounced as those of the cor- 
 responding upper tooth. 
 
 The Neck of the Tooth. 
 — This is shown by a fairly 
 well-marked constriction, but 
 the passing of the mesial 
 surface of the crown into the 
 mesial surface of the root is 
 not broken by this circular 
 depression. On account of 
 this latter feature the neck 
 of this 'tooth is somewhat less 
 pronounced than that of the 
 upper. 
 
 The Root of the Lower Cuspid. — The root of this tooth is 
 somewhat shorter and more flattened on its mesial and distal 
 
 -Lower Cuspid, Distal 
 Surface. 
 
THE LOWER BICUSPIDS. 217 
 
 sides than that of the upper cuspid, this lateral flatness fre- 
 quently amounting to a decided longitudinal depression or 
 groove. As referred to in the description of the crown, the 
 mesial side of the root is continuous in a direct line with this 
 surface of the crown, but as the apical third of the root is 
 approached, there is frequently found a slight distal inclination 
 which affects alike both the mesial and distal sides. The labial 
 and lingual surfaces of the root are abruptly convex and taper 
 very gradually from the cervical line to the apex, while the 
 mesial and distal surfaces taper much more rapidly, the four 
 ending in a slender apex usually flattened from mesial to distal. 
 
 THE LOWER BICUSPIDS. 
 
 In many respects these teeth are similar to the bicuspids of 
 the upper jaw, but there are a few minor points of dissimilarity. 
 They are somewhat shorter and smaller in every respect ; 
 their crowns are much more rounded and the cusps are never 
 so strongly developed. Unlike the upper bicuspids, the buccal 
 and lingual cusps are connected by a transverse ridge. The 
 roots are much less flattened from mesial to distal, and are 
 seldom bifurcated. 
 
 LOWER FIRST BICUSPID. 
 
 Calcification Begins, about the Fourth Year. 
 
 Calcification Completed, Eleventh to Twelfth Year. 
 Erupted, Tenth to Eleventh Year. 
 Average Length of Crown, .30. 
 
 Average Length of Root, .54. 
 
 Average Length over All, .84. 
 
 In general, the crown of this tooth is much more rounded and 
 smaller in all its measurements than that of the upper bicus- 
 pid. The buccal surface presents a much greater convexity, 
 which results in forcing the summit of the buccal cusp well 
 toward the center of the long axis of the tooth. The mesio- 
 distal and buccolingual measurements of the crown are nearly 
 equal, and about correspond to the maximum length ot the 
 crown. As in the upper bicuspids, the development ot this 
 tooth is similar to that of the incisors and cuspids, the buccal 
 
cusp being derived from three lobes, while the lingual results 
 from a single center. 
 
 The Occlusal Surface of the Crown (Fig. 117). — This 
 surface is so unlike that of the corresponding surface of the 
 upper first bicuspid that a separate description without further 
 comparative reference is required. In general outline the form 
 of a rounded triangle is approached, the buccal margin serving 
 as one side of the triangle, while, by the union of the mesial and 
 distal margins to form the lingual, the remaining sides are 
 established. 
 
 The Buccal Qisp. — rAs previously stated, the summit of this 
 cusp is thrown well toward the center of the surface. Descend- 
 ing from it are four well-defined ridges — the buccal ridge to the 
 buccal surface, the mesial cutting-edge, the distal cutting-edge, 
 
 and the triangular ridge, the 
 Summit of Buccal Cusp lattcT descending in a lingual 
 
 direction to meet the lingual 
 
 
 ^^ _^_J Buccal Groove rido;e or cusp. This ridge 
 
 uccal Ridge ^^S -^HM ^j ■ i p-, * ^ ^ 
 
 ^^ ^^ ""^ ' divides the surface into two 
 
 parts, the center of each 
 being marked by a well- 
 defined pit — the mesial and 
 i^ni^ua. iwuK^. distal pits. The mesial and 
 
 Fig. 117. — Lower First Bicuspid, ,. , . 
 
 Occlusal Surface. distal cuttmg-edges are fre- 
 
 quently crossed by the buccal 
 grooves, and mark the line of union between the central and two 
 lateral lobes of the buccal cusp. The marginal ridges, one of which 
 begins at the mesial angle and the other at the distal angle, 
 pass to the lingual, where they unite to form the lingual ridge 
 or cu,sp. 
 
 The Lingual Cusp. — This cusp is seldom well developed, and 
 corresponds to the cervical ridge of the incisors and cuspids. 
 The extent of development in the lobe is extremely variable, 
 in some instances amounting to little more than a continuation 
 of the mesio- and disto-marginal ridges, while in others there is 
 a building-up of the enamel in the form of a small tubercle. 
 When this latter condition is present, the triangular ridge of the 
 buccal cusp contributes to its formation. The triangular ridge 
 
THE LOWER BICUSPIDS. 
 
 Fig. iiS. — Right Lower First Bi- 
 cuspid, Buccal Surface. 
 
 frequently divides into two or more smaller ridges, which usually 
 
 end in the mesial pit, but in some instances they continue to the 
 
 lingual, and divide the linofual 
 
 ridge into two or more smaller 
 
 tubercles. 
 
 The Buccal Surface of the 
 
 Crown (Fig. ii8). — This surface 
 
 is smooth and convex in all direc- 
 tions, and in general outline there 
 
 is but little variation between it 
 
 and the corresponding surface of 
 
 the upper first bicuspid. It is 
 
 traversed from the point of the 
 
 cusp to the cervical line with a 
 
 rounded ridge, the buccal ridge, 
 
 upon either side of which are the 
 
 buccal grooves. 
 
 Lingual Surface of the Crown (Fig. 119). — This surface 
 
 is more or less extensive in accordance with the character of 
 
 the lingual lobe. In most instances 
 the measurement from the summit 
 of the cusp or ridge to the cervical 
 line is about one-half that of the 
 same measurements on the buccal 
 surface. From mesial to distal a 
 well-rounded convexity is present, 
 while from the occlusal margin to 
 the cervical line it is straight or 
 only slightly convex. The surface 
 passes so gradually into the mesial 
 and distal surfaces that no definite 
 lateral margins exist. 
 
 The Mesial Surface of the 
 Crown (Fig. 120). — In the region 
 of the occlusal margin this surface 
 is prominent, with a marked con- 
 vexity from buccal to lingual ; but as the cervical margin is 
 
 approached, the surface recedes to the distal, and is flattened 
 
 al Cusp Triangular 
 Ridge 
 
 Fig. 119. — Left Lower First Bi- 
 cuspid, Lingual Surface. 
 
Fig. 120. — Left Lower First Bicus- 
 pid, Mesial Sukface. 
 
 or is possessed of a slight general convexity. The occlusal and 
 cervical margins alone are well defined, the buccal being grace- 
 fully rounded, while the surface 
 passes to the Hngual with a long 
 curve. 
 
 The Distal Surface of the 
 Crown (Fig. 1 21). — There is but 
 little difference between this and 
 the mesial surface ; the occlusal 
 portion of the surface is some- 
 what less prominent, resulting in 
 less of the bell-shaped appear- 
 ance to this side of the crown. 
 
 The Neck of the Tooth.— 
 The neck of this tooth is marked 
 by a well-defined constriction, 
 the enamel of the crown sud- 
 denly folding in to meet the 
 cementum of the root at the cervical line, forming a band or 
 ridge which completely encircles the tooth. The amount of 
 constriction appears to be evenly 
 
 distributed between the various Triangular Ridge 
 
 parts, so that, viewed in all direc- 
 tions, the neck becomes a dis- 
 tinctive feature of the tooth. 
 
 The Root of the Lower 
 First Bicuspid. — The root of 
 this tooth is usually straight and 
 tapers gradually from base to 
 apex. In rare instances it is bi- 
 furcated, and when thus formed, 
 those portions beyond the point 
 of separation are more or less 
 crooked. In the single root the 
 apical third often curves slightly 
 to the distal. The buccal and 
 
 lingual sides are convex throughout their entire length, while the 
 mesial and distal may be slighdy convex, flattened, or provided 
 
 Lingual Ridge 
 
 121. — Right Lower First Bi- 
 cuspid, Distal Surface. 
 
THE LOWER BICUSPIDS. 
 
 with a slight longitudinal concavity. In passing from buccal to 
 lingual the mesial and distal sides converge, thus resulting in a 
 narrowinor of the lingual side of the root. 
 
 LOWER SECOND BICUSPID. 
 
 Calcification Begins, Between the Fourth and Fifth Year. 
 Calcification Completed, Eleventh to Twelfth Year. 
 Erupts, Eleventh to Twelfth Year. 
 Average Length of Crown, .31. 
 
 Average Length of Root, .56. 
 
 AvER.'iGE Length over All, .87. 
 
 In general contour this tooth is similar to the lower first 
 bicuspid, excepting that the crown is somewhat more rounded 
 and the lingual cusp more fully developed, this latter feature 
 causing it to closely resemble the upper bicuspids. The 
 crown is frequently a trifle 
 shorter than that of the lower 
 first bicuspid, but the length 
 of the root generally exceeds 
 that of the latter, making this 
 the longer tooth of the two. 
 
 The Occlusal Surface of 
 the Crown (Fig. 122). — The 
 occlusal surface of this tooth pre- 
 sents a greater variety in form 
 than any other tooth_of its class. 
 The general outline of the sur- 
 face is that of a broken circle, in most instances the mesial 
 and distal margins showing almost as much of a convexity as 
 that of the buccal and lingual. The summit of the buccal cusp 
 usually extends well toward the center of the surface, but it is 
 sometimes forced toward the buccal by an increased develop- 
 ment in the lingual cusp. The buccal grooves, which cross the 
 mesial and distal cutting-edges of the buccal cusp, are seldom 
 so well defined as those of the first bicuspid, but they occasion- 
 ally pass over these marginal ridges and form well-marked 
 grooves, which end in the mesial and distal pits. The triangular 
 ridge of the buccal cusp is usually more prominent than in the 
 
 122. — Lower Second Bicuspid, 
 Occlusal Surface. 
 
ANATOMY. 
 
 first bicuspid, and divides the surface into two portions, which 
 are about equal in extent, the center of each portion being pro- 
 vided with a small pit — the mesial and distal pits. As in the first 
 bicuspid, the mesio- and disto-marginal ridges begin at the 
 mesial and distal angles of the crown, pass to the lingual, and, 
 uniting, form the lingual ridge or cusp. The lingual cusp, while 
 generally well developed, is never so prominent as the buccal. 
 The lingual lobe is sometimes divided by a groove which passes 
 from buccal to lingual, thus forming three cusps upon the sur- 
 face. When this latter condition is present, the mesial and distal 
 
 grooves are fully outlined from the 
 Buccal Ridge mesio- and disto-marginal ridges 
 
 to the center of the surface, where 
 they unite with the groove previ- 
 ously referred to and form a cen- 
 tral pit or fossa. Another form 
 frequently met with is one in which 
 the surface closely resembles that 
 of the upper bicuspids, two well- 
 defined cusps being present, sepa- 
 rated from each other by a central 
 groove, which passes from mesial 
 to distal and joins the triangular 
 grooves at these points. The re- 
 semblance to the upper bicus- 
 pids is further increased by the 
 presence of two small pits, one on the mesial and one on the 
 distal half of the surface. 
 
 The Buccal Surface of the Crown (Fig. 123). — The 
 principal variation between this and the buccal surface of the 
 lower first bicuspid is that it is less extensive and the buccal 
 grooves somewhat less defined. It presents a general con- 
 vexity, which is most pronounced near the center, between 
 which point and the occlusal margins it is slightly inclined to 
 flatness. The summit of the buccal cusp is usually to the 
 mesial of the center of the occlusal margin, so that the mesial 
 cutting-edge is considerably longer than the distal, this fact also 
 resultine in forcing the buccal ridg^e to the mesial of the center 
 
 123. — Right Lower Second 
 CUSPID, Buccal Surface. 
 
THE LOWER BICUSPIDS. 
 
 124 — Lower Second Bicuspid, 
 Lingual Surface. 
 
 of the surface. The mesial angle of the crown, as observed 
 when looking- directly upon the buccal surface, is in a direct line 
 with the mesial side of the root, 
 
 .. .^ 1 1* 1 1 1 Buccal Grooves 
 
 while the distal angle extends 
 beyond this corresponding line, 
 and gives a prominent or bulging 
 appearance to this section of the 
 crown. 
 
 The Lingual Surface of the 
 Crown (Fig. 124). — Proportion- 
 ately, this surface is more exten- 
 sive than the corresponding sur- 
 face of the first bicuspid, this 
 increase being produced by the 
 additional development of the 
 lingual cusp. It is well rounded 
 from mesial to distal, and passes 
 into these surfaces without the 
 
 existence of a positive line of separation. From the cervical 
 line to the occlusal margin a slight convexity is present. The 
 
 general outline of the surface 
 is much influenced by the con- 
 ditions present upon the oc- 
 clusal surface. 
 
 The Mesial Surface of 
 the Crown (Fig. 125). — In 
 the region of the occlusal 
 margins this surface is decid- 
 edly convex from buccal to 
 lingual, but in passing toward 
 the cervical line a gradual 
 flatness is apparent, which, 
 however, seldom amounts to 
 a perfect plane. While there 
 is a gradual convergence of 
 this and the distal surface to- 
 ward the root, it is not so marked as that of the first bicuspid, 
 resulting in less of the bell-shaped appearance to the crown. 
 
 
 Triangular Ridge 
 
 Lingual Cusp I 
 
 B^IBB 
 
 Mesioniar- 
 
 |^P!^B 
 
 ginal Ridge 
 
 ■ <^M^B 
 
 
 1 r fl 
 
 
 1 ^1 
 
 Buccal Cusp 
 liuccal Ridge 
 
 125. — Lower Second Bicuspid, 
 Mesial Surface. 
 
The Distal Surface of the Crown (Fig. 126). — Tlie descrip- 
 tion given of the mesial surface applies equally well to this, there 
 being but slight variation existing between the two. Occasion- 
 ally this surface will present a greater convexity in the region 
 
 of the occlusal margin, but this is 
 not a constant feature. 
 
 The Neck of the Tooth.— 
 The crown of the tooth being some- 
 what smaller, and the root propor- 
 tionately larger and longer than 
 that of the first bicuspid, results in 
 diminishing the amount of constric- 
 tion at the neck, and for that reason 
 this feature is less definite. 
 
 The Root of the Tooth.— As 
 previously stated, the root of this 
 tooth is larger and longer than that 
 of the first bicuspid. The mesial 
 and distal sides are flattened and 
 frequently provided with a longitudinal groove. In some in- 
 stances it is rather blunt, ending in a heavy, rounded apex ; in 
 others it tapers very gradually from the base to the apex, ending 
 in a sHm, pointed extremity. 
 
 Fig. 126. — Lower Second Bicuspid, 
 Distal Surface. 
 
 THE LOWER MOLARS. 
 
 THE LOWER FIRST MOLAR. 
 
 Calcification Begins, about One Month Before Birth. 
 Calcification Completed, Ninth to Tenth Year. 
 Erupts, Sixth to Seventh Year. 
 Average Length of Crown, .30. 
 
 Average Length of Root, .52, 
 
 Average Length over All, .82. 
 
 The process of development in this tooth corresponds to 
 that of the upper first molar, calcification beginning upon 
 the coronal extremities as early as the eighth fetal month, the 
 crown being completely calcified by the fifth year, the roots 
 formed and the apical foramina established by the eleventh year. 
 
THE LOWER MOLARS. 
 
 Buccal 
 Cusp 
 
 There is, however, one important difference between the devel- 
 opment of this tooth and the corresponding upper tooth : 
 that of calcification taking place usually irom Jive centers instead 
 of four, and, as a result, we find the occlusal surface provided 
 with five well-developed cusps separated from one another by 
 five developmental grooves. When compared with the upper 
 first molar, the crown of this tooth is found to be somewhat less 
 in size ; in general outline it is subject to a greater variation 
 and is much more angular in its nature. The mediodistal 
 measurement of the crown is nearly always greater than the 
 buccolingual, and the length of the crown from the occlusal 
 margins to the cervical line is proportionately less than that of 
 the corresponding upper molar. 
 
 The Occlusal Surface of the Crown (Fig. 127). — The 
 general outline of the crown 
 is best studied when looking 
 directly upon this surface. 
 Two principal varieties exist : 
 one in which the sides or mar- 
 gins of the surface appear to 
 be flattened or straightened 
 out, and the other when these 
 same margins are gracefully 
 rounded. In either form the 
 buccal line is the longest, so 
 that the mesial and distal lines 
 converge to meet the lingual. 
 
 This common form gives to the buccal angles an acute character, 
 while the lingual angles are about equally obtuse. The surface 
 is divided into five distinct or developmental portions, each of 
 which is surmounted by a cusp, named, as their location indi- 
 cates, mesiobuccal, buccal, distobuccal, mesiolingual, and disto- 
 lingual. Separating these parts are five developmental grooves 
 — the mesial, the distal, the buccal, the lingual, and the disto- 
 buccal. The four former cross the marginal ridges from the 
 various surfaces and end in the central fossa, while the latter 
 passes from the distobuccal angle and joins the distal groove, 
 their union being marked by a slight depression or pit — the 
 IS 
 
 Fig. 127.- 
 
 -Lower First Molar, Occlusal 
 Surface. 
 
distal pit. Brandling off from the various grooves are a number 
 of supplemental grooves, the presence of which results in the 
 production of a number of smaller ridges. 
 
 The Marginal Ridges of the Occlusal Stirface. — Properly 
 speaking, these are only two in number, the mesiomarginal 
 ridge and the distomarginal ridge. Those margins which cor- 
 respond to the buccal and lingual ridges of the upper molars 
 are so broken by the various cusps and developmental grooves 
 that a definite marginal ridge scarcely exists, as will be observed 
 by the description of these parts. 
 
 The mesiomarginal ridge is strongly outlined, passing from 
 the mesiobuccal to the mesiolingual angle of the crown in the 
 form of a bold angular ridge. In some instances it is broken 
 near the center by the mesial groove passing over it to reach the 
 mesial surface, in others being further divided by numerous small 
 supplemental grooves. 
 
 The distomarginal ridge is much shorter and less decided 
 than the mesial, and extends from the distobuccal to the disto- 
 lingual angle. In nearly every instance it is broken by the 
 distal groove, which crosses it to reach the distal surface. 
 
 The buccomarginal ridge is formed by the various ridges 
 which descend in a mesial or distal direction from the three 
 buccal cusps. Near the center the margin is broken by the 
 buccal groove, and it is again broken at its distal third by the dis- 
 tobuccal groove, both of which pass over it to reach the buccal 
 surface of the crown. This is much the longest margin of the 
 surface, and in its entirety presents a gradual buccal convexity. 
 
 The linguomarginal ridge is principally made up of the 
 distal incline from the mesial cusp, and by the mesial incline 
 from the distal cusp. Near the center it is broken by the lin- 
 gual groove, which passes over it to reach the lingual surface. 
 This margin, unlike the buccal, is not always convex, but in 
 many instances is almost a straight line, extending from the 
 mesial to the distal angle. 
 
 The Cusps (Fig. 127). — The Mesiobnccal Cusp (Fig. 127). — 
 This is usually the largest, though not always the longest, cusp ot 
 the group. It is bounded by the mesial and buccal surfaces and 
 by the mesial and buccal grooves, which together form the mesio- 
 
THE LOWER MOLARS. 227 
 
 buccal triangular groove. Descending from the summit of this 
 cusp to the distal is a well-defined ridge, — a part of the bucco- 
 marginal ridge, — while in a mesial and lingual direction the de- 
 scending ridges contribute to both the bucco- and mesio-mar- 
 ginal ridges. Descending toward the center of the surface and 
 ending in the central fossa is the mesiobuccal triangular ridge. 
 
 The Buccal Cusp (Fig. 127). — This cusp, which is placed a 
 little to the distal of the center of the buccal surface, is sepa- 
 rated from the mesiobuccal cusp by the buccal groove, and 
 from the distobuccal cusp by the distobuccal groove. It is 
 about one-half the size of the mesiobuccal cusp, and a trifle less 
 in length. Descending from it are two ridges, one in a mesial 
 and one in a distal direction, which form a portion of the bucco- 
 marginal ridge ; descending to the buccal surface is the buccal 
 ridge, while the central incline gives place to a fourth ridge — 
 the buccotriangular ridge. 
 
 The Distobuccal Cusp (Fig. 127). — This cusp is much the 
 smallest of the five, and is located at the distobuccal portion of 
 the crown, in some instances being nearest the buccal surface, 
 in others forced to the distal by an increase in the size of the 
 buccal cusp. It is separated from the buccal cusp by the disto- 
 buccal groove, and from the distolingual cusp by the distal 
 groove. The ridges which descend from it contribute to both 
 the bucco- and disto-marginal ridges, and descending toward 
 the distal pit is the distobuccal triangular ridge. 
 
 The Mesiolingual Cusp (Fig. 127). — This cusp is second in 
 size, and frequently the longest and most pointed. It has for 
 its boundaries the mesial and lingual surfaces, and the mesial 
 and lingual grooves. The ridge which descends from it in a 
 mesiobuccal direction assists in forming the mesiomarginal 
 ridge, while that which passes to the distal forms a part of the 
 linguomarginal ridge. In the direction of the central fossa a 
 pronounced ridge is present, — the mesiolingual triangular ridge, 
 — which is often supplemented by one or more smaller ridges 
 running in the same direction. 
 
 The Distolingual Cusp (Fig. 127). — This cusp usually occu- 
 pies the distolingual portion of the crown, although sometimes 
 being forced well toward the lingual by the distobuccal cusp. 
 
ANATOMY. 
 
 It is separated from the mesiolingual cusp by the hngual groove, 
 and from the distobuccal by the distal groove. Two of the 
 ridges which descend from it assist in forming the Hnguo- and 
 disto-marginal ridges, while the one which descends the central 
 incline is the distolingual triangular ridge. The central incline 
 of the mesiobuccal, buccal, mesiolingual, and distolingual cusps 
 contribute to the formation of the central fossa, while the buccal, 
 distobuccal, and distolingual central inclines assist in forming 
 the distal pit or fossa. 
 
 The Buccal Surface of the Crown (Fig. 128). — This is 
 the most extensive of the lateral surfaces of the crown. It is 
 
 convex from mesial to 
 Buccal Groove distal, and also from the 
 
 occlusal margin to the 
 cervical line. The width 
 of the crown from the 
 mesial to the distal an- 
 gle is always somewhat 
 greater than that at the 
 cervical line, the differ- 
 ence being governed 
 by the typal form of the 
 tooth. A litde to the 
 mesial of the center of 
 the surface is the buc- 
 cal groove, which, after 
 crossing the buccomar- 
 ginal ridge, is usually 
 quite deep ; but as it proceeds in the direction of the root it grad- 
 ually disappears, or it may end abruptly in a well-defined pit 
 — the buccal pit. The distobuccal groove enters the surface near 
 the distobuccal angle, and gradually becomes less pronounced as 
 it passes rootward. It is seldom so well defined as the buccal 
 groove, and usually ends when about half-way to the cervical 
 line. The occlusal margin is made irregular by the presence of 
 the three buccal cusps ; the cervical margin is nearly straight 
 from mesial to distal, and is surmounted throughout by a strong 
 
 -Lower First Molar, Buccal 
 Surface. 
 
THE LOWER MOLARS. 
 
 Distolingual Mesiolingual 
 Cusp Cusp 
 
 Fig. 129. — Lower First Molar, 
 Lingual Surface. 
 
 enamel fold, the cervicobuccal ridge. The mesial margin is 
 longer than the distal, but neither of them are well defined. 
 
 The Lingual Surface of the Crown (Fig. 129). — This sur- 
 face is smooth and convex in every 
 direction. It is generally divided into 
 two portions, a mesial and a distal, 
 which are nearly equal in extent. 
 This separation is formed by the lin- 
 gual groove, which is sometimes deep 
 and sulcate, at others shallow, and 
 not infrequently entirely wanting. 
 The surface is nearly one-third less 
 in extent than the buccal, the con- 
 vergence of the mesial and distal 
 surfaces in passing to the lingual 
 accounting for this difference. The 
 occlusal margin is formed by the 
 double incline of the two lingual 
 cusps; the cervical margin is either 
 
 straight or slightly concave in the direction of the occlusal 
 surface, while the mesial and distal margins are rounded and 
 
 poorly defined. 
 ''""^^'^°=^^ The Mesial Surface of 
 
 the Crown (Fig. 130). — This 
 surface is inclined to flatness, 
 with a slight bulging near the 
 center, which marks the point 
 of contact with the approxi- 
 mate tooth. It is usually 
 smooth, and unbroken by de- 
 velopmental or other grooves, 
 although the mesial groove 
 occasionally traverses it after 
 crossing the marginal ridge 
 from the occlusal surface. 
 Near the center of the cervical third a slight concavity is often 
 present. The margins of the surface are somewhat irregular, 
 the occlusal margin being made irregularly concave by the ridges 
 
 Fig. 130.- 
 
 -Lower First Molar, Mesial 
 Surface. 
 
230 
 
 which descend from the two mesial cusps ; the cervical margin 
 is slightly concave in the direction of the occlusal surface, and, 
 while the buccal margin inclines to the lingual as the occlusal 
 surface is approached, the lingual is almost perpendicular. 
 
 The Distal Surface of the Crown (Fig. 131). — Unlike the 
 mesial, this surface is possessed of a decided convexity in every 
 direction. It is surmounted by a portion of the distobuccal and 
 distolingual cusps, and is frequently broken by the distal groove, 
 which reaches it after crossing the marginal ridge from the 
 occlusal surface. The occlusal margin is irregularly formed ot 
 the marginal ridges which descend from the distobuccal and 
 distolingual cusps; the cervical margin is usually straight, while 
 
 the buccal and lingual are 
 rounded and indefinite. 
 
 The Neck of the 
 Tooth. — One character- 
 istic feature of this tooth is 
 the greater circumference 
 of the crown at the occlu- 
 sal margin over that at 
 the cervical line, giving a 
 flaring appearance to the 
 crown, and resulting in the 
 production of a neck which 
 is much constricted. This 
 is particularly noticeable 
 when looking upon the 
 buccal surface of the tooth ; but when looking upon the mesial 
 or the distal surface, this feature is not so pronounced, although 
 the rather heavy fold of enamel which surmounts the cervical 
 line contributes much to the formation of the neck from these 
 aspects. 
 
 The Roots of the Tooth. — The roots of this tooth are two 
 in number, — one of which Is placed beneath the mesial, and the 
 other beneath the distal half of the crown, — and are named the 
 mesial root and the distah^oot. The fact that the point of bifurca- 
 tion is constantly in close proximity to the neck or crown of the 
 tooth is a sufficient reason for the statement that two roots exist, 
 
 Fig. 131. — Lower First Moi.ar, Distal 
 Surface. 
 
THE LOWER MOLARS. 231 
 
 rather than a single root with two branches. The roots are both 
 mucli flattened from mesial to distal, and broad at the base from 
 buccal to lingual. 
 
 Tlie mesial root is usually the larger and longer of the two. 
 After leaving its base it generally inclines to the mesial, but 
 beyond the center of its length it is provided with a distal turn, 
 which in some instances amounts to a decided crook. The 
 center of the mesial side is occupied by a longitudinal depres- 
 sion, as is also the distal side, making this part of the root thin, 
 giving the appearance of an effort to bifurcate, which condition 
 is occasionally present. The buccal and lingual sides of the 
 root are rounded and smooth, and taper gradually to the apex, 
 which is somewhat broadened from buccal to lingual. 
 
 The distal root is usually straight, with a more gradual taper 
 throughout, ending in an apical extremity more pointed than 
 that of the mesial root. A longitudinal depression is also 
 present upon both the mesial and distal sides, but is never so 
 pronounced as that upon the mesial root. The buccal and lin- 
 gual sides are convex and smooth. The root possesses little 
 or no inclination to bifurcate. 
 
 LOWER SECOND MOLAR. 
 
 Calcification Begins about the Fifth Year. 
 
 Calcification Completed, Sixteenth to Seventeenth Year. 
 Erupts, Twelth to Sixteenth Year. 
 Average Length of Crown, .27. 
 
 Average Length of Root, .50. 
 
 Average Length over all, .78. 
 
 This molar differs in so many particulars from the lower 
 first molar that a separate description will be called for. The 
 principal variation is frequently found In the absence of the 
 fifth lobe or cusp,* resulting in the production of an occlusal 
 surface much less complicated. 
 
 The Occlusal Surface of the Crown (Fig. 132). — When 
 the crown Is studied by looking directly upon this surface, the 
 
 *When five cusps are present, the anatomy of this surface does not differ from that of the 
 first molar. 
 
ANATOMY. 
 
 variations between this and the first molar are readily noted. 
 Four equally proportioned cusps are observed, separated 
 from each other by four developmental grooves. A single pit 
 or fossa is present, the four grooves arising from this one point. 
 In general outline two principal varieties exist : one in which the 
 opposite sides of the crown are nearly of the same length, and 
 parallel with each other, with the angles rounded ; the other, in 
 which either the buccal or lingual margin is the longest, with the 
 mesial and distal margins converging one way or the other, as 
 the case may be. The marginal ridges are formed in a manner 
 similar to those of the first molar, with the exception of the distal 
 portion of the buccal ridge, which is not broken by a develop- 
 mental groove. Each mar- 
 | = a «o ginal ridge is divided near 
 
 °=5 °<^ its center by one of the 
 
 grooves of development, 
 the mesial groove crossing 
 the mesiomarginal ridge, 
 the buccal groove crossing 
 the buccomarginal ridge, 
 the lingual groove cross- 
 ing the lingual ridge, and 
 the distal groove passing 
 over the distal ridge. In 
 many instances numerous 
 supplemental grooves are 
 present, which in turn form a number of smaller ridges. The four 
 cusps are the mesiobicccal , distobuccal, mesiolingual, and distolin- 
 gual. In a general way they are similar to the cusps of the first 
 lower molar, excepdng that they are somewhat larger and prob- 
 ably less pointed and less angular. Each cusp is provided with 
 a number of ridges, which descend from the summit to the base, 
 two of these contributing to the formation of the marginal 
 ridges, one passing to the buccal or lingual, and one, the trian- 
 gular ridge, descending the central incline of each cusp. The 
 names given to these various ridges are identical with those of 
 the first molar. 
 
 32. — Lower Second Molar, Occlusal 
 Surface. 
 
THE LOWER MOLARS. 
 
 al Buccal Mesiobuccal 
 Groove Cusp 
 
 Fig. 133. — Lower Second Molar, 
 Buccal Surface. 
 
 -the buccal pit. 
 
 The Buccal Surface of the Crown (Fig. 133). — The 
 
 principal difterence between this and the corresponding surface 
 
 of the first molar is that pro- 
 duced by the absence of the fifth 
 
 cusp, the surface being divided 
 
 into two parts instead of three. 
 
 The single division is caused by 
 
 the buccal groove, which reaches 
 
 the surface after crossing the 
 
 buccomarginal ridge from the 
 
 occlusal surface. The position 
 
 of this groove is usually a little 
 
 to the mesial of the center of 
 
 the surface. Like the buccal 
 
 groove of the first molar, it 
 
 may disappear gradually as it 
 
 passes toward the cervical line, 
 
 or it may end in a well-marked pit- 
 
 The Lingual Surface of the Crown (Fig. 134). — This 
 surface so closely resembles the cor- 
 1 I I responding surface of the first molar 
 
 iu 1 ■'^u ^^^^ '^ ^^ somewhat difficult to distin- 
 
 c u s guish one from the other. The oc- 
 
 clusal margin may be a trifle less 
 irregular, and in some instances more 
 extensive, than the buccal surface, 
 this latter feature seldom occurring 
 in the first molar. 
 
 The Mesial Surface of the 
 Crown (Fig. 135). — This surface 
 corresponds to the mesial surface of 
 the first molar, being flattened or 
 slightly convex from buccal to lingual, 
 with an inclination to a slight depres- 
 sion or concavity near the cervical 
 margin. 
 The Distal Surface of the Crown (Fig. 136). — On account 
 
 of the absence of the fifth cusp, this surface is less complex than 
 
 Fig. 134. — Lower 
 Second Molar, Lingual 
 Surface. 
 
234 
 
 that of the first molar. It is convex in all directions ; in most 
 instances smooth, in others broken by the distal groove, which 
 
 Fig. 135. — Lower Second Molar, Mesial Surface. 
 
 reaches it after crossing the distomarginal ridge from the 
 occlusal surface. 
 
 The Roots of the Tooth. — Like the first molar, these are 
 
 Mesial Groove 
 
 Fig. 136. — Lower Second Molar, Distal Surface. 
 
 two in number, a mesial and a distal. They are much less con- 
 stant in form, are often nearer together, and in some instances 
 
THE LOWER MOLARS. 
 
 235 
 
 united. When the two roots exist, — which may be considered 
 the normal condition, — they are less flattened upon their mesial 
 and distal sides, with the longitudinal depression wanting or but 
 slightly apparent. These roots, therefore, are more rounded in 
 general, taper more gradually from neck to apex, and end in a 
 rounded apex, this often being provided with a slight distal 
 curve. 
 
 LOWER THIRD MOLAR. 
 
 Calcification Begins, Eighth to Ninth Year. 
 
 Calcification Completed, Eigthteenth Year. 
 Erupts, Sixteenth to Twentieth Year. 
 Average Length of Crown, .26. 
 
 Average Length of Roots, .36. 
 
 Average Length Over All, .62. 
 
 This tooth is probably subject to a greater variety in form 
 than any other tooth in the mouth. There are, however, two 
 varieties which are most frequently met with. In one the crown 
 of the tooth is similar to the lower second molar, being pro- 
 vided with four cusps, which 
 
 are separated from oneanother "s;; glji, 
 
 byfour developmental grooves .b^ ~|5 
 
 (Fig. 137). The other is simi- 
 lar to the lower first molar, 
 having five cusps and five de- 
 velopmental grooves. 
 
 While these two forms are 
 those most commonly met with, 
 the occlusal surface may be 
 so broken by numerous sup- 
 plemental and developmental 
 grooves that even six or eight 
 well-defined cusps may be pre- 
 sent. Whatever complications 
 
 may exist upon the occlusal surface, a central fossa is usually pre- 
 sent, from which radiate the various developmental grooves. 
 When the central fossa is absent, the space which it should occupy 
 is usually taken up bya rounded cusp, by the interference of which 
 the grooves are prevented from uniting, and their course is much 
 
 137. — Lower Thiru Molar, 
 Occlusal Surface. 
 
236 ANATOMY. 
 
 distorted. Along with these variations, the tooth is subject to 
 much variety in size. In some instances the crown is one-third 
 less in circumference than that of either the first or second 
 lower molars, while in others it is a trifle greater. The in- 
 crease in the size of the crown is generally accompanied by an 
 increase in the number of cusps. One feature very common 
 to the crown is its inclination to the circular form, almost result- 
 ing in the absence of the angles common to molars in general. 
 The marginal ridges are, of course, subject to the ever-varying 
 conditions to be found upon the occlusal surface ; in general, 
 
 Disto- 
 
 Disto- Mesio- 
 
 lingual 
 
 buccal buccal 
 
 Cusp 
 
 Cusp Cusp 
 
 Fig. 138. — Lower Third Molar, 
 Buccal Surface. 
 
 Fig. 139. — Lower Third Molar, 
 Lingual Surface. 
 
 they are poorly defined, and are frequently crossed by numerous 
 small supplemental grooves, dividing them into many minute 
 tubercles. The latter are smooth and strongly convex, with 
 their general outlines much influenced by the number of cusps. 
 The Roots of the Tooth. — While this tooth is strongly 
 inclined to be two-rooted, like the other lower molars, this 
 condition is by no means the common one. Like the crown, 
 the roots are probably more variable than those of any other 
 tooth. A single conic root may be present, or a mesial and 
 a distal root may exist ; again, the mesial root may bifurcate, 
 
THE LOWER MOLARS. 
 
 237 
 
 thus resulting in three. In some instances, four, or even five, 
 branches may be given off from a common base. When 
 more than two roots are present, they are usually much twisted 
 
 RT If f'J 
 
 Fig. 140. — Types of Lower Third Molars 
 
 or crooked, and, while generally inclined to the distal, are liable 
 to branch in various directions. 
 
 A better idea in the variations in this tooth may be had from 
 the accompanying illustration (Fig. 140). 
 
CHAPTER X. 
 THE PULP-CAVITIES OF THE TEETH. 
 
 In the preceding chapters the study of the teeth has been 
 confined to their external forms ; it will now be necessary to 
 learn something of their internal anatomy, and for this purpose 
 various dissections of each individual tooth must be made. 
 
 Dissections. — First, a longitudinal dissection of each tooth 
 should be made by sawing or filing from labial to lingual in the 
 anterior teeth, or from buccal to lingual in the posterior teeth. 
 Second, a longitudinal dissection by sawing from mesial to 
 distal. Third, numerous transverse dissections by sawing through 
 the crown or root at various points. 
 
 These dissections will expose to view a central cavity with 
 outlines closely corresponding to those of the tooth itself. This 
 is called ^& pulp-cavity, and in the vital tooth contains the forma- 
 tive and life-sustaining substance of the dentin, the dental-pulp. 
 The pulp-cavity is divided into two principal parts, that portion 
 within the crown of the tooth being l\\& p7ilp-ckamber, while that 
 traversing the root is the pulp-canal. At the apex of the root 
 the canal ends in a small foramen, the apical foramen, which 
 transmits the blood-vessels and nerves to the pulp. The pulp- 
 chamber occupies the center of the crown and is always a single 
 cavity ; the pulp-canals are prolongations from this central cavity, 
 and are usually one for each root, although in some instances two 
 or more canals are present in a single root. The form of the 
 pulp-chamber varies with the shape of the crown, the outline of 
 the cutting-edge in the incisor teeth being reproduced in that 
 part of the chamber nearest to the cutting-edge, wdiile in the 
 bicuspids and molars the occlusal surface is reproduced on the 
 wall of the pulp-chamber, immediately beneath it, the lateral 
 walls corresponding to the various sides of the tooth. In the 
 incisors and cuspids the pulp-chamber passes so gradually into 
 the pulp-canal that a positive line of demarcation between the two 
 
THE PULP-CAVITIES OF THE TEETH. 239 
 
 is not observed. In the bicuspids and molars the canals may 
 be readily distinguished by a sudden constriction and branching 
 out of the cavity into the various roots, which prolongations 
 gradually decrease in size until the apical foramen is reached. 
 The size of the pulp-cavity is much influenced by the age of the 
 tooth, its functional activity, character of the occlusion, etc. 
 The tooth-pulp, as the formative organ of the dentin, gradually 
 decreases in size as the tooth develops (see Development of the 
 Teeth), and as a result of this action the youngest teeth are pro- 
 vided with the largest pulp-cavities. At the time of eruption of 
 a tooth, the diameter of the pulp-cavity is about equal to one- 
 half the diameter of the crown, while the length of the canal 
 must, of necessity, accord with the extent of root-calcification. 
 As the growth of the tooth proceeds, the diameter of both the 
 chamber and canal is gradually diminished ; this gradual reduction 
 in size is continued during the life of the tooth, and if permitted to 
 proceed until old age, the chamber and canal may become almost 
 or entirely obliterated. It must be remembered that while the 
 diameter of the root-canal is diminished with the growth of the 
 tooth, its length increases, continuing to do so until the time of 
 complete root-calcification. During the period of root-develop- 
 ment the diameter of the root-canal is greatest at the free or apical 
 end of the root, at which point it presents a funnel-shaped opening 
 (Fig. 141). As the root continues to calcify, this funnel-shaped 
 extremity of the canal advances in the direction of calcifica- 
 tion, and finally, as the formative process nears completion, the 
 mouth of the funnel gradually disappears, and the apical fora- 
 men is established. The various lobes of the teeth are pene- 
 trated by a prolongation of the pulp-cavity, these being called 
 the horns of the pulp-chamber. The depth to which the horn 
 penetrates the lobe varies in accordance with the form of the 
 latter. If the tooth is one provided with long, penetrating 
 cusps, the horns of the pulp-chamber will also be long, but if 
 the cusps be poorly formed, the horns of the chamber will be 
 short. In the anterior teeth, when the lobal construction is put- 
 lined by well-marked developmental grooves, the horns of the 
 pulp-chamber will be three in number and directed toward the 
 cutting-edge. These are most marked in young teeth, and 
 
gradually disappear as age advances. The functional activity 
 of the teeth also serves to materially reduce the size of the pulp- 
 chamber. Thus, when opposing teeth occlude squarely and 
 firmly against each other, with more or less rubbing or sliding 
 during mastication, the external surface is prone to rapid 
 abrasion, and, as a direct result of this external change, the 
 pulp-chamber undergoes a corresponding alteration by a growth 
 of secondary dentin about its walls. 
 
 THE PULP-CAVITIES OF THE UPPER TEETH. 
 
 Upper Central Incisor. — Figure 141 represents a num- 
 ber of labiolingual sections presenting the relative size and 
 shape of the pulp-cavity in the upper central incisor at various 
 
 Fig. 141. — The Pulp-cavity in the Upper Central Incisor, from the Sixth to 
 THE Tenth Year. 
 
 ages. In No. i the condition existing at about the sixth year, or 
 at a time immediately prior to the eruption of the tooth, is shown. 
 The tooth-crown is fully formed and calcified ; the cervical line 
 may be observed, as well as a small portion of the root-wall. 
 The pulp-chamber, which is represented by the dark portion ot 
 the cut, occupies about one-third of the diameter of the crown 
 at its greatest width. The pulp-chamber at this age, when 
 viewed in this direction, forms almost a perfect cone, the base 
 of which is directed upward or toward the future extremity ot 
 the root, and its apex downward in the direction of the cutting- 
 edge of the tooth. The apex of the cone may end somewhat 
 
THE PULP-CAVITIES OF THE UPPER TEETH. 241 
 
 abruptly, or it may be lengthened into a slender, horn-like pro- 
 jection, extending- well toward the cutting-edge. No. 2 repre- 
 sents the same tooth about the seventh year, or at a time 
 shortly after its eruption. The pulp-chamber has become 
 slighdy reduced in its basal diameter, while but little change 
 has taken place in the apex. That portion of the pulp-cavity 
 above the cervical line represents a part of the future pulp- 
 canal. At this age the canal is a direct continuation of the 
 conic pulp-chamber, ending above in a broad, funnel-shaped 
 extremity. No. 3 shows the condition of the cavity about 
 the eighth year. The diameter of the pulp-chamber is con- 
 siderably diminished, the apex has slightly receded, and the 
 hornlike projection has partly disappeared. The increase in 
 the length of the canal is about fV of an inch over its length 
 at seven years. The two parallel sides of the canal have 
 lengthened proportionately, and the funnel-shaped extremity 
 is reduced in diameter owing to the gradual narrowing of the 
 root-walls. No. 4 gives the relative size of the pulp-chamber 
 and canal at the ninth year, or at a time when root- calcifica- 
 tion is nearing completion. The decrease in the capacity 
 of the chamber is readily apparent ; the horn-like projection 
 has disappeared and the parallel sides of the canal are partly 
 extended into the chamber, thus reducing the length of the cone. 
 In the canal a greater reduction has taken place in its diameter, 
 while its length has increased about j^ of an inch over that 
 at eight years, and the diameter of the funnel-shaped open- 
 ing is but little greater than that of the body of the canal. 
 No. 5, which represents the tooth about the tenth year, shows 
 the calcific action in the root completed, and the apical foramen 
 established. A glance at the illustration will show the gradual 
 decrease in the capacity of the pulp-cavity and the completion 
 of its growth in an apical direction. At this stage of develop- 
 ment the fan-shaped extremity of the canal gradually disappears, 
 and for the first time in the life of the tooth the canal partakes 
 of the external root form throughout its entire extent. 
 
 Figure 142, A, represents the size and form of the average 
 pulp-cavity in the adult upper central incisor. In its entirety 
 it represents a double cone, with a common base near the 
 
cervical line, the pulp-cavity forming one cone and the pulp- 
 canal the other. At this common base the. cavity assumes its 
 largest diameter, which measurement is approximately equal to 
 one-fourth the labiolingual diameter of the tooth. The extent 
 and form of the lower cone, or that represented by the pulp- 
 chamber, varies in the adult tooth with the tooth type. Thus, in 
 the nervous type the cone is long and narrow, with the apex 
 ending in a hair-like projection. In the tooth of the lymphatic 
 temperament the cone is prone to be wide, with its apex ending 
 abruptly. In the sanguine and bilious types the form and 
 extent of the cone do not partake of either of the foregoing ex- 
 tremes, but, in keeping with the outline of the crowns, are inter- 
 mediate between them. Figure 142, B, represents the average 
 
 142. — Pulp-cavity in the Upper Central Incisor. 
 
 condition of the pulp-cavity in the central incisor in advanced 
 age, and shows a general reduction in the size of both chamber 
 and canal. A further study of the pulp-chamber and canal may 
 be made by a mesiodistal section made through the long axis 
 of the tooth (Fig. 142, C). The outline of the cavity, viewed in 
 this way, closely follows the outline of the crown and root of the 
 tooth. There is no distinct division between the chamber and 
 the canal, the former gradually blending into the latter. The 
 outline of the entire cavity is that of a single cone, with its base 
 directed toward the cutting-edge and its apex in the direction 
 of the apical extremity of the root. The lower margin of the 
 pulp-chamber, or that nearest the cutting-edge of the crown, is 
 
THE rULP-CAVITIES OF THE UPPER TEETH. 243 
 
 broad from mesial to distal and thin from labial to lingual. This 
 margin in the average adult tooth is about on a line with the 
 center of the labial surface of the crown, and the lateral walls of 
 the cavity as they pass upward converge slightly, and finally 
 blend into the walls of the canal at a point somewhat beyond 
 the cervical line. During the early life of the tooth the margin 
 of the chamber nearest the cutting-edge presents three well- 
 defined horns, corresponding to the three rudimentary lobes 
 found upon the cutting-edge at this period. These horns 
 rapidly disappear, and are seldom found after the fifteenth 
 year. In certain tooth types, however, the mesial and distal 
 horns may continue present until adult age, and even into 
 middle life, but when this occurs it is not the result of the 
 
 Fig. 143. — Transverse Sections, Root of Upper Central Inxisors, Slightly 
 Enlarged. 
 
 temporary tooth form, but is occasioned by the permanent 
 angular outline of the crown. 
 
 Figure 143 represents a number of transverse sections of an 
 upper central incisor, showing the outline and relative size of 
 the pulp-cavity in passing from the base of the crown toward 
 the apex of the root. No. i shows the oudine of the cavity at 
 the cervical line ; No. 2 represents the condition y^ of an inch 
 nearer the apex of the root ; No. 3 is from the center of the 
 root length, while No. 4 is from the region of the apex. 
 
 Upper Lateral Incisor. — The pulp-cavity in the upper 
 lateral incisor is so nearly identical with that of the central that it 
 will only be necessary to call attention to one or two points 
 which are at variance. Figure 1 44 shows the five stages as repre- 
 sented by the growth of the tooth. In general it will be 
 observed that the cavity is much smaller than that of the 
 central incisor, but this difterence is to be accounted for in the 
 
smaller proportions of the tooth. No. i shows the condition 
 of the crown and pulp-cavity about the sixth year, the pulp- 
 
 FlG. 144. — PULP-CAVITY IN THE UPPER LATERAL InCISOR, FROM THE SiXTH TO THE 
 
 Tenth Year. 
 
 cavity occupying a large portion of the partly calcified tooth- 
 crown. No. 2 represents the conditions present at the seventh 
 
 Fig. 145. 
 
 year, or about the time of the eruption of the tooth. The pulp- 
 chamber at this age resembles a perfect cone, the base of which 
 
THli PULP-CAVITIES OF THE UPPER TEETH. 245 
 
 reaches to the root-walls, and faintly outlines the beginning of 
 the future pulp-canal. In No. 3, at eight years, the length 
 of the root has increased about ^ of an inch, and the par- 
 allel sides of the walls of the pulp-canal have made their 
 appearance. In No. 4, at nine years, by the growth of the root 
 the canal has considerably increased in length and at the same 
 time much decreased in diameter, while in No. 5, at ten years, 
 the root is completely formed, the apical foramen established, 
 and the maximum size of the entire pulp-cavity in the fully 
 formed tooth shown. 
 
 Figure 145, A, shows the average condition of the pulp-cavity 
 in the upper lateral incisor at adult age, while figure 145, B, 
 represents the same tooth in old age. In a mesiodistal section — 
 figure 145, C — a very close resemblance to the pulp-cavity in the 
 central incisor will be noticed. While the pulp-cavity is smaller 
 than that of the central incisor, it is usually a trifle larger in 
 proportion to the size of the tooth. Owing to the marked 
 constriction at the neck of this tooth, there is occasionally found 
 a slight line of distinction between the pulp-chamber and canal, 
 but in the majority of instances this is not to be observed. The 
 horns of the pulp-chamber are in every respect similar to those 
 of the central incisor, excepting w^hen they exist permanently, 
 in which case the mesial horn is usually the longest. By the 
 transverse sections shown in figure 145, the gradual decrease in 
 size and change in form in the root-canal are presented, the 
 sections being similar to those made in the root of the central 
 incisor. 
 
 Upper Cuspid. — The pulp-cavity of this tooth is in gen- 
 eral similar to that of the incisors, excepting that the coronal 
 extremity of the chamber is conic and inclined to a horn- 
 like projection which penetrates the single cusp of the tooth- 
 crown in the direction of its summit. Figure 146 represents 
 a number of labiopalatal sections. No. i shows the condi- 
 tion of the pulp-cavity about the seventh year, or fully five 
 years before the eruption of the tooth. The pulp-chamber 
 partakes of the cone shape previously referred to, but the mar- 
 gins, instead of being straight lines, are somewhat bowed or 
 concave, thus conforming more closely to the outline of the 
 
246 ANATOMY. 
 
 crown. The central horn of the chamber is proportionately 
 longer than that of the incisors, in correspondence with the cusp 
 of the tooth. At this age the formative process has barely 
 extended to the root-walls ; therefore, the width of the cavity is 
 about equal to its length. In No. 2, at eight years, an increase 
 in the capacity of the chamber over that of the incisors is 
 shown, this being the result of the greater bulk in the tooth- 
 crown. The cone-like outline of the chamber is somewhat 
 broken by an effort of its margins to follow the outline of the 
 crown. In No. 3, at nine years, the principal change has taken 
 place in the canal, which has lengthened fully y^^- of an inch, 
 and the funnel-shaped extremity, instead of joining with the 
 
 Fig. 146. — Pulp-cavity in the Upper Cuspid, from the Seventh to the Twelfth 
 
 Year. 
 
 pulp-chamber direct, is continued below by two parallel walls 
 to the true beginning of this cavity. At ten years. No. 4, a 
 more marked transformation has taken place in both portions 
 of the cavity. The diameter of the chamber at the cervical line 
 has diminished, as has also the length of the cone. The 
 increase in the length of the root, which has been proportion- 
 ately greater than that of the preceding year, has extended 
 the length of the canal about j{ of an inch. The walls 
 of the canal are no longer parallel with each other, but are 
 inclined to follow the root-outlines. The funnel-shaped opening 
 is much reduced both in length and breadth. No. 5 represents 
 the condition at the time of the eruption of the tooth, or about 
 the twelfth year. The general outline of the pulp-cavity is 
 
THE PULP-CAVITIES OF THE UPPER TEETH. 247 
 
 that of a double cone, with a common base at a point nearly 
 corresponding to the cervical line. The diameter in both the 
 chamber and canal has considerably decreased, while the central 
 horn in the former has further receded. The calcification of 
 the root externally is about complete and the foramen formed. 
 In this particular the cuspid tooth differs from the incisors, and 
 in fact from all other teeth, in having its root-calcification about 
 completed and the apical foramen established at or soon after the 
 
 Fig. 147. 
 
 time of its eruption. Figure 1 47, A, gives an idea of the capacity 
 of the pulp-cavity in the upper cuspid at maturity, while figure 
 146, B, shows the condition in advanced age. Figure 147, C, is a 
 mediodistal section of a matured upper cuspid. The coronal 
 extremity of the pulp-chamber is square, and but little inclined 
 to follow the outline of the mesial and distal cutting-edges. 
 The chamber passes into the canal without a mark of separa- 
 tion, and the latter gradually diminishes in diameter as the apex 
 of the root is approached. At its point of beginning the canal 
 is sometimes inclined to flatness from mesial to distal, but in 
 
248 ANATOMY. 
 
 passing toward the apex this tendency disappears, and it becomes 
 more circular in outline. In figure 147, D, a transverse sec- 
 tion through the tooth at the cervical line is shown, giving 
 an idea of the proportionate size and form of the canal in the 
 adult tooth, while E, F, and G represent transverse sections 
 through the root of the same tooth at various points between 
 the cervical line and the apex of the root. 
 
 Fig. 148. — Pulp-cavities of the Upper First Bicuspid, from the Seventh to the 
 Twelfth Year. 
 
 Upper First Bicuspid. — The study of the pulp-cavity in 
 this tooth differs in many particulars from that of the incisors 
 and cuspids. First, the line of distinction between the pulp- 
 chamber and the root-canal or canals is, in most instances, defi- 
 nitely marked by the bifurcation of the roots and a corresponding 
 branching of the pulp-cavity into two fine canals, one of which 
 occupies the center of each root. This division of the cavity 
 brings the center of the pulp-chamber almost on a level with the 
 cervical line. In figure 148, No. i shows the partly calcified 
 crown of the upper first bicuspid at the seventh year. A por- 
 tion of the pulp-chamber alone may be studied at this period, 
 and this is found to be somewhat irregular in outline, with a 
 broadened, funnel-shaped opening above, and two small, cone- 
 like projections below, pointing into either cusp of the crown. 
 These latter projections are the horns of the pulp-chamber, and 
 are named in accordance with the cusp which they occupy. In 
 very young teeth it is not unusual to find these horns penetrat- 
 ing the dentin almost to the enamel-wall. No. 2, at eight years, 
 shows the crown fully calcified and the outline of the base of the 
 
THE PULP-CAVITIES OF THE UPPER TEETH. 249 
 
 roots established. The horns of the pulp-chamber have slightly 
 receded, and the branching of the canals is made manifest by the 
 central deposit of dentin. In No. 3, at nine years, the capacity 
 of the pulp-chamber is much decreased, and appears to have 
 receded bodily rootward. The roots are calcified to about one- 
 third their full length, and the canals which traverse them are 
 each provided with the funnel-shaped opening at their free cal- 
 cifying extremities. In No. 4, at ten years, the decrease in the 
 size of the pulp-chamber is not only caused by the deposit of 
 dentin upon the occlusal and lateral walls, but from the direction 
 of the roots as well. The diameter of the root canals is much less 
 than at nine years, but the walls are as yet parallel. No. 5 
 shows the roots fully formed and the apical foramina established, 
 which condition occurs about the twelfth year. The horns of 
 the pulp-chamber have receded somewhat, and the center of this 
 cavity is now almost on a level with the cervical line. The canals 
 have assumed the form of the roots themselves, and their diam- 
 eter is much diminished. The illustration shows the propor- 
 tionate maximum size of the chamber and canals in this tooth 
 after completion of surface calcification. It will be observed 
 that the foramina are proportionately smaller than those of the 
 incisors and cuspids at a corresponding period, this condition 
 resulting from the lesser diameter of the roots. 
 
 Figure 149, A, illustrates the approximate size and form of 
 the pulp-chamber and canals at adult age, and attention is called 
 to the appearance of the horns of the pulp-chamber. It will be 
 observed that the horn which penetrates the buccal cusp is 
 larger and more pointed than that directed toward the lingual 
 cusp ; this condition is fully explained by the buccal cusp being 
 proportionately larger and longer than the lingual. In the same 
 figure, B represents the pulp-cavity in the first upper bicuspid 
 at advanced age. The foregoing description applies only to the 
 two-rooted bicuspids, but as many of these teeth have but one 
 root, an additional description will be necessary. When a single 
 root is present, many varieties in the outline of the pulp-cavity 
 will be presented ; this variation, however, seldom affects the 
 capacity or form of the pulp-chamber. Two distinct canals may 
 exist in the single root (Fig. 149, C), branching off from the 
 
ANATOMY. 
 
 chamber, one from the buccal and one from the hngual portion. 
 These canals gradually taper in the direction of the apex of the 
 root, and may end in a single foramen, or in distinct foramina. 
 Occasionally the canals will unite before reaching the root- 
 apex, and continue as a single canal ending in a single 
 foramen, or they may communicate at one point and again 
 diverge and finally end in separate foramina. In some 
 instances the pulp-canal appears to be a direct continua- 
 tion of the pulp-chamber, extending throughout the length 
 
 Fig. 149. — Pulp-cavities of the Upper First Bicuspid, Enlarged about One-third. 
 
 of the root in the form of a flattened canal, with its 
 greatest diameter from buccal to lingual (Fig. 149, D). 
 When two separate canals exist in the single root, the outward 
 appearance of the root indicates a near approach to two roots ; 
 when the single flattened canal is present, the root is also 
 flattened and shows no sign of bifurcation. Reference has been 
 made to the horns of the pulp-chamber, and in this connection 
 it will be well to speak of the extent to which they may exist. 
 In that type of tooth provided with long penetrating cusps the 
 horns will dip well down into the cusp occasionally to the full 
 
THE PULP-CAVITIES OF THE UPPER TEETH. 251 
 
 depth of the dentin, and in rare instances may penetrate the 
 enamel. In those teeth ladling in cusp-formation the length 
 of the horns will be correspondingly reduced, and may be 
 entirely wanting. In the two-rooted upper first bicuspid the 
 floor of the pulp-chamber, or that part of the cavity directed 
 rootward, is prominent and rounded in the center, from 
 which point it gradually slopes toward the entrances to the 
 canals, one of which arises from the extreme buccal margin, and 
 the other from the extreme lingual margin. Figure 149, E, 
 represents a transverse section of the two roots immediately 
 below the point of bifurcation. F represents a section of the two 
 roots midway between the cervical line and the apical extremity, 
 while G is a transverse section of D at the cervical line. 
 
 Fig. 150. — PuLPrCAViTiEs in the Upper Second Bicuspid, from the Seventh to 
 THE Twelfth Year. 
 
 Upper Second Bicuspid. — The pulp-cavity of this tooth 
 is in many respects similar to that of the first bicuspid, the prin- 
 cipal variations being in the horns of the chamber, which are 
 proportionately smaller in correspondence with the diminution 
 in cusp-formation. There is usually no positive line of demarca- 
 tion between the chamber and canal, the latter being quite 
 large, and broad from buccal to lingual. The extent of the pulp- 
 chamber is sometimes well defined by the presence of two root- 
 canals, similar to those described in connection with the first 
 bicuspid. In rare instances the tooth may possess two roots, 
 each of which would be traversed by a canal. Figure 1 50 repre- 
 sents the various stages of the development of the pulp-cavit}', 
 as shown by a longitudinal section from buccal to lingual. No. i 
 shows the condition at seven years, or at a time when a portion 
 
of the crown only is calcified, in consequence of which the pulp- 
 chamber alone can be studied at this period. The buccal and 
 lingual horns of the chamber may be observed penetrating the 
 dentin in the direction of their respective cusps. No. 2 shows the 
 advance made in the formative process by the eighth year, or at a 
 time immediately prior to the eruption of the tooth ; the outline 
 of the chamber is completed and the walls of the future pulp- 
 canal faintly outlined. At this period there has been but little 
 change in the horns of the pulp-cavity. No. 3 shows the condi- 
 
 FiG. 151. — Section of Upper Second Bicuspid, Slightly Enlarged. 
 
 tion of the tooth at the ninth year, or at the beginning of its 
 eruptive period. The diameter of the chamber has somewhat 
 decreased, the horns have slightly receded, the funnel-shaped 
 extremity of the cavity has advanced beyond the cervical line, 
 and is now confined to the canal alone. No. 4 represents the 
 condition of the pulp-cavity about the tenth year. A gradual 
 decrease in the diameter of both the chamber and canal is 
 observed, and the horns of the pulp-cavity are growing less 
 prominent. The length of the root having increased nearly 
 one-quarter of an inch, we find a corresponding addition to the 
 length of the canal. No. 5 shows the maximum size of the 
 
THE PULP-CAVITIES OF THE UPPER TEETH. 253 
 
 pulp-cavity in the upper second bicuspid, which condition 
 accompanies the completion of the external calcific action at 
 the twelfth year. As previously stated, the cavity, in its 
 entirety, presents no line of separation between the chamber 
 and canal, but gradually tapers from its broadened base in the 
 crown to its ending at the apex of the root. In this tooth, as 
 well as in all those previously described, the apical foramen at 
 the time of completion of root-calcification is comparatively 
 large, and readily penetrated during operations upon it. Figure 
 151 illustrates a number of sections of an upper second bicuspid 
 at maturity. The same figure also represents two transverse 
 sections, A being at the cervical line, B midway between the 
 cervical line and the apex of the root. 
 
 PULP CAVITIES OF 'IHE UPPER MOLARS. 
 The inner anatomy of the molar teeth being much more com- 
 plicated than any of those previously described, it will be found 
 necessary to make a number of dissections in various directions 
 in order to obtain a comprehensive idea of the location and 
 form of the different parts of the pulp-cavity. The line of 
 demarcation between the pulp-chamber and canals is always 
 definite, the former occupying a central position in the crown 
 and seldom extending beyond the cervical line, while the latter 
 are given off from the floor of the chamber and penetrate the 
 various roots, their entrances being marked by small funnel- 
 shaped openings in the floor of the chamber. In the matured 
 tooth the form of the chamber usually corresponds to that of the 
 crown of the tooth. The lateral walls of the chamber are four in 
 number, and are named according to their location — mesial, 
 distal, buccal, and lingual. The average thickness of these walls 
 at maturity is about equal to the diameter of the pulp-chamber. 
 In that type of tooth common to the lymphatic temperament 
 where there is but little constriction at the neck, resulting in the 
 various sides of the tooth-crown being nearly parallel with each 
 other, the pulp-chamber is nearly quadrilateral in form ; but in 
 those teeth marked by a decided constriction at the neck, most 
 marked in the nervous temperament, the extent of surface cov- 
 
ered by the floor of the chamber is much less than that occupied 
 by the occlusal portion. In the former class, the entrances to 
 the various canals are much farther apart than in the latter. 
 The occluding wall is usually much thicker than the lateral 
 walls, and is penetrated by the horns of the pulp-chamber, one 
 of which extends into each cusp. As in the biscuspids, the extent 
 to which the horns penetrate the cusps is controlled by the 
 prominence of the latter. The floor of the pulp-chamber is 
 irregularly rounded, being high in the corner and gradually 
 falling away in the direction of the canals. The entrances to 
 the root-canals, three in number, are placed in the form of 
 an irregular triangle, called the molar triangle. The mesial 
 side of the triangle is usually the longest, the distal next in 
 
 length, and the buccal theshortest. 
 A In young teeth the entrances to 
 
 ^ the canals are usually in the form 
 of funnel-shaped openings, are 
 comparatively easy of access, but 
 ^ after maturity may disappear and 
 be but little larger than the canals 
 themselves. To properly study 
 the position occupied by the en- 
 trance to the canals on the floor 
 of the pulp-chamber, a transverse 
 section of the tooth shouldbemade 
 at a point somewhat above the cer- 
 vical line, at the same timepreservingboth the crown and the roots 
 of the tooth for comparison. The entrance to the lingual canal, 
 which is usually the largest and most readily accessible, may be 
 located by a line drawn through the center of the occlusal sur- 
 face of the crown (Fig. 152) from buccal to lingual, A, and by 
 another line drawn from mesial to distal almost parallel with the 
 linguomarginal ridge, passing through the summits of the mesio- 
 lingual and distolingual cusps, B ; the point at which these two 
 lines intersect will mark the approximate location of the lingual 
 canal. The entrance to the mesiobuccal canal may be located 
 by a line drawn from the inner side of the mesiobuccal angle to 
 a corresponding position near the distobuccal angle, C. This 
 
 Fic. 152. 
 
THE PULP-CAVITIES OF THE UPPER TEETH. 155 
 
 should be intersected by a line drawn from the summit of the 
 mesiobuccal cusp to the summit of the mesiolingual cusp, D, 
 the point at which these two lines cross marking the entrance 
 to the mesiobuccal canal. The location of the entrance to the 
 distobuccal canal is found by the line, C, which is intersected 
 by another line, E, drawn from the summit of the distobuccal 
 cusp to a corresponding point on the distolingual cusp. The 
 nearer the tooth-crown approaches to the quadrilateral, the 
 nearer will the molar triangle approach the equilateral. 
 
 Fig. 153. — PuLP-CAViTY of Upper First Molar, from the Fifth to the Ninth 
 Year. Lingual and Mesiobuccal Canals. 
 
 Upper First Molar. — In the dissection of this tooth, the 
 pulp-chamber and two of the root-canals only can be shown, 
 but these will be sufficient to pursue the study with intelligence. 
 Figure 153 shows a number of longitudinal sections, made in 
 such a manner as to expose the lingual canal, usually the 
 largest, and the mesiobuccal canal. No. i illustrates the 
 approximate size and form of the pulp-chamber at the fifth year. 
 At this period the chamber occupies a large proportion of the 
 center of the tooth-crown. Two of the four horns are seen, one 
 of which penetrates the mesiobuccal cusp, and one the mesio- 
 lingual cusp. In many instances the horns of the molar teeth 
 are quite slender, penetrating the dentin to a greater depth 
 than that shown in the illustration, in the form of minute hair- 
 like projections, which in some instances reach almost to the 
 enamel walls. 
 
 No. 2 illustrates the condition of the pulp-cavity at the sixth 
 year, or at the time of eruption. The outline of the pulp- 
 
256 ANATOMY. 
 
 chamber is completed, and die floor has begun to make its 
 appearance by a central deposit of dentin. It will be observed 
 that the lateral walls of the chamber are somewhat less in thick- 
 ness than the occluding wall, a condition which will become more 
 pronounced as the tooth develops. With the beginning of the 
 formative process in the floor of the chamber we find the 
 trifurcation of the roots established, and the beginning of the 
 canals outlined. The canals at this period are quite similar to 
 those of the bicuspid, being provided with a funnel-shaped 
 extremity, which extends from the free calcifying margins of the 
 roots to the floor of the chamber. No. 3 shows the change 
 which has taken place at the seventh year. While the pulp- 
 chamber is somewhat reduced in size, but little change is notice- 
 able in its outline. By this time the floor of the chamber has 
 become an important factor in the tooth development. By the 
 constant lateral extension of this central deposit of dentin the 
 floor of the chamber is gradually spread out, this alteration 
 being at the expense of the entrances to the root-canals, which 
 become reduced in diameter as the floor is extended. The horns 
 of the chamber are slightly less prominent, but this part ot 
 the cavity has the appearance of having receded bodily root- 
 ward. The roots have advanced somewhat beyond the point of 
 trifurcation, and a definite outline has been given to the canals. 
 At this period the diameter of the root-wall is about equal to the 
 diameter of the pulp-canal. Along with the gradual decrease in 
 the diameter of the roots, there is observed a corresponding 
 decrease in the width of the funnel-shaped extremities of the 
 canals. 
 
 At the eighth year. No. 4, a gradual reduction in the capa- 
 city of both the chamber and canal is noted. Accompany- 
 ing the above condition there is found a corresponding in- 
 crease in the thickness of the surrounding walls. The horns 
 of the pulp-chamber are much reduced in size, and the form of 
 the chamber more closely resembles that of the general contour 
 of the tooth-crown. The increase in the length of the roots is 
 proportionately greater than that of previous years, in conse- 
 quence of which the length of the canals is increased to a greater 
 degree. In No. 5 the maximum size of the chamber and canals 
 
THE PULP-CAVITIES OF THE UPPER TEETH. 257 
 
 is apparent, which condition takes place about the ninth year, 
 or at a time when calcification of the tooth is completed ex- 
 ternally. In some instances, owing to the additional length 
 of the lingual root, the apical foramen may not be established 
 before the tenth year. At this latter period it is safe to assume 
 that all three canals have completed their longitudinal extent, 
 and the foramina, although proportionately large, have been 
 established, so that a more definite description of each canal 
 may be given. ^\\& lingual canal (Fig. 154, A) is usually the 
 
 Fig. 154. — PuLP-CAViTiEs of Upper First Molar, Slightly Enlarged. 
 
 largest, and branches off from the floor of the chamber, near the 
 mesiodistal center of the extreme lingual margin, the entrance 
 in the average tooth being well defined by a circular, funnel- 
 shaped opening. The direction of this canal is usually upward 
 and slightly inward, until the apical extremity is approached, at 
 which point it is inclined to the buccal. The circular form pre- 
 sented at the beginning of the canal is generally continued 
 throughout its entire length, in this respect differing from the 
 two buccal canals. The average length of the lingual canal is 
 about Yi. of an inch. The viesiobuccal canal (Fig. 1 54, B) 
 17 
 
258 ANATOMY. 
 
 branches off from the floor of the chamber, at its extreme mesio- 
 buccal angle, and the entrance, instead of being funnel-shaped 
 and easy of access, is flattened from mesial to distal, and fre- 
 quently difficult to enter. This flattened form continues through- 
 out its course, which for the distance of ^ of an inch is in a 
 buccal and mesial direction ; beyond this point it is usually in- 
 clined to the buccal, until the upper third of the root is reached, 
 where it turns rather abruptly to the distal. This canal is gen- 
 erally a trifle shorter than the lingual, averaging about ^ to yV of 
 an inch. The distobuccal ozxi-aX (Fig. 154, C) branches off from 
 the floor of the chamber at the extreme distobuccal angle. In 
 those teeth which most nearly approach the quadrilateral form, 
 the entrance to this canal will be farther from the center of the 
 tooth, the molar triangle in this instance being almost an equila- 
 teral. It sometimes happens that the entrance to this canal is di- 
 rectly in the floor of the pulp-chamber, near to, but not against, 
 its buccodistal angle. The entrance is usually abrupt, seldom 
 being funnel-shaped, making it by far the most difficult of 
 access. It is inclined to be circular in form, and more or less 
 tortuous in its course. Immediately above the point of begin- 
 ning it is inclined toward the buccal and distal ; near its center 
 it may incline slightly to the mesial ; and finally, at its upper 
 third, turns somewhat abruptly in a distobuccal direction. This 
 canal is usually the shortest of the three, its average length 
 being about ^g of an inch. 
 
 Figure 154 also illustrates a number of transverse sections of 
 this tooth, D being made at the cervical line, looking toward 
 the crown, E looking toward the roots, while F represents 
 a transverse section at a point immediately above the floor of 
 the pulp-chamber. 
 
 Upper Second Molar. — In many respects the pulp- 
 chamber of this tooth is similar to that of the first molar, but 
 there are a few variations which must be briefly described. 
 First, the outline of the tooth-crown being much more flattened 
 from mesial to distal, a corresponding variation is noted in the 
 form of the pulp-chamber, increasing the length of the mesial 
 side of the molar triangle, and decreasing the length of the 
 buccal and distal sides. The chamber is more or less flattened 
 
THE PULP-CAVITIES OF THE UPPER TEETH. 259 
 
 from mesial to distal, making it somewhat oblong from buccal 
 to lingual. Second, on account of a reduction in the promi- 
 nence of the cusps, the horns of the cavity are usually 
 somewhat less pronounced than those of the first molar. 
 Third, the floor of the cavity is less convex, and slopes more 
 gradually toward the entrances of the various canals. In a 
 general way, the rules given for ascertaining the approximate 
 location of the entrances to the canals in the first molar apply 
 to this tooth. The comparative size and form of the pulp- 
 chamber and canals during the development of the tooth are 
 shown in figure 155, extending from the ninth to the sixteenth 
 or eighteenth year, at which latter period the crown and roots 
 of the tooth are fully calcified externally. 
 
 9th year iithyear 13th year islh year l8th year 
 
 Fig. 155. — PuLP-CAviTiEs in the Upper Second Molar, from the Ninth to the 
 Eighteenth Year. 
 
 Upper Third Molar. — In this tooth the conditions are so 
 variable that a description of the pulp-cavity taken from a single 
 tooth would be insufficient. In the majority of instances the 
 outline of the tooth-crown approaches the triangular form, and 
 in consequence the pulp-chamber is triangular rather than 
 quadrilateral or oblong. The mesial border of the chamber Is 
 the longest, the distal next in length, and the buccal the shortest 
 of the three. The horns are generally less in number and much 
 less pronounced than those of either the first or second molars. 
 The floor of the chamber may be broken by irregularities simi- 
 lar to those previously described, or it may be entirely absent, 
 this latter condition occurring when the tooth has but a single 
 root accompanied by a single canal. The various stages of 
 development having been given in connection with the general 
 
description of the tooth, no attempt will be made to describe this 
 by longitudinal sections, the complications in root-form making 
 such a proceeding impracdcable. Instead of so doing, the space 
 will be devoted to a brief description of the variety of pulp- 
 canals found in this tooth. Probably the most frequent condition 
 is that which resembles the first and second molars — i. e., three 
 canals branching off from the chamber in as many different 
 roots, two to the buccal and one to the lingual. When the three 
 canals exist, the entrances to them will be well beyond the 
 cervical line, where they will be found clustered much closer 
 together than those of the first and second molars, this difference 
 in their location being so marked that the diagram previously 
 given can not be depended upon in an attempt to locate them. 
 
 Fig. 156. — Longitudinal Sections, Ui'per Third Molar, Slightly Enlarged. 
 
 The usual course of these canals is first slightly mesial, then 
 distal, and finally in a distolingual direction. On account of 
 the pulp-chamber e.xtending well beyond the cervical line, the 
 canals are much shorter than those of the first or second 
 molars, their average length being less than yi of an inch. 
 Another form frequently met with is that of the flattened 
 single canal, occurring when the tooth has but a single 
 root, which shows no signs of trifurcating (Fig. 156, A). In 
 this instance the pulp-chamber gradually passes into the canal, 
 and the chamber is without a floor. Such a canal is shaped 
 like the chamber at its point of beginning ; but as it passes 
 toward the apex it becomes flattened in the direcdon of the 
 smallest diameter of the root. But litde difficulty is experienced 
 
THE PULP-CAVITIES OF THE UPPER TEETH. 261 
 
 in entering such a canal, and usually it is readily followed to its 
 apex. Another condition frequently met with in the single- 
 rooted third molar is that of one or more canals branching off 
 from the floor of the chamber, their course through the root- 
 substance being without regard to the external contour of the 
 root (Fig. 156, B). These canals, which may exist to the num- 
 ber of five or six, are usually very minute, and in some instances 
 may pass from the floor of the chamber to the apex of the root 
 almost in a direct line, and end in distinct foramina, or they may 
 take a tortuous course, and when near the apex unite, ending in 
 a single foramen. When the tooth is provided with four, five, or 
 even six small roots, as sometimes occurs, each root will be 
 traversed by a minute canal, the entrances to these being 
 variously placed about the floor and lateral margins of the 
 pulp-chamber (Fig. 156, C). In all operations upon this tooth 
 it must be recalled that it is the last to be calcified, and conse- 
 quently the canals and foramina are proportionately larger than 
 in the other teeth ; at the same time, it possesses one advantage 
 over the others — i. e. (with the single exception of the cuspid), 
 being fully calcified at or about the time of its eruption. 
 
ANATOMY. 
 
 PULP-CAVITIES OF THE LOWER TEETH. 
 
 Fig. 157. — PuLP-CAViTiES of the Lower Incisor. 
 
 The outline of the pulp-cavities of the lower teeth, like those 
 of the upper, corresponds to the general tooth contour. The 
 comparative size of the cavity at various stages of tooth develop- 
 ment will not be repeated in this description, the conditions 
 being similar to those in the upper teeth (see also Develop- 
 ment of the Teeth). 
 
 Lower Incisors. — The pulp cavities of the lower central 
 and lateral incisors are so nearly alike that a single description 
 will answer for both. Figure 156, A, represents a labiolingual 
 section of a lower incisor, showing the most frequent form of 
 the pulp-cavity. The tooth from which the section was prepared 
 was one about middle life, the cavity in younger teeth being 
 proportionately larger, while a gradual decrease in diameter 
 would be noted with advancing age. There is no mark of dis- 
 tinction between the pulp-chamber and canal, so that an imagin- 
 ary separation would have to be made at the cervical line, or 
 slightly below that point. Taken In its entirety, the cavity 
 presents the form of a double cone, the common base of which 
 is slightly to rootward of the cervical line. The chamber 
 penetrates the crown fully half-way to the cutting-edge, at 
 which point it ends in a thin, fan-like margin (best observed in 
 
PULP-CAVITIES OF THE LOWER TEETH. 263 
 
 mesiodistal section), while the canal gradually decreases in 
 size until the apical foramen is reached. Although this is the 
 most common form of the pulp-cavity in the lower incisors, it 
 is by no means the constant condition. The tooth is not infre- 
 quently provided with a medium-sized pulp-chamber, which 
 extends somewhat below the cervical line, beyond which point it 
 branches into two fine canals, which are continued separately 
 until the apical third of the root is approached, when they again 
 unite, and finally end in a single foramen. Figure 157, C, 
 represents a mesiodistal section of a young lower incisor, in 
 which the three small horns of the pulp-chamber are apparent. 
 At this period the fan-shaped extremity of the pulp-chamber 
 occupies about one-half of the mesiodistal diameter of the crown, 
 and the horn-like projections extend well toward the enamel cap. 
 Figure 157, B, shows the average size and form of the pulp- 
 cavity at maturity, by a mesiodistal section through the long axis 
 of the tooth. In this it will be observed that the horns of the 
 pulp-cavity have disappeared, and that the capacity of the 
 cavity in general is much reduced. 
 
 Lower Cuspids. — The pulp-chamber and canal in this 
 tooth, while usually conforming to the general contour of the 
 tooth, are frequently found to vary greatly, both in outline and in 
 size. The most common form, however, is that shown in figure 
 158, A, a labiolingual section of an adult tooth. The chamber 
 and canal have no line of demarcation, and unite at a common 
 base considerably below the cervical line, the former penetrating 
 the crown of the tooth to a point about midway between the 
 cervical line and the summit of the cusp, at which point it ends 
 in a sharp, hair-like projection. Accompanying this common 
 form there is much variation in size, even in teeth of the same 
 age. Figure 158, B, shows another labiolingual section of an 
 adult lower cuspid, in which the pulp-cavity fails to accurately 
 follow the outline of the tooth, and its capacity is much less 
 than that shown at A. The root of this tooth is in most 
 instances circular, in which case the canal will be similarly 
 formed ; but occasionally the root will bg much flattened Irom 
 mesial to distal, and as a result of this the canal will also be 
 much flattened. The canal of this tooth is seldom divided. In 
 
264 
 
 figure 158, C, a mesiodistal section of a lower cuspid is 
 shown, and it will be observed that the fan-shaped extremity 
 of the chamber common to the incisors is absent, the cavity 
 
 Fig. 158. — Pulp-cavities of the Lower Cuspids. 
 
 ending rather abruptly, or by a fine line near the center of the 
 crown. The same illustration also shows a number of trans- 
 verse sections, which will give an idea of the form of the cavity 
 at various parts of the tooth. 
 
 Lower Bicuspids. — The pulp-cavities of these teeth may 
 be best described collectively, thus affording an opportunity for 
 comparison. Unlike the upper bicuspids, it is seldom that 
 the canals are definitely separated from the chambers. That 
 part of the cavity within the crown, however, is usually quite 
 wide from buccal to lingual, and unites with the canal by a long, 
 funnel-shaped constriction. The center of the pulp-chamber 
 may be considered as being about on a level with the cervical 
 line. In the first bicuspid the pulp-cavity is provided with a 
 single horn, which extends with more or less prominence in the 
 direction of the buccal cusp. That part of the chamber facing 
 the lingual cusp is usually rounded off. In the second bicuspid 
 
PULP-CAVITIES OF THE LOWER TEETH. 
 
 265 
 
 the occlusal wall of the pulp-chamber generally presents a dif- 
 ferent form ; two well-defined horns are usually present, of which 
 the buccal is the longest ; or the chamber may be prominently 
 rounded at these points. The pulp-chamber of the second 
 bicuspid is generally larger than that of the first. The canals 
 of these teeth are usually circular throughout, and are readily 
 penetrated until the apical third is reached, beyond which point 
 they are extremely small. In some instances the canal divides 
 near the center of the root, and is continued as two canals, end- 
 ing in distinct foramina, or, after separating, they may again 
 unite, and end in a single foramen. In figure 159 the aver- 
 
 FiG. 159. — Sections of Lower Bicuspids. 
 
 age size and form of the canal in these teeth is shown by a 
 number of mesiodistal and transverse sections. 
 
 Lower Molars. — The form of the pulp-chambers of the 
 lower molars corresponds to the general outline of the crown, 
 and the form of the root-canals is similar to the general contour 
 of the roots. The pulp-chambers approach the quadrilateral 
 form ; the buccal and lingual sides are somewhat the longest, the 
 mesial next in length, and the distal, usually slightly rounded, 
 is the shortest. The occluding wall is convex rootward, sloping 
 in the direction of the various cusps, each of which is penetrated 
 by a horn. Like the horns of the pulp-chambers in general, the 
 
extent to which these penetrate the cusps is influenced by the 
 age, type, and functional activity of the organ. The floor of the 
 cavity is convex in the direction of the occlusal surface, but this 
 convexity is principally from mesial to distal. From the summit 
 of this convexity the floor slopes to the entrances of the canals, 
 the opening into which is inclined to be funnel-shaped rather 
 than abrupt. The lateral walls of the chamber are much inclined 
 to follow the general contour of the crown. The horns of the 
 pulp-chamber are usually more pronounced in the first than in the 
 second molar, and still less clearly defined in the third than in 
 
 Fig. i6o. — Sections ok Lower Molars, Enlarged about One-third. 
 
 the second. The roots of the first molar being somewhat further 
 apart than those of the second, the floor of the chamber in the 
 former is slightly more extensive than in the latter. To study 
 the pulp-cavities of these teeth a longitudinal section should be 
 made through the center of the tooth from mesial to distal. 
 Figure i6o. A, shows such a dissection through the first molar, 
 and illustrates the average size and form of the chamber and 
 canals at adult age. The canals join the chamber by a funnel- 
 shaped opening, and but little difficulty will be found in effecting 
 an entrance, but to follow them to their apices will be more per- 
 
PULP-CAVITIES OF THE LOWER TEETH. 267 
 
 plexing. The roots of this tooth being much flattened from 
 mesial to distal, the canals are also flattened in this direction, 
 but broad from buccal to lingual. The tntrances to these canals 
 may be found at the extreme mesial and distal margins of the 
 pulp-chamber, and usually extend from the buccal to the lingual 
 walls of the cavity. It is not uncommon for the mesial canal to 
 divide soon after leaving the chamber, and continue as two 
 canals, ending in separate foramina (Fig. i6o, B). This con- 
 dition is seldom present in the distal canal, which is usually 
 straight from its mouth to the apical foramen. The capacity of 
 the pulp-chamber is usually a trifle less than that of the first 
 molar, and the entrances to the canals are somewhat nearer 
 together. In other respects the cavity is similar to that of the 
 first molar. Figure 160 also shows a number of transverse 
 sections through a lower molar, and gives an idea of the size 
 of the canals at various parts of the roots. In some instances 
 the roots of the second molar coalesce, in which case a single 
 root-canal may be present. In the third molar the most com- 
 mon form of the pulp-cavity is one similar to that of the first, 
 but both the chamber and canals are smaller. Unlike the pulp- 
 cavity of the corresponding upper tooth, this tooth is not sub- 
 ject to so much variation, although it is sometimes found with a 
 single root traversed by a single canal, which may be accom- 
 panied by a rather large pulp-chamber. 
 
CHAPTER XI. 
 
 THE DECIDUOUS TEETH, THEIR ARRANGEMENT, OCCLUSION, ETC; 
 THEIR CALCIFICATION, ERUPTION, DECALCIFICATION, SHEDDING 
 PROCESS, AND AVERAGE MEASUREMENTS; THEIR SURFACES, 
 GROOVES, FOSS^, RIDGES, SULCI, AND PULP-CAVITIES. 
 
 THE DECIDUOUS TEETH. 
 
 Central Incisor Lateral Incisor Cuspid First Molar Second Molar 
 
 Fig. i6i. — The Deciduous Teeth, Upper and Lower, from the Left Side of 
 THE Mouth. 
 
 As implied by the term deciduous, these teeth are temporary 
 in their nature, and, after subserving the purposes of early 
 childhood, are thrown off by an operation of the economy to 
 
THE DECIDUOUS TEETH. 269 
 
 give place to the permanent organs. The shedding process 
 takes place in the incisors between the seventh and eighth years, 
 in the molars from the tenth to the eleventh years, and in the 
 cuspids about the twelfth year. This shedding process, however, 
 does not indicate the period at which the degeneracy of the 
 tooth begins, for, in a year or two after the roots are completely 
 formed and the apical foramen established, decalcification begins 
 at the apical ends and continues in the direction of the crown 
 until absorption of the entire root has taken place and the 
 crown is lost from lack of support. Decalcification in the 
 incisors begins between the fourth and fifth years, in the molars 
 from the seventh to the eighth years, and in the cuspids about 
 the ninth year. 
 
 The deciduous teeth are twenty in number, ten in each jaw, 
 and may be classified as follows : Fonr incisors, tzvo cuspids, 
 and four molars. The incisors, central and lateral, occupy 
 the central portion of the arch, are placed two upon each side 
 of the median line, and are succeeded by the four permanent 
 incisors, which finally occupy the same position. The cuspids 
 are located immediately to the distal of the lateral incisors, and 
 are displaced by the permanent cuspids. The first and second 
 molars come next in the arch, but, unlike the anterior teeth, are 
 followed by permanent successors of another class, the first and 
 second bicuspids, the permanent molars erupting posteriorly to 
 these as the jaw increases in length. 
 
 In general the deciduous teeth resemble their permanent 
 successors, yet there are a number of minor differences which 
 will require a comparative description. Both the crowns and 
 the roots are much smaller in every direction than those of the 
 permanent teeth, but the diameter of the crowns is propor- 
 tionately greater than that of the roots, while the roots are 
 proportionately longer. The fact that the roots are smaller in 
 proportion than the crowns is productive of a neck much more 
 constricted. The roots of the deciduous teeth are the same in 
 number as those of the corresponding permanent teeth, the 
 incisors and cuspids being provided with one, the upper molars 
 with three, and the lower molars with two. 
 
THE OCCLUSION OF THE DECIDUOUS TEETH. 
 
 First Molar 
 Second Molar 
 
 Permanent First 
 
 Cuspid Incisors 
 
 Fig. 162. — The Upper Dental Arch about the Seventh Year. 
 
 The arranjrement of the deciduous teeth in the jaws is similar 
 to that of the permanent organs, the upper teeth describing" 
 the segment of a larger circle than the lower, in consequence 
 of which the upper teeth close over or outside of the lower. 
 The character of the occlusion in the deciduous teeth is not 
 subject to so much variation as that found in connection with 
 the permanent set, this being accounted for by the more 
 constant form in the crowns of the former. The relations 
 existing between the upper and lower deciduous teeth 
 when in contact is such that each tooth, with the exception 
 of the lower central incisor and the upper second molar, 
 occludes with two teeth of the opposite jaw, the upper 
 central incisor being opposed by the entire cutting-edge of the 
 lower central and the mesial third of the lower lateral ; the 
 upper lateral coming in contact with the remaining two-thirds 
 of the lower lateral and a portion of the mesial half of the 
 lower cuspid, this arrangement continuing throughout the 
 series. The foregoing description of the occlusion of the de- 
 ciduous teeth is applicable to but a small part of their transi- 
 tory existence. By the time they are fully erupted and have 
 
THE DECIDUOUS TEETH IN DETAIL. 271 
 
 assumed their respective positions in the arch, the increase 
 in the size of the bone is sufficient to create a slight space 
 between the teeth, which condition is soon followed by a 
 greater separation through the protrusion of the anterior teeth, 
 caused by the growth and approach of the permanent teeth 
 from behind. 
 
 The calcification of the deciduous teeth is similar to that of 
 the permanent, the process in the incisors and cuspids begin- 
 ning along the cutting-edges in three distinct lobes, while in the 
 molars a center of calcification is provided for each cusp (see 
 Development of the Teeth). 
 
 THE DECIDUOUS TEETH IN DETAIL. 
 
 Fourth Year 
 
 Fortieth Week 
 
 Twentieth Week 
 
 Seventh Year 
 
 Fig. 163. 
 
 UPPER CENTRAL INCISOR. 
 
 Calcification Begins, about the Fourth Fetal Month. 
 
 Calcification Completed, Seventeenth to Eighteenth Month after Birth- 
 Erupts, Sixth to Eighth Month after Birth. 
 Decalcification Begins, about the Fourth Year. 
 
 Shedding Process Takes Place, about the Seventh Year. 
 Average Length of Crown, .23. 
 
 Average Length of Root, .39. 
 
 Average Length over All, .62. 
 
 This tooth, as well as all of the deciduous teeth, presents for 
 examination numerous surfaces, margins, and angles, these being 
 the same in name and location as those of the permanent teeth. 
 
The Labial Surface of the Crown (Fig. 164). — Tliis sur- 
 face is smooth and generally convex, but with an inclination to 
 flatness near the incisive margin. The mesial margin is slightly 
 convex in the direction of the length of the tooth, and rounded 
 from labial to lingual. The distal margin is decidedly convex 
 from the cutting-edge to the cervical line, in many instances 
 forming almost a complete semicircle, which is usually at the 
 expense of the distal angle of the crown. The cervical margin 
 is deeply concave in the direction of the root, and the incisive 
 margin is straight over its central portion and rounded or angu- 
 lar at its extremities. The labial grooves 
 are seldom so well defined as those upon the 
 permanent incisors. 
 
 The Lingual Surface of the Crown. — 
 In some instances this surface is smooth and 
 concave near the cutting-edge and convex 
 over the cervical portion, with the marginal 
 ridges well defined. In other cases it is con- 
 cave from the cutting-edge to the cervical 
 ridge being provided with a longitudinal 
 ridge in the center, a slight depression upon 
 eitherside, and marginal ridges poorlydefined. 
 In the former instance the lingual fossa is 
 present ; in the latter it is absent. The mesial and distal sur- 
 faces of the crown are both smooth and convex, the former 
 being inclined to flatness over its cervical third — a condition 
 which is seldom present in the latter. The mesial angle is alone 
 well defined, the cutting-edge passing into the distal surface with 
 a long, gradual sweep, thus in a measure destroying the distal 
 angle. The neck of the tooth is marked by a decided constric- 
 tion, which is principally produced at the expense of the crown 
 alone. The root of the tooth, when compared with the root of 
 the permanent central incisor, is much longer in proportion to 
 the length of the crown. In some instances it is flattened from 
 mesial to distal, these two sides converging as they pass to the 
 lingual ; in others it is flattened from labial to lingual. Gener- 
 ally speaking, it is a straight root, but is occasionally provided 
 
THE DECIDUOUS TEETH IN DETAIL. 
 
 273 
 
 with a slight mesial curve near its apical third, and it is some- 
 times curved slightly from labial to lingual. 
 
 UPPER LATERAL INCISOR. 
 
 Kih / 3 
 
 Seventh Year 
 
 Eighth Ye 
 
 Fortieth Week 
 Twentieth Week 
 
 Fig. 165. 
 
 Calcification Begins, about the Fourth Fetal Month. 
 
 Calcification Completed, Fourteenth to Sixteenth Month after Birth. 
 Erupts, Seventh to Ninth Month after Birth. 
 Decalcification Begins, about the Fifth Year. 
 
 Shedding Process Takes Place, about the Eighth Year. 
 Average Length of Crown, .25. 
 
 Average Length of Root, .45. 
 
 Average Length over All, .70. 
 
 The various surfaces of this tooth so 
 closely resemble those of the central incisor 
 that a separate description will be unneces- 
 sary ; in a general way, however, there are 
 a few minor points of difference. The tooth 
 is smaller in every direction excepting in 
 its length, which is generally equal to and 
 frequently greater than that of the central 
 incisor. The diameter of the root is but 
 little less than that of the central, while 
 the mesiodistal measurement of the crown 
 is about one-third less, in consequence of 
 which the neck of the tooth is not so well defined. The 
 aneles of the crown are more rounded than those of the central 
 
 Fig. 166. — Upper Lat- 
 eral Incisor, Labial 
 Surface. 
 
ANATOMY. 
 
 UPPER CUSPID. 
 
 Second Year 
 
 Fig. 167. 
 
 Calcification Begins, about the Fifth Fetal Month. 
 
 Calcification Completed, about Two Years after Birth. 
 
 Erupts, Seventeenth to Eighteenth Month after Birth. 
 Decalcification Begins, about the Ninth Year. 
 
 Shedding Process Takes Place, about the Twelfth Year. 
 Average Length of Crown, .25. 
 
 Average Length of Root, .53. 
 
 Average Length over All, .78. 
 
 Like the permanent cuspid, the general contour of this tooth 
 is that of a double cone, the lines of which are somewhat broken. 
 The greatest mesiodistal extent of the crown 
 is from angle to angle, and this measurement 
 about corresponds to the width of the crown 
 of the central incisor. 
 
 The Labial Surface of the Crown 
 (Fig. 168). — This surface is strongly convex 
 from mesial to distal, and slightly so from 
 the cutting-edge to the cervical line. It is 
 bounded by five margins : mesial, distal, cer- 
 vical, mesio-incisive, and disto-incisive. The 
 mesial and distal margins are rounded and 
 smooth, the cervical well outlined by the 
 cervical line and base of the cervical ridge, 
 while the two incisive margins are formed by the mesial and 
 distal cutting-edges. The labial grooves are thrown well 
 toward the lateral margins, and are usually more distinct than 
 those upon the incisors. The labial ridge is prominent. 
 
 Fig. 168. — Upper Cuspid, 
 Labial Surface. 
 
THE DECIDUOUS TEETH IN DETAIL. 275 
 
 The Lingual Surface of the Crown. — This surface is 
 generally divided into two portions by the lingual ridge, which 
 extends from the summit of the cusp to the base of the cervical 
 ridge. On either side of this ridge are the lingual grooves, but 
 which appear more in the form of small fossse. The marginal 
 ridges are fairly well defined. 
 
 The Mesial and Distal Surfaces of the Crown. — The 
 extent of these two surfaces is frequently much interfered with 
 by the slope of the mesial and distal cutting-edges, which may 
 be so long that the angles of the crown are forced well toward 
 the cervical line, in some instances almost obliterating these two 
 surfaces. When the cutting-edges are shorter, these surfaces 
 present a marked general convexity. While the summit of the 
 cusp will always be found to be in a direct line with the long 
 axis of the tooth, there is in nearly every instance a difference in 
 the length of the cutting-edees, and, unlike the cutting-edares of 
 the permanent cuspid, the mesial is usually the longer. The 
 neck of the tooth is much constricted and the root straight and 
 conic. 
 
 THE UPPER MOLARS. 
 
 Upper First Molar. 
 
 Fig. 169. 
 
 Calcification Begins, about the Fifth Fetal Month. 
 
 Calcification Completed, Eighteenth to Twentieth Month after Birth. 
 Erupts, Fourteenth to Fifteenth Month after Birth. 
 Decalcification Begins, Si.\th to Seventh Year. 
 
 Shedding Process Takes Place, about the Tenth Year. 
 Average Length of Crown, .20. 
 
 Average Length of Root, .39. 
 
 Average Length over All, .59. 
 
 The contour and lobate construction of the crown of this tooth 
 
276 ANATOMY. 
 
 is peculiar to itself, being dissimilar to any other class of teeth 
 in the mouth. Calcification takes place from three centers, two 
 for the buccal and one for the lingual half of the crown. The 
 general form of the crown may best be studied by an examination 
 of the occlusal surface. 
 
 The Occlusal Surface of the Crown. — The outlines 
 represented are those of an irregular quadrilateral, of which 
 the buccal and mesial sides are the longest. The angles of 
 the quadrilateral are somewhat variable, the mesiobuccal being 
 acute, the mesiolingual obtuse, while the two distal angles are 
 rounded right angles. The surface is surmounted by three 
 cusps, a mesiobuccal, a distobuccal, and a lingual. These 
 various cusps are separated from one another by three develop- 
 mental grooves — the mesial, the distal, and the buccal. The 
 marginal ridges are sharp and well defined, this being particu- 
 larly true of the buccal and lingual, which resemble cutting- 
 edges. The mesio-marginal ridge begins at the mesiobuccal 
 angle, and, after making a long distal curve, ends in the mesial 
 incline of the lingual cusp. The center of the surface is deeply 
 and Irregularly concave, producing the central fossa, and de- 
 scending from the various ridges and cusps surrounding it are 
 numerous supplemental grooves and ridges. The various 
 developmental grooves are not inclined to cross the marginal 
 ridges although in some instances one or two may be found to 
 do so. 
 
 The Buccal Surface of the Crown (Fig. 169).— This sur- 
 face is generally smooth and convex, with an excessively devel- 
 oped cervical ridge, which is particularly prominent at its mesial 
 extremity. The buccal groove is in the form of a slight 
 depression, and the buccal ridges, common to all molars, are 
 scarcely to be observed. The mesial, occlusal, and cervical mar- 
 gins are distinctly outlined, while the distal margin is obliterated 
 by the gradual passing of this surface into the distal surface. 
 
 The Lingual Surface of the Crown. — This surface is 
 circular in outline, decidedly convex and smooth, and is seldom 
 broken by grooves and ridges. It is most prominent near the 
 center, from which point it slopes in every direction. The 
 cervical ridge is not so pronounced as that of the buccal 
 
THE DECIDUOUS TEETH TN DETAH.. 
 
 surface, but there is a sudden rounding of tlie surface in a 
 cervical direction to meet the Hngual root. 
 
 The Mesial Surface of the Crown. — This surface is 
 probably more extensive than any of the others ; it is inclined 
 to flatness, with a slight conic convexity over its occlusal 
 third, and a slight concavity near the cervix. The buccolingual 
 measurement of the surface is nearly twice as great as that 
 from the occlusal margin to the cervical line. It is much more 
 prominent near the occlusal margin, so that a V-shaped space 
 usually exists between it and the distal surface of the cuspid. 
 
 The Distal Surface of the 
 Crown.— The extent of this 
 surface is much less than that 
 of the mesial ; it presents a 
 general convexity, and is sel- 
 dom broken by grooves or 
 ridges, although occasionally 
 the distal groove crosses its 
 occlusal margin. Like the de- 
 ciduous teeth previously de- 
 scribed, the neck of the tooth 
 is marked by a decided and 
 abrupt constriction, this form 
 appearing to arise from the 
 heavy enamel folds which are 
 present near the cervical line, 
 
 rather than from any marked constriction in the base of the roots 
 themselves. 
 
 The roots of the tooth are three in number — a mesio- 
 buccal, a distobuccal, and a lingual ; of these, the latter is 
 usually the largest and longest. The two buccal roots are 
 much flattened from mesial to distal, while the lingual is com- 
 pressed in the opposite direction. The apical ends of the roots 
 are much separated from one another, the triangle which these 
 points form being almost twice the size of the triangle formed 
 by the base of the roots. The apical ends are usually provided 
 with a central curve. 
 
 9 ^ 
 
 170. — Occlusal Surfaces of the 
 Deciduous Molars. 
 
278 
 
 Upper Second Molar. 
 
 Fig. 171. 
 
 Calcification Begins,, between the Fifth and Sixth Fetal Months. 
 
 Calcification Completed, Twentieth to Twenty-second Month after Birth. 
 Erupted, Eighteenth to Twenty-fourth Month after Birth. 
 Decalcification Begins, Seventh to Eighth Year. 
 
 Shedding Process Takes Place, Eleventh to Twelfth Year. 
 Average Length of Crown, .22. 
 
 Average Length of Root, 46. 
 
 Average Length over All, .68. 
 
 The most remarkable feature about the crown of this tooth 
 is its close resemblance to the crown of the upper perma- 
 nent first molar. The various surfaces are 
 almost identical, the developmental process, 
 and consequently the cusp-formation, is 
 the same, the marginal and other ridges 
 common to the occlusal surface correspond, 
 and both the central and distal fossae are 
 present, together with the various develop- 
 mental grooves. A description of the crown 
 will, therefore, be unnecessary ; suffice it to 
 say that it is much smaller in every direction 
 and is somewhatmore constricted at the neck. 
 The roots are the same in name and number 
 as those of the first permanent molar, but 
 they are more widely separated at their apical extremities. In 
 general form they are smaller than those of the upper first 
 deciduous molar. 
 
 Fig. 172. — Upper Sec- 
 ond Molar, Buccal 
 Surface. 
 
THE DECIDUOUS TEETH IN DETAIL. 
 
 THE LOWER DECIDUOUS TEETH. 
 A description in detail of the lower incisors and cuspids 
 would practically be a repetition of that given of the corre- 
 sponding upper teeth, and for that reason will be passed with 
 a limited reference to each. The lower molars being in many 
 respects unlike the upper, they will require a separate de- 
 scription. 
 
 Lower Central Incisor (Fig. 173). 
 
 Calcification Begins, about the Fourth Fetal Month. 
 
 Calcification Completed, Sixteenth to Eighteenth Month after Birth. 
 Erupted, Si.xth to Eighth Month after Birth. 
 Decalcification Begins, about the Fourth Year. 
 
 Shedding Process Takes Place, about the Seventh Year. 
 Average Length of Crown, .19. 
 
 Average Length of Root, .35. 
 
 Average Length over All, .54. 
 
 This is the smallest of the lower teeth, in this 
 respect being at variance to the upper central, 
 which is larger than the lateral. The mesio- 
 distal diameter of the crown is but little less 
 than that from the cutting-edge to the cervical 
 line. The mesial and distal angles are similar, 
 both being pointed and square. The cervical 
 ridge is quite pronounced and the neck much con- 
 stricted. 
 
 The root is usually straight and tapers gradu- 
 ally from base to apex. It is broader on the 
 labial than on the lingual side, and the mesial 
 and distal sides are but little flattened. 
 
 Fig. 173.— 
 Lower Central 
 Incisor, Labial 
 Surface. 
 
 Lower Lateral Incisor (Fig. 174). 
 
 Calcification Begins, about the Fourth Fetal Month. 
 
 Calcification Completed, Twelfth to Fourteenth Month after Birth. 
 Erupted, Seventh to Ninth Month after Birth. 
 Decalcification Begins, about the Fifth Year. 
 
 Shedding Process Takes Place, about the Eighth Year. 
 Average Length of Crown, .19. 
 
 Average Length of Root, .39. 
 
 Average Length over All, .5S. 
 
 This tooth is larger than the central incisor, and closely resem- 
 bles the upper lateral both in size and form. The crown is 
 
ANATOMY. 
 
 Fig. 174. — 
 Lower Lateral 
 Incisor, Labial 
 Surface. 
 
 more rounded in its nature than that of the central, forming a 
 greater general convexity to the labial surface, and less con- 
 cavity to the lingual. The mesial angle of the 
 crown is fairly well defined, while the distal is 
 usually much rounded by a long, circular sweep 
 of the cutting-edge to meet the distal surface. 
 The mesial surface of the crown is flattened and 
 somewhat prominent at the angle, while the dis- 
 tal surface is strongly convex. The labial grooves 
 are but slightly visible, while the corresponding 
 lingual grooves are quite pronounced. The neck 
 of the tooth is even more marked than that 
 of the lower central incisor. The root is long 
 and tapering, slightly flattened from mesial to 
 distal, with a decided longitudinal groove on 
 both the mesial and distal sides. The labial 
 and lingual sides are rounded, and there is an inclination to 
 crookedness, which is usually from mesial to distal. 
 
 Lower Cuspid (Fig. 175). 
 
 Calcification Begins, about the Fifth Fetal Month. 
 
 Calcification Completed, about Two Years after Birth. 
 
 Erupted, Seventeenth to Eighteenth Month after Birth. 
 Decalcification Begins, about the Ninth Year. 
 
 Shedding Process Takes Place, about the Twelfth Year. 
 Average Length of Crown, .23. 
 
 Average Length of Root, .45. * 
 
 Average Length over All, .68. 
 
 The principal variations between this tooth 
 and the upper cuspid are observed in the dim- 
 inished mesiodistal measurement of the crown, 
 together with it being somewhat less angular 
 in outline. The ridges and grooves common 
 to the various surfaces are not so marked as 
 those of the upper cuspid, resulting in a 
 smoothly formed crown throughout. The root 
 is larger in proportion to the size of the crown 
 than that of its upper opponent, thus pro- 
 ducing a neck much less constricted. It is 
 usually straight, or provided with a slight distal 
 
THE DECIDUOUS TEETH IN DETAIL. 281 
 
 inclination near its apical extremity, and much flattened from 
 mesial to distal, these two sides converging to the lingual, 
 forming a rounded triangular outline. 
 
 Lower First Molar (Fig. 176). 
 
 Calcification Begins about the Fifth Fetal Month. 
 
 Calcification Completed, Eighteenth to Twentieth Month after Birth. 
 Erupted, Fourteenth to Fifteenth Month after Birth. 
 Decalcification Begins, Si.\th to Seventh Year. 
 
 Shedding Process Begins, about the Tenth Year. 
 Average Length of Crown, .24. 
 
 Average Length of Root, .38. 
 
 Average Length over All, .62. 
 
 Upon making an examination of the occlusal surface of this 
 tooth it will be observed that the crown is made up of four 
 irregularly formed lobes, separated from one another by four 
 well-defined grooves. Each lobe is pro- 
 vided with a cusp, more or less prominently 
 developed. Between the various cusps are 
 two fossse — one occupying the distal two- 
 thirds of the surface (the distal fossa) and 
 the other the remaining or mesial third (the 
 mesial fossa). The outline of this surface, 
 which represents the contour of the crown in 
 
 general, is that of an oblong square, with its Fig. 176. — Lower 
 , , 1111- First Molar, Buccal 
 
 angles more or less rounded, and havmg a surface. 
 
 slight variation in its parallel lines. Each 
 
 lobe denotes a separate center of calcification, and the four 
 
 grooves the lines of union between the various parts. 
 
 The mesiobuccal lobe is somewhat irregular in contour 
 and is frequently the largest of the four. It assists in forming 
 the mesiobuccal angle of the crown and the greater part of the 
 mesial fossa. Descending from this cusp to the lingual is a 
 pronounced triangular ridge, which is made continuous by 
 uniting with a similar ridge from the corresponding lingual 
 cusp. By this union a transverse ridge is established, separating 
 the mesial from the distal fossa. The central boundary of this 
 lobe is formed by the mesial groove, which arises from the distal 
 fossa, passes over the transverse ridge to the mesial fossa, from 
 
282 ANATOMY. 
 
 which it continues to the lingual, and by the buccal groove, 
 which branches off from the mesial somewhat to the distal of the 
 transverse ridge, passing over the buccomarginal ridge to the 
 buccal surface. 
 
 The Distobuccal Lobe. — This cusp is generally smaller than 
 the mesiobuccal, and is more pointed and more regular in outline. 
 It assists in forming the distobuccal angle of the crown, and 
 by its central incline forms about one-third of the distal fossa. Its 
 boundaries are formed by the buccal, mesial, and distal grooves, 
 the latter beginning in the distal fossa, and passing over the 
 distomarginal ridge to the distal surface. 
 
 The Mesiolingual Lobe. — In the recently erupted tooth 
 the summit of this cusp is long and pointed, and frequently 
 remains the most pronounced of the four. It is triangular in 
 outline, and, as above referred to, furnishes a triangular ridge, 
 which, by uniting with a like ridge from the mesiobuccal cusp, 
 forms the transverse ridge. By its central incline it assists in 
 forming the mesial fossa. Its boundaries are formed by the 
 mesial groove and the lingual groove, the latter arising near 
 the center of the distal fossa, passing to, and sometimes cross- 
 ing, the linguomarginal ridge. 
 
 The Distolingual Lobe. — This is usually the smallest of 
 the four. It is inclined to be rounded, rather than angular, and in 
 some instances is poorly developed. It assists in forming the 
 distolingual angle of the crown, as well as a portion of the distal 
 fossa. Its central boundaries are formed by the lingual and 
 distal grooves. 
 
 The marginal ridges of the surface are abruptly but irregularly 
 formed, asecndingand descending the various cusps in a manner 
 similar to those previously described. 
 
 The Buccal Surface of the Crown (Fig. 176). — This sur- 
 face is smooth and generally convex, with a mesiodistal measure- 
 ment about twice as great as that from the cervical line to the 
 occlusal margin. The surface is most prominent over its 
 cervical third, forming a well-rounded and bold cervical ridge, 
 a feature strongly characteristic of this tooth. The distal center 
 of the surface is broken by the buccal groove, which usually 
 ends near the center in a shallow depression or pit. 
 
THE DECIDUOUS TEETH IN DETAIL. 283 
 
 The Lingual Surface of the Crown. — This surface is 
 much less extensive than the buccal. It is smooth and convex 
 throughout, and is broken near its distal center by the lingual 
 groove, which gradually disappears as it passes rootward. 
 The cervical ridge is not so prominent as that of the buccal 
 surface. 
 
 The Mesial and Distal Surfaces of the Crown. — These 
 are slightly convex in every direction, the former passing, 
 by a gradual sweep, into the lingual surface, destroying the 
 angularity of the crown at this point, while the latter passes 
 more abruptly, forming an acute angle. These surfaces are both 
 prominent near the occlusal margin, making the point of contact 
 with adjoining teeth near that surface. The bold cervical ridge 
 of the buccal surface is discontinued or greatly diminished upon 
 these surfaces, both of which are inclined to pass very gradually 
 Into the base of the roots. 
 
 The roots of this tooth are the same In name, position, and 
 number as those of the lower permanent molars. They are 
 much flattened from mesial to distal, the center of their flattened 
 sides being further compressed by a deep longitudinal groove, 
 which extends from the base to the apex of each root. In passing 
 from the base of the roots to their apices they become more 
 widely separated, until these extremities are much wider apart, 
 proportionately, than those of the permanent molars. 
 
 Lower Second Molar (Fig. 177). 
 
 Calcification Begins, between the Fifth and Sixth Fetal Months. 
 
 Calcification Completed, Twentieth to Twenty-second Month after Birth. 
 Erupted, Eighteenth to Twenty-fourth Month after Birth. 
 Decalcification Begins, Seventh to Eighth Year. 
 
 Shedding Process Takes Place, Eleventh to Twelfth Year. 
 Average Length of Crown, .21. 
 
 Average Length of Root, .44. 
 
 Average Length over All, .65. 
 
 The anatomy of this tooth being almost identical to that of 
 the lower first permanent molar, it will be unnecessary to 
 enter into a description in detail. The lobes, and consequently 
 the grooves, are the same in position, name, and number, and 
 
28+ ANATOMY. 
 
 a similar developmental process is recorded. The tooth 
 is not characterized by a prominent cervical ridge, such as is 
 found upon the lower first molar, the crown passing very gradu- 
 ally into the root-base with a neck moder- 
 ately constricted. 
 
 THE PULP-CHAMBERS AND CANALS OF 
 THE DECIDUOUS TEETH. 
 A few general remarks in reference to 
 these cavities, in connection with the infor- 
 mation to be derived from the accompany- 
 ing chart and its annexed description, will 
 sufficiently instruct the reader, without the 
 necessity of treating each tooth individually. 
 Second molI^,^bu'ccal The pulp-chambers and canals, like those 
 Surface. ^^ ^.j-^g permanent organs, assume the 
 
 form of the external contour of the tooth, 
 the crown of the tooth being provided with a central cavity, 
 the pulp-chamber, partaking of outlines closely resembling those 
 of the crown, while the root is traversed by the pulp-canal, like- 
 wise conforming to the shape of the root. One very important 
 distinction between the pulp-chambers and canals of the de- 
 ciduous teeth and those of the permanent organs is that the 
 former are proportionately larger. It must also be noted that 
 the apical foramina in these teeth are so transitory in their 
 nature that there remains but a very brief period during which 
 the canals may be said to be fully formed. It will be recalled 
 that in a very short time after the roots have become completely 
 calcified, decalcification begins, and this process of degeneracy, 
 beginning at the apical extremities of the roots, very early 
 destroys the foramina, which have in a measure served as a pro- 
 tection to the surrounding parts during operations upon the 
 canals. 
 
 With the canals proportionately larger than those which occupy 
 the roots of the permanent teeth, the foramina during their very 
 limited existence are also much larger, and much more readily 
 penetrated. With these ever-changing conditions in the pulp- 
 canals of the deciduous teeth, it is of importance that a definite 
 
THE DECIDUOUS TEETH IN DETAIL. 
 
 -85 
 
 knowledge of what takes place should be acquired, and it is for 
 this purpose that the accompanying chart has been prepared 
 (Fig. 178). 
 
 Mo. Old 
 Twelve 
 Mo. Old 
 
 Fig. 178. — Ch.^rt showing Calcification and Decalcific.a.tion of the Deciduous Teeth and xiiE 
 Consequent Length of the Pulp-canal at Various Periods. — {After Peitxe.) 
 
CHAPTER XII. 
 
 DEVELOPMENT OF THE TEETH— THE DENTAL GERMS, ENAMEL 
 ORGAN, AND DENTIN ORGAN; THE DENTAL FOLLICLE; CALCI- 
 FICATION AND ERUPTION. 
 
 DEVELOPMENT OF THE TEETH. 
 
 Neck of Cord 
 
 Papilla 
 
 Fig. 179. — Developing Tooth-germ. X 3°°- 
 
 In order that the student may obtain a general idea of the 
 structural changes which take place at a very early period, and 
 which eventually result in the formation of the teeth, the genesis 
 of the subject will be briefly referred to. Preparation for the 
 development of the teeth takes place as early as the middle of 
 
 2S6 
 
DEVELOPMENT OF THE TEETH. 287 
 
 the second fetal month, this preparatory alteration in the 
 tissues beginning before the process of ossification in the bony 
 structures which finally surround and give support to the 
 organs. At this early period there will be found following 
 the line of the future alveolar ridge a slight heaping up of 
 the surface epithelium, while immediately beneath this pro- 
 liferation of cells there appears a dipping in of the deep 
 epithelial layer in the direction of the future alveolar walls. 
 This epithelial reflection is known as the epithelial band or 
 tooth-band. This so-called tooth-band is not, as might be sup- 
 posed, a special inflection for each tooth-germ, but is continu- 
 ous from one end of the future jaw to the other. It must be 
 remembered that at this time the outline of the jaw has not 
 been established, and the tooth-band, although not generally 
 considered as essential to the developmental process, is princi- 
 pally instrumental in directing the position of the dental 
 organs. The position and form of this epithelial band may 
 best be studied in vertical transverse section. When first 
 making its appearance it is somewhat broad and shallow, but 
 as it passes more deeply into the parts it partakes of the out- 
 line of the letter V with its open end directed toward the sur- 
 face. In penetrating the subjacent tissue, the free extremity of 
 the band is inclined to the lingual, its external surface is slightly 
 convex, and its internal surface correspondingly concave. His- 
 tologically considered, the tooth-band is composed of elements 
 similar to those which serve to make up the epithelial layer 
 of the oral mucous membrane. After the tooth-band has 
 assumed certain proportions, there appears on its inner or con- 
 cave surface a thin niembranous plate, which is likewise a 
 continuous structure, extending the full length of the epithelial 
 band. 
 
 This lamina does not spring from the free margin of the tooth- 
 band, but is given off at a point about midway between this 
 border and the base of the band. The structure of this secondary 
 band is so similar to that of the primary one that it should be 
 considered as an inflexion from it rather than a new structure. 
 We find then between the seventh and eighth week, the maxillary 
 regions giving place to two bow-shaped bands (one for each 
 
288 ' ANATOMY. 
 
 jaw), each of which is preparing to throw out from its secondary 
 lamina ten Httle buds, which soon develop into the germs for the 
 twenty deciduous teeth. When these buds make their appear- 
 ance they are simple, rounded bodies, placed somewhat closely 
 together, but they do not long retain this simple form. The 
 first change which takes place is one in which they appear to 
 lengthen out into slender cords, the extremities of which soon 
 begin to extend laterally, and the primitive enamel organ is 
 formed. Accompanying this lateral extension of the periphery, 
 
 Ef itl ehum of Lower Ja 
 
 Tlellate Retic- 
 
 j L 11 imel Organ 
 Dentin Papilla 
 
 De\ eloping Tooth ei \ 1 \\ llfth \\ eeiv > 40. 
 
 a bell-shaped outline is assumed, which phenomenon is rapidly 
 increased by a specialization of the surrounding cellular tissue 
 forcing into the concavity. 
 
 This bell-shaped proliferation of cells, given off directly from 
 the tooth-band, to which it continues for a time attached, 
 together with the specialized connective tissue crowding into its 
 concavity, constitute the tooth-germs, the former being the enamel 
 organ, and the latter the dentin organ. It will, therefore, be seen 
 that the enamel is dependent upon the oral epithelium for its 
 development (ecdermic), while the dentin springs from an en- 
 
DEVELOrMENT OF THE TEETH. 289 
 
 tirely different source — the connective tissue of the jaw (ender- 
 mic). The enamel organ rapidly undergoes a cellular transfor- 
 mation : its concavity is increased, and the bell-shaped outline 
 more strongly defined. Accompanying this change in form it 
 gradually recedes from the surface, and its connection with the 
 tooth-band becomes less secure. The connective-tissue cells, 
 which have been rapidly filling in the concavity of the enamel 
 organ, are also preparing to take upon themselves a special 
 function, that of the formation of the dentin. Up to this period 
 (tenth week) the enamel and dentin germs are not definitely 
 separated from the surrounding cellular structure, but now a 
 gradual transformation takes place, whereby the tooth-germs 
 become enveloped in a sac-like covering — the dental follicle. 
 
 Enamel Organ (Figs. 179, 180, and 181). — This portion of 
 the tooth-germ, as previously stated, is derived from the concave 
 or lingual surface of the tooth-band, which in turn is derived from 
 the surface epithelium. From the free extremity of its slender 
 cord-like attachment it spreads out and forms a hood-like cover- 
 ing to the dentin germ. The surface of the organ contiguous to 
 the dentin germ, or dentin papilla, as it is frequendy called, is 
 concave in the direction of the oral surface, being thickest over 
 the center of its concavity, thinning down as its periphery is 
 approached. Externally, the enamel organ is covered by an 
 epithelial layer, which is reflected upon its inner surface or that 
 in contact with the dentin papilla. These two layers are named 
 according to their location, the external and internal epithelium 
 of the enamel organ. Placed between these two layers, and 
 constituting the bulk of the organ, are numerous stellate bodies 
 which penetrate a layer of rounded cells, the stratum intervie- 
 diiim, and finally reach the internal epithelial layer known as the 
 enamel cells or ameloblasts. It is from this internal layer of epi- 
 thelial cells that the enamel is calcified, and they are, therefore, 
 the essential cells of the enamel organ. In the fully developed, 
 enamel organ, there are to be' found, therefore, four distinct lay- 
 ers of cells, the external epithelium, stellate reticulum, stratum 
 intermedium, and internal epithelium, ox ameloblasts . As its name 
 implies, the function of the enamel organ is principally that of 
 enamel calcification, but in the opinion of many writers its pri- 
 19 
 
mary activity is that of molding the tooth-form as represented 
 by the dentin papilla, and it is not until this latter organ has 
 assumed the form and extent of the future tooth-crown that 
 dentin calcification begins. 
 
 The life of the enamel organ may properly be considered as 
 beginning when the bulbous extremity of the specialized cells 
 given off from the lingual face of the tooth-band become invag- 
 inated, and from this by a rapid proliferation of its cells it passes 
 
 Fig. i8i. — Developing Tooth-germs, Enamel Organ, and Dentin Papilla. 
 
 on by successive stages assuming the various forms common to 
 it. This proliferation and differentiation ot cells continues up 
 to the time of beginning of calcification, but with the advent of 
 this phenomenon certain parts of the organ begin to degenerate. 
 This degeneration may or may nc)t be classed as an atrophy of 
 the cells interested, but the fact that a new tissue is generating, 
 and gradually occupying the space previously taken up by the 
 formative cells, calls forth a demand for the removal of the latter 
 by the former. The cells which first undergo this change are those 
 
DEVELOPMENT OF THE TEETH. 291 
 
 of the internal epithelium and stratum intermedium, the individ- 
 uality of these two layers evidently being kept up by migratory 
 cells from the stellate reticulum. It is argued by some writers 
 that the external epithelium begins to atrophy at this period ; 
 by others this change is not recorded until the enamel cuticle 
 has been deposited to effectually seal the young tissue and pro- 
 tect it until well desiccated. While there appears to be a decided 
 disposition upon the part of this outer layer of cells to change, 
 
 Fig. 1S2. — Developing Tooth-germs. Longitudinal Sections from Buccal to 
 Lingual. 
 
 they do not disappear, and the alteration is not one which affects 
 the shape of the cells, for they remain flattened or prismatic 
 with their long axis placed parallel with the anlage of the crown. 
 The stellate cells making up the bulk of the organ are, in com- 
 mon with those which inclose them, continually undergoing a 
 degenerative change, at least this is true of those cells closely 
 associated with the stratum intermedium, for in this location 
 
they rapidly proliferate, shed their many processes, and grad- 
 ually take on the characteristics common to this layer of which 
 they eventually become a part. A careful examination of no 
 less than one hundred enamel organs in all stages of develop- 
 ment, and by section cut transversely, obliquely, longitudinally, 
 etc., fully justifies the statement that the real life of the enamel 
 organ begins as previously stated, and continues until the 
 structural arrangement of the enamel is completed. 
 
 Fig. 183. — Developing Tooth-gerjis. Longitudinal Section from Mesial 
 TO Distal. 
 
 The question of form in the enamel organ — that is, its exter- 
 nal epithelium — is one which may be advantageously used in 
 the consideration of the life and function of its different cell 
 layers. It has been said that the apparently extravagant area 
 taken up by the enamel organ subserves the purpose of reserv- 
 ing space for the growing tooth-crown, but there are many 
 reasons why this theory cannot be accepted. In the first place. 
 
DEVELOPMENT OF THE TEETH. 293 
 
 the extent of the organ or the space existing between the den- 
 tin papilla and the outer enamel epithelium does not in very 
 many instances correspond to the bulk of enamel when this 
 tissue is completed at a given point. In the developed tooth 
 we find the enamel thickest over the cutting-edges of the ante- 
 rior teeth and about the summits of the cusps of the cuspidate 
 teeth, while these same parts are represented during the cell- 
 ular stage of development by the external layer of cells closely 
 associated with the surface of the papilla. 
 
 Again, in very many instances the outline of the tooth is 
 definitely represented by the cells making up the dentin papilla 
 (Figs. I Si and 182), but the surrounding epithelial cells are 
 characterized by an unbroken semicircular margin describing 
 the extent and form of the enamel organ. Exception may be 
 taken to this hypothesis from the standpoint of generative 
 changes, and these in a great measure have much to do with the 
 relative outlines assumed by the two organs, but by studying 
 very many sections representing nearly every stage of the 
 process, and all of them in a measure showing the same char- 
 acteristics, nothing but a definite opinion can result. 
 
 Of the many changes in general form which the enamel organ 
 undergoes, none are so pronounced and positive in character as 
 those described by the inner tunic, and first recorded when the 
 bulbous end of the specialized cells becomes invaginated by the 
 mesodermic connective-tissue cells forcing themselves into it. 
 This is an alteration which is gradual and continuous up to the 
 time of beginning of calcification, and while the cells forming 
 the dentin papilla are generally accorded the power of "push- 
 ing" or "forcing" their way into those derived from the epiblast, 
 the latter have always been recognized as having a controlling 
 influence over the former. In this connection a reasonable 
 doubt presents itself covering the theory so long accepted that 
 the early function of the enamel organ is one which in a meas- 
 ure superintends the contouring of the tooth-crown as first rep- 
 resented in the dentin papilla. When the character of the 
 two embryonal tissues making up the two germs is compared, 
 we find the dentin germ possessing all the characteristics favor- 
 able to a rapid proliferation of its cells resulting in a highly 
 
vascular, compact tissue. On the other hand, the bulk of the 
 enamel organ is a gelatinous-like mass, one that would readily 
 succumb to the pressure exerted by those active connective- 
 tissue cells within its borders. When thus considered, the evi- 
 dence is almost sufficiently convincing to reverse the generally 
 accepted theory, placing the general form of the enamel organ 
 as subservient to the dentin papilla. 
 
 Fig. 184. — Developing Tooth-germs in Transverse Section. 
 A, Stellate reticulum. B, Papilla. C, Cartilage cells. 
 
 Figures 181, 182, and 183 illustrate some of the variations 
 common to the general form of the enamel organ, and afford a 
 good idea of the relationship existing between the enamel organ 
 and the dentin papilla, in teeth both of the simple and complex 
 class. These were taken from sections which represent a period 
 just prior to the generation of the ameloblasts and odontoblasts, 
 at which time the external and internal epithelial layers of the 
 enamel orean most closelv resemble one another in greneral out- 
 
DEVELOPMENT OF THE TEETH. 
 
 295 
 
 line. It is from this aspect and from sections cut longitudinally 
 that most of the information given by the older writers has been 
 derived. Few attempts have been made to show this organ in 
 section transverse to the long axis of the tooth anlage. In 
 figure 184 the germs of two teeth are shown by a section made 
 in this direction. One striking feature here illustrated is the 
 relationship existing'between the inner and the outer tunic of 
 
 a 
 
 
 
 '<-.. fS*- 
 
 '4 
 
 ■**"*^. *'^" 
 
 ^'^'1%^«7 
 
 Fig. 1S5. 
 A, Inner tunic of enamel organ, B, Cells of dentin papilla. 
 
 ■ 3. 
 
 the enamel organ, and attention is called to the apparent coales- 
 cence of these two layers at those points which represent the 
 mesial and distal surfaces of the developing crowns. This con- 
 dition is apparently brought about by the cartilage cells forcing 
 the peripheral cells of the enamel organ into direct contact with 
 the inner tunic, completely obliterating the stellate reticulum in 
 these localities. As a result of this lateral pressure the outer 
 epithelial cells representing the labial and lingual surfaces 
 
296 ANATOMY. 
 
 have become widely separated, but with no perceptible alter- 
 ation in the character of the cells composing the stellate 
 reticulum. The relationship existing between the tooth-germs 
 and the surrounding parts is one that will continue throughout 
 the generation of the organs, and makes questionable the theory 
 that the stellate reticulum performs the function of reinforcing 
 or providing the ameloblasts with nutrient or calcific material. 
 
 
 :ff^ 
 
 Fig. 1S6. 
 A, Cells of dentin papilla. B, Elongated cells of inner tunic. 
 
 If these same germs were examined, as they usually are, in 
 longitudinal section (see Figs. 181, 182, and 183), the investi- 
 gator would at once arrive at the conclusion that there was an 
 equal distribution of the stellate cells about all sides of the 
 dentin papilla. In their very early life they apparently establish 
 an equal bulk about all sides of the dentin germ, but with the 
 preparation for the growth of the alveolar walls they may assume 
 the proportions shown in figure 184. At a period correspond- 
 
DEVELOPMENT OF THE TEETH. 297 
 
 ing to the complete envelopment of the dental germs by the 
 dental follicle the development of the buccal and lingual walls 
 is well under way, but as yet no provision has been made for 
 the septa between the teeth, and it is undoubtedly to the 
 approach of this latter phenomenon that a definite lateral pres- 
 sure is brought to bear upon the approaching walls of the fol- 
 licles. 
 
 Now let us pass to a consideration of some of the charac- 
 teristics of the various cell layers composing the enamel organ. 
 These are designated according to their location, so far as 
 three of the four layers are concerned; in fact, the remaining 
 cells, or those which receive their name from their form, can 
 scarcely be classified as a distinct layer, these stellate cells not 
 being of uniform thickness in all parts of the organ. The first 
 layer of cells, or those making up the inner tunic, will be traced 
 from their primary spherical condition to their final generation 
 into ameloblasts. Figure 185 shows the character of these cells 
 at a very early period, corresponding to the sixteenth week in 
 the human fetus. They are for the most part spherical or slightly 
 oblong multinucleated cells, and are more or less closely asso- 
 ciated. They partake very much of the nature of the connec- 
 tive-tissue cells surrounding them, being differentiated from 
 these principally by a transparent zone not unlike the special- 
 ized matrix immediately surrounding cartilage cells. About 
 the first change recorded in these cells (see Fig. 1S6) is one in 
 which they become markedly elongated or cylindrical, but dur- 
 ing this process of differentiation some of the cells apparently 
 recede, while others advance in the direction of the papilla, lin- 
 ing up in a single layer to become the early enamel cells, the 
 cells which have been thus forced to the rear subsequently 
 developing into ameloblasts as the older cells atrophy. At this 
 period the stratum intermedium also asserts itself in the form of 
 a distinct layer of rounded cells, to be described later on. When 
 first observed, these cylindrical cells are devoid of processes, but 
 are provided with rounded extremities, with little or no variation 
 between the end directed toward the papilla and that looking in 
 the opposite direction. This form is one which persists in all 
 of the cells included in this layer until a definite body of cells is 
 
298 
 
 ANATOMY. 
 
 formed contiguous to the dentin papilla, these latter cells be- 
 coming more markedly elongated and further differentiated by 
 the addition of processes, while the remaining cells, or those 
 nearest the stratum intermedium, continue for a time unchanged. 
 The next alteration in the character of the inner tunic is one 
 well illustrated in figure 186, in which the body of the generat- 
 
 A, Stellate reticulum. B, Stratum intermedium. C, Ameloblasts. D, Forming enamel. 
 E, Calcified dentin. F, Odontoblasts. 
 
 ing ameloblastic cells rapidly recede from the surface of the 
 papilla, while the elongating processes reach out to this latter 
 point, all of this occurring before the appearance of the odonto- 
 blasts. Soon after this latter change in the cells of this layer 
 the odontoblasts are developed and form the periphery of the 
 dentinal tissue. All of these changes are of course first re- 
 
DEVELOPMENT OF THE TEETH. 299 
 
 corded about the free extremity of the tooth-crown, becoming 
 less noticeable as the union of the outer and inner tunics is 
 approached. 
 
 A study into the special characteristics of the fully developed 
 ameloblasts shows that these active cells are the result of a 
 gradual change in the character of the columnar epithelia com- 
 
 A, Generating ameloblasts. 
 
 B, Rounded cells of stratum intermedium. C, Stellate 
 reticulum. 
 
 mon to both the external and internal epithelial layers in the 
 primitive enamel organ. 
 
 Next in importance to the internal epithelial layer are those 
 closely associated cells making up the stratum intermedium (Fig. 
 188). Primarily oval or spheroidal in form, we find these cells 
 gradually assuming a columnar outline and occupying a position 
 parallel to the long axis of the crown. It may be said that the 
 general character of these cells is intermediate between those 
 
destined to become the proper enamel cells and those stellate 
 cells making up the bulk of the organ. There appears to be 
 much confusion, at least considerable doubt, in regard to the 
 office of the cells of the stratum intermedium. It is most likely 
 that these cells are not only intermediate in character, but are 
 also intermediate in function to those cells upon either side of 
 them, recruiting the ameloblasts as they fall, while in turn they 
 themselves are supplied with nutriment from the enamel pulp 
 or stellate reticulum. No stronger proof that these cells are 
 secondary in importance to the ameloblasts need be mentioned 
 than reference to the fact that they are always more generously 
 supplied to those parts about to undergo calcification. Nor is 
 their increase in numbers the only reason for believing that they 
 are thus employed, for at the same time those cells most closely 
 associated with the developing ameloblasts take upon them- 
 selves a decided change in outline. This alteration may be 
 brought about by the conditions which influence the shapes of 
 all cells, i. e., by the pressure of surrounding cells or by their 
 preparation for functional activity, or both. Some of the older 
 writers speak of the cells of this layer as being branched, and 
 in this way closely resembling those of the stellate reticulum. 
 By strong amplification it is somewhat difficult to distinguish 
 between the two layers, but most certainly if there are branched 
 cells present they are confined to the intermediate zone, and 
 should properly be classed with those of the stellate reticulum. 
 The cells of this layer do not long remain columnar with a 
 general direction at right angles to the forming ameloblasts, but 
 as these latter cells appear they become spheroidal and ex- 
 tremely closely associated in the deeper portion of the layer ; in 
 fact, cells corresponding to these in general appearance may be 
 found in connection with the fully developed ameloblasts, being 
 observed to best advantage by the aid of a high power objective 
 and a full flood of light from a powerful sub-stage condenser. 
 The cells thus found appear to be distributed at regular inter- 
 vals about the ameloblastic layer, and are so closely allied to the 
 cells of the stratum intermedium that they may be considered as 
 migratory cells from this layer. In the earlier stages there ap- 
 pears to be no definite line of demarcation between the cells of 
 
DEVELOPMENT OF THE TEETH. 301 
 
 the inner tunic and those composing the stratum intermedium, 
 but soon after the establishment of the ameloblasts the two lay- 
 ers are strongly differentiated by the interposition of a highly 
 transparent membrane covering the outer extremities of the 
 ameloblasts. After they are thus definitely separated from the 
 enamel-forming cells, a most radical change takes place in their 
 character ; they become markedly elongated, and by anasto- 
 mosing form a series of continuous chain-like belts about the 
 ameloblastic layer, the number and further character of which are 
 dependent upon the extent to which the ameloblasts have per- 
 formed their function. If at any time there is a similarity 
 between the cells of the stratum intermedium and the stellate 
 reticulum it is at this period, because the former cells begin to 
 lose their individuality, although under low power they still 
 appear as a distinct layer (Fig. 187). 
 
 There is probably no body of cells directly interested in the 
 development of the tooth tissues so widely discussed as those 
 making up the so-called stellate reticulum, and while the chief 
 basis for argument has been with reference to their function, the 
 general character and form of the cells have received but little 
 consideration. Ever since the first description of this portion of 
 the enamel organ the cells therein have been characterized as 
 "star-shaped," and while this stellate form is the most common, 
 it is by no means a universal condition. The form of the cells 
 in common with the other cells composing the organ appears to 
 be much influenced by the position which they occupy, and by 
 the age of the organ, those cells in the region of the inner tunic 
 partaking of the globular form characteristic of this layer (see 
 C, Fig. 188), while those closely associated with the outer tunic 
 are inclined to be columnar or somewhat elongated. While the 
 bodies of the cells in these respective locations are more or less 
 influenced by their environments, they still retain to a certain 
 extent the stellate feature by their many processes. But it is in 
 the center of this myxomatous epithelial product that the most 
 perfect stellate cells are located. We find, therefore, where this 
 part of the organ is of the greatest width, that the true stellate 
 cells are the most numerous, while at the summit of the crown 
 and at the base of the organ, at both of which points the outer 
 
302 ANATOMY. 
 
 and inner epithelial layers are closely associated, the star-shaped 
 cells are almost wanting. In the study of this layer very much 
 depends upon the thickness of the section, only the thinnest 
 possible sections affording an opportunity for a correct concep- 
 tion. This is, of course, true of all parts of the organ, but the 
 peculiar character of the stellate reticulum makes it especially 
 necessary that great care be bestowed upon the preparation of 
 the section. In transverse section the cells present no charac- 
 teristic differences from those shown when the section is made 
 longitudinally. One very pronounced feature about the cells of 
 the stellate reticulum is the granular appearance of their proto- 
 plasm, resembling very closely the flattened squamous cells from 
 the epithelium of the mouth, and it is no doubt this special fea- 
 ture which furnishes the ground for the opinion of many writers 
 that it is a peculiarly modified epithelium. One peculiarity in 
 connection with this dssue which is contrary to the generally 
 accepted character of epithelial cells is the abundance of inter- 
 cellular cement substance ; but when the many minute spines or 
 processes are considered as a part of the individual cell, the 
 proportionate quantity of cellular and intercellular substance is 
 somewhat decreased. The connecting processes are quite sim- 
 ilar to those described by Stohr as connecting bridges of proto- 
 plasm, while the cells themselves may be otherwise described as 
 prickle-cells. The change in the form of the cells of this layer 
 is not due to the presence of neighboring cells, as is the case 
 with most epithelial cells, but, being soft and extremely plastic, 
 it is more than likely that their form is strongly influenced by 
 the tension of their connecdng filaments. One of the most 
 marked alterations in the general character of this part of the 
 enamel organ is that which takes place at a time corresponding 
 to the beginning of amelification, and is no doubt attributable 
 to this phenomena. The cells which up to this period have 
 remained widely separated now become more closely associated, 
 not so much by a change of position as by what appears to be 
 an increase in the size of the cell body with a corresponding 
 decrease in the length of the anastomosing processes. 
 
 It is a fact admitted by most histologists that the peculiar star- 
 like nature of the cells of the stellate reticulum is one princi- 
 
DEVELOPMENT OF THE TEETH. 303 
 
 pally brought about by postmortem changes, and that in reality 
 they are polygonal cells filling up a greater part of the tissue 
 with but little intercellular substance. That some shrinkage and 
 distortion does take place may be proven by the examination of a 
 section which has accidentally or otherwise become for a moment 
 dry during its preparation, in which case litde can be seen but 
 the connecting processes, and even these are much shrunken. 
 All the cells contained within the organ are more or less affected 
 by this procedure, but none of them exhibit such a marked change 
 in the outline as those of the stellate reticulum. 
 
 The layer of cells which is usually considered of least impor- 
 tance is that which makes up the outer tunic. In the young 
 enamel organ the cells partake very much of the nature of those 
 forming the inner tunic, but the older the organ becomes, the 
 more dissimilar are the two layers. Primarily this layer is con- 
 structed of a single row of elongated cells, placed with remark- 
 able regularity, upon the inner side of which are a number of 
 similarly formed cells variously disposed, but with a common 
 direcdon at right angles to those previously referred to. Like 
 the internal epithelial layer, the cells of the outer tunic partake , 
 more or less of the nature of the stellate cells in passing from 
 the single row of well-defined cells toward the stellate reticulum. 
 While in the beginning the external epithelial layer is strongly 
 differentiated from the surrounding cells, this is of but short 
 duration. The atrophy of this layer begins with the appearance 
 of the fully developed ameloblasts, by which the regular arrange- 
 ment of the cells is greatly disturbed by an apparent breaking 
 up of the entire layer. Many reputable writers claim that the 
 external epithelial layer is of little or no interest, save, as Tomes 
 puts it, "as a matter of controversy." This admission upon the 
 part of so eminent an authority practically opens up a new field 
 for research, especially so when we consider that various other 
 writers (Waldeyer, Kolliger, and Magitot) have expressed con- 
 flicdng opinions in regard to it. After carefully following the 
 changes which occur in this layer from its earliest inception up 
 to an advanced stage of calcification, it would appear that while 
 marked changes occur in the character of the individual cells as 
 well as in the general appearance of the layer, it is nevertheless 
 
304 AJNAlUMi. 
 
 persistive, and in some way is essential to the process of amelifi- 
 cation, even to a more marked degree than are the cells of the 
 stellate reticulum. One important reason for this belief is based 
 upon the fact that in the cuspidate teeth there appears at a time 
 corresponding to the beginning of amelification, a decided dis- 
 position in the cells of this layer to dip down and completely 
 divide the stellate reticulum between the forming cusps. That 
 this alteration is one instrumental or essential to the calcifying 
 process receives additional proof by referring to figure i8i, 
 
 Fig. 189.— Section through thi, I i..,.i; ,., mi. Mouth of Human Embryo. 
 Twelfth Week. , , 30. 
 
 which shows the fully developed enamel organ with the excep- 
 tion of the actual appearance of the ameloblasts, and the lack 
 of any attempt upon the part of the external epithelial layer to 
 penetrate between the cusps. 
 
 Dentin Organ (Fig. iSo). — This part of the tooth-germ, 
 formed from the connective tissue of the primitive jaw, 
 occupies the concavity of the enamel organ, and at an early 
 period begins to assume the form of the future tooth-crown. 
 Thus, primarily, the papillae for the incisors will have their 
 cutting-edges ouriined by three small lobes, each of which 
 
DEVELOPMENT OF THE TEETH. 305 
 
 represents a separate point of calcification, while the papillae 
 for the molars will be molded according to the number of 
 cusps of the future tooth, a small tubercle making its appear- 
 ance for each cusp. In its inception the dentin papilla is 
 composed of cellular tissue identical with that of the surround- 
 ing parts. The growth of the papilla is in the direction of the 
 surface ; at the same time the enamel organ forces itself more 
 deeply into the substance of the parts, not only overhanging 
 the coronal extremity of the papilla, but extending about and 
 inclosing its lateral walls. Accompanying the growth of the 
 papilla is a rapid change in its structure, becoming more 
 vascular throughout, and its peripheral cells, differentiating, 
 form the essential dentin cells — the odontoblasts. This layer 
 of cells is in close relation to the enamel cells of the enamel 
 organ, the combined activity of the two finally resulting in the 
 calcification of the tooth-crown. The dentin papilla, which 
 eventually becomes the tooth-pulp, decreases in size as calcifi- 
 cation proceeds in the dentin, all additions to the calcifying 
 surface taking place from within ; while the enamel organ may 
 be said to increase in size, the calcific action in the enamel 
 progressing from within outward. 
 
 The Cells of the Dentin Papilla. — In the early life of the 
 dentin germ, the cells are all simple embryonal connective-tissue 
 cells. After differentiation takes place they are widely scattered 
 and are of four varieties: spindle-shaped, round, stellate, and 
 the elongated or club-shaped odontoblasts. None of these are 
 constant in location except the layer of odontoblasts, w^hich, as 
 has been said, are arranged in a single row on the surface of the 
 periphery of the organ, this zone being classed by the older writers 
 as the 77ieinbrana. ebo7-is. Like the ameloblasts of the enamel 
 organ, the odontoblasts do not make their appearance until the 
 papilla has assumed certain proportions, this about correspond- 
 ing to the size and form of the dentin of the future tooth. Imme- 
 diately beneath the layer of odontoblasts appears a zone almost 
 devoid of cells. This is followed by a district in which the cells 
 are quite numerous, and finally when the central portion of the 
 papilla is reached the cells are again few in number and widely 
 scattered. For the most part the cells in the interior of the 
 
3o6 ANATOMY. 
 
 papilla are spindle-shaped or stellate, having rounded nuclei 
 about which there is a small amount of protoplasm which pene- 
 trates the intercellular substance by numerous hair-like processes. 
 
 The Odontoblasts, — These are club-shaped or flask-shaped 
 cells, each provided with a large nucleus which usually assumes 
 the outline of the enlarged end of the cell which is directed 
 toward the interior of the papilla. From the opposite end of 
 the cell, or that directed toward the enamel organ, and in close 
 proximity to its concave surface, one or more protoplasmic 
 processes are given off. These persist and are finally encap- 
 suled within the calcified dentin, forming the dentinal fibers. 
 These cells are very closely associated, so much so, in fact, that 
 their enlarged extremities are almost or quite in actual contact, 
 more or less space existing between the constricted portion of 
 the cells as they pass toward the surface. 
 
 Germs for Permanent Molars. — Reference has been made 
 to the fact that the enamel organs for the deciduous teeth are 
 o-iven off from the tooth-band at a point somewhat distant from 
 its free margin, so that the tooth-band is continued beyond the 
 primitive enamel germ, this free margin of the band afterward 
 generating the enamel organ for the succedaneous tooth'. As 
 the twelve permanent molars are not succedaneous teeth, some 
 other means must be provided for their development. 
 
 Opinions of various writers upon this subject are somewhat 
 conflicting. The theory is advanced by some that as the jaw 
 increases in length the tooth-band and lamina primarily pro- 
 vided for the deciduous teeth are extended backward, first giv- 
 ing off a bud for the first permanent molar ; at a somewhat 
 later period, and with the increase in the growth of the jaw, an 
 additional bud is generated for the second molar, the third 
 molar being provided for in a like manner. Another theory, 
 and one generally accepted as correct, is that the cords for the 
 permanent molars spring individually and directly from the 
 subepithelium. There may be found an exception to this in 
 the case of the first permanent molar, which sometimes appears 
 to have its origin from the distal follicular wall of the second 
 deciduous molar. Whatever theory be accepted in regard to 
 the genesis of these permanent organs, the process of develop- 
 
DEVELOPMENT OF THE TEETH. 307 
 
 ment after the appearance of the primary bulb or enamel germ 
 is identical with that of the deciduous teeth. 
 
 The Dental Follicle, or Tooth-sac. — During the early 
 life of the tooth-germ, both the enamel organ and the dentin 
 papilla are differentiated from the surrounding parts by dissimi- 
 larity of structure only, but as development proceeds, a more 
 definite separation appears between the tooth-generating organs 
 and the general tissues of the primitive jaw, this separating 
 medium being known as the dental follicle. The term "follicle" 
 is only one of a number applied to these parts, "dental saccu- 
 
 Calcified Dent 
 
 Dentin Papilla, 
 or Tooth-pulp ;v 
 
 Wall of Follicle Sfe^; 
 
 Fig. 190. — Developing Tooth about the Fourth Fetal Month. Appearance of 
 THE Tooth-follicle. 
 
 lus," "tooth-sac," and other appellations being employed with 
 equal significance. By some writers it is customary to apply the 
 term " follicle " up to the period of complete closure, the term 
 "sac" or "sacculus" being employed after that time. There 
 appears, however, to be little foundation for such a distinction, 
 the terms being synonymous. Again, the follicle is frequently 
 referred to as meaning the sac and its contents, but this usage 
 is a misapplication of the term. There appears to be no well- 
 founded reason why the follicular wall or sac should not be 
 
3o8 ANATOMY. 
 
 referred to as such, regardless of the formative organs within. 
 As to the development of the tooth-foUicle, it appears to be a 
 generally accepted theory that at a very early period there is 
 developed from the base of the papilla cells which, differenti- 
 ating, form the walls of the follicle. By this growth of cells the 
 periphery of the papilla is first surrounded, and this step is soon 
 followed by an extension of the cellular structure In the direction 
 of the surface epithelium, to the deep layer of which the cells 
 become firmly attached, and in so doing inclose the enamel 
 organ, which hangs like a hood over the extremities of the 
 
 Calcified Dentin 
 Enamel 
 
 Outer Enamel 
 Epithelium 
 
 Fig. igi. — Development of Deciduous Incisor, from Human Fetus. — 
 ■ {After Gysi.) 
 
 papilla. The tissue thus formed from the base of the dentin 
 germ Is continuous with and similar in its origin to the pulp- 
 substance. The primitive tooth-germ, during the formation of 
 the follicular wall, is found swinging in a membranous pocket, 
 being supported by the epithelial band, which. In turn. Is 
 attached to the oral epithelium ; but as the walls Increase and 
 completely Inclose the germs, which Is accomplished iabout the 
 fourth fetal month, the epithelial band is broken and the second 
 or saccular stage of tooth-development Is reached. The walls 
 of the follicles are made up of two layers ; the outer layer 
 
DEVELOPMENT OF THE TEETH. 309 
 
 is dense and firm, and finally becomes the dental periosteum ; 
 the inner layer is thin, frail, and in the recent state some- 
 what transparent, and at an advanced period assists in the 
 formation of the cementum. 
 
 Having thus briefly described the primary stage of tooth-de- 
 velopment, the careful study of which can only be pursued with 
 the aid of the microscope, we will now pass to the secondary or 
 saccular stage. By the introduction of a number of illustrations, 
 prepared from original dissections by the author, this phase of 
 the subject will be readily comprehended. 
 
 Before continuing the subject of tooth-development, it will be 
 eminently proper to briefly describe those parts directly con- 
 cerned in the process. At a very early period of fetal life we 
 
 That Part of Cartilage not yet Ossified. 
 
 Head of Malle 
 
 Handle of Malleus 
 
 Ossified MandiWe 
 
 Fig. 192. — Developing Mandible, Three-month Fetus. 
 
 find preparations are being made for the development of the 
 maxillary bones. That these are about the first bones to be 
 called into functional activity accounts in a measure for their 
 very early development. The osteoblastic activity in the inter- 
 cellular substance destined to become the inferior maxilla begins 
 about the middle of the second month of fetal life, while at a 
 somewhat later period a similar action takes place in the region 
 of the superior maxilla. A detailed description of the body of 
 these bones having been given on another page, it will not be 
 repeated here, but to that portion which gives lodgment to the 
 tooth-germs, and which in a measure is controlled by their pres- 
 ence, some attention must be given, and for this purpose the 
 mandible will principally be used. 
 
3IO 
 
 Figure 192 represents the lingual face of the lower jaw after 
 removal from a three months' fetus. Attached to it is the re- 
 maining portion of Meckel's cartilage, which by this time is 
 much wasted. It will be recalled that this cartilaginous 
 band appears in the mandibular processes before the begin- 
 ning of the second fetal month, being formed in two distinct 
 halves, the free ends of which finally unite at the median line, 
 forming a continuous support or framework, about which ossifi- 
 cation takes place. At a corresponding period, and in a similar 
 manner, two like processes are thrown out for the superior 
 maxillae, but, unlike Meckel's cartilage, these do not unite at the 
 median line, but stop short of this, the space thus resulting 
 being provided for by two additional processes, which shoot 
 
 down from the region of the fore- 
 head and provide for the develop- 
 ment of the intermaxillary bones. 
 About the middle of the second 
 month a center of ossification ap- 
 pears in the neighborhood of the 
 future mental foramen, quickly fol- 
 lowed by others at the symphysis 
 and at the angle. These secondary 
 centers soon unite with the primary 
 one, and by the end of the second 
 fetal month the osseous contour of 
 the primitive jaw is established. 
 While ossification takes place in the 
 membrane surrounding Meckel's 
 cartilage, the cartilage itself does not appear to be directly 
 concerned in the process, and by the sixth or seventh fetal 
 month the mandibular portion completely disappears, while that 
 portion near the tympanum is ossified into the malleus. That 
 portion of the bone which forms above Meckel's cartilage and 
 the inferior dental nerve is that which finally gives support to 
 the tooth-germs. This cartilage is not confined to the human 
 species, but is the common heritage of reptiles, rodents, birds, 
 and fishes, in all of which it gives support to the developing 
 lower jaw. 
 
 Fig. 193. — Evolution of the 
 Mandible from the Third Fetal 
 Month to Birth, Two-thirds 
 Actual Size. 
 
DEVELOPMENT OF THE TEETH. 
 
 3" 
 
 Figure 193 represents the evolution of the mandible from the 
 middle of the third fetal month to the time of birth. It will be 
 observed that during this interval there is a gradual increase in 
 the size of the bone, but little alteration in its contour. By a 
 constant and gradual osseous deposit about the distal extremity 
 of the bone its length is increased to accommodate the additional 
 teeth as they make their appearance. While the external form 
 of the bone shows but slight variation during this period, the 
 internal structure, or that wherein the tooth-germs lie, is under- 
 going a complete transformation. 
 
 Figure 194 is illustrative of these changes; beginning with 
 a simple groove, or gutter, into which the tooth-follicles hang, 
 the follicles exerting a con- 
 trolling influence over its 
 form. Next comes the ap- 
 pearance of septa between 
 the anterior follicles, which 
 at this period are some- 
 what irregularly placed in 
 the arch, followed in a few 
 weeks by a well-defined 
 partition between the cusp- 
 ids and molars, until final- 
 ly, at birth, each follicle is 
 inclosed in its individual 
 crypt, with the single ex- 
 ception of the second mo- 
 lar, in which the distal septum, or that which is to separate it 
 from the permanent first molar, has not yet made its appear- 
 ance. As the tooth-follicles increase in size, by the devel- 
 opment of the teeth within, they become more perfectly in- 
 closed in the bony vaults, the sides of the alveolar walls 
 arching over and almost completely inclosing the developing- 
 teeth. Figure 195 shows the lower jaw of a seven-months-old 
 child embodying the condition above referred to. No sooner 
 have the crypts grown to this extent, than the resorptive action 
 produced by, or provided for, the advancing crowns speedily 
 results in their downfall, to be again built up with the evolution 
 of the permanent teeth. 
 
 Fig. 194. — Evolution of the Mandible 
 FROM Third Fetal Month to Third Month 
 AFTER Birth. 
 
About the first visible sign of preparation for tlie develop- 
 ment of the teeth, other than that made apparent by dissection, 
 may be observed as early as the beginning of the third fetal 
 month, when, upon opening the cavity of the mouth and looking 
 
 nd Periosteum Lifted Up 
 
 Fig. 195. — Inferior Maxilla of Seven-months -old Child. 
 
 upon the palate, a well-defined infolding of the epithelial 
 eminence will be seen. In figure 196 this condidon is shown 
 by a dissection through the oral cavity of a four months' fetus, 
 the outer fold being that of the cheeks and lips, while within are 
 the hard palate and primitive alveolar ridge. The mouth at this 
 
 Labiodental Space Labial Fold 
 
 Fig. 196. — Section Through the Mouth of Four-month Fetus. 
 
 period has passed the rudimentary state, the transverse plates 
 which contribute to the formation of the hard palate having 
 approached each other until the oral and nasal cavities, hereto- 
 fore existing as a single buccal cavity, have become separate 
 
DEVELOPMENT OF THE TEETH. 
 
 and distinct. The infolding of the oral epithelium, as outlined 
 on the summit of the primitive alveolar ridge, — the primitive 
 dental furrow, so called, — marks the position of the tooth-band, 
 from which are given off the incipient tooth-bulbs. For the 
 purpose of further investigation, a dissection of these parts was 
 made and the maxillary bones removed, after which they were 
 divested of their fibrous covering, including the periosteum. 
 That portion which overlies the palatal processes was readily 
 lifted in one sheet, while that upon the facial surface was sepa- 
 rated at the median line and stripped independently of the other 
 (Fig. 197). The removal of these tissues is readily accomplished 
 until the margins of the partly 
 formed alveoli are reached. Here 
 the periosteum dips down into the 
 various crypts, and serves as a 
 lining membrane for them, and 
 probably contributes fibres to the 
 outer layer of the follicular walls. 
 After advancing thus far, the de- 
 tached tissues may be grasped, 
 and by careful manipulation the 
 tooth-follicles containing the form- 
 ative organs removed from their 
 respective vaults and turned over 
 for examination. 
 
 Figure 198 shows the result of 
 such a dissection. On the left, the palatal plates and alveolar 
 walls of the divested bones may be observed; on the right, is the 
 fibrous covering, which has been turned completely over after re- 
 moval from the bones, having firmly attached to it the ten tooth- 
 follicles for the deciduous teeth. If this dissection be made with- 
 out the precaution of lifting the periosteum, the follicles would 
 not cling to the oral membrane with sufficient tenacity to permit 
 of their ready removal. It may be of some interest to note that at 
 this early period the position of the follicles containing the germs 
 for the lateral incisors is that which the tooth is forced to occupy 
 up to and frequently beyond the eruptive period, being crowded 
 within the tooth-line by the central and cuspid follicles, in con- 
 
 Oral Mucous Membrane 
 
 Fig. 197. — Superior Fetal 
 Maxilla, showing manner of 
 Dissection to Expose Tooth- 
 sacs. 
 
sequence of which the lateral crypts are thrown well into the 
 palatal plates. 
 
 Figure 199 represents the sacs broken down, exposing to 
 view the dentin papillae, or those structures destined to become 
 
 Tooth-foUicles 
 
 Maxilla Oral Mucous Membrane 
 
 Fig. 198. — Dissection upon Superior Maxilla, Fourth Fetal Month, Exposing 
 Tooth-follicles. 
 
 the tooth-pulps. The position which these occupy in the 
 illustration is exactly the reverse from that which they assume 
 when in position in the follicle, being thus reversed that a better 
 idea of their shape may be obtained. Prior to the twelfth or 
 thirteenth week of fetal life this incipient bulb or papilla is with- 
 
 Oral Mucous Meuibr; 
 
 e, Turned Completely Ov 
 Fig. 199. 
 
 out definite form ; but by the latter period each papilla begins 
 to assume the contour of the future tooth-crown, as faintly out- 
 lined in the illustration, those of the incisors presenting the 
 angular form of the future cutting-edge, the cuspids that of the 
 
DEVELOPMENT OF THE TEETH. 
 
 31S 
 
 single cone, while the coronal extremities of the molars are 
 represented by outlines corresponding to the future cusps and 
 marginal ridges. Besides the dentin papilla, there is contained 
 within the follicular walls the organ which later on is productive 
 of the enamel, but which up to this time has been actively 
 
 Oral Mucous Membrane and Periosteum Dissected from Mandible 
 
 Attachment of Follicle to Oral Membrane (Enlarged One-third) 
 
 Fig. 200. — M.a.nner of Dissection to Expose Tooth-sacs. 
 
 engaged in molding the tooth-form as outlined by the papilla. 
 To return to the tooth-follicle, the dissection in this instance 
 being upon the lower jaw of a four months' fetus. Figure 200 
 shows the mandible removed and the dissection carried to the 
 
 Tooth-follicles Oral Membrane 
 
 Fig. 201.— Tooth- follicles Removed from Mandible, Fourth Fetal Month. 
 
 point at which the follicles may be lifted from their bony encase- 
 ments, this being accomplished by an incision along the base ot 
 the bone, followed by a stripping of the membrane first from 
 the facial and then from the lingual side of the bone. When 
 these two flaps reach the margin of the crypts, they are firmly 
 
3i6 ANATOMY. 
 
 grasped and the follicles removed from their sockets, as illus- 
 trated in figure 201. 
 
 At the beginning of the saccular stage of development the 
 form of the future tooth-crown is well outlined by the dentin 
 papilla, which in figure 202 is brought into view by a dissection 
 of the walls of the follicles shown in figure 201 without breaking 
 the attachment existing between the two. As in the case of the 
 follicle, much confusion of terms in regard to this structure 
 exists, the "dentin bulb," the "pulp," "dentin germ," and the 
 " papilla " being used ad libitum, without apparent regard for the 
 structural changes which are continuously affecting the organ. 
 It will, therefore, be proper to simplify this conglomeration of 
 
 Space Occupied by Oral Mucous 
 Enamel Organ Membrane 
 
 Follicular Wall 
 
 Dentin Papillae 
 
 to Beginning 
 of Calcification 
 
 Fig. 202. — Tooth-follicles shown in Figure 201 Opened. 
 
 terms by a classification appropriate to the various stages of 
 development. The term "dentin papiUa" will best describe this 
 part of the tooth-germ up to the time of beginning of calcifica- 
 tion, subsequent to which the term, "pulp " should be employed. 
 As previously stated, the enamel organ, until this period, has 
 been principally devoting its energies to the molding of the 
 tooth-form, and it is not until this model, as represented in the 
 papilla, is complete that the process of calcification begins. 
 About the fourth fetal month preparations for the calcification 
 of the deciduous teeth are begun by the development of the 
 odontoblastic cells for the dentin, which first make their appear- 
 ance on the periphery of the dentin papilla, the summits of the 
 
DEVELOPMENT OF THE TEETH. 317 
 
 various cusps in the molars and the future cutting-edges of the 
 incisors being first affected. This phenomenon is soon followed 
 by the appearance of the ameloblastic cells for the enamel, 
 which establish themselves in the internal epithelial layer of 
 the enamel organ. 
 
 Figure 203 is prepared from a dissection made in a manner 
 similar to that shown in figure 199, but at a period about a 
 month later, being from the superior maxilla of a five months' 
 fetus. The dissection shows the extent of calcification at this 
 period, which process also defines the position of the odonto- 
 blastic cells upon the extremity of the papillse. In the incisors 
 (one of which was lost in the preparation of the specimen) the 
 
 Calcified Caps Tooth-pulp Maxilla: 
 
 Fig. 203 
 
 dentin may be seen capping the cutting-edges. The cuspids in this 
 subject have not yet begun to calcify, although it is not unusual 
 to find the cusp of this tooth receiving its lime-salts at this early 
 period. In the molars the summits of the various cusps, as well 
 as a portion of the various ridges descending therefrom, are 
 undergoing the change produced by the impregnation of the 
 lime-salts. It is quite probable that these delicate caps are at 
 this time composed of dentin alone, the calcoglobulin which 
 precedes the enamel calcification forming somewhat later. 
 From this time forward the pulp undergoes a gradual trans- 
 formation as to size and form, and there is likewise a change in 
 its cellular construction on those parts adjacent to the calcific 
 action. While the outline of the pulp is gradually changing, its 
 
31 8 ANATOMY. 
 
 original form is permanently recorded upon the periphery of the 
 dentin cap, which, when once formed, is immutable, all additions 
 taking place from within. 
 
 Figure 204 illustrates the result of a dissection upon the lower 
 jaw of the same subject, disclosing practically the same condi- 
 
 Calcified Dentin Oral Mucous Membrane 
 
 Space Occupied by 
 Enamel Organ 
 
 Fig. 204. — Tooth-follicles Opened, Exposing Dentin Papillae and Beginning of 
 Calcification, Fifth Fetal Month. 
 
 tions, with the exception of the sac containing the developing 
 cuspid, which was found with a slightly calcified cap of dentin. 
 This slight variation between the development of the upper and 
 lower teeth is one that is present in nearly every instance, the 
 latter being somewhat in advance of the former. 
 
 In figure 205 the tooth-pulps, with their primitive cappings 
 
 Fig. 205. 
 
 of dentin, have been removed from the follicles, and a better 
 opportunity of studying the relations between the two parts is 
 presented. By the conversion of the coronal extremities of the 
 dentin papilla into odontoblasts, and their active calcification, 
 some positive union between the two parts might be expected. 
 
DEVELOPMENT OF THE TEETH. 319 
 
 On the contrary, the dentin caps are readily removed, leaving 
 the pulp beneath without the slightest rupture, so that we find 
 calcification is not a secretory or excretory metamorphosis, but 
 that the change takes place within the substance of the papilla 
 itself, whereby it is altered from an organic to an inorganic 
 substance. 
 
 The next dissection was one upon the mandible of a six 
 months' fetus. Figure 206 shows the tooth-follicles removed 
 from the partially formed bony crypts in which they have been 
 incased. At an early period of fetal life, and at a time prior to 
 the completion of the tooth-follicles, there is deposited beneath 
 the tooth-germs a thin layer of bone, which at once begins 
 to assume the form of the partially developed follicular 
 walls. As the growth of the follicle proceeds, there is a corre- 
 
 Liiigual Surface of Mandible 
 Fig. 206. 
 
 sponding increase in the osseous deposit, the alveolar walls 
 extending about and accommodating themselves to the mem- 
 branous sacs. Thus we find in this portion of the maxillary 
 bones a feature peculiar to itself — that of a condnuous trans- 
 formation from its earliest inception to the adult period, first 
 developing about the temporary tooth-sacs and completely 
 incasing them, which is speedily followed by complete resorption 
 of the walls, again followed by a rebuilding during the evolution 
 of the permanent teeth, and again swept away with the loss of 
 these organs. Figure 207 illustrates the opposite side of the 
 same jaw, with its outer or facial plate removed, together with 
 the intervening septa. The follicles are opened, and the extent 
 of calcification at this period (six months) made apparent. The 
 
320 ANATOMY. 
 
 pulps and calcified caps are approximately as found when 
 dissected, save a slight settling of all the parts. The incisors 
 have calcified to about one-third their full coronal length ; the 
 unicusped contour of the cuspid has been established, as shown 
 by the deposit of the lime-salts upon its summit, and the 
 upbuilding of the mesial and distal cutting-edges. The first 
 
 Follicular Wall Calcified Caps Oral Mucous Membrane 
 
 Dentin Papilla, 
 First Perma- 
 nent Molar 
 
 Tooth-pulps 
 
 Fig. 207. 
 
 molar has about completed its occlusal surface, and, while the 
 cusps of the second molar are nearing completion, there is a 
 lack of union in the central and distal fossse. Immediately 
 posterior to the second deciduous molar, the sac containing 
 the formative organs for the first permanent molar is shown 
 opened, exposing to view the dental papilla, which at this early 
 
 M ** U^ 
 
 period has assumed the form of the future tooth-crown, and 
 calcification is about to begin. Figure 208 illustrates the extent 
 of calcification in the deciduous teeth at the sixth fetal month. 
 As the growth of the teeth proceeds, it will be observed that 
 the angularity which originally accompanied the calcifying caps 
 of the molars is gradually disappearing, as is also the tri- 
 
DEVELOPMENT OF THE TEETH. 321 
 
 tubercular form of the incisors and cuspids, this change being 
 brought about by the deposition of enamel to the parts. 
 
 Figures 209 and 210 show the calcified caps removed from 
 the pulps, and so arranged that both their external and internal 
 anatomy may be studied. Prior to this time there has been but 
 little alteration in the form of the dentin pulp, only a gradual 
 decrease in its size being noted ; but now we find it being 
 divested of many of its angles, particularly those which origi- 
 
 FiG. 2og. 
 
 nally served as a basal form for the coronal extremities of the 
 future tooth. With the disappearance of these the concavity 
 within the cap is slowly assuming the form of the future pulp- 
 chamber. 
 
 That a better understanding of the saccular stage of tooth- 
 development might be had, a transverse section was made 
 through the molar follicles, as shown in figure 211. In this the 
 
 attachment of the follicular walls to the deep epithelial layer is 
 visible, while within the walls is the enamel organ, the calcified 
 dentin, and the tooth-pulp. As previously stated, the enamel 
 organ is seen suspended above and forming a hood-like invest- 
 ment to the calcifying structure. This organ not only over- 
 hangs the occlusal surface of the tooth-crown, but completely 
 envelops the sides of the calcified cap and dentin pulp. Previous 
 to the beginning of calcification the enamel oroan is in close 
 
proximity to the dentin papilla, the original form of the latter 
 being represented by the calcified dentin. 
 
 We have now arrived at that period of fetal existence when it 
 is possible to study the macroscopic development of the perma- 
 
 Enamel Organ 
 
 Follicular Wall 
 
 Tooth-pulp Floor of Tooth-follicle 
 
 Fig. 211. — Dissection Showing Pulp, Calcified Cap, and Enamel Organ. 
 
 nent first molar. Figure 212 represents a section of the lower 
 jaw of a six months' fetus, and displays not only the sacs of the 
 deciduous teeth, but also that of the permanent first molar. In 
 most respects the evolution of this tooth is similar to that of the 
 temporary organs, having its origin from the deep epithelial 
 layer, either directly or by continuation of the tooth-band 
 backward. Preparations for its growth are begun as early as 
 
 the third fetal month, at which 
 Oral Mucous Membrane time the enamel organ is given 
 
 off, and thereafter the develop- 
 mental process is identical with 
 that of the deciduous teeth. 
 
 There is one structure, how- 
 ever, intimately connected with 
 the development of the perma- 
 nent teeth not found in connec- 
 FiG. 212. tion with the deciduous organs — 
 
 the gubernacuhun, or leading cord. 
 Figure 213 represents another section of a six months' fetal 
 mandible, with the dentin papilla for the permanent first 
 molar turned out from the follicle after being rolled from its 
 bony incasement. Attached to the apex of the tooth-sac (which 
 
DEVELOPMENT OF THE TEETH. 323 
 
 has been turned back), and leading- from it to the epithelium of 
 the jaw, is the gubernaculum. This fibrous structure was at 
 one time thought to be directly concerned in the development 
 of the tooth. Although this is denied at present, little is 
 said in regard to its function, but it undoubtedly serves the 
 purpose of directing the tooth to that position which it should 
 occupy in the jaw, and where the least resistance to its eruption 
 is formed by the foramen which the cord has established. Each 
 of the permanent teeth is provided with a similar membranous 
 cord, an illustration and more complete description of which will 
 follow later on. 
 
 We have now arrived at a period when the subject under 
 
 Oral Mucous Membrane Gubernaculum 
 
 II 
 
 i^^ 
 
 
 Dentin Papilla 
 Fig. 213. 
 
 consideration naturally becomes of deeper interest. I refer to 
 that time when the being changes from a complex dependent 
 condition to one of self-providing independence. Previous to 
 the time of birth the teeth appear to be but little disturbed by 
 certain morbid conditions which might be present in the parent, 
 and from their earliest inception up to this period their develop- 
 ment proceeds with but little interruption and with much regu- 
 larity. Figure 214 illustrates the condition of the deciduous teeth 
 at birth ; the central incisors are calcified externally to the cer- 
 vical line, the lateral incisors to a point corresponding to the 
 summit of the palatocervical ridge ; the cuspids have advanced 
 somewhat beyond the angles of the crown, while the molars have 
 their crowns calcified to about one-half their completed length. 
 
With all this progress as represented by the external contour 
 of the tooth-crowns, the internal form appears to be somewhat 
 slow in assuming the shape of the future pulp-chamber. From 
 the beginning of the saccular stage of development up to the 
 time of birth there is but little increase in the diameter of the 
 tooth-sac, but there occurs a gradual increase in its length. 
 
 Fig. 214. — Deciduous Teeth at Birth. (Reflected picture.) 
 
 Figure 215 shows the mandible from a child one week old, with 
 the greater part of the external or facial surface of the bone 
 removed, exposing not only the sacs containing the developing 
 deciduous teeth, but also that of the permanent first molar. 
 The relation of the sacs to the inferior dental canal is apparent, 
 as well as the firm attachment of the follicular walls to the oral 
 membrane. In figure 216 the tooth-sacs have been dissected 
 
 Fig. 215. 
 
 and the pulps removed from the calcified caps, presenting an 
 additional illustration of the amount of dentin deposit at this age- 
 To further illustrate the size and form of the pulp as compared 
 with the calcified cap at birth, a transverse incision was made 
 through the left superior maxilla, at a point corresponding to 
 the base of the pulp, as shown in figure 217. The calcified 
 
DEVELOPMENT OF THE TEETH 
 
 325 
 
 parts remain in position resting against the remaining portion 
 of the enamel organ, while the pulps are dislodged and may be 
 observed resting upon the incised surface. In this illustration 
 
 Dentin Papilla of 
 Permanent First 
 Molar 
 
 the dentin papilla for the first permanent molar is also seen, 
 being supported by the walls of the follicle, which in turn are 
 attached to the oral epithelium by the gubernaculum. It may 
 
 Calcified Caps, Resting against 
 Enamel Organ 
 
 Tooth-pulps Rolled Out 
 
 Section of Superior Ma 
 
 Pulp of Permanent First Molar 
 Fig. 217. 
 
 also be noted that those parts of the pulp corresponding to the 
 cusps and marginal ridges show a decided convergence of the 
 surface toward the center. 
 
326 
 
 ANATOMY. 
 
 Reference has been made to the formation of the follicular 
 walls by a differentiation of cells, which at an early period are 
 given off from the base of the papillae, and to the continuity of 
 the two structures. Figure 218 was prepared for the purpose 
 of showine these intimate relations. The sides of the sacs 
 
 Dentin Papilla for 
 
 i 
 
 1 
 
 Molar 
 
 Papilla 
 Calcified Cap 
 
 
 Walls of Tooth- 
 
 
 
 
 f5 
 
 were opened and turned back ; the calcified tooth-caps with pulps 
 in position were grasped and given several revolutions, thus 
 twisting the remaining portion of the walls, the floor of which is 
 seen as a continuous structure given off from the pulp and con- 
 necting it with the epithelium of the jaw. 
 
 PREPARATIONS FOR THE DEVELOPMENT OF THE 
 PERMANENT TEETH. 
 A little before the time of birth sufficient advance has been 
 made in the development of the permanent teeth to permit a 
 study of their relations with the temporary organs. The early 
 preparation for the growth of these teeth was for a long time 
 a subject of much controversy, some writers advancing the 
 theory that the buds for the permanent teeth were produced or 
 given off from the sacs of the temporary teeth ; others con- 
 tending that the cords were derived from the remnants of the 
 
DEVELOPMENT OF THE PERMANENT TEETH. 327 
 
 primitive cords immediately after their rupture. The theory 
 now generally accepted is that the cord is given off from the 
 primitive cord at a point in close proximity to its attachment to 
 the deciduous enamel organ. This can only apply to those 
 teeth which are succedaneous, and, therefore, does not include 
 the permanent molars, as heretofore stated. Whatever theory 
 be accepted in regard to the genesis of the permanent teeth, 
 there can be no mistake in regard to that part of the process 
 which we are permitted to ocularly investigate. I shall, there- 
 fore, proceed to describe the position and contents of the per- 
 manent tooth-sacs at birth. Figure 219 presents the result of a 
 vertical dissection through the superior maxillary bones, the 
 
 Guberiiaculuni Tooth-sac of Receding Permanent Tooth 
 
 Fig. 219.— Section through Superior Maxill.«, Sixth Month after Birth. 
 
 inner surface of the right maxilla being exposed to view. 
 Many of the frail processes, particularly those entering into 
 the construction of the nasal cavities, were lost during the 
 preparation of the specimen, the whole purpose of the dissec- 
 tion being to show the sac of the permanent incisor and its 
 relationship to its predecessor. By this time calcification in the 
 deciduous incisor has so far advanced that the contour ot the 
 tooth-crown may be plainly outlined through the walls of the 
 sac. Resting against the palatal concavity of the crown of the 
 temporary incisor is the sac containing the formative organs 
 for its permanent successor. This permanent tooth-sac does 
 not long remain in such close proximity to the deciduous tooth- 
 
328 ANATOMY. 
 
 crown, for as the latter advances toward the surface of the gum 
 the former recedes and is soon inclosed in a separate crypt, 
 which, were it not for the gubernacular foramen, w^ould com- 
 pletely inclose it. Figure 220 represents a section of the left 
 superior maxilla, introduced at this point for the purpose of 
 showing the position of the foramina for the gubernacula. 
 These may be observed immediately posterior to the incisor 
 and cuspid teeth. At birth these foramina do not exist as such, 
 the partially formed vaults containing the sacs for the permanent 
 teeth appearing as an extension of the temporary crypts in a 
 palatal direction ; but as the temporary teeth advance and the 
 
 Foramina for Gubernacula 
 
 permanent teeth recede, the roof of the crypt is completed, and 
 the foramen established by the presence of the gubernaculum. 
 This extension of the temporary crypts is more clearly demon- 
 strated in figure 221, which represents one side of the lower 
 jaw at birth with the partially calcified deciduous teeth in posi- 
 tion in the bone. Suspended above this is the gum, which has 
 been dissected from the bone, having attached to its under 
 surface the sacs for the permanent teeth. Those for the 
 incisors are particularly well defined and their place of lodg- 
 ment in the bone readily noted. In the case of the cuspid, both 
 
DEVELOPMENT OF THE PERMANENT TEETH. 329 
 
 the deciduous tooth and the permanent tooth-sacs are in posi- 
 tion in the crypt. The cords which support the incisors are 
 somewhat lengthened from the weight of the sacs, the guber- 
 nacula not assuming this thread-like form until the permanent 
 sacs have further receded. 
 
 Figure 222 shows the result of a dissection upon these 
 
 ; for Permanent In 
 
 Deciduous Teelh in Bony Crypts 
 Fig. 221. 
 
 permanent tooth-follicles. The dentin papillae of the various 
 teeth are seen in a reversed position, with the follicular walls 
 attached to their bases. At this period the papillae for the 
 permanent incisors may be compared to the tail of a fish, being 
 perfectly transparent over its free extremity, which feature is 
 
 Oral Mucous IMembrane 
 
 Follicul 
 Wrc 
 
 arWall.Tur 
 ug Side Out 
 
 Denti 
 
 led 
 
 -^l 
 
 r"^ 
 
 Papilla for Perma 
 Molar 
 
 
 ,Pap 
 
 ilia: for Permj 
 
 nent Teeth, Upside Down 
 Fig. 222. 
 
 
 gradually lost as its thickened base is approached. The fish-tail 
 appearance is further represented by the division of the free 
 extremity into three distinct parts, each of which provides a 
 separate point of calcification. The cuspid papilla is missing, 
 and the bicuspids have advanced little beyond the form of the 
 
primitive bulb. The first molar is shown with the full diameter 
 of the crown represented by the pulpal mass, and the tips of the 
 cusps are already beginning to take on the calcific action. 
 
 Tooth-sacs oi Permanent Teeth 
 
 Lingual Surface ol Mandible 
 
 Fig. 223. 
 
 Toolh-sacs of Deciduous Teeth 
 
 Tooth-sac of Permanent Tooth 
 
 Fig. 224.— Same as Figure 223, Except on Upper Jaw. 
 
 A further illustration of the progress of the development of 
 the permanent teeth and their relation to the deciduous organs 
 may be seen in figure 223, the dissection in this instance being 
 
DEVELOPMENT OF THE PERMANENT TEETH. 
 
 331 
 
 upon the lower jaw of a one-month-old child. The membrane 
 has been lifted from the bone with the tooth-sacs attached to it. 
 Immediately posterior to the sacs containing the crowns of the 
 temporary incisors and cuspids are those for their corresponding 
 successors, the papillae of which have already assumed the 
 tubercular outline of the future cutting-edge. While the per- 
 manent tooth-sacs are distinctively independent pouches, there 
 appears, nevertheless, to be a well-established fibrous connec- 
 tion existing between the outer layer of the two follicular walls. 
 This fibrous union is gradually broken as the permanent sacs 
 recede and become incased in their own vaults. 
 
 While the permanent tooth-sacs are generally referred to as 
 " receding," it is a question if this term is fully justified. 
 
 Tooth-sacs of Decidu 
 
 Periosteum of Hard Palate 
 
 Fig. 225. — Tooth-follicles for Deciduous and Permanent Teeth, Three Months 
 AFTER Birth. 
 
 While the follicles do not remain in close relation with their 
 predecessors, the change in the relative position of the two is 
 principally brought about by the advance in the deciduous sacs, 
 this forward movement being accompanied by a marked growth 
 of the bone in the direction of the future alveolar ridge, thus 
 leaving the permanent tooth-sacs well buried in the substance 
 of the jaw. 
 
 Figure 225 represents the result of a dissection upon the 
 superior maxillae of a three-months-old child. The mucous mem- 
 brane covering the hard palate, together with the periosteum. 
 
332 
 
 ANATOMY. 
 
 has been dissected from the bones and turned over for exam- 
 ination. The tooth-follicles for all the deciduous teeth, as well 
 as those of the succedaneous permanent organs, may be ob- 
 served firmly attached to the fibrous tissue. The permanent 
 incisor sacs at this age are almost equal in size to those of their 
 predecessors, and the dentin papillae within possess a mesio- 
 distal diameter almost equal to those of the calcified temporary 
 caps. The sacs containing the germs for the permanent cuspids 
 and bicuspids are somewhat diminutive, but the enamel organs 
 within are already molding the contour of the future tooth- 
 crowns upon the dentin papillae. 
 
 By the beginning of the second month after birth calcification 
 in the crowns of all the deciduous teeth is about complete, and 
 preparation for the growth of the roots is under way. While 
 
 at this period the tooth-crowns may be said to be almost com- 
 pletely calcified, this does not apply to the interior of the 
 crowns, the deposit of dentin internally being a continuous 
 process, resulting in a gradual reduction in the capacity of the 
 pulp-cavity. It is also quite probable that the enamel organ is 
 somewhat active up to the eruptive period, and, if this be true, 
 the enamel covering of the crown is not complete until this 
 time. Whatever be the condition in the crowns, the time for 
 the formation of the roots has arrived, and it is principally 
 through the activity of the tooth-pulp that they are generated. 
 We have seen that the contour of the tooth-crown was first 
 molded upon the dentin papilla ; so it is with the tooth-root : by 
 a gradual elongation of the sac, accommodations are afforded 
 the tooth-pulp for a corresponding growth. As the pulp 
 
DEVELOPMENT OF THE PERMANENT TEETH. 333 
 
 lengthens out toward the future apex of the root, it is molded 
 to the root-form, and calcification takes place by the generation 
 of odontoblastic cells upon the periphery of this organic root- 
 form. 
 
 While the process of root-formation in the single-rooted tooth 
 may be readily comprehended, the bifurcation or trifurcation 
 of the molar roots presents a complication which calls for special 
 reference. Figure 226 will assist in e.xplaining this phenome- 
 non. In the illustration three deciduous molar crowns are 
 shown, two of which are incased in their tooth-sacs, the third 
 being- stripped of this membrane. The view is directly upon 
 the base of the tooth-sacs, immediately beneath which is the 
 base of the pulp. Up to this period the odontoblastic cells have 
 been generating about the occlusal surface and lateral walls of 
 the crown only, but now an accumulation of these cells is to be 
 found upon the base of the pulp, lining up in the position of 
 the future root-walls. This structural change is faintly out- 
 lined in the illustration. By this inward extension of the odon- 
 toblastic cells from various points about the margins of the 
 pulp, and their union near the center of the mass, provision is 
 made for the calcification of the various roots, which process is 
 considered separately by an extension and molding of the pulp 
 into two or more divisions. 
 
 Calcification of the Cementum. — While the dentin of the 
 root is derived from the tooth-pulp, the external covering of the 
 root (the cementum) is generated from another source. In 
 every respect cementum is closely allied to bone, and we find 
 its development provided for in a similar manner. As stated in 
 another part of this chapter, the tooth-sac is made up of an 
 outer and an inner layer, both of which are rich in blood- 
 vessels. These membranous walls continue to invest the roots 
 of the teeth during their upbuilding. The outer layer of the sac 
 remains as a permanent structure placed between the root and the 
 alveolar walls, forming the alveolodental membrane, while upon 
 the surface of the inner layer osteoblasts (cementoblasts) are de- 
 veloped, which are speedily converted into bone or cementum. In 
 this process the tooth-root may be compared to one of the long- 
 bones of the body, and the development of the cementum con- 
 
sidered under the head of Subperiosteal Ossification. The only 
 variation to be observed between this and subperiosteal de- 
 velopment of bone is in the presence of a single Haversian 
 canal (as the pulp-cavity may be considered), and even this dif- 
 ference is sometimes overthrown by small canals running at 
 right angles to the pulp. These small canals are generally 
 found near the apex of the root, at which point the cementum 
 is the thickest. Like the enamel cap of the tooth-crown, the 
 cementum is deposited upon the surface of the dentin of the 
 root, thus increasing its diameter. 
 
 Eruption of the Teeth. — Up to this time no reference has 
 been made to that process by which the teeth burst forth from 
 their bony incasements, and, penetrating the mucous membrane, 
 make their appearance in the mouth. Attention has been 
 called to the growth of the bone about the tooth-follicles, — first 
 forming beneath them as an open gutter, next surrounding their 
 lateral walls and inclosing each follicle in a separate compartment, 
 and finally each tooth becoming more completely enveloped by 
 an arching-over of the mouth of the bony vault. This condi- 
 tion in the maxillary bones is reached between the seventh and 
 eighth month after birth, and, almost simultaneously with the 
 completed incasement of the teeth by the bone, active resorp- 
 tion begins, that portion of the bone which was last in forming 
 being gradually removed. The cause of the resorption of the 
 bone may readily be attributed to the advancement of the 
 tooth, but the forces which are responsible for this latter phe- 
 nomenon do not appear to be clearly understood. In a general 
 way, the advancement of the crown may be said to result from 
 the elongation of the root by the addition of dentin to its free 
 extremity. But, when it is taken into consideration that the cus- 
 pid teeth, both deciduous and permanent, have their roots fully 
 or nearly calcified before they begin to advance toward the 
 surface, an exception to the generally accepted theory is estab- 
 lished. The eruptive process takes place first in the anterior 
 teeth,* and the bone overlying the labial surface is first removed. 
 
 This loss of the bony structure is continued until fully one-half 
 
 * See Description of the Teeth in Detail, p. 136. 
 
DEVELOPMENT OF THE PERMANENT TEETH. 335 
 
 of the labial surface is uncovered, and, as the crowns continue 
 to advance toward the surface, they assume a more prominent 
 position in the arch, and thus their cutting-edges become bared. 
 The palatal or lingual face of the crypt serves a double purpose, 
 forming not only a covering to the deciduous tooth, but also 
 serving the permanent tooth-sac in the same capacity. This 
 part of the crypt remains unabsorbed, the tooth-crown glides 
 by its margin, and, after penetrating the mucous membrane, 
 makes its appearance in the mouth. Closely following the 
 resorptive process comes a rebuilding of the parts, until, finally, 
 when the tooth is fully erupted, it is firmly supported by the 
 new bone filling in about the base of the root. Accompanying 
 the eruption of the anterior teeth and their establishment 
 in the arch is an increase in the depth of this portion of the 
 jaw, and, as the molar teeth advance and assume their position, 
 there is a corresponding increase in the depth of the jaw in this 
 locality. At the beginning of the eruptive period the roots of 
 the deciduous teeth are but partially calcified, but as the crowns 
 advance the calcific action at the extremity of the roots is con- 
 tinued, and, in the majority of instances, by the time the crowns 
 are fully erupted the roots are completely formed. During the 
 period of eruption the transitory nature of the alveolar portion 
 of the jaw-bone is made manifest, accommodating itself to the 
 growth of the teeth as well as to their change of position. The 
 free margins of the alveolar walls are taking on new structure, 
 which advances with, and becomes adapted to, the base of the 
 tooth-root. Coincident with this the deeper portion of the 
 alveolar process is formed by a rapid fiUing-in about the root 
 as the tooth travels onward to assume its final position in the 
 jaw. The eruption of the teeth is usually by pairs, with a slight 
 intermission between each class. The central incisors first make 
 their appearance, followed by the laterals, after which the first 
 molars are erupted. The cuspids usually follow the first molars, 
 and, finally, the second molars take their place in the arch. 
 While this brief description of the eruption of the teeth refers 
 to the deciduous organs only, the process in the permanent 
 teeth is almost identical with this. Further reference to the 
 
336 ANATOMY. 
 
 eruption of the permanent teeth will be made in connection 
 with the degeneracy of the temporary set. 
 
 To return to the subject of tooth-development, attention is 
 called to figure 227, prepared from a dissection upon a nine- 
 months-old child, the illustration representing the hard palate, 
 or roof of the mouth, at this period. The four incisor teeth 
 have made their appearance, the labial surfaces of the crowns 
 being fully exposed, while those facing the palate are but 
 slightly uncovered. The approach of the remaining deciduous 
 teeth is plainly indicated by the fullness of the alveolar borders, 
 and the margins of the crypts are now being removed by 
 resorption. 
 
 Fig. 227. — Hard Palate from a Nine-months-old Child, Actual Size. 
 
 If the mucous membrane should be removed, the crowns of 
 the advancing teeth would be brought to view after the removal 
 of the walls of the tooth-sacs, while the approaching cuspids and 
 second molars yet remain partly covered by an arching over of 
 the walls of the crypts ; the resorptive process has also begun 
 in these parts. It would also be observed that, while the walls 
 of the crypts are molded to the outlines of the tooth-crowns, 
 there exists a well-defined interspace between the two. During 
 the growth of the tooth this interspace is filled by the walls of 
 the tooth-sacs, and even after the teeth have passed the saccular 
 stage of development, and assumed their positions in the mouth, 
 
DEVELOPMENT OF THE PERMANENT TEETH. 337 
 
 there yet remains between the roots and the alveolar walls 
 a slight space which is occupied by the alveolodental mem- 
 brane. 
 
 The next dissection is one upon the superior maxillae of a 
 two-year-old child (Fig. 228), representing the roof of the 
 mouth of this subject. In this specimen it will be noticed that 
 all of the deciduous teeth are erupted with the exception of the 
 second molars. The lingual surfaces of the incisors are fully 
 uncovered, while in the cuspids the labial surfaces are much 
 more exposed than the lingual. In figure 229 the mucous 
 membrane and sufficient of the bone have been removed to 
 
 Fig. 22S. — Hard Palate from a Two-year-old Child, Actual Size. 
 
 expose the tooth-sacs of the developing permanent teeth. The 
 dissection furnishes no additional information over that ob- 
 tained from figure 22S, excepting that the primitive follicles for 
 the permanent second molars make their appearance at this time. 
 At this early period the jaw has not lengthened sufficiently to 
 permit of these follicles occupying their future position ; conse- 
 quently they are found generating immediately over the tooth- 
 sacs of the first permanent molars. As the first molars advance 
 and the jaw lengthens backward, these follicles will be carried 
 to the distal by the extension of the mucous membrane, to which 
 they are firmly adherent. If these follicles were to be dissected 
 
33S ANATOMY. 
 
 at this time, the papillae would be without definite form, showing 
 that the early function of the enamel organ has not yet begun. 
 The tooth-sacs containing the permanent lateral incisors are 
 found immediately beneath the palatal plates, and frequently 
 during their earlier life they are not even protected by the 
 bone, being in immediate contact with the mucous membrane. 
 On account of the imperfect protection frequently afforded these 
 sacs, the germs are sometimes injured and the teeth fail to make 
 their appearance. 
 
 Sac for Perma- 
 nent Second 
 Molar 
 
 Fig. 22g. — Roof of the Mouth of a Two-year-old Child. 
 
 In figure 230 the walls of the sacs shown in figure 229 have 
 been opened, and the relations existing between the first and 
 second dentition at the end of the second year become apparent. 
 The crowns of the permanent incisors are deeply set in the 
 substance of the jaw, while the partially calcified crowns of the 
 permanent laterals are in close proximity to the palatal surface. 
 The partially formed crowns of the permanent cuspids are still 
 more deeply seated in the substance of the jaw than those of 
 the central incisors, and are not visible in the illustration. In 
 this connection it will be well to again refer to the gubernaculum, 
 and to its function — that of directing the tooth to its proper 
 position in the arch. By reference to the illustration the crowns 
 of the permanent teeth will be observed heading in various 
 directions, and, while in this instance there appears to be a 
 
DEVELOPMENT OF THE PERMANENT TEETH. 339 
 
 general tendency for them to advance and assume their proper 
 positions in the arch, in many cases they will be found directed 
 at right angles to the point at which they should emerge from 
 
 Fig. 230. — Development of the Teeth about the Second Ye.4r. 
 
 the bone. The gubernaculum, which appears to be nothing 
 other than an elongation of the follicular walls, not only directs 
 
 Tootli-sac for First Bicuspid 
 Fig. 231. — Dissection of Lingual Face of Lower Jaw, Child Nine Months Old. 
 
 the tooth by the tension of its fibers, but the foramen which 
 its presence creates stimulates the resorptive action over the 
 tract to be traveled by the tooth. Figure 231 was prepared 
 
ANATOMY. 
 
 for the purpose of better showing the gubernacula, and the 
 manner of connecting the tooth-sacs with the oral mucous 
 membrane. This condition is well shown in the anterior teeth, 
 the tooth-crowns having receded well toward the body of the 
 
 jaw. The follicle for the first 
 bicuspid may be observed at- 
 tached to the lingual face of 
 the deciduous molar sac, and 
 the leading cord is not yet an 
 adjunct to the developmental 
 process, but this structure will 
 make its appearance as the fol- 
 licle recedes from the surface. 
 
 In figure 232 the deciduous 
 molars have been removed 
 from the jaw and the relations existing between these teeth 
 and the developing bicuspids is shown. The tooth-follicles 
 for the succedaneous teeth are found immediately beneath the 
 gingival margin, and apparendy attached to the deep layer of 
 the mucous membrane. This relationship between the per- 
 
 FiG. 232. — Deciduous Molars with 
 Tooth-sacs for Bicuspids Attached 
 TO THE Gingival Tissue. 
 
 Deciduous Incisors 
 
 Fig. 233. — Same as Figure 231, with Tooth-sacs Opened Showing Developing 
 Teeth in the Jaw. 
 
 manent and temporary organs is present about the eruptive 
 period, but as the deciduous tooth advances and the permanent 
 tooth-sac recedes, the two organs become more widely sepa- 
 rated, and the permanent follicle is connected to the surface 
 
DEVELOPMENT OF THE PERMANENT TEETH. 341 
 
 only by the elongated follicular fibers which form the guber- 
 naculum. 
 
 Decalcification of the Deciduous Teeth. — By the close 
 of the second year the twenty deciduous teeth have taken their 
 place in the dental arch, their roots have become fully calcified, 
 and the apical foramina established ; it is only for a short 
 
 Fu;. 234. — Development of the Teeth about the Sixth Year. 
 
 period, however, that they remain thus perfect, the process of 
 decalcification beginning about the fourth year. This resorptive 
 action begins at the apical extremities of the roots and gradu- 
 ally progresses in the direction of the crowns. Commencing 
 about the fourth year with the central incisor, decalcification 
 takes place in the teeth in the order of their eruption, the 
 lateral incisor following the central, the first molar followino- the 
 
342 ANATOMY. 
 
 lateral, etc. By reference to figure 234 an approximate idea 
 of tiie progress of decalcification may be obtained, and it will 
 be observed that about three years elapse from the beginning 
 of this rather obscure process to its completion, and the final 
 casting-off or shedding of the tooth-crowns. In reference to the 
 causation of this dissolution of the deciduous teeth, but little 
 appears to be known. It has been said to result from the 
 presence and pressure of the advancing permanent teeth, but 
 there is no question but that it occurs absolutely indepen- 
 dent of these organs, decalcification frequently taking place 
 when from some obscure reason, one or more of the successional 
 teeth are absent. During the entire period of root decalcifica- 
 tion, the pulp of the tooth, which is also involved in the destrucv 
 tion, retains its vitality, but with the loss of vitality in the pulp 
 resorption of the root ceases ; so that the gradual removal of 
 the root-substance must be considered as a purely physiologic 
 action. 
 
 Figure 234 shows a dissection upon the jaws of a six-year- 
 old child, by a careful study of which, a fair knowledge of the 
 extent of resorption in the deciduous teeth at this period may 
 be obtained. 
 
 Advance of the Permanent Teeth. — By referring to figure 
 234, the relations existing between the deciduous and the per- 
 manent teeth at about the sixth year may be noted. While 
 the crowns of the deciduous teeth remain in position, a part of 
 the space formerly occupied by their roots is taken up by the 
 advancing crowns of the permanent teeth, the latter being 
 calcified but little beyond their cervical lines. Between the 
 seventh and eighth years the crowns of the deciduous incisors 
 are cast off, and gradually the crowns of the permanent incisors 
 force their way through the gum, the arch by this time having 
 sufficiently increased in size to accommodate the additional 
 width possessed by them. Previous to this time, or about the 
 sixth year, by a backward extension of the jaws, the perma- 
 nent first molars have erupted, assuming a position in the 
 arch immediately posterior to the deciduous second molars. 
 Between the tenth and eleventh years the crowns of the decidu- 
 ous molars are lost, and the bicuspids advance to take their 
 
DEVELOPMENT OF THE PERMANENT TEETH. 343 
 
 places. Usually by the twelfth year there has been sufficient 
 increase in the length of the jaws to permit of an additional 
 tooth, and the permanent second molar gradually takes its 
 position immediately posterior to the first. Between the twelfth 
 and thirteenth year the deciduous cuspids are lost by decalcifi- 
 cation of their roots, and they are succeeded by the permanent 
 cuspids. We therefore find, by the fifteenth year, fourteen 
 
 Fig. 235. — The Completed Dentition. 
 
 fully developed teeth occupying the dental arch of each jaw, 
 the full number, thirty-two, or sixteen in each jaw, not being 
 present until the eruption of the third molar, which, like the 
 other teeth of this class, is compelled to await accommodations 
 by a further increase in the length of the maxillary bones. 
 This tooth usually takes its place between the eighteenth and 
 twenty-first years, and thus completes the dentition (Fig. 235). 
 
PART II.— HISTOLOGY. 
 
 CHAPTER I. 
 
 GENERAL HISTOLOGY: THE TISSUES OF THE BODY: EPITHELIAL 
 TISSUES; CONNECTIVE TISSUES; MUSCULAR TISSUES; NERVOUS 
 TISSUES. 
 
 Part first of this work has been devoted to a gross description 
 of the mouth, its structures, the macroscopic arrangement of the 
 tissues composing the various parts, their relations to one another 
 as made manifest by dissection, etc. The remaining chapters 
 will be given up to the study of the intimate structure of the 
 oral tissues according to their form and organization. The 
 necessity and value of thus continuing the subject may be 
 presented as follows : If any of the structures or organs of 
 the mouth — such as the mucous membrane, the mucous glands, 
 or the muscular fibers common to various parts — are taken and 
 submitted to a minute dissection, it will be found that the 
 component parts may be separated into smaller and smaller 
 portions. Take, for example, the muscles of the tongue : these, 
 to the unaided eye, are distinctly fibrous in appearance, and 
 these fibers may be readily separated from one another by 
 removal of the interposed substance. In like manner the oral 
 mucous membrane is composed of a dense fibrous connective 
 tissue, which may be separated and examined in a similar way. 
 But the possibilities of investigation by this method are limited, 
 as the parts thus dissected are similar to one another, and are 
 soon reduced to microscopic proportions, and when thus exam- 
 ined certain definite anatomic forms present themselves which 
 are no longer capable of being divided. The reduction of any 
 structure to such definite proportions without artificial mutila- 
 tion or disarrangement of its parts is productive of what is 
 termed an anatomic element. It is only in very rare instances 
 that a tissue is composed of a single anatomic element, but 
 usually two or more kinds are mingled together, and the tissue 
 thus formed derives its texture, quality, and appearance from 
 
 344 
 
THE EPITHELIAL TISSUES. 345 
 
 the variety and number of anatomic elements present. Again, 
 taking the muscular tissues as an example, they are found to 
 be composed principally of one anatomic element — muscular 
 fiber, arranged in parallel bundles. In close relation with the 
 fibers are numerous nerve-filaments and capillary vessels, the 
 whole being surrounded by a thin layer of connective tissue. 
 Numerous bundles of this nature unite to form larger bundles, 
 with larger nerve-filaments and blood-vessels. In the hard struc- 
 tures the same conditions are present, so that a definite under- 
 standing may be obtained by a minute examination only. 
 
 Beyond the tissues and the anatomic elements is the elemen- 
 tary organism — the cell. 
 
 Embryonal 
 
 Mucous 
 Membrane 
 
 
 Fig. 236. — Vertical Tr.^nsverse .-MXiiu.N ihrijuuh Head of Human Embryo, about 
 THE Sixth Week, showing Single Buccal Cavity. X 3°- 
 
 A cell is a structural element, primarily oval or spheroid in 
 form, capable of self-nourishment, development, and reproduc- 
 tion. It is composed of two essential parts — the cell-substance, 
 consisting principally of a soft albuminous matter, the proto- 
 plas7n, and generally a well-defined central portion, the necessary 
 part of a typical cell — the p-iiclens. The nucleus is usually round 
 and situated near the center of the cell-substance. In many 
 instances there is within the nucleus a small spheric body, the 
 
346 HISTOLOGY. 
 
 nucleolus, which, although not having its function definitely 
 established, undoubtedly is subordinate to the life activity of the 
 cell. At the beginning of development the cells composing a 
 part are all of the same general form, and similar in other 
 respects ; as development proceeds, the cells arrange themselves 
 in germ-layers, and coincident to this change in relationship cease 
 to resemble one another and become differentiated. By this 
 aggregation of similar cells tissues are formed ; and by a com- 
 bination of different tissues, a structure of definite form and 
 function, an organ, is generated. 
 
 The tissues of the body are divided into four grand divisions 
 — namely, epitlielial tissue, connective tissue, muscular tissue, and 
 nervous tissue. During early life these tissues are composed 
 of similar elements — of cells ; but as growth proceeds, a twofold 
 change takes place, in one of which the cells produce a special 
 deposit, which accumulates between them and forms the inter- 
 cellular substance ; in the other the tissues of one kind become 
 mixed with those of another. 
 
 The Epithelial Tissues. — The cells composing the epithelial 
 tissues are known as epithelial cells ; they are definite in outline, 
 and consist of the cell-substance, protoplasm, and a nucleus. Two 
 forms are most frequently met with — the flattened or squamous, 
 and the columnar or prismatic. The sqtiavious or pavement cells 
 are flattened and scaly; in the former the nucleus is round, while 
 in the latter it is flattened. The columnar cells present a greater 
 variety in outline, being conic, club-shaped, or spindle-shaped, 
 sometimes short and sometimes long. The nucleus is inclined 
 to the form of the cell-substance, usually being more or less 
 oval or oblong. In size the epithelial cells are quite variable, 
 this difference occurring in cells of the same part as well as in 
 those of distinct parts. By the arrangement of the cells the 
 character of the epithelium is established ; thus, if they are dis- 
 posed in single layer, a single-layered- epithelium is produced ; 
 or if stratified, forming several superposed layers, a stratified 
 epithelium results. The consistency of the epithelial cells is 
 such that they readily succumb to the pressure of neighboring 
 cells, resulting in much variation in their outline. They are 
 cemented to one another by an exceedingly thin layer of an 
 
THE CONNECTIVE TISSUES. 347 
 
 albuminous cement-substance, being in contact by their flattened 
 sides or by irregularly formed processes, the result of force 
 applied by adjacent cells. 
 
 A third class of epithelial cells are those columnar cells which 
 are beset upon their free surfaces with numerous minute pro- 
 cesses which during life are constantly vibrating; these are 
 known as ciliated cells. Continuous masses of epithelial cells, 
 " epithelia," are found covering the surface of the skin, and lining 
 internal canals and organs. They are found in abundance, 
 covering all parts of the mucous membrane of the mouth, and 
 lining the numerous ducts which empty into that cavity. In 
 some instances the epithelia are composed of a single stratum, 
 in others of a number of strata, and the following varieties 
 are to be observed : simple squamoits, simple columnar, and 
 simple ciliated epithelium, when a single stratum is present ; 
 and stratified squamous, stratified columnar, and stratified cili- 
 ated epithelium, when the several strata are present. The epi- 
 thelium of the mouth is principally of the stratified squamous 
 variety. Another classification is that known as glandular 
 epithelium, composing the numerous glands and ducts (see 
 Glands of the Mouth). In addition to this, one other variety 
 exists, known as neuro-epithelium. 
 
 One of the special characteristics of epithelial tissue is the 
 relatively small amount of intercellular substance as compared 
 to the cells themselves. 
 
 The Connective Tissues, — In general this term is applied 
 to all those tissues which support and connect other tissues. 
 While the cells are numerous, they are proportionately less 
 numerous than in the epithelial tissues. In the connective tissues 
 the intercellular substance predominates where it is prominently 
 developed and variously differentiated. The intercellular sub- 
 stance is characteristic of the connective-tissue group, and is espe- 
 cially interested in its function. By a variation in the quantity, 
 nature, and disposition of the intercellular substance, three classi- 
 fications are formed — namely, fibrous connective tissue, cartilage, 
 and bone (including dentin and cementum). Each of these 
 groups is subdivided into several varieties, but in all instances 
 the intercellular substance is to be distinguished from the cells. 
 
348 HISTOLOGY. 
 
 Fibrous Connective Tissue. — This tissue is present in the skin 
 and mucous membrane, in the intermuscular tissues, in tendons, 
 in fascia and aponeuroses, and in the tissues connecting various 
 organs. It is composed of a meshwork of fine fibers of two 
 kinds. The first, which makes up the greater part of the tissue, 
 is formed of very fine, white, structureless fibers arranged closely 
 in bundles and bands crossing and intersecting in all directions. 
 The second variety, or the yellow, elastic fiber, has a much 
 sharper and darker outline, not arranged in bundles, but is inti- 
 mately mingled with the white fibers by twisting around and 
 among its filaments. These are known as the elementary con- 
 nective-tissue fibers. The size of the connective-tissue bundles 
 depends upon the number of elementary fibers present, and by 
 a variation in the arrangement of the bundles variety in the 
 character of the fibroconnective tissue is produced in different 
 localities. When the fibrous connective tissue is formed into an 
 unbroken mass, as in mucous membrane, the minute bundles are 
 collected into smaller or larger groups (the trabeculcB), and these 
 are in turn associated into groups. In the skin and mucous 
 and serous membranes, the trabeculae of the connective-tissue 
 bundles are separated, and, by crossing and recrossing one 
 another, form a dense, fan-like structure. In other tissues, as the 
 tendons and fascia, the bundles are arranged in parallel layers. 
 In the submucous tissues the connective-tissue fibers are 
 loosely woven, the fibers crossing and intermingling, with the 
 intervening spaces unusually large, resulting in a loose, flabby 
 tissue — areolar tissue. Three varieties of fibrous connective tis- 
 sue are distinguished — namely, mucous connective tissue, fibril- 
 lar connective tissue, and reticular connective tissue. Mucous 
 connective tissue consists of an abundance of undifferentiated 
 intercellular substance in which are a few bundles of fine fibrils 
 and a number of round or oval cells. Fibrillar connective tissue, 
 or areolar tissue, consists of an abundance of intercellular sub- 
 stance differentiated into connective-tissue fibers and cells. Retic- 
 ular connective tissue, as its name implies, is a network of slender 
 bundles of connective tissue associated with flattened, nucleated 
 cells. 
 
 The fibrous connective-tissue cells are few in number, of 
 
CARTILAGE. 349 
 
 several varieties, and variously shaped, being flattened, stellate, 
 or apparently distorted by pressure from surrounding cells or 
 fibrous bundles. In the mucous membrane the cells are oblong 
 and somewhat flattened, having many branches which reach 
 out and, uniting with like processes from neighboring cells, form 
 a network. Other connective-tissue cells are comparatively 
 larger, oval or rounded in form, granular in appearance, rich in 
 protoplasm, and are known as plasma-cells. The body of con- 
 nective-tissue cells, besides containing a nucleus, frequently 
 contains pigment-granules ; these are known as pigment-cells. 
 These are seldom found in mucous or serous membranes, 
 being principally confined to the integument. Fat-globules 
 may also be found in fibrous connective tissue, and when of 
 considerable size unite and form a rounded cell, called a fat-cell. 
 Numerous fat-cells uniting, and well supplied with blood-vessels 
 and nerves, form adipose tissue, or fat. Fat-cells are frequently- 
 found in areolar tissue as well. When fibrous connective tissue 
 is immediately contiguous to epithelium, it becomes somewhat 
 modified and a new membrane is formed, called the basement 
 membrane, or menibrana propria. This membrane is a thin, 
 transparent, structureless layer, and, when in connection with 
 those mucous membranes provided with a layer of vascular 
 fibrocellular tissue, may appear as the formative substance out 
 of which successive layers of epithelial cells are generated. In 
 the ducts and glands — for example, the salivary glands — the 
 basement membrane forms the proper walls of the tubes, and 
 the cells here generated, and corresponding to the epithelial 
 cells of the coarser mucous membranes, are known as gland- 
 cells, rather than epithelial cells. This, however, is a distincdon 
 without a perceptible difference, the location and function as 
 secreting cells being alike in each. 
 
 Cartilage. — Cartilage is a semi-opaque, non-vascular tissue, 
 white in color, and composed of a matrix containing nucle- 
 ated cells. The matrix is somewhat elastic and rather dense. 
 The cells are simple in form, being spheric or slightly inclined 
 to angularity. The variation in the character of cartilage is 
 due rather to the difference in the character of the matrix 
 than to the cellular structure, the principal variation in the 
 
350 HISTOLOGY. 
 
 cells being in their size. The cells lie in the spaces or la- 
 cunae of the matrix, which they completely fill. Investing the 
 free surface of most cartilaginous tissue (articular cartilage ex- 
 cepted) is a thin but tough and firm fibrous membrane — xX^o. peri- 
 chondrium. This membrane is well supplied with blood-vessels 
 and nerves, and is essential to the growth and maintenance ot 
 the cartilage. There are three varieties of cartilage — namely, 
 hyaline cartilage, elastic cartilage, and fibrocartilage. 
 
 Hyaline cartilage is of a faint pearly-blue color, slightly trans- 
 parent, and is found investing the articular ends of the bones — 
 for example, the condyles of the mandible ; also forming the costal 
 and nasal cartilages, as well as those of the trachea, bronchi, and 
 a part of the larynx. Hyaline cartilage is distinguished by a 
 granular or homogeneous matrix. The cells, which contain a 
 nucleus with nucleoli, are usually grouped together in patches, 
 and are somewhat irregular in outline, appearing flattened near 
 the free surface of the tissue in which they are placed, and in- 
 clined to be perpendicular to the surface in the more deeply- 
 seated portions. The matrix is dimly granular in appearance, 
 resembling ground glass, and receiving its name from this fact. 
 That part of the cartilage close to the perichondrium is sup- 
 plied with cells much smaller than those occupying the lacunae 
 In the substance of the mass, and the growth of the cartilage is 
 most active in this part. Lining each lacuna is a delicate mem- 
 brane (the capsule), which primarily is but partly filled out, but 
 as the cell or cells increase in size, this membrane is carried to 
 the walls of the lacuna. Articular hyaline cartilage is non- 
 vascular, being nourished by the blood-vessels of the bone 
 beneath. 
 
 Elastic cartilage is of a dull-yellow color, and is sometimes 
 called yellow cartilage. It is not present in the mouth, but 
 occurs in the external ear, in the epiglottis, and in part of the 
 larynx. Its structural composition is quite similar to hyaline 
 cartilage, but may be distinguished from it by a network of fine 
 elastic fibers which penetrate the matrix. The cells are rounded 
 or oval, containing nuclei and nucleoli. 
 
 Fibrocartilage is yellowish or milky white in color, and is 
 much more widely distributed throughout the body than the 
 
elastic variety. It is present in the temporomandibular articula- 
 tion. Like those previously described, it is composed of cells 
 and a matrix, the latter being made up of fibrous connective 
 tissue arranged in bundles, and for this reason it is scarcely 
 deserving the name of cartilage, only that in other portions 
 continuous with it cartilage-cells may be found in abundance. 
 Between the strata of the fibrous bundles are numerous 
 nucleated cells, which are oval and more or less flattened, and 
 each enveloped in a delicate capsule. 
 
 Cartilage is further classified into two divisions, — temporary 
 zx\.^ permanent, — the former term being applied to that kind of 
 cartilage which in the fetus and in youth is destined to be con- 
 verted into bone (for example, Meckel's cartilage) ; the latter 
 class including all those cartilages w^hich are generated as such, 
 and continue to serve in that capacity. Temporary cartilage 
 closely resembles the hyaline variety, being formed of a matrix 
 in the lacunae of which the cells are located. These cells, how- 
 ever, are not grouped together as in hyaline cartilage, but are 
 more uniformly distributed throughout the matrix. 
 
 Bone. — Bone is mainly composed of tricalcium phosphate 
 and cartilage. The matrix of osseous tissue has a distinguish- 
 ing feature produced by the blending of organic and inorganic 
 substances, resulting in hardness, solidity, and elasticity. The 
 combination of organic and inorganic elements in bone is of 
 such a nature that either part may be removed without destroy- 
 ing the other. The matri.x is composed of the salts of lime, 
 especially calcium phosphate, and of slender fibrils united by a 
 cement-substance into bundles of various sizes. The cement- 
 substance is chiefly composed of insoluble lime-salts, princi- 
 pally carbonates and phosphates. These two kinds of struc- 
 ture are found to be present in different parts of the same 
 bone, forming a dense or compact, and a spongy or can- 
 cellated tissue. The former occur in the shaft of long bones 
 and in the outer layer of flat or irregularly formed bones. Can- 
 cellated bone-substance occurs in the extremities of the long 
 bones and in the interior of flat and irregular bones. The 
 irregularly formed maxillary bones give place to both kinds oi 
 bony structure ; the external layer of the superior maxillae and 
 
352 
 
 HISTOLOGY. 
 
 the body and rami of the inferior maxilla are composed of com- 
 pact tissue, while the interior of these bones and the condyloid 
 processes of the mandible are spongy or cancellated in their 
 nature. When examined by the microscope the bony substance 
 is found occupied by numerous little spindle-shaped spaces — 
 lacuncB. Branching- out from these in various directions are 
 minute canals — canaliculi — which anastomose with similar 
 canals from neighboring lacunse. In the maxillary bones no 
 other canals than these may be visible, but if a transverse 
 
 Fig. 237. — Developing Bone. X 4°- 
 
 section be cut through one of the long bones, an additional 
 space makes its appearance (Fig. 238). 
 
 These spaces are known as the Haversian canals. They are 
 circular in outline and appear as a center for a small, circular 
 district mapped out by concentric layers, the lacunse and canal- 
 iculi following the same concentric plan, and through each other 
 communicating with the Haversian canals. The general direc- 
 tion of the Haversian canals is longitudinal with the long axis 
 of the long bones, and in the flat or irregular-shaped bones 
 they are somewhat irregular in formation and ramify in various 
 directions. In the osseous matrix each lacuna contains a 
 
BONE. 353 
 
 bone-cell. These are nucleated, protoplasmic cells. In devel- 
 oping bone, these cells, which do not completely fill the lacunae, 
 are connected by numerous branches or processes passing 
 through the canaliculi; in older bone very few processes are 
 observed. 
 
 There are two processes by which bone may be prepared 
 for histological examination, by one method which results in 
 the destruction of the organic elements, or by another which 
 removes the inorganic elements. In the former process the 
 organic matter is removed by simply drying the structures, after 
 
 
 
 Concentric ^ ''^^ - ^ j, \^ "' 
 
 Haversian ^f^^. ' . -■ , ^^ \ 
 
 
 r''. ',"■ , ^ '■--- *^.--^ 
 
 Fig. 23S.— Transverse Section through Shaft of Long Bone. X 3°- 
 
 which thin sections may be prepared and carefully examined 
 under the microscope, when the Haversian canals, lacunae, and 
 canaliculi will be seen forming a complete concentric network. 
 In the latter method the inorganic substance is removed by 
 immersing a fresh bone in dilute picric acid, C6H3(NOJ30H, 
 which readily decalcifies it, and when properly prepared sections 
 are placed under the microscope the organic contents of the 
 lacunae and canaliculi alone are visible. 
 
 The concentric laminee of bone is riveted together by numer- 
 
354 HISTOLOGY. 
 
 ous delicate rods or processes named Sharpeys fibers, these 
 delicate fibers passing through the laminae to perform this office. 
 Periosteum and Bone-marrow. — The interstices of spongy 
 bone are filled with a soft mass, — the bone-marrow, — and the 
 external surface of the bone is covered by a fibrous membrane 
 — the periosteum. This membrane is absent where bones are 
 joined to each other by ligament or cartilage, and over articular 
 surfaces. The periosteum is a compact connective-tissue mem- 
 brane. It consists of two layers: an obiter, 'vibxow's, layer rich in 
 
 
 Fig. 239. — Longitudinal Section of Long Bone. X 30- 
 
 blood-vessels, which forms the connection with adjacent struc- 
 tures ; an inner or osteogenetic layer containing few blood- 
 vessels, loose in texture, but rich in elastic fibers and spheric 
 connective-tissue cells, with oval nuclei. These are the forma- 
 tive cells of bone and are called osteoblasts. These cells appear 
 in the lower strata of the inner layer, or the layer in contact 
 with the bone, and are especially numerous during the period 
 of development. Through the blood-vessels of the bone the 
 marrow, internally, is placed in communication with the perios- 
 teum externally ; small branches given off from the numerous 
 
NON-STRIATED MUSCULAR TISSUE, 355 
 
 arteries and veins of the periosteum enter the Haversian canals, 
 upon which they pass to the canaliculi, thus communicating with 
 the blood-vessels of the marrow. In like manner numerous 
 nerves enter the substance of the bone, first passing into the 
 Haversian canals, after which they become closely associated 
 with the minute blood-vessels and are distributed to the perios- 
 teum and bone-marrow. The bone-marrow, besides filling the 
 interstices of the spongy substance, is also found occupying the 
 central cavity of long bones, and in the larger Haversian canals. 
 The marrow is of two varieties, distinguished by its color, being 
 either red or yellow. Red marrow is found in the flat bones 
 (including the maxillae), the vertebrae, and ribs, while yellow 
 marrow occurs in the long bones of the extremities. Red mar- 
 row is composed of a delicate connective-tissue network sup- 
 porting, besides the marrow-cells, a few fat-cells and giant-cells. 
 In the long bones the yellow marrow is surrounded by a con- 
 nective-tissue membrane lining the medullary canals. Marrow- 
 cells and giant-cells are present in abundance. Marrow is very 
 vascular and contains many osteoblasts. 
 
 Dentin. — This structure, as well as cementum, which in many 
 particulars closely resembles bone, will be fully considered in 
 connection with the histology of the tissues of the teeth. 
 
 Muscular Tissues. — The muscle-fibers, or the structural 
 elements of the muscular tissues, are divided, according to the 
 arrangement of their bundles, into two classes — non-striated 
 and striated. 
 
 Non-Striated, Smooth, or Involuntary Muscular Tissue. 
 — This tissue consists of contractile fiber-cells, which are elon- 
 gated, spindle-shaped, and cylindric, with exceedingly elongated 
 extremities, which become shorter and thicker through contrac- 
 tion. They are quite variable in length (yV to ^i^j of an inch), 
 and are composed of a pale, homogeneous-looking protoplasm, 
 each inclosing an elongated or rod-shaped nucleus, which is 
 flattened if the cell is so formed. The muscular fibers are 
 firmly bound together by a cement-substance, forming fasciculi, 
 which in turn are collected into strata or membranes, which 
 may be disposed parallel, or crossing and recrossing, forming 
 an intricate network. The connective-tissue septa provide a 
 
356 
 
 HISTOLOGY. 
 
 passageway for the larger blood-vessels, while the capillaries 
 penetrate the fasciculi forming a complicated network with 
 oblong meshes. Involuntary muscular tissue is not found in the 
 mouth except in the ducts of the salivary glands. 
 
 Striated or Voluntary Muscular Tissue. — Striated mus- 
 cular tissue is composed of long, cylindric fibers, which are 
 regularly transversely striated. In most instances their extrem- 
 ities are attached to bones by means of tendons, as, for example, 
 the cheek- and lip-muscles. The fibers are grouped together by 
 fibrous connective tissue into various sized bundles, forming 
 
 Fig. 240. — Transverse Section of Striated or Voluntary Muscular Tissue. X A°- 
 
 fasciculi. There is much variation in the length of the fibers 
 composing the fasciculi in different muscles. In most instances 
 the fasciculi which serve to make up the bundles of a single mus- 
 cle condnue parallel with one another throughout their length. 
 Surrounding the muscular fasciculi, and forming a covering or 
 sheath for the individual bundles, is a layer of connective tissue 
 called the perimysium, and passing from this into the substance 
 of the bundle is a delicate connective tissue, the endomysium, 
 which separates the individual fibers from one another. The 
 
STRIATED OK INVOLUNTARY MUSCULAR TISSUE. 357 
 
 former structure carries the larger blood-vessels and nerve- 
 fibers, while the latter supports the capillaries. 
 
 Each muscular bundle may again be divided into smaller 
 bundles, which in turn are ensheathed iri a similar manner and 
 further divisible, so continuing until the primitive fasciculi, or 
 so-called muscular fiber, is reached. Striped muscular fiber 
 consists of a structureless, elastic sheath, the sarcoleinvia, which 
 structure represents the cell-membrane, and closely invests a 
 number of filaments or fibrils. Besides the fibrillee, there is con- 
 tained within this fine, structureless, transparent membrane the 
 
 Fig. 241. — Striated or Voluntary Muscular Tissue. X 40- 
 
 sarcoplasm, a faintly granular substance resembling protoplasm, 
 but not identical with it. This substance serves in the capacity 
 of a matrix for the fibrillae. The fibrillse are arranged parallel 
 to one another, being supported by the sarcoplasm. It will 
 thus be seen that each fiber of a striated muscle comprises the 
 sarcolemma, the muscle-nuclei, the fibrillae, and, finally, the 
 sarcoplasm, filling all the interstices, first between the fibrillae 
 of each muscle-column, between the columns of each group, 
 and between the groups themselves. The disposition of the 
 
358 
 
 HISTOLOGY. 
 
 sarcoplasm may be most favorably studied by a cross-section 
 
 through the fibers, appearing as 
 a delicate but clear network, 
 within the meshes of which are 
 the muscle-columns. Striated 
 muscular fibers are usually spin- 
 dle-shaped, tapering off and be- 
 coming thinner toward their ex- 
 tremities. In rare instances 
 they are branched at their ends. 
 This condition is present in the 
 tongue, the extremities of the 
 fibers passing transversely into 
 the oral mucous membrane, 
 where they become further sub- 
 divided. The striated or vol- 
 untary muscles make up the 
 muscular tissues of the lips, 
 cheeks, tongue, and soft palate. 
 Nervous Tissues. — Until 
 within recent times it has been 
 stated that the nervous tissue 
 consists of two histologic ele- 
 ments known as nerve-cell and 
 nerve-fiber; that these two ele- 
 ments differed not only in their 
 mode of origin, but in their 
 structure and physiologic en- 
 dowments. At the present time 
 it is believed that the entire 
 nervous system consists of an 
 infinite number of definite in- 
 dependent morphologic units, 
 which, though having a common 
 origin and a similarity of struc- 
 ture, have, nevertheless, differ- 
 ent functions in different parts 
 of the body. This neurologic 
 
 Fig. 242. — Diagram of a Neuron. — 
 [Fi-om Stok}-'s "Histology.") 
 
NERVOUS TISSUES. 359 
 
 unit has been termed the neuron, and, as represented schemati- 
 cally in figure 242, may be said to consist of: First, the nerve- 
 cell, or neurocyte ; second, nerve-process, or axon ; third, the 
 end-tufts, or terminal branches. Each of these three main 
 portions of the neuron presents a variety of secondary features 
 which are related to their functional activities. 
 
 The Nerve-cell, or Neurocyte. — The nerve-cells are found in 
 the cortex of the brain, in the interior of the spinal cord, in the 
 various ganglia of the cerebrospinal and sympathetic nervous 
 systems, and in the organs of special sense. All neurocytes are 
 the modified descendants of independent oval or pear-shaped 
 
 Epiiieur u 
 
 
 Perineurium 
 Endoneuriun 
 
 Fig. 243. — Transverse Section, Bundles of Nerve-fibers, Human Median Nerve. 
 
 X30- 
 
 cells (the neuroblasts), originating from the epithelial cells 
 which form the medullary tube. The neurocyte is at first 
 smooth, devoid of processes, and endowed with ameboid move- 
 ment. In the course of development the cells project a greater 
 or less number of processes and assume a variety of shapes 
 and sizes, in accordance with variations in functions; thus, the 
 cells may be spheroid, pyramidal, spindle-shaped, stellate, etc. 
 The body of the cell consists of a protoplasmic basis, more or 
 less granular, containing a well-defined nucleus and nucleolus. 
 A centrosoma has also been found in the nerve-cell in many 
 
36o 
 
 HISTOLOGY. 
 
 situations. There is no evidence, liowever, of the existence of 
 a cell-membrane. From the body of the neurocyte there arises 
 one or more protoplasmic processes, which, passing outward in 
 various directions, divide and subdivide into a greater or less 
 number of branches, which are collectively known as dendrites 
 or dendrons. The ultimate subdivisions and terminations of a 
 dendrite, though forming an intricate feltwork, always end 
 free, never anastomosing with one another. Arising from the 
 cell-body, the dendrites resemble in appearance and structure 
 the cell-protoplasm, or cytoplasm. In the cortex of the cerebrum 
 
 
 •^ 
 
 
 .■J^i 
 
 Fig. 244. — Portion of Transverse Section of Human Median Nerve. X 200. 
 
 and in the cortex of the cerebellum the dendrites are character- 
 ized by short, lateral projections known as lateral buds or gem- 
 mules, which impart to the dendrite a feathery appearance. 
 
 The Axon, or Ne^^ve-processi — The axon is the first outgrowth 
 of the protoplasm of the neuroblast, but with the development 
 of the neurocyte it becomes so differentiated from the dendrites 
 that it can be readily distinguished from them. It usually arises 
 from a cone-shaped projection of the cell-body, though occa- 
 sionally it arises from a dendrite itself. It is characterized by a 
 short, regular outline and a hyaline appearance. The majority 
 
THE END-TUFTS, OR ARBORIZATIONS. 361 
 
 of the cells, especially in the mammalia, possess but one axon, 
 though in the developing ganglion-cells of the spinal nerves two 
 distinct axons are present. In their subsequent development 
 the two axons appear to blend together to form but a single 
 axon, which, at a short distance from the cell, again divides into 
 two branches, which pursue opposite directions, one passing 
 directly into the spinal cord, the other toward the periphery. 
 The axon may continue as an individual structure for an indefi- 
 nite distance, varying from a few millimeters to 100 cm. In the 
 former instance the axon, at a distance of a few millimeters from 
 the cell, breaks up into a number of branches, which form an intri- 
 cate feltwork in the neighborhood of the cell. This type of cell is 
 not widely distributed, being confined largely to the cerebellum. 
 In its course the axon, more especially in the central nervous sys- 
 tem, gives off a number of side-branches or collaterals, which 
 do not differ from the axon itself, either in structure or appear- 
 ance. The axon of the peripheral nerves, especially the spinal 
 nerves, are devoid of collaterals throughout their extent, except, 
 perhaps, in the immediate neighborhood of the cell. The more 
 or less elongated axon becomes inclosed at a short distance 
 from the cell wnth a thick layer of fatty material, forming a 
 medulla or myelin, inclosed by a delicate cellular sheath (the 
 neurilemma), and thus constitutes what is commonly known as 
 a medullated nerve-fiber. In the central nervous system the 
 neurilemma is frequently wanting. In the sympathetic system 
 the myelin is wanting, though the axon is inclosed by a deli- 
 cate sheath resembline the neurilemma, thus constituting a non- 
 medullated nerve-fiber. The collateral branches are provided 
 with similar investments. 
 
 The End Tufts, or Arborizations. — Each axon, as it ap- 
 proaches its final termination, breaks up into a number of 
 branches, which vary in complexity and appearance in different 
 regions. They are always free from any medullary investment, 
 and appear to be formed by the splitting of the axon into a 
 number of fine filaments, which remain independent of one 
 another. In peripheral organs, as muscles, glands, and blood- 
 vessels, the tufts are in direct organic connection. In the 'central 
 nervous system the end-tufts are in more or less intimate rela- 
 tion with the dendrites of other neurons. 
 
362 HISTOLOGY. 
 
 Nerves. — Nerves are to be regarded, therefore, as groups of 
 axons, with their medullary investments connecting the periph- 
 eral organ with the central nervous system. 
 
 The nerves are arranged in two great systems — the cerebro- 
 spinal and the sympathetic. In the cerebrospinal nerves the 
 conducting media — the nerve-fibers — are arranged in parallel or 
 interlacing bundles, and these are further grouped into nerve- 
 branches or nerve-trunks. The bundles are connected by inter- 
 vening fibrous connective tissue (the epinezirhtiii), and through 
 this tissue the principal blood-vessels ramify to supply the nerve- 
 trunks, together with a plexus of lymphatics and numerous fat- 
 cells and plasma-cells. 
 
 The size of the nerve-bundles, or funiadi, is regulated accord- 
 ing- to the size and number of nerve-fibers which they contain. 
 Investing each funiculus, or primary bundle of nerve-fibers, is 
 a connective-tissue sheath — the perineurmm. The fibers com- 
 posing this sheath are arranged in lamellae, being separated from 
 one another by lymph-spaces variable in size, through which 
 communication is afforded the lymphatics of the epineurium. 
 Within the bundles the nerve-fibers are held together by fibrous 
 connective-tissue — the eiidoneitrhmt. The epineurium holds 
 together and envelops the several funiculi of the nerve-trunk, 
 the perineurium investing each funiculus, or primary bundle 
 of nerve-fibers, and the endoneurium extending among and 
 around the individual fibers. Nerve-fibers are divided into two 
 classes, — which classification is dependent upon the presence or 
 absence of a medullary sheath or covering, — into the medullated 
 or za/iiie, and the non-medullated or gray . The viedidlary sheath, 
 or white substance of Schwann, is a bright, fatty substance (the 
 myelin) surrounding the axon, or axis-cylinder, the conducting 
 or central part of a nerve-fiber. Between the medullary sheath 
 and the axis-cylinder there is present a small amount of albumi- 
 nous fluid. Closely surrounding the medullary sheath, and form- 
 ing the outer boundary of the nerve-fiber, is the neurilemma, or 
 sheath of Schwann. Between this delicate, structureless mem- 
 brane and the medulla there are placed at intervals oblong 
 nuclei, surrounded by protoplasm ; these are the nerve-coipuscles . 
 Besides the division of nerve-fiber into medullated and non- 
 
NERVES. 363 
 
 medullated, each division is susceptible of further subdivision, 
 dependent upon the presence or absence of the neurilemma. 
 Non-medullated nerve-fibers without a neurilemma are composed 
 of an axis-cylinder only ; they are cylindric or band-like in 
 form, transparent, and show faint, longitudinal striations. Non- 
 medullated nerve-fibers widi a neurilemma are composed of an 
 axis-cylinder surrounded by a neurilemma, and are homogene- 
 ous throughout their extent. 
 
 Medullated nerve-fibers are those which are pardy, but never 
 entirely, invested by a medullary sheath. They may or may not 
 possess a neurilemma; in the former instance they consist of an 
 axis-cylinder and a medullary sheath only. The axis-cylinder, 
 or essential part of the nerve-fiber, is cylindric or band-like, oc- 
 casionally exhibiting a delicate, longitudinal striation, which 
 appearance is due to its being composed of a primitive fibrillae. 
 
 The nerve-cells or ganglia-cells are found in the ganglia as 
 well as along the course of the nerves. They are composed of 
 granular or faintly striated protoplasm, inclosing a characteristic 
 nucleus within which is a nucleolus. They differ greatly in form 
 as well as in size, the spheric, spindle-shaped, and irregularly 
 stellate forms being the most common. In the latter numerous 
 processes are given off, forming the stellate outlines. The cells 
 are variously named, according to the number of processes. If 
 one process is present, the cell is termed a unipolar cell ; if two, 
 a bipolar ; and if a number of processes exist, they are named 
 multipolar. The processes are of two varieties — the axis-cylinder 
 process and the branched protoplasmic process. The various 
 forms are most readily distinguished in the multipolar cells. 
 The axis-cylinder process is readily characterized by its hyaline 
 appearance and unbroken outline. The protoplasmic processes 
 are thicker, granular, and striated. 
 
 Literature. 
 Stohr, "Text-book of Histology," 1896. 
 Sudduth, "American System of Dentistry," vol. i, 1SS6. 
 Klein, " Elements of Histology," 1889. 
 Holden, "Human Osteology." 
 
 Strieker, " Human and Comparative Histology," vol. i, 1870. 
 Morris, " Human Anatomy," 1S96. 
 Lee, " The Microtomist's Vade Mecuni," 1896. 
 
CHAPTER II. 
 
 THE MUCOUS MEMBRANE OF THE MOUTH; OF THE LIPS; OF THE 
 CHEEKS; OF THE GUMS; OF THE ROOF OF THE MOUTH, HARD 
 AND SOFT PALATE; OF THE FLOOR OF THE MOUTH; THE 
 TONGUE. 
 
 HISTOLOGY OF THE TISSUES OF THE MOUTH. 
 
 Mucous Membrane of the Mouth. — The mucous mem- 
 brane lining the cavity of the mouth consists of two parts — the 
 epithehum and the tunica propria ; beneath the latter, and form- 
 ing the deeper part of the mucous membrane, is the submucosa- 
 
 
 -S^ C 
 
 V 
 
 Fig. 245. — Vertical Section, Mucous Membrane of the Mouth, Human Embryo. 
 
 X 150- 
 
 T/ie epithelutin of the mouth is a thick, stratified, squamous 
 epithelium, the most superficial cells being scale-like or horn-like. 
 The cells are arranged similar to those in the epiderm, are 
 columnar in form, and contain very little pigment. 
 
 364 
 
MUCOUS MEMBRANE OF THE MOUTH. 365 
 
 The tunica propria is a somewhat dense feltwork of inter- 
 lacing connective-tissue bundles, interspersed with elastic fibers. 
 The tunica propria penetrates the epithelium in the form of 
 cylindric or conic papillae, which differ in length with the 
 variation in the thickness of the epithelium. As the mucosa is 
 usually thickest in the lips, gums, soft palate, and uvula, accord- 
 ingly the papillae are of the greatest length in these parts. The 
 tunica propria passes into the submucosa so gradually that a 
 positive line of demarcation can not be established. 
 
 The siibmucosa consists of a bundle of fibrous connective 
 tissue with but few elastic fibers. This structure is somewhat 
 loose in texture and is loosely attached to the underlying perios- 
 teum. Over the major portion of the gums and the entire hard 
 palate the submucosa is attached to the bones of the mouth 
 through the medium of their periosteal covering. It is in this 
 loosely constructed tissue that the glands of the mucous mem- 
 brane are situated. These are for the most part branched, 
 tubular, mucous glands. Besides adipose tissue in the form of 
 groups of fat-cells, striped muscular tissue is present in the sub- 
 mucosa. In some parts of the mouth this tissue forms a con- 
 spicuous portion — namely, in the sphincter muscle of the lips 
 (orbicularis oris) ; also in the soft palate, uvula, and pillars of 
 the fauces. 
 
 The blood-supply to the mucous niembraiie of the mouth is 
 principally distributed in two systems, the larger vessels to the 
 submucosa and the capillaries to the tunica propria. The larger 
 vessels break up and send a dense network of capillaries through 
 its substance and to the numerous papillae which extend into the 
 epithelium. Numerous veins ramify through the superficial part 
 of the tunica propria. The lymphatics form two networks, the 
 submucosa giving place to the coarser vessels, while the fine 
 parts are distributed to the tunica propria. 
 
 Nerve-supply to the Mucous Membrane of the Mouth. — In 
 the submucosa the medullated nerve-fibers form a wide-meshed 
 reticulum, from which numerous primitive fibrillae pass to the 
 tunica propria, where they terminate or continue as non- 
 meduUated nerve-fibers, and penetrate the papillae of the epi- 
 thelium, forminof networks. 
 
366 HISTOLOGY. 
 
 Mucous Membrane of the Lips. — Beginning as a direct 
 continuation of the integument or external covering of the lips, 
 the labial covering, including the integument, may be divided 
 into three parts — namely, a cutaneous portion (best described 
 in this connection), a transitory portion, and a mucomembranous 
 portion. 
 
 The cutaneous portion, covered by a thin epidermis, consists 
 of a double layer of somewhat flattened epithelium. Immedi- 
 ately beneath this is a thin, cellular, mucous layer, the cells com- 
 posing it being spheroid in form, and containing nuclei which 
 are proportionately large. Subjacent to this is the cutis, com- 
 posed of fasciculi of fibers intersecting and closely woven 
 together, the principal fibers passing toward the free border of 
 the mucous membrane covering the contiguous surface of the 
 lip. These fibers are for the most part connective-tissue fibers, 
 intermingled with elastic-tissue fibers. Numerous small, vascular 
 papillae are found upon the surface of the cutis ; these are cylin- 
 dric or conic in form, and project for some distance into the 
 rete mucosa — the lower layers of living cells of the epidermis. 
 Equally distributed at various depths in this tissue are numerous 
 hair- and sebaceous follicles. The general direction of the hair- 
 follicles in the upper lip is downward, while those occupying the 
 lower lip are turned upward. Other than the distinction noted 
 by the difference in color of the parts, the cutaneous portion may 
 be distinguished from the transitional mucous membrane by the 
 absence of hair-follicles and sebaceous glands in the latter. 
 
 The transitional portion of the mucous membrane of the lips 
 is outlined externally by the outer border of the red portion of 
 the lips, and internally by that prominent part of the labial con- 
 vexity which comes in contact with the opposing labial fold, 
 leaving the transitional portion exposed to view when the lips 
 are in occlusion. The epithelial layer of this surface does not 
 begin where the hair-follicles cease to exist, a slight interspace 
 appearing upon the cutaneous portion which is devoid of these 
 follicles. At its line of beginning the transitional portion of the 
 labial mucous membrane is quite thin, but rapidly increases in 
 thickness in passing toward the mucomembranous portion. 
 Superficially the cells are much flattened, closely associated with 
 
MUCOUS MEMBRANE OF THE CHEEKS. 367 
 
 one another, and devoid of nuclei. Tlie cells of the middle and 
 deeper layers are oblong or spheric, and provided with irregu- 
 larly shaped nuclei. The chief fibrous tissues of the transitional 
 portion, which are thinnest at the point where the hair-follicles 
 cease to exist, are united into fle.xiform fasciculi, which are sepa- 
 rated at various points to give passage to numerous minute 
 blood-vessels. The fibrous tissues increase in thickness as the 
 mucomembranous portion is approached. Numerous thin and 
 somewhat elongated papillae are distributed over the surface of 
 the transitional portion. 
 
 The mucomembranous portion of the mucous membrane of 
 the lips includes all that portion covering the labial folds within 
 the mouth, beginning at the line of occlusion on the contiguous 
 surface and extending to the gums. The epithelium is much 
 thicker than that previously described, and presents the char- 
 acteristic layers common to stratified, squamous epithelium. 
 Superficially the cells are flattened and tubular, provided with 
 nuclei of similar form. In the middle layer the cells are flat- 
 tened and oblong, followed in the deeper layer by irregularly 
 formed nucleated cells. A variety of fibers make up the 
 structure — one class fine in texture and united into fasciculi, 
 intermingled with elastic fibers, together with another set of 
 coarse, strongly looped fibers. Whenever the fibers of the 
 tunica propria assume a definite general direction, they are hori- 
 zontal, passing from right to left and encircling the oral aper- 
 ture. The tunica propria is beset with numerous conic papillae 
 which project into the epithelium ; these are longest where the 
 epithelium is thickest. The mucous membrane forming the 
 labial frena is covered by an epithelial layer which is much 
 thinner than that distributed to other parts of the lips. The 
 fibers in these are irregularly distributed, and the papillae are 
 small and not so numerous. The coronary arteries and their 
 accompanying veins course through the lips near the junction 
 of the transitional with the mucomembranous portion of the 
 mucous membrane. 
 
 Mucous Membrane of the Cheeks. — The mucous mem- 
 brane of the cheeks presents but little variation in its struc- 
 ture from that of the mucomembranous portion of the labial 
 
368 
 
 HISTOLOGY. 
 
 mucous membrane. The buccal epithelium is the same in 
 structure and thickness as that of the lips, excepting the dispo- 
 sition of cells in the middle layer, where they are greater in 
 number and more closely associated, being somewhat distorted 
 by contact. The papillae, which project from the mucosa into the 
 epithelium, are somewhat broad at their base, with elongated ex- 
 tremities, the height of which is quite variable, in some instances 
 
 -Section through the Mucous Membrane of the Cheek, showing the 
 Papill/e of the Mucosa in Transverse Section. 
 
 penetrating well into the epithelium, at others merely entering 
 its deeper layer. At the anterior portion of the cheek, or that 
 in the region of the angle of the mouth, the mucous membrane, 
 by its submucous portion, is in immediate contact with the fibers 
 of the buccinator muscle, and throughout the entire surface of 
 the cheek it is closely associated with this muscle. The mem- 
 brana propria is dense immediately beneath the epithelium, but 
 as the buccinator is approached it becomes much less so. 
 
MUCOUS MEMBRANE OF THE GUMS. 
 
 369 
 
 Mucous Membrane of the Gums. — The mucous mem- 
 brane covering these parts is, on account of the numerous tendi- 
 nous fasciculi which enter into its construction, extremely dense 
 and tough, these characteristics being more strongly manifest 
 here than in any other portion of the oral mucous membrane. 
 These qualities are especially pronounced about the gingival 
 margins and over the major portion of the alveolar walls, being 
 
 Fig. 247. — Section through thk Gums, showing Epitheliuji and Basement 
 Membrane. 
 
 closely bound down to the bone by direct prolongations of the 
 tendinous fasciculi of the periosteum which penetrate the mem- 
 brane. As the gingival mucous membrane passes into that of 
 the lips and cheeks it gradually becomes less dense. The epi- 
 thelium of the mucous membrane of the gums is composed of 
 lamina of tessellated and ribbed cells. The superficial cells are 
 the flattened cells of pavement epithelium ; subjacent to this 
 they become thicker and deeply ribbed, while the deepest cells 
 24 
 
370 HISTOLOGY. 
 
 are conic or cylindric with conic extremities. The tissue com- 
 posing the tunica propria is made up of flattened fasciculi of 
 connective tissue, the fibers of which run parallel with one 
 another. Numerous elastic fibers are also present. Three sets 
 of fibers are to be distinguished in the mucous membrane of 
 the gums — those which run vertically, those which pass in a 
 horizontal direction, and those which radiate or are distributed 
 fan-like. Of the first named, the fibers extend from above 
 downward ; in the second class they pass from right to left par- 
 allel with the surface ; the third class, including those fibers 
 which are reflected from the alveolodental membrane, are dis- 
 tributed in fasciculi about the margins of the alveoli. 
 
 Mucous Membrane of the Roof of the Mouth. — Hard 
 Palate. — The mucous membrane covering the hard palate is, in 
 very many respects, dissimilar to that surrounding the necks of 
 the teeth and forming the palatogingival margins. Like the 
 mucous membrane of the gums, that overlying the hard palate 
 is dense and tough. The papillee of the tunica propria, which 
 penetrate the epithelium, are not so numerous as those upon the 
 gums. In the posterior third of the hard palate they are some- 
 what more numerous and generally a little more prominent than 
 those in the anterior portion. In the median raphe and over the 
 rugae, the papillse are especially sparingly distributed. The epi- 
 thelium is of the pavement variety, somewhat thinner in front 
 than behind, the cells being more freely distributed at some 
 points than at others. The mucous membrane of the hard 
 palate is less in thickness anteriorly than posteriorly. The dis- 
 tribution of the fibers is such that they radiate from the alveolar 
 borders toward the center of the palate, the anterior fibers 
 passing obliquely backward, while those from the lateral walls 
 pass parallel with one another to the median line. For the most 
 part the fibers are broad and form a plexus between the epithe- 
 lium and the submucous tissue. The submucous tissue is 
 sparingly distributed over the central portion of the hard palate, 
 but laterally is somewhat more abundant, containing a few 
 fat-cells. 
 
 Soft Palate, Uvula, and Fauces. — Passing backward from 
 the posterior margin of the hard palate, the mucous membrane 
 
MUCOUS MEMBRANE OF THE FLOOR OF THE MOUTH. 371 
 
 overlies the fibrous aponeurosis of the soft palate and its median 
 and lateral prolongations — the uvula and pillars of the fauces. 
 The epithelium is of the laminated pavement variety, with the 
 deeper cells larger than those placed superficially. The sub- 
 stance of the mucous membrane is composed of fasciculi of 
 connective tissue, intermingled with a plexus of elastic fibers. 
 The fibers are distributed in three principal directions — from 
 side to side, or horizontally, longitudinally, and obliquely. The 
 oblique fibers are instrumental In forming the submucous tissue 
 of both the soft palate and uvula. Numerous conic papillae 
 project from the tunica propria into the epithelium ; these are 
 larger and more numerous on the uvula than on the soft palate. 
 The tunica propria Is somewhat variable in thickness to accom- 
 modate the glands, which are more or less numerous, and pres- 
 ent In greater numbers in one Instance than In another. In 
 general the membrane as a whole is thinnest along the margin 
 of the hard palate, gradually increasing In thickness as the free 
 border is approached. The folds of mucous membrane forming 
 the pillars of the fauces present no peculiarity differing from 
 that of the soft palate, save a more generous supply of elastic 
 fibers. 
 
 Mucous Membrane of the Floor of the Mouth. 
 
 The Tono-jie. — The entire unattached surface of the tongue is 
 covered by a reflection of the mucous membrane of the floor of 
 the mouth. In this organ the general structure of the mucous 
 membrane does not vary from that of other oral mucous mem- 
 brane, being composed of an epithelium, a tunica propria, and a 
 submucosa. The mucous membrane covering the dorsum of 
 the tongue presents special characteristics, which differ from that 
 of the under surface and the floor of the mouth in general. In 
 the former location the papillary elevations of the tunica propria 
 are conspicuously developed, and with their covering of strati- 
 fied, scaly epithelium cause the peculiar furred appearance. 
 Three classes of papillae are distinguished, named, In accordance 
 with their iorm, filiform paplllje, fungiform papillae, and circum- 
 vallate papillae. 
 
 The filiform papilla;, which are very numerous over the entire 
 
HISTOLOGY. 
 
 dorsum and sides of the tongue, are conic and frequently pro- 
 longed into numerous horn-like processes, known as secondary 
 
 Fig. 248. — Longitudinal Section through Mucous Membrane of the Human 
 Tongue. X 20. 
 
 Fig. 249 — Longitudinal Section of the Mucous Membrane of the Human Tongue, 
 showing the Fungiform and Secondary Papill.^. X 80. 
 
 papillae. As elevations from the tunica propria they are com- 
 posed of well-defined fibrillated tissue, intermingled with numer- 
 ous elastic fibers. The pavement epithelial cells are found 
 
MUCOUS MEMBRANE OF THE FLOOR OF THE MOUTH. 373 
 
 overlapping one another, and provided witli processes which 
 project beyond the papillae. 
 
 The finigiform papillce are also distributed over the entire 
 dorsum and sides of the tongue, but are somewhat less numerous 
 than the filiform variety. They appear as well-defined eleva- 
 tions, and are connected with the tunica propria by a constricted 
 portion or neck. The entire free or rounded surface of these 
 papillae is beset with secondary papillee. The epithelium is 
 slightly thinner than that over the filiform papillae, this being the 
 principal distinguishing feature. The numerous capillaries pro- 
 duce a rich red color, plainly observable through the transparent 
 
 Fig. 250. — Section through Epithelium, Near the Tip of the Tongue. X 4°- 
 
 epithelium. Connective-tissue bundles make up the bulk of 
 these papillae, few elastic fibers being present. 
 
 The cii-cumvallate papilla are placed on the posterior portion 
 of the dorsum of the tongue, and are few in number (eight to 
 sixteen). They are much larger than those already described, 
 and in general resemble modified fungiform papillae. They 
 are flattened and broad, and differ from the fungiform by having 
 a circular furrow or wall surrounding them. Secondary papillae 
 are present on the free surface only, the sides, and in some 
 instances the walls surrounding them, being occupied by the 
 end organs of the special sense of taste — the taste-buds. Other 
 
374 HISTOLOGY. 
 
 taste-buds are found upon the lateral margins of the tongue 
 posteriorly, nestled in a group of parallel folds of mucous mem- 
 brane — the papillae foliata. The connective tissue within these 
 papillae is similar to that in the fungiform papillae. On other 
 parts of the tongue, or those portions not occupied by these 
 specially constructed papillae, the epithelium is similar to that in 
 other parts of the mouth. The tunica propria is less in thick- 
 ness in and about the tip of the tongue, and is intimately con- 
 nected with the subjacent muscular structure. As the root of 
 the organ is approached, the tunica propria becomes thicker 
 and more dense. The submucosa Is especially intimately con- 
 nected with the underlying parts at the margins and tip of the 
 tongue. The extreme portion of the root of the tongue has its 
 mucous membrane particularly modified by a special aggrega- 
 tion of adenoid tissue — developed lymph-nodules. These are 
 large and readily perceptible to the naked eye. They are pro- 
 vided with a central opening, which dips down into a well- 
 defined vault or crypt, which is lined by a reflection of the 
 stratified oral epithelium. 
 
 Blood-supply to the Mucous Membrane of the Mouth. 
 — The oral mucous membrane derives its supply of blood froni 
 numerous branches of the external carotid artery — namely, the 
 superior and inferior coronary, buccal, lingual, transverse facial, 
 pterygopalatine, and the alveolar. Entering the submucosa, 
 the minute terminal branches of these arteries are distributed 
 parallel to the surface, and by anastomosis form plexuses from 
 which other minute branches are given off to supply the papillae 
 of the tunica propria. After coursing through the papillae the 
 blood is discharged into a similar venous plexus, and thus 
 conveyed from the parts. In a like manner the mucous mem- 
 brane and papillae of the tongue are supplied, branches of the 
 lingual artery conveying the blood to the parts. The dorsalis 
 linguae supplies the mucous membrane of the dorsum of the 
 tongue and pillars of the fauces, while the ranine artery by its 
 minute branches supplies the remaining mucous membrane. 
 Each papilla is entered by two or more arterial terminals, which 
 divide, anastomose, and finally send off capillary branches to 
 the secondary papillae. 
 
NERVE-SUPPLY TO THE MUCOUS MEMBRANE OF THE MOUTH. 375 
 
 Nerve-supply to the Mucous Membrane of the Mouth. 
 
 — The distribution of the nerve-fibers to the oral mucous mem- 
 brane is approximately similar in all parts. The fibers, which 
 are of the medullated variety, are first distributed to the sub- 
 mucosa, forming a wide-meshed reticulum. From this fibers 
 are given off to the tunica propria, terminating in end-bulbs, 
 or, after losing their medullary sheath, are distributed to the 
 epithelium, where their free extremities lie between the epi- 
 thelial cells. The nerves of the mucous membrane of the 
 tongue (the glossopharyngeal and lingual branch of the fifth) 
 may have their endings similar to those in other parts of the 
 mouth, or they may be intimately associated with the taste-buds. 
 
 Literature. 
 Legros and Magitot, 1S80. 
 Klein, " Structure of the Oral Lips," 1S68. 
 
 Sebastian, "Anatomy and Physiology of the Labial Glands," 1842. 
 KoUiker, " Mikroskopische Anatomie." 
 Kirke, "Physiology." 
 
 Strieker, " Human and Comparative Histology." 
 Stohr, " Text-book of Histology," 1896. 
 
CHAPTER III. 
 
 GLANDS AND DUCTS OF THE MOUTH; OF THE LIPS; OF THE CHEEKS 
 OF THE HARD AND SOFT PALATES; OF THE TONGUE.— THE SALI- 
 VARY GLANDS. 
 
 GLANDS AND DUCTS. 
 
 Glands of the Mouth. — The glands of the mouth, Hke the 
 glands of other parts of the body, are composed almost en- 
 tirely of epithelium, and may, therefore, be classed with the 
 epithelial tissues. Glands exist in two principal forms — tubular 
 and saccular (alveolar). The former occur either singly or in 
 groups, and are further subdivided into simple tubular and com- 
 pound tubular glands. A like condition is present in the saccular 
 glands and similar terms are employed to qualify them — simple 
 saccular glands and compound saccular glands. 
 
 A simple tubular gland \s one composed mainly of a simple 
 tube-like structure ; 2l compotmd tubular gland x?, one composed 
 of a number of smaller tubes emptying into a single duct. 
 
 A simple saccular gland is one iormed by a sacculation of 
 serous or mucous membrane into a single, simple sac, or by 
 branched saccules having an excretory duct (alveolar system) ; 
 a compound saccidar gland is composed of a combination of 
 branched saccules. 
 
 In the larger glands a sheath is formed by the surrounding 
 connective tissue, from which numerous septa are given off to 
 the interior of the gland, dividing it into compartments varying 
 in size. These are known as gland-lobides. The connective- 
 tissue walls of the gland-lobules carry the larger blood-vessels 
 and nerves. Most glands are divided into two essential parts, 
 — the gland-follicle and the excretory duct, — the former being 
 specialized for the secretory function, while the latter, by com- 
 municating with the surface, conveys the secreted substance to 
 that point. 
 
 77^1? gland-follicles are composed of a layer of gland-cells, 
 376 
 
THE GLANDS OF THE LIPS, 377 
 
 usually simple in character, surrounding the follicular walls. 
 External to these is a specially modified connective tissue, form- 
 ing the basement membrane, or membrana propria. The 
 appearance of the gland-cells and their nuclei is continually 
 changing, being thus influenced by their functional activity. 
 
 The excretory ducts consist of a wall of connective tissue and 
 elastic fibers, lined by a columnar epithelium, either simple or 
 stratified. In some instances the arrangement of the e.xcretory 
 
 Fig. 251. — Section through the Glandular Tissue ok the Tongue. >( 4°- 
 
 ducts is much complicated, being divided into secretory tubes, 
 which in turn are subdivided into smaller tubules — intercalated 
 tubes. 
 
 The Glands of the Lips {Labial Glands). — The glands of 
 the lips are situated in the submucosa, and are first observed 
 immediately within the line of labial occlusion, at which point 
 the thickness of the epithelium becomes somewhat definite and 
 general. These glands are variable in size, but all are suffi- 
 ciently large to be observed without the aid of the micro- 
 
37S HISTOLOGY. 
 
 scope. They are of the compound tubular variety, and com- 
 municate with the surface through an excretory duct, which 
 throughout the greater part of its extent is Hned with stratified, 
 scaly epithelium. In passing from the surface toward the gland- 
 follicle, the main duct takes a spiral course obliquely through 
 the tunica propria, and upon reaching the submucosa gives off 
 numerous branches and twigs which terminate in the individual 
 acini. The larger branches from the main duct are lined with 
 stratified squamous epithelium, while the smaller twigs are pro- 
 vided with columnar epithelium. In many instances the main 
 excretory duct, in its passage through the tunica propria, receives 
 the principal duct from small accessory ducts. The framework 
 of the labial glands is formed by the flexiform tissue composed 
 of fasciculi of the fine connective-tissue fibers belonging to the 
 submucous layer, together with delicate, coiled elastic fibers. 
 This framework gives support to a minute system of capillaries 
 and small nerve-fibers supplying the acini. The acini are so ar- 
 ranged that those belonging to a large duct are united into a 
 lobule by the submucous connective-tissue fasciculi, and these in 
 turn are formed into lobes. By a continuation of the same fas- 
 ciculi and fibers which limit a lobe, and in the meshes of which 
 the acini are situated, a sheath to the excretory duct is formed. 
 Besides the branched, tubular, mucous glands of the lips, there 
 are occasionally found, at the edges of the lips, sebaceous glands. 
 The Glands of the Cheeks {Buccal Glands, Molar Glands). 
 — The glands of the cheek are also situated in the submucous 
 layer of the mucous membrane. They, like the labial glands, 
 are of the compound tubular variety, and when microscopically 
 examined are found to be similar in structure. They are some- 
 what larger than the labial glands and proportionately less 
 numerous. The chief duct from each of these glands usually 
 opens with a narrow mouth on the surface of the oral mucous 
 membrane, and in its passage through the tunica propria takes 
 a vertical or oblique direction. In the submucosa the chief duct 
 branches into two or more smaller ducts, taking up alveoli. As 
 the buccal glands are somewhat larger than the glands of the 
 lips, they are composed of a greater number of ducts and 
 alveoli. 
 
THE GLANDS OF THE TONGUE. 379 
 
 The Glands of the Hard and Soft Palate {Palatal Glands). 
 — The mucous glands of the hard palate are situated in the sub- 
 mucosa and closely associated with the periosteum. They are 
 compound tubular glands, and in all essential particulars are 
 similar to the labial and buccal glands. They are quite numer- 
 ous (200 to 300), isolated in the anterior portion, but are 
 grouped into a single row or into two rows posteriorly. The 
 glands are freely distributed in each lateral half, but are absent 
 at the median line. 
 
 In die soft palate the glands are of the same character, some- 
 what variable in size, the largest being found in the uvula. The 
 excretory ducts from these glands vary in diameter, in the 
 nature of their fibrous structure, and in the direction taken in 
 passing to the surface. Over the surface of the soft palate the 
 mouth of these ducts are represented by minute orifices slightly 
 smaller than die body of the duct, but in the uvula the opposite 
 condition is present, the mouth of the duct being wider than the 
 body. The course taken by the excretory duct is seldom a 
 direct one, but after receiving all tributary branches passes 
 obliquely through the tunica propria, and before entering the 
 epithelium turns at an abrupt angle, and so continues until the 
 surface is reached. The ducts are lined by a simple columnar 
 epithelium, which in some instances is ciliated ; the walls of the 
 tubes consist of gland-cells and a structureless membrana pro- 
 pria. In some instances the surface epithelium may be reflected 
 for a short distance and partly serve in the capacity of a lining 
 to the tubular walls. 
 
 The Glands of the Tongue {Lingual Glands). — In this 
 organ two varieties of glands are found, occurring both in the 
 mucous membrane and in the superficial muscular strata, being 
 principally distinguished by the nature of their secretions. The 
 gland-cells of the one set are mucigenous, secreting mucin ; 
 these are the mucous glands. The other set is productive of a 
 serous fluid, thin, watery, and containing albumin ; these are 
 the serous glands. 
 
 The mucous glands of the tongue are found along the lateral 
 margins and over the root of the organ, being most numerous in 
 the latter situation. They are of the compound tubular variety. 
 
38o 
 
 HISTOLOGY. 
 
 and in most particulars are identical with the mucous glands of 
 other parts of the oral cavity. The ducts are lined with ciliated 
 columnar epithelium, and the walls of the duct consist of a 
 homogeneous membrana propria and gland-cells. The glands 
 occupying the root of the tongue are frequently found with 
 their excretory ducts opening into the follicular crypts. The 
 tubules consist of a structureless membrana propria and num- 
 erous gland-cells, the latter varying in appearance according to 
 their function or functional activity. The crypts of the folli- 
 cles constitute reservoirs for the acinous glands, and these 
 
 «Si5s5^ 
 
 
 Fig. 252. — Section through Base of Tongue, showing Serous Glands. 
 
 receptacles frequently extend for some distance beneath the 
 surface, receiving at various points the main excretory ducts 
 from the mucous glands. These saccular-like reservoirs are 
 lined by a well-defined capsule surrounded by a fibrous sheath, 
 internal to which is an epithelial covering, a prolongation of 
 the common epithelium of the mouth. Between these two 
 layers are a number of minute, closed lymph-follicles placed in a 
 single layer. The mucous glands on the lateral walls of the 
 tongue are, for the most part, situated near the middle or 
 
THE SALIVARY GLANDS. 381 
 
 posterior portion. The ducts from these glands usually open 
 directly toward the cheek, but in rare instances they pass 
 obliquely downward and open near the proper floor of the 
 mouth. At the tip of the tongue, burled beneath the mucous 
 membrane and some of the muscular fibers, may be found a 
 pair of mucous glands (Nuhn's) which open by free orifices 
 on the under surface. At the root of the tongue, flat, len- 
 ticulated elevations of the mucous membrane are present, 
 beneath which is imbedded conglobate, glandular substance. 
 These show a central orifice leading to a small pit lined with 
 tessellated epithelium. 
 
 The serous glands of the ioiigue are compound tubular glands, 
 and are found in the region of the circumvallate papillse, closely 
 associated with the taste-buds. The excretory ducts, lined with 
 a simple or stratified columnar epithelium, the latter sometimes 
 ciliated, open near the base of the papilla, or between the 
 papilla and its wall. The tubules are similar to those in the 
 mucous glands, consisting of a delicate, structureless membrana 
 propria and gland-cells. The gland-cells are composed of a 
 frail, transparent protoplasm, containing rounded nuclei. 
 
 The Salivary Glands. — The parotid, submaxillary, and 
 sublingual glands each consists of an excretory duct, branch- 
 ing frequently in a tree-like manner into smaller ducts, lined 
 throughout with a layer of epithelial cells. From the smaller 
 ducts terminal branches are given off, which in turn are lined 
 with epithelium. The other portions of the glands are invested 
 by. columnar epithelium, and arranged like grapes about the 
 main excretory duct, and consequently belong to the group of 
 racemose glands. The terminal branches or alveoli attached to 
 the smaller excretory ducts are so numerous that they become 
 much compressed from pressure, and the grape-like appearance 
 is more or less destroyed, and but little space is left for inter- 
 stitial tissue. Each gland is inclosed in a fibrous connective- 
 tissue capsule, and from this numerous septa of fibrous 
 trabeculae pass to the interior and divide the glandular sub- 
 stance, first into lobes, these being subdivided into lobules, the 
 lobules by further subdivision forming the alveoli. The glandu- 
 lar connective tissue is loose in texture, containing many elastic 
 
382 HISTOLOGY. 
 
 fibers and lymphoid cells. Fine bundles of fibrous tissue, 
 together with branched connective-tissue corpuscles, constitute 
 the connective-tissue matrix between the alveoli. 
 
 The Ducts. — Entering the interior of the gland, the chief duct 
 divides into a number of large branches, one of which passes 
 to each lobe, each of these giving off several branches which 
 connect with the several lobules. Upon close examination the 
 central tube of each lobule is observed to throw off several 
 small tubes — the intralobular tubes. Following these are the 
 intermediate tubules, which continue into the terminal compart- 
 ments. The chief excretory duct consists of a double layer of 
 cylindric epithelium and fibro-elastic cartilage. Close beneath 
 the epithelium is a compact membrana propria. The intralob- 
 ular tubes are each provided with a distinct lumen. The walls 
 are composed of a membrana propria lined by a layer of 
 columnar epithelium, the cells of which contain a central round 
 nucleus. 
 
 The Parotid Gland. — The distinguishing histologic feature 
 in this gland is found in its excretory duct (Stenson's duct), 
 Avhich is provided with a membrana propria, especially broad 
 and compact, placed immediately beneath the epithelium. The 
 duct is composed of a double layer of cylindric epithelium and 
 fibrous tissue, intermingled with elastic fibers. The main duct 
 divides and passes into the intralobular tubes, beyond which 
 are the intermediate tubules. The intralobular tubes are lined 
 by columnar cells, while the intermediate tubules are lined by 
 elongated, spindle-shaped cells. The salivary cells lining the 
 acini are different in character from those in the submaxillary 
 and sublingual glands. The parotid gland is a true salivary 
 gland, and the serous gland-cells composing its epithelial lining 
 are disposed in a single layer. The cells are columnar or pyra- 
 midal in form and composed of a dense protoplasm, containing 
 a spheric nucleus. 
 
 The Submaxillary Gland. — The excretory duct (Whar- 
 ton's duct), like the main duct of the parotid gland, is composed 
 of a double layer of columnar epithelium, external to which is 
 a layer of cellular connective tissue, the whole being surrounded 
 by a thin stratum of muscular fibers placed longitudinally. The 
 
NERVE SUPPLY TO THE SALIVARY GLANDS. 383 
 
 intralobular tubes are lined by a specialized, elongated, cylindric 
 epithelium, which, in the intermediate tubules, becomes clothed 
 with cubic cells. The acini are lined either with serous gland- 
 cells similar to those lining the acini of the parotid gland or with 
 mucous gland-cells, the former being most constant in their 
 presence. The two kinds of acini are uninterruptedly connected. 
 In most instances there are but a few mucous acini present 
 within the lobule, but occasionally they are found in abundance. 
 The submaxillary is a mixed or mucosalivary gland. 
 
 The Sublingual Gland. — The excretory duct (Rivini's 
 duct) is similar in structure to the chief excretory duct of the 
 submaxillary gland. The intralobular tubes are lined with col- 
 umnar epithelium. The intermediate tubules are not positively 
 known to exist, and it is quite probable that the intralobular 
 tubes pass directly into the terminal compartments. The acini 
 are composed of a membrana propria and gland-cells, both 
 mucous and serous. The former are much more numerous than 
 in the acini of the submaxillary. The membrana propria is 
 composed of stellate connective-tissue cells. This gland is also 
 a mixed or mucosalivary gland. 
 
 Blood-vessels and Lymphatics in the Salivary Glands. 
 — The lobules of the salivary glands are richly supplied with 
 blood-vessels. The many arterial branches break up into 
 numerous capillaries, which, forming a dense network, sur- 
 round the acini, being supported by the interalveolar connec- 
 tive tissue. The lymphatic vessels accompanying the intralobu- 
 lar tubes are in communication with numerous lymph-spaces 
 which exist between the interalveolar connective tissue and the 
 walls of the acini. The substance of the gland is further sup- 
 plied with blood by numerous plexuses of lymphatics which are 
 carried or supported by the interlobular connective tissue. 
 
 Nerve-supply to the Salivary Glands. — The nerve-fibers 
 distributed to the salivary glands are both of the medullated and 
 non-medullated variety, and other nerve-tissue in the form of 
 ganglion-cells is present. The medullated nerve-fibers are 
 abundantly numerous, and are distributed to all parts of the 
 gland. In many respects the fibers are peculiarly constructed. 
 They are extremely delicate, made so by the frail nature 
 
384 HISTOLOGY. 
 
 of their medullary sheath ; they divide and give off so many 
 branches as to almost give them a feathery fineness. This 
 peculiarity is especially noticeable toward their extremities, 
 where the fibers lie between the alveoli and give off minute 
 branches in all directions. The nerve-fibers are placed in close 
 relation to the tubes and tubules, which they freely encircle ; 
 they perforate the membrana propria and break up into finer 
 subdivisions, from which they are distributed to the exterior of 
 the epithelial cells. In the alveoli two kinds of nerve termina- 
 tions are found. The primitive fibers branch between the alveoli 
 and are distributed to the membrana propria, upon entering 
 which numerous branches are thrown off which pass to the 
 epithelial cells beneath. The non-medullated fibers, which are 
 much less numerous, are composed of an extremely delicate 
 fasciculi of transparent fibers resembling axis-cylinders, and 
 invested by a sheath of connective-tissue cells containing nuclei. 
 The distribution of these fibers is similar to the medullated fibers, 
 encircling the tubes and penetrating the membrana propria, 
 being similarly distributed to the alveoli. 
 
 Literature. 
 
 Stohr, " Text-book of Histology," 1896. 
 
 Strieker, "Human and Comparative Histology," vol. i, 1870. 
 
 Klein, " Elements of Histology," 1889. 
 
 Sebastian, " Recherches anatomique, physiologiques, pathologiques, les Glans 
 Labiales," 1842. 
 
 Ward, "On Salivary Glands," Tood's " Cyclopedia of Anatomy and Physi- 
 ology." 
 
 Klein and Vernon, Strieker's " Human and Comparative Anatomy," vol. i, 
 ehap. XVI. 
 
 Sudduth, " Embryology and Dental Histology," " Ameriean System of Den- 
 tistry," vol. I, part III. 
 
 Brubaker, " Transactions Odontologieal Soeiety of Pennsylvania," i88g-'95. 
 
 Todd and Bowman, "Physiological Anatomy," vol. i. 
 
 Szontagh, " Essays on Minute Anatomy of Hard Palate in Man," 1866. 
 
CHAPTER IV. 
 
 MUSCULAR TISSUES OF THE MOUTH; OF THE LIPS; OF THE CHEEKS; 
 OF THE SOFT PALATE; OF THE TONGUE. 
 
 MUSCULAR TISSUES OF THE MOUTH. 
 
 Muscular Tissues of the Lips. — The minute bundles 
 forming the fasciculi of the oral sphincter muscle — the orbicu- 
 laris oris — are distributed between the submucosa of the muco- 
 membranous portion and the subcutaneous tissue of the 
 cutaneous portion of the lips. The muscular fibers radiate in 
 three principal directions upon either side of the median line : 
 from the angle of the mouth toward the median line, and from 
 the fleshy slips of the maxilla and mandible — the musculi incisivi. 
 As the fibers from the angle of the mouth pass to the sub- 
 stance of the lip, they are arranged in a laminated manner. 
 When the median line is reached, one set of fibers terminate 
 somewhat abruptly in the subcutaneous tissue, another set is 
 continued beyond the median line and attached to the cutis of 
 the opposite side, while a third set, without crossing the median 
 line, is attached to the incisive fossae of the maxilla and 
 mandible. The numerous muscular fibers of the internal 
 labial or mucomembranous portion, and the external, facial, or 
 cuticular portion, penetrate the parts and terminate in close 
 proximity to the epithelium or to the base of the papillae. Deli- 
 cate, hair-like fibers which are continuous with the sarcolemma 
 slightly penetrate the cutis and membrana propria. A few of 
 the fibers, which may be classed with the terminals of the out- 
 running muscles from the lips, are arranged in a number of 
 fasciculi In the subcutaneous portion, pass through the fasci- 
 culi of the orbicularis oris, reach the submucous tissue, where 
 they cross and recross one another, and finally pass into the 
 membrana propria, where they end in fan-like terminals. The 
 fasciculi of the orbicularis differ somewhat in the upper and 
 lower lips ; in the former the bundles are strongly developed 
 25 3S5 
 
386 HISTOLOGY. 
 
 toward the angle of the mouth, while in the latter the median 
 bundles are the strongest. The labial muscular tissues are of 
 the transversely striated variety. The fibers are cylindric in 
 form, having rounded or pointed extremities in the interior, and 
 broad or flattened ends where they come in contact with the 
 periosteum. When examined with a high power each fiber 
 shows alternately broad and narrow strise, the former being 
 dim, while the latter is bright in appearance. With a stronger 
 power both the broad and narrow strise are seen to be trans- 
 versely striated. 
 
 Muscular Tissues of the Cheeks. — The muscles entering 
 into the construction of the lateral walls of the mouth have 
 already been described in part i, page 24, giving the relations 
 existing between the individual muscles, together with the gen- 
 eral disposition of the various fasciculi. Histologically con- 
 sidered, these muscles partake of all the characteristics of 
 striated or voluntary muscular tissue. In the body of the buc- 
 cinator and masseter muscles the fibers are cylindric and have 
 definitely pointed or rounded ends. Near their termini, par- 
 ticularly in the latter muscle, the inner extremities of the ter- 
 minal fibers are pointed, while the outer ends, or those by which 
 the attachment is formed, are broad and rather flat. 
 
 Muscular Tissues of the Soft Palate. — The disposition ot 
 the striated muscular tissue of the soft palate is extremely com- 
 plicated. The azygos uvulee, the only true longitudinal muscle 
 in the soft palate, has its origin from aponeurosis of the soft 
 palate and from the nasal spine of the palate-bone, the fibers 
 passing backward upon either side of the median line. This is 
 a double muscle, and near its point of origin the two portions 
 are distinct and separated by a definite space, but upon reaching 
 the base of the uvula they become closely associated. The 
 fasciculi do not continue to the apex of the uvula, but imme- 
 diately beyond the center of its length are thrown out fan-like 
 toward the sides, terminating in a manner similar to the fibers 
 of the lips. In passing from before backward a number of 
 small fasciculi are given off which reach out laterally and 
 traverse the glandular lobes, completely surrounding them, 
 after which they again return to the principal fibers at the 
 
MUSCULAR TISSUES OF THE TONGUE. 387 
 
 median line. The palatopharyngeus muscle is divisible into 
 two parts, the upper extremities of which lie partly in front and 
 partly behind the levator muscles. The greater number of the 
 fibers of one set, situated in front of the levators, iorm a curved, 
 flattened aponeurosis. The fibrous border of the hard palate 
 serves as an attachment for the convex border of this portion, 
 while the other border, which is concave, is directed toward the 
 arch of the levators. The fibers of the palatopharyngeus, 
 situated behind the levators, form a number of loose fasciculi 
 interspersed by fat-cells. In passing toward the free border 
 of the soft palate the fibers become much more delicate, 
 and, separating, some course in front and others behind this 
 muscle. In this location the fibers become closely associated 
 with the glands, and either end here or are continued to the 
 submucosa, or even to the membrana propria of the mucous 
 membrane. The fibers of the palatopharyngeus unite with the 
 fibers of the levators, and an arch-like fasciculus is formed by 
 this union which, subdividing, passes in front of the azygos 
 uvulae to the opposite side. All of these fibers run outward 
 and downward, and unite with the extremities of the other 
 palatal muscles, the fibers of which are somewhat more regu- 
 larly distributed. Like the muscles of the lips and cheeks, the 
 several fasciculi of the palatal muscles form a delicate plexus, 
 and a quantity of fatty tissue is found between the various 
 fasciculi. 
 
 Muscular Tissues of the Tongue. — The tongue is divided 
 into two equal lateral portions by a median septum — the septum 
 linguae. This central septum, composed of a vertical layer of 
 compact, fibrous, connective tissue, extends the entire length 
 and depth of the lingual median line. Beginning at the hyoid 
 bone, it gradually increases in prominence until the middle of 
 the organ is reached, beyond which point it becomes less pro- 
 nounced and finally disappears near the tip. The bundles of 
 the muscular tissues are arranged longitudinally, transversely, 
 and vertically. The former lie immediately beneath the mucous 
 membrane, including the superior lingualis above and the in- 
 ferior lingualis below, together with the greater part of the 
 styloglossus. The superior lingualis extends from the base to 
 
388 HISTOLOGY. 
 
 the tip of the organ, and by short fasciculi its fibers are attached 
 to the overlying tissues. The fibers of this muscle are placed 
 between the hyo- and styloglossi muscles of the opposite side, 
 both of which overlap the fibers of the llngualls near the base 
 of the tongue. The Inferior llngualls also gives off several 
 small fasciculi and fibers to the mucous membrane beneath, and 
 is composed of two bands which reach from the base to the 
 apex, each being placed between the hyoglossus and genlo- 
 hyoglossus muscles. The transverse fibers, which are placed 
 between the superior and Inferior llngualls muscles, originate 
 from the septum linguae, and form the bulk of the organ. From 
 their point of origin these fibers course outward and upward to 
 the sides of the tongue. Those fibers which are vertically dis- 
 posed decussate with the transverse fibers, and pass from the 
 dorsum toward the under surface of the tongue, the fibers 
 curving gracefully with their concavity directed toward the 
 under surface. In most instances the ascending vertical fibers, 
 as well as the transverse fasciculi, pass between those longitu- 
 dinally disposed and connect with the submucosa. 
 
CHAPTER V. 
 
 TISSUES OF THE TEETH-ENAMEL; DENTIN; CEMENTUM ; THE 
 TOOTH-PULP.— THE ALVEOLODENTAL MEMBRANE. 
 
 TISSUES OF THE TEETH. 
 
 Knamel. — The enamel, which forms a cap-Hke covering 
 of varying thickness over the entire crown of the tooth, is a 
 
 Fig. 253. — Section of Enamkl from Human Tooth (Specimen by J. Howard Mum- 
 mery). X 350- — {After Williavis.) 
 
 vitreous, hyaUne substance, containing but little, if any, organic 
 matter. The thickness of the enamel cap appears to be strongly 
 
 3S9 
 
HISTOLOGY. 
 
 influenced by the function of thie different parts of the tooth- 
 crown, being- thickest over the cutting-edges of the anterior 
 teeth, while in tlie cuspidate teeth, the entire occlusal surface is 
 provided with the thickest enamel layer. It is about evenly dis- 
 tributed over the lateral walls of the crown, but as the cervical 
 line is approached, its thickness is gradually diminished (Fig. 254). 
 Chemically, enamel is composed of the salts of lime, calcium 
 phosphate predominating. Calcium carbonate, magnesium phos- 
 phate, and calcium fluorid are present in smaller quantities. 
 The proportionate quantity of lime-salts in enamel is not fixed, 
 a slight variation in density occurring in the enamel of different 
 individuals. These essential differences are regulated by the 
 proportionate quantity of calcium phosphate and carbonate — 
 a greater amount of the former being productive of additional 
 hardness, while an increase in the latter beyond the minimum 
 amount decreases this quality. As a general rule, the teeth of 
 males contain a greater amount of calcium phosphate than the 
 teeth of females, as shown by the following analysis by von Bibra: 
 
 Calcium phosphate and fluorid, 
 
 Calcium carbonate. 
 
 Magnesium phosphate, 
 
 Other salts, 
 
 Cartilage, 
 
 Fat, 
 
 Total organic. 
 Total inorganic, 
 
 Man. 
 
 89.82 
 
 4-37 
 
 1-54 
 
 .88 
 
 3-39 
 
 3'59 
 )6.4i 
 
 Woman. 
 
 81.63 
 
 8.88 
 
 3-55 
 
 •97 
 
 5-97 
 
 a trace. 
 
 5-97 
 94-03 
 
 In general structure enamel is composed of numerous hex- 
 agonal prisms, with a common direction at right angles to the 
 long axis of the tooth. These prisms are known as enamel 
 ■prisms, enamel fibe7-s, or enainel rods. While the general direc- 
 tion of the fibers is, as previously stated, nearly at right angles 
 to the body of the tooth, they do not pursue a perfectly straight 
 course in passing from the dentin to the surface, but are dis- 
 posed in a tortuous or wave-like manner. The enamel prisms 
 may be said to sit on end against the surface of the dentin, 
 minute depressions in the latter receiving the extremities of the 
 rods. The direction of the enamel prisms, as compared to the 
 
ENAMEL. 391 
 
 body of the tooth-crown, varies according to the part of the 
 crown which they occupy. Taking the entire crown of the tooth, 
 they radiate in such a manner from the surface of the dentin 
 that at the cutting-edge or occlusal surface of the tooth they are 
 more or less vertical, while over the lateral surfaces they tend 
 to the horizontal direction. An examination of the prisms 
 when isolated and decalcified exhibits numerous evenly dis- 
 tributed varicosities, producing a transversely striated appear- 
 ance to the rods. Tomes has pointed out that the enamel rods 
 
 Fig. 254. — Enamel and Dentin from Human Tooth, showing Gradual Reduction 
 IN THE Thickness of the Former as the Cervix is Approached. V lO- 
 
 are variously disposed in that portion of the enamel most closely 
 associated with the dentin. On the cusps of the teeth they are 
 twisted and curved in various directions, while near die surface 
 on the incisors they are uniform and straight. In general, the 
 enamel rods, which begin on the surface of the dentin, are con- 
 tinuous through the entire thickness of the enamel. In passing 
 from the interior to the exterior, the individual rod, to occupy a 
 proportionate space in all parts, would have to increase in diam- 
 eter; but this it does not do. In consequence of this arrange- 
 
392 HISTOLOGY. 
 
 ment there exist numerous supplemental or peripheral rods, 
 which extend but a short distance from the surface, filling in the 
 interprismatic spaces formed by the longer rods. With the 
 exception of the faint transverse striations, the enamel prisms 
 appear to be structureless. A variety of opinions have been 
 expressed in regard to the cause for the striated appearance of 
 the enamel rods. It was claimed by Hertz to be attributable 
 to a temporary arrest of calcification, but more recent investi- 
 gation has shown the cause to be the presence of varicosities 
 
 Fig. 255. — Comparison in the Appearance of the Enamel and Dentin under Low 
 Power of the Microscope. X 4°- 
 
 in the individual fibers, precisely as the varicosities in the 
 muscular fibers produce the striated appearance in that tissue. 
 Bodecker asserts that fully developed normal enamel is non- 
 striated, and Von Ebner practically makes the same statement, 
 claiming that they are due to the preparation of the specimen, 
 which usually being mounted in Canada balsam, suffers suffi- 
 ciently from the slight acid reaction to produce the striated 
 appearance. These statements Williams emphatically denies, 
 saying that, while in some specimens the varicosities are ap- 
 
parent in some parts, they are decided in others. If this be 
 accepted, it would seem to entirely overthrow the theory of Von 
 Ebner in regard to the action of the acid, which would be dis- 
 tributed to all parts alike. 
 
 According to Williams, the varicosities ot one enamel prism 
 are opposite those of the adjoining prisms, and by the coming 
 together of the varicosities the prisms become united by means 
 of processes which they send out. In like manner the varicosi- 
 ties upon the same rod are connected by processes running 
 
 Fig. 256. — Human Enamel. Transverse Ground Sections. — {After Gysi.) 
 
 parallel with the prism. According to Von Ebner, enamel is 
 traversed by numerous minute canals, and Heitzmann claims 
 to have found organic fibers in its substance. Williams, while 
 admitting the enamel structure to be far more complex than 
 past research has shown, appears to have fully demonstrated 
 that neither canals nor organic fibers are present — in fact, he 
 denies the presence of the least trace of organic matter in this 
 structure. The interprismatic matrix, heretofore considered by 
 most authorities to be an organic structure, now appears, by 
 
394 HISTOLOGY. 
 
 the thorough methods employed by the last-named gentleman, 
 as a transparent, inorganic substance. By numerous experi- 
 ments he was enabled to secure a specimen in which the inter- 
 prismatic spaces of one layer were not backed up by the rods 
 of another layer. In some instances the specimen showed the 
 rods well separated and the interspace closed by a perfectly 
 transparent substance, in the interior of which might be seen 
 connecting processes passing from one rod to another. That 
 the enamel is practically of inorganic material, and therefore 
 not capable of transmitting or receiving sensations, may be 
 demonstrated by the simple experiment of immersing a thin 
 section of this tissue in a weak solution of chromic acid, the 
 result of which will be a speedy separation of the enamel 
 prisms which have been liberated by the destruction of the 
 interprismatic substance. What does this signify? Chromic 
 acid is one of the best preservatives of organic tissue known, 
 and if the cementing substances in enamel were organic or even 
 partly so, the prisms by this test would not be freed, but instead 
 would become more firmly cemented together. Therefore we 
 infer from this that the interprismatic substance is even less 
 highly organic than the prisms themselves, these not being acted 
 upon until after the material which holds them together. In ad- 
 dition to the striated appearance formed by the varicosities of 
 the individual prisms of fully developed enamel, other structures 
 of a different character, and upon a much larger scale, are 
 present and known as the "brown striae of Retzius" (Fig. 257). 
 These markings, readily seen with a low power, are of a 
 brownish color, and run nearly parallel with the surface of the 
 dentin or enamel. Those strise nearest the surface of the 
 dentin are inclined to follow the contour of that structure, ex- 
 tending in many instances the entire length of the crown. The 
 lines nearest the surface are longest in the region of the cutting- 
 edge, or occlusal surface of the crown, becoming shorter as the 
 neck of the tooth is approached, being directed at an acute 
 angle to the surface of the dentin at that point. A number of 
 theories are advanced to account for the presence of the 
 "brown strise of Retzius." Tomes suggests that, coinciding as 
 they do with the outer surface of what was at one time the 
 
ENAMEL. 395 
 
 primitive enamel cap, they might be considered as in a measure 
 outhning- the stratifications of the primary deposit. Another 
 theory, but one seemingly without foundation, is to the effect 
 that the strife are produced by an arrest in the calcifying 
 process ; while a third theory attributes the cause to a variation 
 in the character of the nourishment taken by the mother during 
 pregnancy. The acceptance of this latter theory would seem to 
 indicate a set diet for all mothers and at stated intervals, the 
 
 Fig. 257. — Thick Section of Enamel oi' Human Tooth, showing Brown Stri/E of 
 Retzius. X 40. 
 
 striae always being present and somewhat regularly distributed 
 throughout the tissue. 
 
 Still another set of lines or markings are to be observed 
 in the substance of sections of enamel, these being known as 
 the "lines of Schreger." Figure 258 shows these lines as they 
 appear in the enamel by reflected light, the same being quite 
 invisible by transmitted light. The presence of these lines is 
 due to the various directions assumed by the contiguous groups 
 of enamel rods. Beginning at the surface of the dentin they 
 are well defined, but gradual!}^ become less marked as the ex- 
 
396 
 
 HISTOLOGY. 
 
 Fig. 258. — Enamel and Dentin, Human Tooth. — [Afiei- Gysi. 
 
 Oral Epithelium 
 Heaped up 
 over Band 
 
 Connective Tissue 
 
 Fig. 259. — Vertical Section through Jaw ni Human Embryo. Formation of 
 Tooth-band, akout .Sixtieth Day. /. 300. 
 
terior of the enamel is approached. At the line of union be- 
 tween the enamel and dentin irregularly formed cavities are 
 occasionally observed, into which the dentinal tubules may ex- 
 tend, and in rare instances individual tubules may pass beyond 
 the boundary-line of the dentin and enter the enamel, but in all 
 probability both of these conditions are pathologic. Such a 
 state of affairs could hardly be considered normal when we 
 take into consideration that the dentin and enamel calcify in 
 opposite directions, and that the outer wall of the former is 
 completed before enamel calcification begins. 
 
 Ep'Uielii 
 
 ^^^'WTW^^. 
 
 Infant 
 Layer 
 
 Connec- 
 tive 
 Tissue 
 
 Fig. 260.— Vertical Section, Tooth-band, Human Embryo. Tenth Week. X 3°°- 
 
 Development of Enamel. — Preparations for the development 
 of the enamel begin toward the close of the second fetal 
 month, appearing first as a multiplication of the primitive epi- 
 thelial cells in the form of a continuous linear projection extend- 
 ing somewhat obliquely into the subjacent connective tissue. 
 From this crest, or tooth-band, the germs for the future enamel 
 organs are given off. These primary dental bulbs, as they are 
 called, number one for each tooth to be generated, and coinci- 
 dendy with their appearance an aggregation of closely associated 
 
398 HISTOLOGY. 
 
 connective-tissue cells make their appearance in the surrounding 
 submucous tissue. This papilla-like specialization of the submu- 
 cous tissue is the primitive dentin germ, or dentin papilla. It 
 will thus be observed that the enamel is a product of the surface 
 epithelium, ecderritic, while the dentin is generated from the 
 connective tissues, endermic. Soon after the appearance of this 
 club-shaped thickening, or tooth-bulb, by further differentiation 
 its- form becomes bell-shaped, with the concavit}' directed toward 
 the surface. The dentin papilla gradually pushes into the con- 
 cavity of the forming enamel organ, and at a later period the 
 
 Dental Ridge 
 
 
 Connective Tissue 
 
 Fig. 261.— Same as Figure 260. About Twelfth Week. X 200. 
 
 odontoblastic cells are generated about the periphery of the 
 papilla, closely followed by a surface calcification of the dentin. 
 Soon after the forming of the external layers of dentin the 
 ameloblasts or enamel-forming cells become active, and a 
 deposition of enamel prisms takes place upon the exterior of 
 the dentin cap. 
 
 Before taking up the subject of enamel calcification, brief ref- 
 erence will be made to the further development of the enamel 
 oro-an. As the growth of this organ proceeds there is, as the 
 result of a rapid proliferation of the cellular structure, a marked 
 
tendency for the organ to become separated from the tooth-band. 
 The peripheral cells or external epitlieliiini are columnar or 
 prismatic, and remain so, while those in the center, primarily 
 polygonal, soon become transformed into a radiating network 
 or stellate reticulum. The appearance of a stellate reticulum is 
 first observed to take place in the cells occupying the central 
 portion of the enamel-organ, this cellular transformation pro- 
 gressing from the center outward, but ceasing before reaching 
 the columnar surface cells contiguous to the dentin papilla. 
 
 :-iWi 
 
 Epillieliumof 
 Upper Jaw 
 
 Neck 01 Cord 
 
 J 1 iiamel Org 
 -J Dentin Papilla 
 
 '^-: 
 
 Fig. 262. — Vertical Section through TiH.rn.iuM]. Cord, Dentin Papilla, and 
 Enamel Organ, about Fifteenth Week. X 'S°- 
 
 Between the enamel cells and the stellate reticulum is a layer 
 of unaltered cells — the stratum intermedut-in. In the earlier 
 stages of the development of the enamel organ the peripheral 
 cells are alike, being columnar or prismatic, but almost coinci- 
 dent with the appearance of the dentin papilla, the cells most 
 closely related to it are observed to become elongated, and 
 form the internal epithelium of the enamel organ. As the cells 
 forming this internal epithelium become elongated, their nuclei, 
 instead of occupying the center of the protoplasmic body, are 
 carried to their extremities. It will thus be seen that the com- 
 
400 HISTOLOGY. 
 
 pleted enamel organ consists of four divisions or layers of cells. 
 Beginning with its convex surface is an external epithelium or 
 outer tunic, successively followed, in passing toward the dentin 
 papilla, by a stellate reticulum, stratum intermedium, and an 
 internal epithelium or inner tunic. As the growth of the enamel 
 organ proceeds, the tooth-band becomes smaller and smaller in 
 size, until finally a complete rupture takes place. This rupture. 
 
 -Ti 
 
 JD. 
 
 — a 
 
 Fig. 263. 
 
 -Section of a Developing Tooth of Lamb. X 600. 
 a, Ameloblasts ; D, dentin ; P, dental pulp. 
 
 however, does not occur until the enamel organ has about or 
 fully completed its development, and, after remaining so long 
 under the influence of the oral epithelium, it must be considered, 
 as before stated, an epithelial structure. It is through the 
 agency of the internal epithelial cells of the enamel organ, the 
 enamel cells or ameloblasts, that calcification of the enamel takes 
 place, and that subject will next be considered. 
 
AineIiJicat2on{¥\g. 263). — Two theories are advanced in regard 
 to the calcification of the enamel. In one it is claimed that the 
 ameloblasts or enamel cells become directly calcified or converted 
 into enamel ; in the other the ameloblasts are simply considered 
 as controlling agents, by secreting or depositing the calcium salts 
 which form the enamel prisms. In the latter theory it is gener- 
 ally believed that the enamel is secreted or shed out from the 
 
 ~^ 
 
 :gK„an,e, 
 ,•-§; Rods 
 
 ''M 
 
 jiW Outer 
 
 7/ Laverof 
 ■ ./ E.iamel 
 
 im^s 
 
 — ^ — 1.-1 — Papillse 
 
 200. — [After Williams.) 
 
 extremities of the ameloblasts, thus being productive of enamel 
 fibers corresponding in size and position to the secreting cells. 
 By the direct calcification of the ameloblasts, it would be natural 
 to expect the process to begin on the exterior of the cell and 
 gradually pass into its interior, the central portion being the last 
 to calcify. This would result in an enamel prism corresponding 
 in size and form to the generating cell, and in a measure this 
 26 
 
402 HISTOLOGY. 
 
 similarity between the calcified and uncalcified structure does 
 exist and is one of the potent factors in the recognition of this 
 theory, but it is hardly sufficiently convincing to warrant a gen- 
 eral acceptance of the beliel. 
 
 By examining figure 263 the importance of the secretory 
 theory is favored. Here we note that the early formed enamel at 
 A records what appears to be the definite action of the ame- 
 loblasts by prolongations of partly calcified tissue extending 
 from the cells, these markings corresponding in number and 
 location to the cells themselves. Between these prolongations 
 and the ameloblasts are many highly refractive granular bodies 
 which seem to be the actual lime deposit shed out from 
 the free extremities of the cells, from which they pass into the 
 substance of the then organic matrix beyond at A and form the 
 enamel prisms. Williams takes exception to this latter view, 
 substantiating his opinion by stating that while the ameloblasts 
 of many animals are similar in shape and arrangement, the 
 enamel produced from these similarly arranged cells varies 
 greatly in structure. The same writer also states that, when 
 such a similarity of arrangement exists between the amelo- 
 blasts and the enamel prisms, it occurs near the commence- 
 ment of enamel calcification, and that at a later period the 
 relative position of the ameloblasts and the prisms is always 
 in longitudinal section. Dr. Williams calls attention to the 
 fact of the enamel prisms or rods not extending through the 
 entire distance between the enamel cells and the calcified 
 dentin (Fig. 263). That part of the structure lying between 
 the ameloblasts and the extremities of the enamel rods is 
 made up of a double set of fibers, some of which are almost at 
 right angles with the long axis of the ameloblasts. In figure 
 265 D the two sets of fibers previously mentioned are found to 
 join and become closely interwoven. 
 
 The ameloblasts are connected with the cells of the stratum 
 intermedium, and more recent investigation goes to prove that 
 this latter structure is directly interested in furnishing to the 
 ameloblasts the proper material for the calcifying process. The 
 stratum intermedium can not, however, take part in the primary 
 enamel calcification, as this process commences before the 
 
stratum intermedium is fully developed. This being the case, it 
 is generally supposed that the stellate reticulum furnishes the 
 material for the upbuilding of the first enamel prisms. 
 
 Lying between the free extremities of the ameloblasts and 
 the enamel in the course of formation is what has been generally 
 considered as a structureless basement membrane or membrana 
 
 of Capillary Loop 
 
 Fig. 265. ^Section of Incisor of Rat, showint. Partial Decalcification of Enamel 
 X 600. — (After Williains.) 
 
 prcefonnativa. The existence, exact location and structure ot 
 this membrane has been and still remains a matter of conjec- 
 ture. The generally accepted theory appears to be that given 
 above, but Williams refers to it as a layer of newly formed 
 enamel, and does not consider it as a structureless membrane. 
 The structure is to be observed in figure 265, at either extremity 
 
404 HISTOLOGY. 
 
 of the ameloblastic cells, this writer claiming that the so-called 
 structureless membrane is present at both of these points. 
 
 As to the formation of the enamel rods, Dr. Andrews, in 
 1894, referring to the presence of calcoglobulin in the enamel 
 cells considered these refractive bodies as calcospherites, which, 
 after being taken up by the ameloblasts, were excreted by 
 them, and after coalescing formed globules of larger size, from 
 which the rods were built up. Williams partly agrees with this 
 statement, but he is of the opinion that the calcospherites 
 coalesce while in the ameloblasts, forming large, spheric 
 bodies, but that the deposit of this substance is in no way pro- 
 ductive of building the enamel rods. The theory of Tomes in 
 regard to the forming of enamel rods was that the walls of the 
 ameloblasts themselves became calcified, while the contents of 
 the cells also became solidified, the first forming the interpris- 
 matic substance, while the second became the enamel rod. 
 Whatever theory be accepted as to the formation of the enamel 
 rods or prisms, there appears to be no question in regard to the 
 general process of enamel calcification. In the first place, an 
 organic matrix is formed, into which the first-formed layer of 
 enamel is deposited. Gradually the organic matter disappears, 
 leaving behind the inorganic elements closely resembling in 
 appearance the organic matrix, which it has by atomic change 
 supplanted. The question of an organic interprismatic cement- 
 substance is also one upon which various writers disagree. 
 Klein partly believes that such a substance does exist, basing his 
 opinion upon the fact that the ameloblastic cells, in common 
 with all epithelial cells, are separated from one another by a 
 homogeneous intercellular substance, and that a certain propor- 
 tion of this organic substance must remain between the enamel 
 prisms after calcification. Dr. Sudduth, by a series of experi- 
 ments made some years ago, appeared at that time to have 
 furnished conclusive proof that an organic, interprismatic 
 cement-substance does not exist between the enamel prisms of 
 fully developed enamel. By the use of a dilute solution ot 
 chromic acid, the action of which is the preservation of organic 
 substance, the prisms were liberated, which would not have been 
 the result had they been cemented by an organic cement-sub- 
 
ENAMEL. 405 
 
 Stance. By substituting dilute muriatic acid, the action of which 
 is the destruction of organized tissue, the prisms were not liber- 
 ated, the acid acting evenly upon the whole mass of enamel, and 
 finally resulting in its complete destruction, not leaving the slight- 
 est trace of an organic matrix behind. Dr. Williams claims that 
 this transparent cement-substance is formed by the distribution 
 
 O liter Amelo 
 blastic Mem- 
 brane 
 
 Flu. 266. — Section of Developing Tooth of Embryo Lamb. X i5°- — (^fter Williams.) 
 
 of a translucent liquid substance about the previously formed 
 pattern for the enamel rods. This pattern, generated through 
 the activity of the enamel cells, is composed of a translucent 
 material somewhat more solid than that structure which sur- 
 rounds it. These two substances calcify together, the latter 
 forming the enamel prisms, while the former creates the cement 
 
4o6 
 
 HISTOLOGY. 
 
 or interprismatic substance. There is no better method by 
 which to study the character or mode of development of a grow- 
 ing or matured tissue than by an artificial disassociation of its 
 component parts. In enamel it matters but little in what part 
 of the tissue or at what period of its growth the examination be 
 made to learn of the action of the decalcifying agent ; it will 
 never be found to take place in a manner corresponding to the 
 
 Fig. 267. 
 
 direction of the enamel fibers, but decalcification takes place in 
 older enamel more in the form of a general breaking up of the 
 structure, as shown at A in figure 267, while at B, which repre- 
 sents the newly formed tissue, the action is one which appears 
 to indicate a breaking up of the interprismatic substance, favor- 
 ing the theory of secretory amelification. 
 
 This distinction between the enamel cells and their product 
 
ENAMEL. 
 
 407 
 
 possesses none of the characteristics to properly classify it as 
 structureless. There is but little doubt as to its character, being 
 the primary product of the ameloblasts, while the corresponding 
 zone at the distal end of the enamel-forming cells results from 
 the functional activity of the stratum intermedium. 
 
 Figure 268 shows a section near the point of the cusp of a 
 
 developing molar and exhibits a portion of the enamel organ at 
 a time immediately prior to the beginning of enamel calcifica- 
 tion. A is the uncalcified dentin, B the ameloblasts, now 
 closely associated, and a very regular layer of elongated 
 cells, and behind these another layer of cells, which un- 
 doubtedly serve as feeders to the ameloblasts, the stratum inter- 
 
4oS HISTOLOGY. 
 
 medium. This section is especially valuable in that it shows a 
 number of capillaries distributed through the body of the stellate 
 reticulum and actually penetrating the stratum intermedium, as 
 seen at B. 
 
 When viewed with a low power, these minute blood-vessels 
 appear to form a complete network, and in the district between 
 the cusps pervade the entire structure, from the stratum inter- 
 medium on one side to the same cells on the other. The 
 appearance of this animated vascular supply to the enamel is 
 coincident with the process of calcification, for during the early 
 life of the tooth-germ it is non-vascular. The growth of 
 enamel, strata upon strata, from Avithin outward is therefore by 
 the direct calcification of the enamel cells or ameloblasts, and 
 while this is going on, and as long as the crown of the tooth is 
 incased in its epithelial cap, the enamel organ, the growth of the 
 tissue is stimulated through the blood-vessels everywhere pres- 
 ent in the stellate reticulum. The presence of this specialized 
 blood supply to the central portion of the enamel organ was 
 for a long time doubted, but at present it can be readily ob- 
 served (Fig. 267). As soon, however, as the tooth passes 
 through the surface tissue, carrying with it the external epithe- 
 lium of the enamel organ as the enamel cuticle, the possibility 
 of nourishment has been cut off, and after a little time it be- 
 comes a petrified dental epithelium, no longer nourished and 
 absolutely non-vital. 
 
 Dentin. — This tissue, which constitutes the principal bulk 
 of the hard part of the tooth, forms a complete cap-like in- 
 vestment over the pulp, from which it is generated. It is 
 white or slightly yellowish-white in color, somewhat elastic, and 
 a trifle harder than bone, which it resembles in many of its 
 characteristics. In a perfectly developed tooth no part of the 
 dentin appears upon the surface, that part Avithin the crown 
 being covered by the enamel, while that of the root is inclosed 
 by the cementum. While the thickness of the dentin varies 
 somewhat over the different parts of the tooth, there is a de- 
 cided disposition to an equal distribution in every direction. 
 Dentin, unlike enamel, consists of an organic matrix — a reticular 
 tissue of fine fibrils richly impregnated with the salts of calcium. 
 
in this resembling the matrix of bone. Traversing the matrix 
 are long, fine canals or tubes (Fig. 270), — the dentinal tiihdes, — 
 which pass from the margins of the pulp toward the surface. 
 Immediately surrounding the dentinal tubules the matrix is 
 especially dense, forming a lining or sheath to the tubes, known 
 as the dentinal sheaths. Occupying the lumen of the dentinal 
 tubules are solid elastic fibers — the deiitinal fibers. Dentin, 
 therefore, presents for examination, first, the matrix ; second, the 
 dentinal tubules ; third, the dentinal sheaths ; ,and fourth, the 
 dentinal fibers. 
 
 -Section through Crown of Human Cuspid. 
 
 The Matnx. — As previously stated, the matrix is composed 
 of organic and inorganic substances, but the proportionate 
 quantity of organic and inorganic constituents Is so variable 
 that it is impossible to furnish a definite chemic analysis. The 
 relative quantity of organic and inorganic matter is not only 
 variable in the teeth of different individuals, but is continually 
 changing in the teeth of the same individual, the former being- 
 present in larger quantities during youth and gradually dimin- 
 ishing as age advances. From an examination of perfectly 
 
4IO HISTOLOGY. 
 
 dried dentin, the following approximate analysis has been 
 obtained : 
 
 Organic matter (tooth-cartilage), 27.61 
 
 Fat, 0.40 
 
 Calcium phosphate and fluorid, 66.72 
 
 Calcium carbonate, 3.36 
 
 Magnesium phosphate, 1.08 
 
 Other salts, 0.83 
 
 The organic basis of the matrix appears to be structureless 
 and transparent, and, although closely resembling the matrix of 
 
 
 Fig, 270. — Section through Root of Human Incisor, showing many Dentin 
 Tubules in Transverse Section. X 200. 
 
 bone, is not identical with it. While the matrix is usually 
 structureless, there are instances in which the presence at one 
 time of connective-tissue fibers is indicated. 
 
 T/ie Dentinal Tzibiiles (Figs. 271, 272, 273). — Beginning by a 
 free opening about the walls of the pulp-cavity, the dentinal 
 tubules permeate the matrix in all directions. The tubules are 
 generally disposed in a direction perpendicular to the surface, 
 so that in different parts of the tooth they radiate in various 
 directions. Beginning upon the surface of the pulp-cavity, at 
 
which point they are of greatest diameter, they pass more or 
 less in a spiral manner toward the surface (Fig. 273), before 
 reaching which they become gradually reduced in size, as a result 
 of the numerous branches which they give off (Fig. 272). The 
 branches given off from the main tubes are quite variable in size, 
 and anastomose with one another or with the branches from other 
 tubules. In the region of the pulp the tubules are so closely 
 associated that but little space is provided for the intertubular 
 substance or matrix ; but as the surface is approached they 
 become more widely separated, and, in consequence, the matrix 
 substance is present in greater abundance. While the general 
 
 
 Dentinal Tubul. 
 
 
 Fig. 271. — Dentin and Cementum from Root of Human Molar. — (^After Cysi.) 
 
 direction of the tubes is perpendicular, they do not pursue 
 a direct course, but are more or less curved as they pass 
 from within outward. The curvature of the tubuli may be 
 divided into two classes, — long curves and short curves, — 
 usually referred to as the primary and second curvatures of 
 the dentinal tubules. The primary curvatures are few in number 
 and are most prominent in the crown, while the secondary curva- 
 tures, principally found in the roots, are smaller and more 
 numerous. The branches from the main tubes terminate in 
 various ways, either by anastomosis, by gradually fading out into 
 hair-like terminals, or by ending in hooks and loops. In rare 
 
412 HISTOLOGY. 
 
 instances they are said to enter the substance of the enamel or 
 cementum, but it is doubtful if they do so normally. The 
 branches from a main tube are usually two in number, the latter 
 being almost equal in diameter to the former, and from this first 
 set of branches a number of minute branches are given off 
 almost at right angles. In the crown this latter class of tubules 
 are seldom observed, excepting near the enamel margin, but 
 in the root they are everywhere noticed. Small varicosities are 
 frequently present, but not in sufficient numbers to produce a 
 striated appearance on the surface of the dentin. 
 
 Fig. 272. — Longitudinal Section through Root of Human Molar. Branching 
 OF THE Dentinal Tubules. X 200. 
 
 The Dentinal Sheaths. — While the dentinal tubules ramify 
 through the matrix in the form of well-defined channels, the walls 
 of the channels are not formed by the matrix, but by an indestruc- 
 tible substance the exact character of which is not fully under- 
 stood. The walls of the tubes, or the dentinal sheaths, as 
 they are termed, are believed by some histologists to be cal- 
 cified, while others, though acknowledging their apparent inde- 
 structibility, are doubtful as to the correctness of this theory. 
 Neumann being the first to accurately describe the walls of 
 the tubules, they have become known as " Neumann's sheaths." 
 
The existence of tlie dentinal sheaths may best be dem- 
 onstrated by subjecting the tissue to the action of strong acid 
 for a sufficient time to destroy the intervening matrix, which 
 process usually requires several days. The fibrous mass re- 
 maining will be found to contain a collection of tubes, which, 
 however, by careful examination, are found not to be the 
 dentinal tubules themselves, but the walls of these canals. 
 Magitot and Sudduth deny the existence of a wall to the 
 dentin tubes. Tomes, while inclined to the belief that the 
 
 Fig. 273. — Transverse Section through R^hji ..1 Human Molar, showing the 
 Curvature ok the Dentin Tubules about the Pulp-canal. X 4°- 
 
 tubes are provided with definite walls, suggests that they may 
 have been produced artificially during the preparation of the 
 specimen, and that they are only brought into existence by the 
 action of the agents used for this purpose. In conclusion, the 
 same writer adds that that part of the matrix immediately 
 surrounding the fibril differs in its chemic constituents from the 
 body of the matrix. 
 
 The Dentinal Fibers. — Occupying the lumen of each dentin 
 tube is a soft, elastic fiber, which is continuous with and has its 
 origin from the odontoblastic cells upon the periphery of the 
 
414 HISTOLOGY. 
 
 pulp. The existence of these elongated processes of the odon- 
 toblasts having first been demonstrated by Tomes, they are 
 otherwise known as Tomes' fibers. By means of these fibers, 
 which not only fill the lumen of the larger tubes, but the 
 minute branches as well, the substance of the dentin is both 
 nourished and rendered slightly sensitive. There is still some 
 doubt as to the real nature of the fibrils, but, if they are 
 processes from the odontoblasts, it would appear that the 
 substance would be identical with that of the cell-protoplasm. 
 Bodecker claims that thev are not round but inclined to 
 
 Fig. 274. — Longitudinal Section through Root of Human Tooth, showing 
 Primary Curvature ok Dentin Tubules. X 4°- 
 
 angularity, but Tomes infers that this form has been pro- 
 duced by the action of some reagent. Klein advances the 
 theory that the odontoblasts are active in the generation of 
 the matrix for the dentin only,, and that the dentinal fibrils 
 are not processes from them, but originate from cells inter- 
 vening between the odontoblasts and connecting with the 
 dentin tubes. It has never been fully demonstrated that 
 true nerve-fibers enter the dentin along with or in the sub- 
 stance of the dentinal fibril, but, while the evidence is not at 
 present forthcoming, there is but little doubt that the sensitive- 
 
ness of the dentin is produced by the presence of organized 
 tissue in the tubuH. Some contend that the contents of the 
 tubules are made up of, first, a creative portion, that given oft 
 directly from the odontoblasts ; second, a circulatory portion, a 
 minute vessel traversing each tubule, entering either by the side 
 of the cell-bodies or passing through them, and that the nerve 
 terminals are distributed in the same manner. Others say that 
 minute nerve-filaments from the pulp pass directly through the 
 odontoblasts and are continued in the center of the tubule sur- 
 rounded by a simple connective tissue, the cell process, and that 
 
 Cemen- . 
 
 
 turn . ..■; '^ 
 
 :r^ .. 
 
 •^^SS^-- 
 
 '-'■, '^ 
 
 
 >0^^'^' '■■ ■ 
 
 
 .^'. 
 
 ...,M*is*> -•**** 
 
 -?;-<--, -^ 
 
 Fig. 275. — Transverse Section through the Root of a Human Incisor, showing 
 THE Dentin Surrounded ey the Cementum. X j^- 
 
 in this way sensations are conveyed. It is now generally con- 
 ceded that dentin is a highly organized connective tissue ; that it 
 has a circulatory system and is endowed with sensation to a 
 slight degree ; that these conditions are brought about not by 
 actual entrance into the tubules of separate vessels and nerve- 
 filaments, but more in the way of the tubules being occupied by 
 a general connective-tissue substance resembling in all essential 
 features the pulp itself, being the semi-fluid interfibrillar ground- 
 substance of the pulp ; that dendrites of sensory neurons every- 
 where present in the pulp, after losing their medullary sheaths 
 
4l6 
 
 HISTOLOGY. 
 
 divide into fine varicose fibers and become closely associated 
 with the peripheral cells, pass between these, and enter the 
 cone-shaped openings of the tubules and terminate soon after 
 doing so. 
 
 While the microscope reveals in some instances what appear 
 to be prolongations from the dentinal fibers penetrating the 
 enamel, or between its prisms, such a condition is improbable 
 if not impossible. If this arrangement is present at all, it is 
 so slieht as to have no influence whatever over the enamel 
 
 Fig. 276. — Tomes' Granular Layer. X 4°- 
 
 either as to nourishment or sensation. No conclusions can be 
 drawn with positive certainty from sections, since the slightest 
 deviation from parallelism in the surfaces may easily produce 
 deceptive appearances. It is just as common, and even more 
 so, to find hair-like lines interwoven and running parallel with 
 the surface of the dentin immediately between this tissue and 
 the enamel, as it is to see slight fibers crossing beyond their 
 boundary-line to penetrate the enamel. The most likely place 
 of all to find such a condition would be in the beginning of cal- 
 cification, and here it is never observed. The peripheral pulp- 
 
cells, usually all classed as odontoblasts, are never found outside 
 their own territory, the dentinal papilla ; but their location 
 in the beginning on the very surface of the papilla, almost in 
 direct contact with the inner tunic of the enamel organ, would 
 make it possible for their processes, when appearing, to pene- 
 trate between the cells of the enamel organ if they were grown 
 out from the body of the cells from which they spring. This, 
 however, they do not do. They do not grow out from the 
 cell-body, so to speak, but the cell recedes, leaving them behind. 
 By this arrangement the terminals of the future fibers become 
 definitely established, all increase in length taking place in the 
 opposite direction, toward the pulp. While the active enamel- 
 forming cells are present some little time prior to the odonto- 
 blasts, calcification of the enamel does not take place until after 
 a definite cap of dentin has been formed, imprisoned in which 
 are the terminal branches of the fibers. Therefore the fact that 
 this cap of dentin is formed first, and this is not a question in 
 dispute, with the fibers or cell processes securely encapsulated 
 within it, would seem to be sufficient evidence to qualify the 
 statement that the dentinal fibers do not penetrate the enamel. 
 The ' examination ot very many sections of young growing 
 teeth exhibits the fact that the early formed dentin and enamel 
 will separate bodil)', leaving a positive clear line of separation 
 and a surface absolutely devoid of anything resembling the 
 prolongation of the fibers extending from the surface of the 
 dentin. 
 
 Interglobular Spaces. — In that part of the dentin which 
 immediately underlies the cementum numerous intercommuni- 
 cating, irregularly branched spaces are found. These are 
 known as the interglobular spaces (Fig. 276). On account of 
 the granular appearance which this portion of the dentin ex- 
 hibits under low magnifying power. Tomes has designated it as 
 the "granular layer." The granular layer is also found upon 
 that portion of the dentin which underlies the enamel, but in this 
 region it is far less marked. Many of the dentin tubes have 
 their endings in these spaces. While the interglobular spaces 
 are most numerous near the peripheral portion of the dentin, 
 they are by no means confined to these parts. They are present 
 27 
 
4l8 HISTOLOGY. 
 
 in all parts of the dentin, but not so closely associated, and may 
 be observed, when a dried section of dentin is examined, as 
 spaces with irregular outlines and sharp-pointed processes ex- 
 tending in various directions (Fig. 277). The term "interglob- 
 ular spaces" becomes partly a misnomer when the so-called 
 "spaces" are more carefully examined. In normal dentin 
 the "spaces" are filled with a soft, living plasma, having a 
 structural arrangement similar to the general matrix of the 
 dentin, and it is only in a dried specimen that a true space is 
 found by the shrinking or shriveling of the organic contents. 
 The interglobular spaces forming the granular layer, which are 
 
 Fig. 277. — So-called Interglobular Stages in Dried Section of Dentin. X '°o- 
 
 much more numerous, but of smaller size, than those found in 
 the body of the dentin, are also filled with a soft living plasma, 
 and they communicate, on one hand, with the dentinal fibers, 
 and, on the other, with the lacunae and canaliculi of the cem- 
 entum. According to Sudduth, the interglobular spaces (so 
 called) are occupied by masses of calcoglobulin which have 
 not become fully calcified. 
 
 Deiitmifi cation. — The dentin bulb, or papilla from which the 
 dentin is formed, having already been described in part i, 
 the process of calcification Avill at once be taken up. It will 
 be recalled that calcification of the dentin does not beorin 
 
until the dentin papilla has developed to the form and size of 
 the dentin of the future tooth-crown. When this has taken place, 
 there is generated upon the surface of the papilla a modified 
 form of connective-tissue cells called odontoblasts (Fig. 278). 
 These cells, which are arranged in a single row upon the exterior 
 of the papilla, vary in form according to their activity. When 
 most active, they are broadest at the extremity directed toward 
 the interior of the papilla. Proceeding from a single odonto- 
 blast there may be one or more processes, which are supposed to 
 eventually occupy the tubes of the dentin, as the dentinal fibers. 
 These cells each contain an oblong nucleus, which occupies 
 
 
 Pulp-cells 
 
 Calcified Dentin 
 
 
 
 ^^0% 'i 
 
 Odontoblasts 
 
 Fic. 278.— Pulp and Forming Dentin from an Incisor Tooth.— (,4/?«- Gysi.) 
 
 the extremity of the cell most distant from the dentin, but during 
 the period of greatest activity becomes elongated or pointed 
 in the direction of the process. The odontoblastic cells, while 
 actively engaged in the calcifying process, are closely associated 
 or crowded together, but previous to this time there is more or 
 less space between them, which is filled with an indifferent tissue. 
 The first layer of dentin being formed upon the surface of the 
 papilla, it will be observed that all additions to its bulk take 
 place from within (the reverse being true of enamel). 
 
 As stated elsewhere, calcification of the dentin begins upon 
 the coronal e.Ktremities of the crowns, the cutting-edges of 
 
420 HISTOLOGY. 
 
 the incisors and cuspids, and the summits of the cusps in 
 the cuspidate teeth first receiving their Hme-salts. While the 
 odontoblasts undoubtedly superintend the calcifying process, the 
 part taken by these cells appears to be somewhat indefinitely 
 determined. It is generally supposed that the lime-salts are 
 secreted under the superintendency of the odontoblasts. The 
 secretion, however, does not take place around the cells, and in 
 
 
 .^^ffii^^ 
 
 
 
 
 
 
 ^/ , '^^mu/P-'ij i^^"^ 
 
 ' 
 
 Fig. 279. — Section through Pulp and Forming Dentin. 
 
 that way completely encapsule them, but around their fibrils. 
 While this is taking place the odontoblasts remain free upon the 
 surface of the pulp, and the fibrils assume their places as the 
 organic dentinal fibrils. As the body of dentin becomes thicker, 
 the odontoblasts are forced to recede, and in so doing the fibers 
 lengthen. The dentinal tubules are, of course, formed in a like 
 manner, the walls of the tube being first calcified from the secre- 
 tion of lime-salts by the fibrils ; and as the fibrils lengthen by 
 
the increasing thickness of dentin and the receding of the odon- 
 toblasts, the tubes also lengthen. 
 
 The general character of the pulp cells at a time immediately 
 prior to the appearance of the ameloblasts is vastly different 
 from the same cells at maturity or after calcification of the 
 dentin has taken place. The reason for this is obvious, con- 
 sidering that the connective-tissue mass does not assume its 
 principal function until the odontoblasts are generated about its 
 periphery. While at a later period the cells of the pulp are 
 oblong in shape, with slender tail-like processes given off from 
 each end, we find the same cells in the early embryo (sixteenth 
 to twentieth week) spheroidal in outline and distributed, as they 
 continue to be, at irregular intervals about the semi-gelatinous 
 matrix. (See Fig. 279.) 
 
 When the periphery of the pulp is reached, a definite layer 
 of cells is present, corresponding in every particular to those of 
 the interior, and it is from these spheric bodies that the dentin- 
 forming cells are derived. While the odontoblasts are usually 
 characterized as spindle- or flask-shaped cells, this can only 
 apply to the cells of later life, as those active at the beginning 
 of calcification do not partake of either of these forms. Figure 
 280 (twentieth to twenty-fourth week) shows the first formed 
 odontoblasts actively engaged in their function of dentinification. 
 It will be observed that the cells, instead of being individualized 
 as they appear at a later period, now present a racemose arrange- 
 ment, such a cluster appearing about the entrance to each den- 
 tinal tubuli, which at this period are widely separated and 
 apparently without anastomosing branches. The nearer the 
 summit of the crown is approached, the less apparent is this 
 grape-like association of the cells, showing conclusively that it 
 is a primary condition. 
 
 After a definite thickness of calcified dentin appears about the 
 surface of the tooth-pulp, the character of the odontoblastic 
 cells becomes materially changed (twenty-fourth week), but 
 even yet they do not answer to the description accorded them. 
 The elongated, spindle-shaped or club-shaped odontoblasts are 
 without question found in connection with the tissue only after 
 calcification has progressed to a considerable extent ; and while 
 
422 HISTOLOGY. 
 
 it does not appear possible to detect the minute processes which 
 penetrate the calcifying structure before this stage of the phe- 
 nomena has been reached, they have nevertheless existed from 
 the earliest inception of this specialized layer of cells. 
 
 In this connection the query presents itself in regard to the 
 manner in which the intercommunication between the dentinal 
 fibers is established, and the probable cause for the so-called in- 
 
 
 
 ik"v -^»^ 
 
 
 
 ^ 
 
 
 ^^-T.l^. 
 
 ' "" - ■ ■■ \^!iisl^M^^xKM 
 
 ^^^^^H 
 
 ' « .' ^^i^l^iH 
 
 ■j 
 
 * '""^^vwuL'^'^jJtl^^^^^^l 
 
 
 •— ^ jj^m^w^T.yMHwB^^^^B 
 
 ^^^^^^B 
 
 >^fyHH 
 
 ^^B-})tn^.... 
 
 "*** '' ' ' '<^'' Jfilk '' jA' K^^l^^^^^^^^^^^l 
 
 ^^^^^^m 
 
 r 'w3f\TyM^^&u^^^^^^^^^^^^K^ 
 
 Hw 
 
 ; I'f^^^^H 
 
 f 
 
 < '"jM" W^^^^^l^^^^r 
 
 
 ■ "■jIm^^^ 
 
 
 Fig. 28o.-^Young Odontoblasts Attached to Forming Dentin. 
 
 terglobular spaces about the periphery of the dentin. The 
 former can probably be explained by an examination of the 
 peripheral cells of the pulp at a time immediately prior to the 
 beginning of calcification, when it will be found that these prim- 
 itive odontoblasts communicate with one another in a manner 
 quite similar to the canaliculi between the lacunae of the true 
 bone, the connecting processes being encapsuled within the sub- 
 stance of the calcifying tissue. 
 
Figure 281 is taken from a very thin section of a growing 
 tooth at a time in which we would most naturally look for the 
 appearance of the interglobular spaces, and many such imperfec- 
 tions, if they may be so classified, are observed within the sub- 
 stance of the newly formed tissue. 
 
 Exceptions might be taken to the statement concerning the 
 
 Fig, 2S1. — Section through Crown of Growing Tooth of Lamb. 
 
 racemose appearance of the early odontoblasts previously re- 
 ferred to, by claiming the section to be one not directly through 
 the long axis of the cells, or perhaps transversely through them. 
 The examination of a number of sections, one of which is shown 
 in figure 282, shows the cells cut transversely; the forming 
 dentin at a appears with the tubuli squarely cut off, showing the 
 
424 HISTOLOGY. 
 
 dentinal fibers confined, or radier appearing as diough projecting 
 from the lumen of the tubes. It will also be noted that the 
 odontoblasts are irregular in outline, some of them being almost 
 hexagonal, and as the calcified tissue is approached, they grad- 
 ually become reduced in size and much modified in contour. 
 
 After a dentin cap or matrix of considerable thickness has 
 made its appearance and the enamel cells are about to assume 
 
 Fig. 282. — Odontoblasts in Transverse Section. 
 
 their functional activity, the odontoblasts ior the first time begin 
 to resolve themselves into the elongated flask-shaped cells, thus 
 answering the description usually accorded them, as illustrated 
 in figure 278. In fact it would appear that they assume this 
 shape only when the actual lime deposit begins. If we examine 
 the line of union between the dentin and enamel during the 
 early growth of these tissues, it will be ascertained that, not- 
 withstanding the dissimilarity of the two structures at maturity. 
 
there appears at this line of junction a matrix which may be 
 differentiated only by the free extremities of the ameloblasts, as 
 shown in figure 283. When the enamel matrix begins to form, 
 a faint line of demarcation between the two may be observed, 
 the difference in the appearance of the groundwork of the two 
 
 Fig. 283. — Section thkough Pulp, Dentin, and Forming Enamel. A. Calcified 
 dentin. B. Pulp. C. Ameloblasts. 
 
 Structures being one brought out by difterential staining, that of 
 the enamel taking the darkest stain. 
 
 It will be observed, therefore, that after the dentin germ has 
 assumed the exact size of the dentin of the future tooth, certain 
 cells appear upon its periphery, and under their superintendence 
 a definite laj'er of dentin soon results. This first lormed layer 
 
426 HISTOLOGY. 
 
 of dentin is definite and unchangeable in location, and it has 
 within its substance the minute processes from the dentin-form- 
 ing cells which are destined to become and really are the ter- 
 minals of the dentinal tubules. All who have given the subject 
 of dentin calcification careful consideration are practically agreed 
 as to the part which the peripheral pulp-cells play in the process. 
 This is to the effect that not about the body of the cells them- 
 selves, but around their processes the lime salts are deposited. 
 After a distinct layer of specialized cells has become fully estab- 
 lished upon the very periphery of the papilla, the first change 
 which takes place is a slight withdrawal of these cells from this 
 point, leaving behind slender hair-like processes which occupy a 
 portion of the space previously taken up by them, and about the 
 extremities of the cells and their processes which are directed 
 toward the enamel organ calcified material is generated. Zone 
 upon zone of calcified dentin appears in this way, the body of 
 the cell receding, leaving in its wake its processes encapsuled 
 within the calcified structure as the dentinal fibers. 
 
 In connection with the primitive layer of dentin-forming cells, 
 there are usually described lateral processes passing from cell 
 to cell, apparently serving the purpose of communication be- 
 tween the cells. But these have recently been shown to be 
 simply a network of connective tissue fibers supporting the body 
 of the cells. The theory of Andrews, brought out some years 
 ago in regard to the specialized layer of pear-shaped cells — 
 dentin corpuscles, as he termed them — may be accepted, and 
 these should be considered as having something to do with the 
 process of dentinification. The presence of these pear-shaped 
 cells at the beginning of calcification and during the continuance 
 of this process can be easily demonstrated, and if we accept 
 them as being concerned in the process of dentin formation, 
 they might in a measure modify the function now accorded the 
 elongated club-shaped cells, the odontoblasts. It is questionable 
 whether the odontoblasts alone are responsible for the growth 
 of dentin ; they undoubtedly control the actual process of lime 
 deposit, but the additional cells, no doubt, contribute to the 
 structural make-up of the tissue. It may be that by modifying 
 certain parts of the matrix, the result in the general structure 
 
CEMENTUM. 427 
 
 is the dentinal sheaths ; this part of the tissue being so markedly 
 different from the bullc of the intercelkilar substance would 
 lead us to believe that it was developed from specialized cells. 
 Further, it is said that while the dentinal tubules are filled with 
 a living substance, this substance is not solely the product of 
 the processes of the odontoblasts. That there is a special 
 distribution of non-medullated nerve terminals as well as a rich 
 plexus of blood-vessels about the periphery of the pulp is 
 unquestionable, and this supply is just as plentiful, or perhaps 
 more so, at maturity as it is at the beginning of calcification 
 when the dentin cells are most active. From this we might 
 be led to believe that this special blood and nerve supply 
 to the periphery of the pulp is not solely for the upbuilding of 
 the dentin and therefore distributed to the peripheral cells, but 
 also for the permanent welfare of the resultant tissue, this being 
 brought about by some circulatory system throughout the tubules 
 of the dentin. 
 
 Cementum (Fig. 284). — Investing the roots of the teeth is a 
 substance which, both chemically and physically, is closely allied 
 to bone. This external covering is known as the cementum, and 
 while generally regarded as being confined to the roots of the 
 teeth, by some it is considered to extend to and completely 
 invest the crowns during the early part of their existence, in 
 this latter location being known as the enamel cuticle, or mem- 
 brane of Nasmyth. 
 
 Generally speaking, the cementum begins by a thin margin at 
 the neck of the tooth or cervical line. It may commence at the 
 free enamel margin of the crown, or it may slightly overlap this 
 structure. It is thinnest at the neck of the tooth, and gradually 
 increases in thickness as the apex of the root is approached. 
 In teeth with closely associated roots the cementum frequently 
 extends from one root to the other, resulting in a firm, osseous 
 union. Histologically considered, the structure of cementum, 
 like ordinary bone, consists of a gelatinous, basal substance, 
 combined with the salts of lime, and of numerous little hollow 
 spaces — lactmcB. Branching in every direction from the lacunae 
 are many minute processes — canaliculi. 
 
 The Matrix. — The matrix is so nearly identical with that of 
 
428 HISTOLOGY. 
 
 bone that it is with difficulty that they can be distinguished. By 
 decalcification it retains its form and structure, and by the inti- 
 mate blending of organic and inorganic substances it is provided 
 with hardness, solidity, and elasticit}\ Calcium salts and col- 
 lagenous fibrils, united by a small amount of cement-substance, 
 in finer or coarser bundles, compose the ground-substance, or 
 matrix, of cementum. 
 
 Let us first take up the study of this tissue at different periods 
 
 lijgnrf^- "• ' ■ :;?^ter^ 
 
 
 i 
 
 Fig, 2S4. — Cementu.m irom Root of Molar. X 200. 
 
 of its existence, and in this manner learn ot its character, its 
 mode of development, and the changes which take place as its 
 growth proceeds. The striated markings of the tissue have led 
 to the belief that there are, during the process of cementification, 
 periods of activity and periods of rest or little activity. An 
 examination of the structure under low power (Fig. 285) shows 
 the incremental lines placed, with more or less regularity, one 
 
CEMENTUM. 429 
 
 beyond the other, and when thus studied adds much to the 
 strength of the theory of interrupted development. 
 
 Figure 286 is prepared from a developing deciduous incisor 
 three months after birth. At this period the developing organ 
 is made up of enamel and dentin alone, the process of cementi- 
 fication not yet being under way. The establishment of the 
 dentinal periphery, which surface is unchangeable, provides a 
 basis for the first layer of cementum generated by the cemento- 
 blasts, which at this period are forming about the inner wall of 
 
 Fig. 285. — Longitudinal Section through Root of Human Molar. 
 Incremental Likes of Cementum. X 30. 
 
 the tooth-follicle. In close proximity to the surface the inter- 
 globular spaces are observed somewhat widely distributed, and 
 proportionately large in size, resulting in a surface poorly calci- 
 fied and forming a ready attachment for the cemental tissue. 
 Figure 287 shows the process of cementification under way, the 
 section being prepared from a six-month- old tooth. In an ex- 
 amination of the ground-substance of this developing tissue there 
 is an unbroken granular appearance, possessing neither stria- 
 tions, fibers, nor cement-corpuscles. This appearance is one 
 which persists in the oldest or first-formed stratum, and is again 
 
430 HISTOLOGY. 
 
 noticeable in the outermost or youngest stratum. Wliile the 
 oldest stratum or strata retain this primary character, this can 
 not be said of those subsequently laid upon it, for they succes- 
 sively develop in their matrix the partially calcified cells and fibers 
 from the formative tissue. 
 
 Figure 288, taken from a one-year-old tooth, shows a further 
 advance in the process of cementification. Many of the trans- 
 verse fibers of the alveolodental membrane are observed pene- 
 trating the developing tissue, and will, at a later period, by their 
 
 -„■■ .>*^v 
 
 Fig 286 — Section through Developing Incisor, Three Months after Birth. 
 
 X30- 
 
 partial calcification, become a part of its substance. Already 
 there has been established an intimate blending of the cemental 
 tissues with the dentinal tissues through the medium of the 
 o-ranular layer, and by the further calcification of the latter this 
 union gradually becomes more thorough. Figure 289 illus- 
 trates three distinct zones of developing cementum : the older 
 unbroken granular zone at A, now beautifully cemented to 
 the granular layer; a second or intermediate zone, B, having 
 encapsuled within its ground-substance many of its formative 
 cells ; and an outer zone, C, but recently laid down, showing 
 
CEMENTUM. 431 
 
 numerous, longitudinal, wave-like striations, emblematic of the 
 cementoblastic activity. In this outer zone the minute laminations 
 disappear as the tissue becomes more thoroughly calcified and 
 the matrix gradually partakes of the nature of the older tissue. 
 The position occupied by the cementum on the root has much 
 to do with its character. In the region of the cervix the cement- 
 corpuscles are few in number, and when present possess e.x- 
 tremely short and irregular processes. In the region of the apex 
 the structure is much more complex in character, longitudinal 
 
 Gra.uila 
 Lay« 
 
 Terminals r 
 the Demi 
 iial Tubuli 
 
 Kic. 2S7. — Devkixu'Iing Cemkntum, from Six-mo.nth-old Tulith. X 200. 
 
 striae, transverse fibers, cement-corpuscles, and zones of appar- 
 ently unbroken granular matrix all serving to this end. 
 
 To continue the study of this tissue let us exariiine in detail 
 the lamells, the cement-corpuscles, and the cement-fibers. 
 
 The LamellcB. — We are told that the lamellae are about the 
 same in number over all parts of the tooth-root, but that they 
 are much thinner at the neck than at the apex. In addition to 
 this they are usually considered as running parallel, or nearly 
 parallel, to the surface of the dentin. While these statements 
 might, and probably do, describe the disposition of the lamellae 
 
HISTOLOGY. 
 
 in young cementum, they do not apply with so much certainty 
 to the conditions after the adult period. The lamella; in the 
 
 Fig. 2S8. — Section through One-ye.-vr-old Tooth. X 60. 
 
 
 '-^^^''-.i^^^^r-^t 
 
 ^^.;-^*i 
 
 .-^ 
 
 
 Fig. 289. — Developing Ce.me.ntum, from Transverse Section of Bicuspid. X loo- 
 
 region of the apex are not only of greater width, but are usually 
 greater in number than those occupying the cervix of the same 
 root. 
 
CEMEN'TUM. 433 
 
 Figure 290 is prepared from a transverse section of an adult 
 bicuspid in the region of the apex, and shows how the disposi- 
 tion of the lamella; may vary in thin, normal cementum. At 
 A, which represents the granular union of the cementum with 
 the dentin, the incremental lines are observed to follow the sur- 
 face of the dentin. As the center of the area is approached 
 this regularity is much interfered with, some of the lamellae 
 being discontinued, others greatly thickened, while the field, 
 taken in its entirety, exhibits anything but regularity in the 
 
 
 Fig. 290. — Transverse Section from Root of Bicuspid, showing Variation in the 
 Disposition of the Lamell.s;. )< 40- 
 
 laying down of the different strata. This same condition may 
 be observed in longitudinal section. While the lamella; are 
 usually characteristic of the cemental tissue in general, they are 
 seldom found in interdentinal cementum, or that growth which 
 takes place between roots, resulting in their fusion (Fig. 291). 
 This, of course, refers to the tissue as formed between closely 
 associated roots of an individual tooth, and not to that union 
 which sometimes takes place between the roots of different 
 teeth. The interdentinal tissue previously referred to appears to 
 
434 HISTOLOGY. 
 
 have many characteristics common to itself; thus, the cement- 
 corpuscles are peculiar in form, fibers are few in number, and, as 
 before stated, the lamellae are not decided. 
 
 Cement-corpuscles. — Many of the cementoblasts of the peri- 
 dental membrane, like the osteoblasts of the periosteum, become 
 encapsuled within the developing tissue, and persist as irregu- 
 larly shaped spaces, filled with a protoplasmic mass, and are 
 known as cement-corpuscles. These correspond to the lacunae 
 of bone, but, unlike these, are verv variable in size, in form, and 
 
 i^ 
 
 
 Fig. 291. — Transverse Section through Fused Roots of Molar Tooth, 
 SHOWING Interdentin.al Cementum. X so. 
 
 in the number and direction of their processes. Figure 284 
 shows a number of cemental lacunae and canaliculi. In the 
 majority of instances the body of the corpuscle will be found to 
 be oval or slightly oblong, with its long a.xis parallel to the sur- 
 face ; but it is by no means uncommon to find them very irreg- 
 ular in outline, with the greatest diameter in the opposite direc- 
 tion. The processes are quite variable in length and irregular 
 in their course, and, while there is a general disposition for them 
 to extend toward the surface, they in many instances radiate in 
 various directions. All of these features are in contradistinction 
 
CEMENTUM. 435 
 
 to the lacunae and canaliculi of bone, which are placed with much 
 more regularity in the osseous matrix, the corpuscles being oblong 
 or cylindric in outline, with their processes about equally distrib- 
 uted in every direction, and uniting directly and positively with 
 the canaliculi of neighboring lacunae. As previously stated, the 
 cement-corpuscles are very variable in outline, this difterence in 
 form appearing to be much influenced by the part of the tooth 
 examined. The younger corpuscles (Fig. 292), or those associ- 
 ated with the outer strata, are usually distinctly outlined and 
 
 
 
 
 Fig. 292. — Cement-corpuscles of Outer or Younger Strata. X 4°- 
 
 provided with delicate processes, the majority of which are 
 directed toward the surface. In the older strata the outlines of 
 the corpuscles are much more irregular, the processes short and 
 extremely clumsy. 
 
 The proportionate distribution of the corpuscles to the various 
 parts of the tooth-root is as follows : The innermost or oldest 
 zone and the outermost or youngest zones contain but few ; in 
 the intervening strata they are most abundant, especially in the 
 region of the apex, becoming less numerous in passing crown- 
 ward. In interdentinal cementum the corpuscles are somewhat 
 
436 
 
 HISTOLOGY. 
 
 regularly distributed throughout the ground-substance adjacent 
 to the granular layer, but near the center of this confused mass 
 of imperfectly calcified tissue they are seldom present. When 
 the interdentinal space is slight, peculiarly formed corpuscles 
 are often observed (Fig. 293), provided with a long, rod-like, 
 central portion or trunk, from which are given off numerous 
 tree-like branches, the terminals of which are frequently lost in 
 the granular layer upon either side. 
 
 Cement-fibers. — In a manner similar to that in which the 
 cementoblasts become encapsuled within the developing ce- 
 
 FiG. 293. — Cement-corpuscles Common to Interdentinal Cementum. >< i°°- 
 
 mental tissue forming the cement-corpuscles, many of the fibers 
 of the peridental membrane undergo a like transformation, and 
 are found in -the tissue as more or less imperfectly calcified 
 fibers transversely disposed. By many writers these filament- 
 ary, thread-like structures have been compared to the delicate, 
 net-like processes which pass through the concentric lamellae of 
 bone, serving to hold them together and designated as Sharpey's 
 fibers ; but, according to Black, these are the principal fibers of 
 the alveolodental periosteum, and, as already stated, become a 
 part of the cemental tissue during its evolution. In figure 294 
 the fibers are shown under high power; A represents the 
 
CEMENTUM. 437 
 
 primary or older stratum of the tissue, and it is from the outer 
 margin of this zone that the fibers first make their appearance, 
 passing more or less directly in the direction of the surface 
 until the next incremental line is reached, at which point they 
 gradually disappear, but recur in the succeeding lamellse. There 
 is a marked disposition for the fibers of each concentric lamella 
 to keep within its borders, or, in other words, to become indi- 
 vidualized ; but in many instances they pass .through from one 
 lamella to another, and occasionally extend unbroken through 
 the entire thickness of the tissue. It occasionally happens that 
 
 Fig. 294. — Transverse Section through Root of Molar, showing Cemental 
 FiBEKS. X 3°°- 
 
 the fibers are plentifully distributed to a region comprising three 
 or four lamellje, followed by a zone of similar proportions in 
 which they are entirely absent. The cement-fibers considered, 
 as the partially calcified residue of the principal fibers of the 
 peridental membrane, would naturally assume a general direc- 
 tion relative to their manner of distribution before this change 
 had taken place, and in most instances they are thus disposed. 
 In figure 295, taken from the center of a long axis of a growing- 
 bicuspid, the disposition of the fibers, which are alone observed 
 in the second lamella, is slightly crownward. The inclination 
 
438 
 
 HISTOLOGY. 
 
 for the fibers to be thus disposed is most pronounced in young 
 cementum, but after middle life, or at a period when the tissue 
 has greatly increased in thickness, the course of the fibers, even 
 in the same locality, is greatly at variance. 
 
 In figure 28S, also from a young tooth, the fibers are shown 
 springing directly from the peridental membrane, with their 
 free extremities penetrating this tissue. This illustration is pre- 
 pared from a transverse section in the cervical region, and the 
 inclination of the fibers is such as to warrant the belief that 
 they were some ot those whose function it has been to return 
 
 ■ ' « '"*¥ s^ .a""- 
 
 the tooth to its normal position when slightly rotated upon itself. 
 Another class of fibers common to the cement-tissue are those 
 which appear to be grouped in bundles, springing more or less 
 regularly, at intervals, from the granular layer and penetrating 
 the basement layer of the cementum as though serving to tie 
 this tissue to the periphery of the dentin. In figure 296 a 
 number of these bundles are shown at A, B, and C. While 
 the field is but a small proportion of the circumference of the 
 root, they are observed, under low power, to be distributed in a 
 like manner to all parts. These circumferential fibers, as they 
 
CEMENTUM. 439 
 
 may be called, are also observed in longitudinal section, being 
 distributed with considerable regularity throughout the whole 
 extent of the root. They are also present in the tissue at the 
 earliest period at which its character may be studied, the indi- 
 vidual bundles at this time being proportionately larger. These 
 might be, and probably are, considered as prolongations from 
 the dentinal fibers, but it is doubtful if the true fibers of the 
 dentin are ever found penetrating the cementum. 
 
 Cementification. — We have seen in the study of the develop- 
 
 ment of the teeth, that the tooth-generating organs were confined 
 in a closed sac or follicle, and while the walls of this sac were 
 not directly interested in the calcification of the dentin or enamel, 
 this can not be said of the cementum. Attention has also been 
 directed to the fact that at the time of the eruption of the crown 
 of the tooth a portion of the root only is calcified. As the growth 
 of the root continues, the follicular wall becomes closely adherent 
 to it. Upon the inner face of this vascular membrane a layer of 
 osteoblastic cells (cementoblasts) is generated, and as a result 
 of the calcification of these cells the cementum is formed. It 
 
440 HISTOLOGY. 
 
 will thus be seen that the process of cementification is but a 
 slightly modified form of subperiosteal bone development. At 
 the beginning of cementum calcification the diameter of the 
 dentin of the root is as great as it will ever be, all additions to 
 its bulk taking place from within. But while the diameter of the 
 dentin is thus fixed, the diameter of the root is increased by the 
 additional layers of cementum as they are deposited upon its 
 surface. As previously stated, a single layer of cementoblasts is 
 first formed in the membrane surrounding the root, these soon 
 becoming inclosed in a spherule of lime. By the time this 
 has taken place another layer makes its appearance, assuming 
 all the characteristics of the first formed layer. Other layers 
 are formed in turn until the cementum assumes its mature 
 thickness. 
 
 The Dental Pulp (Fig. 297). — The tooth-pulp, or formative 
 organ of the dentin, occupies the central or pulp-cavity, and in 
 the fully developed tooth assumes a general outline closely cor- 
 responding to the exterior of the organ.* Along with its pri- 
 mary function of generating the dentin, it becomes the medium 
 through which this structure receives its vascular and nervous 
 supply. 
 
 Histologically considered, the pulp may be described as a 
 mucus-like, protoplasmic matrix, containing delicate connective- 
 tissue fibers not formed into bundles and numerous nucleated 
 cells, the latter being especially numerous on the peripherj^ of 
 the pulp, or that portion which comes in contact with the dentin. 
 The cells are not closely enough associated to form a complete 
 tissue in themselves, but are found embedded in a mucoid matrix, 
 with always a definite space between them. In general the cells 
 are elongated or spindle-shaped, with a delicate, hair-like process 
 attached to either extremity. In the pulp-chamber the cells vary 
 somewhat in outline, in some instances being spheroid, in 
 others appearing as slender filaments, so that the cell proper 
 can scarcely be distinguished from its processes. A third 
 class of cells may be met with, from which three or more fila- 
 
 * The pulp not only occupies the central cavity in the tooth-crown, but the canals of the 
 roots as well; therefore the form of the pulp corresponds to the outline of the pulp-cavity, 
 already described. 
 
THE DENTAL PULP. 441 
 
 merits are given off. As stated, the distribution of cells varies 
 considerably in different parts of the pulp, this being true not 
 only as regards numbers, but also as to the relations existing 
 between the cells. In the coronal portion of the pulp the posi- 
 tion assumed by each individual cell appears to be without 
 regard to the position of neighboring cells, while in that portion 
 of the pulp occupying the root-canals the cells are arranged 
 parallel with the length of the root. The cells are least in 
 
 Fig. 297. — Longitudinal Section through Human Cuspid, showing Tooth-pulp.- 
 {Afler Gvsi.) X 10 
 
 number in the interior of the pulp, but gradually become more 
 plentiful as the periphery is approached. (See Cells of Dentin 
 Papilla, page 305.) 
 
 The Odontoblasts (Fig. 298). — The most active cells of the 
 pulp are those direcdy on its periphery, in contact with the 
 dentin, and known as the odontoblasts. The odontoblastic 
 layer, otherwise known as the membrana eboris, is composed of 
 a single row of cells, each of which contains, near the extremity 
 most distant from the dentin, a well-defined nucleus. They are 
 
442 HISTOLOGY. 
 
 large, elongated cells, each furnished with three sets of fibers 
 or processes — the dentinal process, the pulpal process, and the 
 lateral process. The dentinal process or processes — there 
 may be more than one present — communicate with the deeper- 
 lying cells of the pulp, while by means of the lateral processes 
 the cells are brought Into communication with neighboring cells. 
 The processes given off In the direction of the dentin, or the 
 
 Fig. 298. — Transverse Section through Pulp. Blood-vessels and Nerves 
 Cross-cut. 
 
 dentinal processes, may be one for each cell. In which case they 
 are of considerable size, and are inclined to taper as they enter 
 the substance of the dentin. Again, a single cell may give off 
 a number of smaller processes in this direction. The odonto- 
 blasts vary much in form according to their functional activity. 
 Before the period of dentlnification they are spheroid' or pyri- 
 form, during the period of calcification the dentin extremity be- 
 comes somewhat flattened and square, while in advanced years 
 
THE DENTAL PULP. 443 
 
 they again return to their primitive, rounded form. Covering 
 the entire surface of the pulp Hlce an epithehum, the odonto- 
 blasts are especially closely associated at the end nearest the 
 dentin, forming an unbroken layer, while the pulpal extremities 
 are inclined to assert their individuality by disassociation. 
 
 Blood-vessels of the Pulp. — The pulp is richly supplied with 
 blood-vessels, forming networks extending principally in a 
 
 Fig. 299. — PuLr and Dentin in Longiiudinal Section. 
 
 direction parallel to the long axis of the tooth, and finally 
 terminate in a capillary plexus closely associated with the odon- 
 toblastic layer. The veins of the pulp are ordinarily somewhat 
 larger than the arteries, and form numerous anastomoses. This 
 organ appears to be destitute of lymphatics — at least, none are 
 known to occur in Its substance. The blood-vessels of the 
 pulp are provided with a longitudinal layer of thinly distributed 
 
HISTOLOGY. 
 
 muscular fiber, but otherwise the walls of the vessels are noted 
 for their delicacy. 
 
 Ftg. 30c. — Section through Pulp. Fig. 299 in Transverse Section. 
 
 Nei^ves of the Pidp. — After entering the apical foramen either 
 by one large trunk or by two or more minute ones, the fibers 
 pursue a parallel course, breaking up but little or giving off but 
 few fibers in that portion of the pulp confined to the canal. 
 When the expanded or coronal portion of the pulp is reached, 
 numerous subdivisions occur which are distributed in every 
 direction, and ending in a rich plexus beneath the odontoblastic 
 layer, or membrana eboris. In the body of the pulp the fibers 
 are medullated, but those occupying the periphery are non- 
 medullated and supposed to pass into the dentinal tubes. While 
 this latter hypothesis is in all probability correct, such a distri- 
 bution of the germinal fibers has never been definitely demon- 
 strated. Two investigators (Ball and Maoitot) claim to have 
 
NASMYTH'S MEMBRANE, 445 
 
 partially satisfied themselves in regard to the final distribution 
 of the non-medullated fibers. The former states that he has 
 traced these fibers into continuity with the larger medullated 
 fibers in the deeper pulp-tissue, and claims to have found them 
 passing through the membrana eboris, beyond which point they 
 assumed a direction parallel to the dentinal tubules. This theory 
 is controverted by Magitot, who claims that the dentinal fibers 
 are, in a measure, themselves prolongations of the nerves, being 
 so constituted through the medium of the branched stellate cells 
 
 Branching ol Main 
 Nerve-trunk into 
 Single Fibers 
 
 hing of Main 
 Blood-vessels into 
 Capillaries 
 
 Fig. 301. — DisTRiBUTinN of Blood-vessei.s and Nerves to the Pulp of 
 Human Molar. — [AfU'i- Gysi.) X 20. 
 
 which lie immediately beneath the membrana eboris, and by 
 which the nerves are made continuous. 
 
 Nasmyth's Membrane. — Nasmyth's membrane, otherwise 
 known as the enamel cuticle or persistent dentinal capsule, is 
 an exceedingly thin and peculiarly indestructible structure, en- 
 tirely covering the enamel. As to the presence of this mem- 
 brane, which can be demonstrated only by chemic detach- 
 ment, there appears no doubt, but in regard to its origin and 
 definite structure much difference of opinion has been ex- 
 pressed. By some writers (Tomes and Magitot) it is main- 
 
446 HISTOLOGY. 
 
 tained that it is continuous with, and similar in structure to, the 
 cementum covering the root, being an extension of the outer- 
 most layer in the region of the neck of the tooth ; and, in view 
 of the fact that lacunae are found in its substance, this theory 
 would appear to be correct. On the other hand, it is considered 
 to be a product of the epithelium (Huxley and Kolliker) and in 
 no manner connected with the cementum. In the opinion of 
 the author, it would be difficult to understand how the theory 
 advanced by Tomes could be accepted. During the entire 
 period of saccular development the crown of the tooth is in 
 close relationship to the enamel organ, this structure intervening 
 between the forming enamel and the wall of the tooth-sac, from 
 which the cementum is developed. It would, therefore, appear 
 that this membrane is generated from the external epithelial 
 layer of the enamel organ by a change in the character and form 
 of these cells. Sudduth attributes its tormation to a metamor- 
 phosis of the ameloblastic layer, the prismatic cells assuming a 
 horizontal direction. The ameloblasts are observed to be pris- 
 matic in form up to the point at which the enamel prisms are yet 
 unfinished, but as the surface is approached they are observed to 
 shorten and widen, and near the gum-margin they assume a longi- 
 tudinal direction instead of being at right angles to the body of 
 the crown. Mrs. Emily Whitman has devoted much time to the 
 study of the development of mammalian teeth, and appears to be 
 of the opinion that the cuticula dentis is the result of a change 
 in the form and character of the enamel cells, this metamor- 
 phosis taking place either before or after calcification of the 
 underlying tooth-tissues. Nasmyth's membrane shows many 
 characteristics which differ from those of the body of enamel 
 subjacent to it, serving as an indestructible, highly polished 
 surface-capping to the enamel prisms. The indestructible nature 
 of this membrane by reagents would appear to indicate that in 
 structure it is closely akin to the structure lining the dentinal 
 tubules, the lacunse, etc. 
 
 Alveolodental Membrane (Fig. 300). — As a general 
 description of this membrane has already been given in part 
 I, it alone remains to treat of its histologic character, which 
 may best be accomplished by first referring to the duties 
 
ALVEOLODENTAL MEMBRANE. 447 
 
 which it has to perform. These may be divided into three 
 classes — functional, physical, and sensory. The functional office 
 is accomplished through its cellular elements — the osteoblasts 
 and cenientoblasts ; the physical office is performed by the 
 fibrous elements, through which the tooth is fixed in its position ; 
 and the sensory office through the abundance of nerves, which 
 are richly distributed to all parts of the membrane. We, there- 
 fore, find in this structure, besides connective tissue, cells, fibers, 
 nerves, and blood-vessels. The principal cells, as already stated. 
 
 '^H^i 
 
 Alveolar Wall 
 
 Fig. 302, — Transverse Section through Root of Human Incisor and Surround- 
 . ING Alveolar Wall, with Alveolouental Membrane Intervening. X 4°- 
 
 are the osteoblasts and cementoblasts, but there are also present 
 fibroblasts and osteoclasts. 
 
 TJie osteoblasts, which are instrumental in the upbuilding of a 
 portion of the alveolar walls, are found lying against the bone, 
 between the principal fibers. These cells do not appear to be 
 evenly distributed, being numerous and crowded together in 
 some parts, while others will appear to be almost destitute of 
 them. They are most plentiful in the young subject, and seldom 
 present at all in old age. In youth the alveolodental membrane 
 is thickest, and, as the building of bone occurs on the inner wall 
 
HISTOLOGY. 
 
 of the alveolus, it can only progress as the membrane becomes 
 reduced in thickness. The osteoblasts are polygonal cells, in- 
 clining to the oval form, and vary greatly in size, with their 
 longest diameter at right angles with the surface of the forming 
 bone. During the period of the development of the young 
 alveolar wall they are inclined to be crowded together, and are 
 frequently much distorted from pressure upon one another. As 
 age advances this condition becomes less pronounced, and the 
 cells separate into groups. 
 
 Fig. 303. — Section through Root of Tooih, Alveolodental Memhkane, and 
 Alveolus. 
 
 The Cenientoblasts . — Stationed upon the opposite side of the 
 membrane, or that in contact with the root of the tooth, are 
 another class of cells — the cementoblasts — or those cells which 
 are concerned in the formation of the cementum. Like the 
 osteoblasts, these cells are found lying between the principal 
 fibers of the root-membrane. They differ in form from the 
 osteoblasts, notwithstanding that they have a similar function. 
 Instead of the polygonal form common to the osteoblasts, we 
 
ALVEOLODENTAL MEMBRANE. 449 
 
 find these cells to be more or less flattened, with outlines some- 
 what irregular. Extending from the body of the cell, which 
 contains a well-defined nucleus, are a number of irregular pro- 
 cesses, which penetrate the neighboring fibers or the interfibrous 
 substance. Unlike the osteoblasts, the cementoblasts appear 
 at all times to be evenly distributed over the surface of the 
 cementum, occupying all the space except that taken up by the 
 fibers as they leave the cementum. As to the development of 
 
 Epitheliu 
 
 Alveolo- 
 Hental 
 Membrane 
 
 Fig. 304. — Transverse Section through Root of Tooth, Alveolodental Mem- 
 brane, Thin Wall of Alveolus, and Gingival Tissue. 
 
 the osteoblasts and cementoblasts, they appear to be carried to 
 the fibrous meshes of the membrane by the blood as leukocytes 
 or ameboid cells, after which, by differentiation, they become 
 fitted for the development of bone or cementum, assuming their 
 respective places against the surface of one or the other of 
 these structures. 
 
 Fibroblasts and Osteoclasts. — Fibroblasts and osteoclasts are 
 also present in the alveolodental membrane, the former for the 
 purpose of the increase or renewal of the fibrous tissue, the 
 29 
 
450 HISTOLOGY, 
 
 latter being functionally concerned in the removal of a part of 
 the alveolar walls to accommodate the ever-varying position 
 of the teeth, or acting in a similar manner upon the cementum of 
 the root. The osteoclasts, or giant-cells, are generally inclined 
 to the round or oblong form, and usually contain a number of 
 nucleoli. They vary much in size, and are seldom branched or 
 provided with processes. In addition to the four classes of 
 cells already mentioned as being present within the meshes 
 of the fibrous tissue of the root-membrane, there is another 
 
 Fig. 305. — Longitudinal Section through Root of Growing Tooth near the 
 Cervix. 
 
 class, present, however, during youth only, which appears to 
 be in course of development, and, therefore, without apparent 
 function. 
 
 The Fibe7^s of the Alveolodental Membrane. — The principal fi- 
 bers of the alveolodental membrane are those which extend from 
 the cementum on one side to the alveolar wall on the other, and 
 become firmly fixed at either extremity by penetrating the cal- 
 cified structures. The fibers are all of the white, or inelastic, 
 connective-tissue variety. It Is by means of the connective-tissue 
 fibers that the actual attachment of the membrane both to the 
 
ALVEOLODENTAL MEMBRANE. 451 
 
 bone and to the cementuni takes place, the fibers passing directly 
 into the hard tissues, which they traverse for some distance, 
 being here known as Sharpey's fibers. 
 
 The arrangement of the fibers is somewhat dififerent over 
 the various parts of the root. In the region of the gingival 
 margin they pass out from the substance of the cementum, 
 retaining their solid form or dividing into fasciculi of finer 
 fibers. In general the fibers lie parallel with one another, devi- 
 ating only to give place to blood-vessels and nerves. There 
 
 -LO.^GITUDINAL Sf.CTION THROUGH ALVEOLODENTAL MEMIRANE, GINGIVAL 
 
 Tissue, and Root of Tooth. Cervical District. 
 
 is some variation in the distribution of the fibers about the 
 different gingival surfaces. Upon the labial and lingual 
 surfaces they pass out directly into the fibrous tissue of the 
 gum, and soon become lost in this tissue. On the mesial 
 and distal surfaces the fibers passing the lower margin of the 
 alveolar wall join the fibers of the neighboring tooth. This 
 disposition for the fibers to bend toward the adjacent tooth is 
 first observed at the various angles of the gingival margin. All 
 about the free border of the eum the fibers from the alveolodental 
 
452 ,. HISTOLOGY. 
 
 membrane assist in forming this tissue, which is covered by a 
 dense epithelial coating of moderate thickness, surrounded or 
 surmounted by the peridental fibers. As the border of the al- 
 veolar wall is approached, the fibers are observed to pass under 
 the proper tissues of the gum, and unite with the outer perios- 
 teal layer overlying the outer alveolar wall. The fibers imme- 
 diately within the alveolus are slightly inclined in an apical 
 
 Fig. 307. — Section showing Fibers of Alveolodental Membrane, Attached to 
 AND Passing Out from the Cementum. 
 
 direction, while those occupying the central portion of the 
 membrane, or that midway between the apex and the gingiva, 
 pass nearly straight across from the cementum to the bone. It 
 is in this locality that the largest and strongest fibers are found. 
 As the apex of the root is approached the inclination of the fibers 
 is crownward from the cementum to the alveolar wall. In this 
 situation the single fibers are inclined to break up the fasciculi. 
 
ALVEOLODENTAL MEMBRANE. 
 
 453 
 
 Immediately surrounding the apex of the root the fibers are 
 irregular during youth, but are disposed more regularly or fan- 
 like in older subjects. 
 
 While this account briefly furnishes a description of the distri- 
 bution of the fibers in various locations, and is in most instances 
 correct, they occasionally vary from this arrangement. While 
 in most respects the fibers of this membrane closely resemble 
 the corresponding fibers of attached periosteum, they possess 
 some peculiarities. It might be supposed that the fibers passing 
 
 Fig. 30S. — Transverse Section through Growing Roots and Alveolus. 
 
 out from the cementum would in some way difter from those 
 springing from the alveolar wall, but, with the exception ot 
 being somewhat less in size, they ai'e otherwise of the same 
 character. 
 
 Interfibrous Elenieiits. — Besides the various forms of cells, 
 blood-vessels, and nerves, there is present in the alveolodental 
 membrane an interfibrous tissue. This tissue is principally 
 composed of the fibroblasts belonging to the principal fibers, 
 and other fibroblasts accompanied by delicate fibers which 
 appear to be independently distributed. This interfibrous 
 
454 HISTOLOGY. 
 
 tissue, which is thus seen to be ordinary fibrous connective 
 tissue, appears to pervade the entire membrane wherever suf- 
 ficient space is found to permit of its presence. In some parts 
 of the membrane this tissue appears to be more plentiful than 
 the principal fibers themselves. The interfibrous tissue also 
 forms an investment for the blood-vessels and nerves in addition 
 to the tissues properly belonging to their walls. 
 
CHAPTER VI. 
 EMBRYOLOGY OF THE MOUTH AND TEETH. 
 
 In the consideration of this subject it will be appropriate to 
 briefly refer to general embryology, which includes an investi- 
 gation into the mode of formation and the gradual development 
 • of the animal fetus. The history of the subject is replete with 
 well-defined epochs, each of which represents for a period the 
 theories or discoveries of some well-known investigator. While 
 not a few of the older histologists were well informed in regard 
 to very many important embryologic facts, their opinions varied 
 greatly, and they were all for a time inclined to misinterpret 
 certain vital points, and it was principally this latter fact which 
 stimulated and encouraged further research. 
 
 Aristotle held views which were for a long time accepted as 
 correct, his hypothesis being that all living creatures were gene- 
 rated in one of three ways : /. e., the egg- was deposited, incu- 
 bated, and hatched (oviparous), or a fully formed and independent 
 offspring was brought forth alive (viviparous), or a third, in 
 which the being was accorded a spontaneous birth, this latter 
 class including the lower order of animals, parasites, insects, 
 etc. Little or no exception was taken to the first and second 
 modes mentioned, but by persistent investigation it was gradu- 
 ally determined that the number of occurrences in which genera- 
 tion took place spontaneously was much less frequent than had at 
 first been supposed. In fact it was for a time acknowledged 
 that spontaneous generation was never responsible for the 
 development of insects or animalcules. More recently the sub- 
 ject has again been taken up, and it is conceded at the present 
 time that certain forms of uncertain infusoria are reproduced 
 by a spontaneous subdivision of unicellular organisms (fission, 
 fissipara). 
 
 Up to the time of Harvey (1631) there existed a misunder- 
 455 
 
456 EMBRYOLOGY. 
 
 Standing in regard to the similarity existing in the generation of 
 species, be they of oviparous or viviparous origin. Previous to 
 this there was supposed to be a distinct difference in the two 
 modes of development, but Harvey's bold assertion that "all 
 animals whatsoever, even the viviparous and man himself not 
 excepted, are generated from ova," revolutionized the study of 
 embryology, and established a fundamental principle (the mag- 
 nitude and value of which was never known to him) through 
 which all subsequent investigations were made blessed. 
 
 It is found, therefore, that the origin and a considerable por- 
 tion of the early development of the embryo take place in a 
 similar manner in all animals, from the impregnated egg of the ' 
 female, and this being the case we are particularly favored in 
 our early investigations by using the egg of a fowl. Therefore 
 attention will be briefly directed to the history of the develop- 
 ment of the chick. 
 
 Upon examining a longitudinal section of a hen's egg, in pass- 
 ing from the periphery toward the center the following struc- 
 tures are found : First, that part commonly known as the shell, 
 which is made up of variable proportions of organic and inor- 
 ganic substances. To provide for the early process of respira- 
 tion this structure is amply porous to permit the free passage of 
 gases from without inward, and vice versa. The shell is made 
 up of two distinct layers, but these, of course, are not directly 
 or indirectly interested in the development of the embryo. Im- 
 mediately within the shell is the shell membrane, wdiich is like- 
 wise composed of two layers. These two layers are closely 
 associated throughout their entire extent except in the district 
 represented by the broad end of the egg ; here they exhibit a 
 marked tendency to separate, the outer layer remaining in close 
 contact with the inner wall of the shell, while the inner layer re- 
 mains as a direct covering to the white of the egg proper. In 
 this manner an air chamber is formed which usually increases 
 with the age of the egg. 
 
 Immediately within this is what is commonly known as the 
 white of the egg, which upon careful examination exhibits a sort 
 of laminated appearance. 
 
 The next layer is known as the yolk, or that part which is 
 
THE BUCCAL CAVITY. 457 
 
 essential to the production of the embryo, inclosed by a thin layer 
 known as the vitelline membrane. 
 
 To simplify our study, let us banish from mind all other parts 
 of the egg and continue by describing the early changes which 
 take place in the yolk. In fact, it will be well at this time to 
 consider that we have under discussion the development of an 
 embryo, not particularly of the fowl, but of the mammalia as 
 well. This spherical body may be compared to a single cell, 
 that part which is known as the vitelline membrane, or zona 
 pellucida, corresponding to the cell wall ; the body of the yolk, or 
 vitellus, representing the cell protoplasm, within this the germi- 
 nal vesicle, for the cell nucleus, while the individualized central 
 area of the vesicle is given up to the nucleolus or germinal 
 spot. Without further considering this primitive cell, let us pass 
 on to a description of the germinal membrane known as the 
 blastodemn. The time at which this membrane makes its ap- 
 pearance is so variable in the different species that no allusion 
 will be made to this part of the subject. Primarily the blasto- 
 derm which lies upon the internal surface of the vitelline mem- 
 brane is composed of two layers, and from these two layers the 
 embryo is generated. In a very short time a third layer makes 
 its appearance, not, as might be supposed, upon one side or the 
 other of those already present, but between them, constituting 
 the three primary layers of the germinal membrane — the epi- 
 blast, mesoblasi, and hypoblast. These three layers are found 
 in connection with the early embryo of all vertebrates, if not in 
 all invertebrates. 
 
 Following carefully the development of the embryo from this 
 time, we find that the outer layer of cells (epiblast) is productive 
 of the following tissues of the mouth : the epithelial lining of the 
 cavity, and the enamel. From the middle layer (mesoblast) 
 arises the dentin, all the connective tissue, blood-vessels, and 
 lymphatics, together with the bones which form the framework 
 of the mouth, while the inner layer (hypoblast) gives origin to 
 the epithelial lining of the alimentary canal other than the oral 
 cavity. 
 
 The Buccal Cavity. — The early appearance of the entrance 
 to the alimentary canal is found in the formation of an open 
 
458 EMBRYOLOGY. 
 
 cavity bounded by the primitive maxillary processes above and 
 mandibular arch below. 
 
 The cavity thus formed is the common buccal space, the 
 upper portion being the respiratory or nasal section, while 
 below is the true mouth. The cavity of the mouth, as such, 
 does not exist until these two are completely separated by the 
 palatal plates forming the future roof of the mouth. 
 
 Figure 309 shows a vertical transverse section through this 
 common buccal cavity. At this early period the lateral walls 
 
 /i Dental Ridg 
 // Lowerjaw 
 
 Fig. 309. — Vertical Transverse Section through Head of Human Embryo, 
 ABOUT the Tenth Week. X 3°- 
 
 and floor ot the mouth are manifest by certain cellular elements, 
 but the roof of the cavity, as already stated, is not complete 
 until the palatal plates, now separated by the tongue, grow 
 inward and unite at the median line. 
 
 The Oral Cavity.— The Roof of the Mouth.— When 
 these two processes which arise from the mesoblast unite at the 
 median line, they establish a permanent horizontal septum, 
 dividing this part of the stomodeum into a respiratory or nasal 
 section and an oral section, the mouth. The cells entering into 
 
THE ORAL CAVITY. 
 
 this part of the fetal head at this time (eighth to tenth week) 
 are of three varieties, being connective-tissue cells, cartilage 
 cells, and epithelial cells, the latter being distributed in a layer 
 of varying thickness over those parts destined to become a 
 part of the lining membrane of the mouth. 
 
 In figure 310 (twelfth week) the superior maxillary processes 
 are shown united and the permanent separation between the 
 mouth and nasal cavity established. This embryonal bridge is for 
 
 Meckel's Cartilag 
 
 Denial Ridge 
 Oral Cavity 
 
 Village of Lower Ja 
 
 Fig. 310. — Vertical TransV-ERsk .Skciiun iiirough Head of Human Embryo, 
 
 ABOUT THE TWELFTH WEEK, SHOWING THE SINGLE BUCCAL CavitY TRANSFORMED INTO 
 
 THE Oral and Nasal Cavities. X 3°- 
 
 the most part made up ot connective-tissue cells, about isolated 
 bundles of which osteoblasts arrange themselves, resulting in 
 the production of two intermembranous bony plates. 
 
 By the fourteenth week a further advance in the generation 
 ot the hard palate is noted, the septum now being largely com- 
 posed ot calcified tissue. The disposition for these primitive 
 bony plates to exist as separate and distinct processes is ex- 
 emplified at the median line by a definite separation formed 
 by the connective-tissue sheath from which they are derived. 
 
46o EMBRYOLOGY. 
 
 Covering- the surface of the hard palate there now appears a 
 thin layer of mucous membrane. 
 
 The Floor of the Mouth. — Having thus briefly noted the 
 evolution of the roof of the mouth, let us next consider the floor 
 of the cavity, the tongue and its attached muscles, together 
 with considerable glandular tissue making up the bulk of this 
 
 Fig. 311. — Section through Base uf Tongue and Lower Jaw. x 4°- 
 
 district. Figure 311 is a vertical transverse section through the 
 floor of the mouth about the tenth week in the human fetus, or 
 at a period somewhat later than that shown in the previous 
 illustration. An examination of the parts in general at a time 
 prior to this is of little value, save the early preparation for the 
 development of the teeth, which will be referred to later. The 
 tissues and organs here shown will be recogfnized as the tongue 
 (A), the glandular tissues (B), the forming jaw [C), with devel- 
 oping tooth-germs at D D. 
 
THE FLOOR OF THE MOUTH, 
 
 461 
 
 The tongue appears on the floor of the mouth between the 
 thirtieth and thirty-sixth days as a bud from the mesoblast cov- 
 ered by a layer of cells of epiblastic origin. The muscle-fibers, 
 be they intrinsic or extrinsic, are all of the striated variety. In a 
 very short time, and at a comparatively early period, the tongue 
 becomes an independent organ, presenting most of the char- 
 acteristics common to it after birth. Not a small portion of the 
 floor of the mouth is made up of another class of tissue which, 
 
 
 
 g^ ^^^%ja 
 
 
 
 
 |S 
 
 } ■ 
 > 
 
 \ ■■ 
 
 
 
 H 
 
 1^ "^^^^^ 
 
 Sl"' 
 
 
 s 
 
 
 
 ^ta 
 
 ^w 
 
 
 
 Mi 
 
 w 
 
 Fig. S12. — Section of Sublingual District. 
 
 although eventually a distinct organism, is composed almost 
 entirely of epithelium. These cells, together with the connec- 
 tive-tissue cells, and eventually blood-vessels, unite in the pro- 
 duction of a true salivary gland, the sublingual. Figure 312 
 shows the early character of the tissue, together with its relation 
 to surrounding parts. The section is one from the region of 
 the premolars, and is bounded above by the tongue, laterally 
 
462 EMBRYOLOGY. 
 
 by the borders of the jaw, and below by fibers of the mylo- 
 hyoid and digastric muscles. Three distinct, lobes or sections 
 of the gland are observed, the two largest being separated by a 
 reticular network of connective tissue. 
 
 The general character of these developing glands even at this 
 early period (about the twelfth week) appears to be very similar 
 to the matured organ, being composed of a number of small 
 tubes emptying into a single duct, constituting a gland of the 
 compound tubular variety. 
 
 Let us next give some consideration to the embryology of the 
 mouth In its entirety ; and to do this, it is necessary to make sec- 
 tions of the parts in various directions. 
 
 The growth of the cavity is usually studied, and probably to 
 the best advantage, by vertical transverse sections, and attention 
 will first be called to a number of sections made in this way^ 
 beginning at the lips and passing backward through the incisor 
 region, and finally through the districts occupied respectively 
 by the cuspids and molars. The period at which such an in- 
 vestigation Is made has much to do with the character of the 
 tissue involved, but the time best suited to the purpose is in- 
 cluded between the fortieth and sixtieth days. At this time 
 nearly all the tissues making up the organs and parts which 
 enter into the construction of the cavity have advanced to such 
 a degree of perfection that the investigation may proceed with 
 considerable satisfaction. 
 
 Figure 313 shows a cross-section through one of the primitive 
 labial folds about the period named. Little is to be observed in 
 this district at this early period except the simple cells of three 
 varieties which serve to make up the parts, but attention is at 
 once attracted to the abundant thickness of the epithelium given 
 to the lip. 
 
 If a section be made somewhat to the distal of that previously 
 shown, a marked change in the relationship existing between 
 the various cell layers is observed in a body of cells of another 
 character, those which are destined to become the cartilage of 
 Meckel, and about which the younger layer of cells of mucous 
 membrane are observed outlining a new district. 
 
 If a section be made through this same location, say about the 
 
THE FLOOR OF THE MOUTH. 
 
 463 
 
 forty-eighth day, a vast change in the appearance of the parts is 
 noticed (Fig. 314). The buccal walls of the mouth have in a 
 measure become complete by a union of the upper and lower 
 sections, the union at this time being accomplished through the 
 agency of the embryonal epithelium. A cartilaginous nasal 
 septum has made its appearance, and active preparation for the 
 ossification of the maxillae is apparent. In the center of the sec- 
 
 FiG. SI V — -Embryonal Labial Mucous Membrane. 
 
 tion is a distinct body ot cells forming Meckel's cartilage, and 
 early preparations for the growth of the teeth may be seen at a 
 by a dipping down of the surface epithelium. 
 
 A transverse section through the same district about the six- 
 tieth day (Fig. 315) shows all the parts strongly differentiated. 
 Calcification has taken place to a considerable extent in the lower 
 jaw, the two halves being at this period, and for some months 
 
464 EMBRYOLOGY; 
 
 afterward, separate and distinct. Many muscle bundles are 
 observed beneath the jaw, and beyond these the integument 
 with its numerous blood-vessels and nerves, most of which are 
 seen in transverse section. A cross-section upon the same subject 
 about the sixtieth day in the region of the cuspids finds the tissues 
 and organs advanced to a certain degree of perfection. (See Fig. 
 311.) The tooth-germs of the cuspid teeth have their crowns out- 
 
 FiG. 314. — Section through Base of Jaw. 
 
 lined by the cells composing them ; the tongue with its complex 
 muscular arrangement has become a specialized and independent 
 organ, while beneath it we see that product of the epiblast, the 
 glandular structure, so plentifully supplied to the floor of the 
 mouth in this locality. 
 
 Passing further back into the region of the molars, the 
 appearance of the parts does not differ to any marked degree 
 
THE FLOOR OF THE MOUTH. 
 
 465 
 
 from that in the cuspid district, except in the general distribu- 
 tion of the muscular fibers of the tongue, and the appearance 
 of the submaxillary gland, here appearing in three distinct lobes 
 or parts. 
 
 It has been previously stated that sections made in the direc- 
 tion of those already considered are usually employed to study 
 these parts, but much is to be gained by supplementing these 
 with sections made in other directions. 
 
 Fig. 315. — Section through the Wall of the Mouth of an Embryo, Sixtieth 
 
 Day. 
 
 Figure 316 shows a longitudinal section, or one made from 
 mesial to distal through the lower jaw at or near the median 
 line, the parts included within the field being the labial folds at 
 A, the mandible at C, the tongue at D, and a tooth-germ at E. 
 An examination of the lips shows them to be covered with a 
 varying thickness of embryonal epithelial cells which are con- 
 
466 
 
 EMBRYOLOGY. 
 
 tinued backward over the future alveolar ridge and thence to 
 the hard palate above, or over the floor of the mouth and the 
 surface of the tongue below. 
 
 Meckel's Cartilage. — One of the earliest products of the 
 mesoblast is that which results in the production of Meckel's 
 cartilage, which is closely associated with the growth and early 
 
 e — iH 
 
 Fig. 316. — Longitudinal Section through Chin of Emkryo Lame. 
 
 support ot the lower jaw. In the beginning, as already pointed 
 out, the mandibular and hyoid arches resemble one another, but 
 soon after they become fully established they take on different 
 functions, and with this become dissimilar. The first appear- 
 ance of this cartilage as a distinct body of cells is found about 
 
MECKEL'S CARTILAGE. 
 
 467 
 
 the middle of die second month, and when a transverse section 
 of the jaw is made for the purpose of studying its location and 
 environments (see Fig 317), it is found near the base of the fetal 
 head, considerably below and to the outside of the base of the 
 tongue. At mid-jaw it appears as a circular body of cells sepa- 
 rated from the surrounding parts by a distinct layer of elongated 
 
 Fig. 317.— Section through Base of Lower J.wv, showing Meckel's Cartilage. 
 
 cells. Even at this early period a portion of the bony structure 
 of the jaw is outlined by an aggregation of connective-tissue 
 cells, and the forming cartilage appears to subserve the purpose 
 of controlling the outline of the future jaw. The bow-shape of 
 the cartilage is manifest as we pass toward the symphysis by 
 
468 EMBRYOLOGY. 
 
 the lateral halves approaching each other (Fig. 31 8), but the cir- 
 cular character of the cartilage in cross-section is still retained. 
 Figure 319 represents a section through the symphysis about 
 the eighteenth week, and shows the two halves of the cartilage 
 closely associated, but not united, the separation being by a 
 layer of connective-tissue cells passing between the two. It 
 will be noted also that the cartilaee, instead of belne near the 
 
 Fig. 318. — Section through Lower Jaw. M. C. Meckel's cartili 
 
 base of the jaw as in figure 318, now appears near the floor of 
 the mouth. 
 
 Figure 320 shows the relations existing between the two 
 halves of Meckel's cartilage and the growing mandible at the 
 median line [a). It also illustrates how little the development 
 of the bone is dependent upon the cartilage, the growth ot 
 the former being in this district far below and apparently dis- 
 
MECKEL'S CARTILAGE. 
 
 469 
 
 tinct from the latter. Here, as in the upper jaw, the periosteal 
 cells from either side are observed to unite at the symphysis and 
 pass as a somewhat thickened layer between the two bones, the 
 only difference in the final change which takes place between 
 the two being that in the upper jaw a suture results, while 
 in the lower jaw a layer of solid bone is formed. The charac- 
 ter of this cartilaginous framework as well as the cells which 
 
 Fig. 319. — Meckel's Cartilage {M. C.) at the Sy.mi'hysis. 
 
 divide the two halves is shown in figure 321, the cardlage cells 
 being oblong or cylindrical, with a bountiful supply of intercel- 
 lular substance, while the connective-tissue cells are oblong or 
 spindle-shaped. 
 
 As soon as ossification in the jaw takes place to any extent, 
 the cartilage begins to atrophy, that portion lying next to the 
 jaw deo-eneratino- first, so that by the tenth or twelfth week it 
 
EMBRYOLOGY. 
 
 has entirely disappeared, but before this takes place we find it 
 surrounded by the periosteum, and finally completely inclosed 
 within the bone. 
 
 Figure 322 shows the character of the cartilage cells about 
 the time that they are beginning to atrophy. It will be observed 
 that the cells are inclined to a change in form, and that they are 
 
 Fig. 320. — Ossification of the Mandible at the Median Line. 
 
 proportionately larger with large nuclei and nucleoli. A repre- 
 sents the district nearest the jaw, and the cells in this region 
 have already lost their characteristic outline. 
 
 Further Consideration on the Subject of Tooth Devel- 
 opment. — One phase of the subject to which special attention 
 will be given in this chapter is that which denotes the period at 
 
Fig. 321. — Section of Meckel's Cartilage at Median Line. 
 
 Fig. 322. 
 
472 EMBRYOLOGY. 
 
 which the various events take place. This is a part of the study 
 which is very difficult to determine, and it would appear, for this 
 reason, if for no other, that investigators of recent years have 
 been perfectly satisfied to accept the results arrived at by their 
 predecessors without any apparent effort to qualify the deduc- 
 
 FiG. 32J. — Transverse Section through Primitive Jaws of Human Fetus. 
 
 tions. It has for a long- time been conceded that the primitive 
 changes which ultimately result in the formation of a tooth-germ 
 are first noted in a heaping up of the epithelial cells over the 
 district representing the surface of the future jaw. While in 
 many instances this is true, there are reasons why it cannot be 
 considered an essential feature. In the first place, such a con- 
 
TOOTH DEVELOPMENT. 
 
 dition is not always present, as shown in figure 323, a transverse 
 section through the primitive jaw of a human fetus about the 
 fortieth day. The tooth bands at A and B have penetrated the 
 submucous tissue for a considerable depth, but the surface epi- 
 theHum does not show a greater thickness at these points than 
 it does over the general surface of the cavity. 
 
 Figure 324 shows a section made in the same direction upon 
 
 Fig. 324. — Transverse Section through Lower Jaw, Human EiMURYO, Sixtieth 
 Day. 
 
 a human embryo about the sixtieth day, and while the tooth 
 band {A) has penetrated the embryonal connective tissue to a 
 greater depth, there is yet no increase in the thickness of the 
 epithelium, but rather a disposition for the parts to become 
 depressed. Another reason why the heaping up of the super- 
 ficial layer of cells forming the embryonal mucous membrane 
 
474 EMBRYOLOGY. 
 
 should not be considered the first sign of the preparation for 
 tooth development lies in the fact that these cells are not 
 directly interested in the process, but that the inflection of cells 
 which results in the formation of the tooth band results from 
 the deep or infant layer of cells known as Malpighi's layer, as 
 shown at B (Fig. 324). 
 
 Fig. 325. — Section through Tooth Band of Hum.-vn Embryo. 
 
 There is no question but that the location from which the sec- 
 tion is taken has much to do with the character and thickness 
 of the older layer of epithelial cells, and that they do at certain 
 points constitute an epithelium exceeding in thickness that of 
 other parts of the cavity, but this condition most frequently 
 occurs after the enamel organ has assumed definite proportions. 
 
 After the formation of the tooth band, which, it rhust be 
 remembered, encircles the entire jaw in the form of a well- 
 defined body of oval epithelial cells from the infant layer (shown 
 
TOOTH DEVELOPMENT, 475 
 
 at A in cross-section, Fig. 325), the next step in the process is 
 one which concerns the location for the individual buds for the 
 enamel organs of the various teeth, and the approximate time 
 at which these appear. 
 
 In the human subject we find ten such spots appearing upon 
 the lamina given off from the lingual face of the tooth band. 
 These do not appear, however, at the free extremity of the band. 
 
 Fig. 326. — ToOTH-GERM, EMHRYO L.'VMI!, CoRKESl'ONDING TO SIXTIETH DAY (HUMAN). 
 
 X 4°- 
 
 but at some little distance toward the surface from this point, as 
 shown in figure 326. In this section the tooth-germ is severed 
 from the surface epithelium, but this is not a true condition at 
 this period, as it still retains its connection with the surface by a 
 narrow band of cells, the neck of the enamel organ. Two dis- 
 tinct classes of cells are now (sixtieth day) concerned in the 
 process of tooth development, those at A being of epithelial 
 
476 EMBRYOLOGY, 
 
 origin and forming the future enamel organ, while at B an aggre- 
 gation of cells from the mesoblast provides for the generation of 
 the pulp and dentin. At C the narrow band of cells which should 
 continue to the surface is shown, while the free extremity of 
 the same body of cells at D will persist and eventually become 
 the germ for the succeeding tooth. In regard to the time at 
 which the buds for the various teeth appear, it might be ex- 
 pected that the same variation which follows the development 
 and erupdon of the teeth throughout would obtain, but such is 
 not the case, the buds for the deciduous incisors appearing 
 about the sixtieth day, while the germs for their permanent suc- 
 cessors are but httle later in forming. 
 
 By referring to figure 316, which shows a longitudinal section 
 through the lower jaw about the twelfth week, the deciduous 
 incisor is seen well outlined by its formative cells, while imme- 
 diately to the lingual appears a section of the germ for the per- 
 manent cuspid. Notwithstanding this, there elapses a period of 
 several years between the eruption of these teeth. The same 
 relative progress will be noted between the first and second 
 teeth, be the subject human or otherwise ; requiring many years 
 to complete dentition, in the former, while in most of the lower 
 animals the same process occupies but a comparatively short 
 time. 
 
 The next stage in the development of a tooth to which atten- 
 tion will be called is that in which the entire tooth-crown is out- 
 lined by the dentin papilla and surrounded by its epithelial cap, 
 the enamel organ. Such an advance in the process is shown 
 in figure 327, together with the surrounding structure. When 
 this stage is reached, the individual cells of the tooth-germ are 
 strongly differentiated, and the odontoblasts are making their 
 appearance about the summits of the cusps. 
 
 Up to this time the cells present are those which result in the 
 formation of but tWo of the calcified tooth tissues, but now there 
 is a marked disposition upon the part of the periosteum of the 
 jaw to pass down by the side of the enamel organ {A), this being 
 the first indication of the formation of the tooth follicle, the 
 alveolodental membrane, and cementum. At this period it will be 
 observed that there appears in this, the molar region, a "heap- 
 
TOOTH DEVELOPxMENT. 477 
 
 ing up " not only of the surface epithelium, but also of the con- 
 nective tissue as well. 
 
 Figure 328 shows a section through the growing mandible 
 taken from a portion of the tissue not occupied by a tooth-germ. 
 This is of interest, first, as giving a view of the detached tooth 
 band in cross-section, at A ; second, by showing the distribution 
 of the periosteum to the interior of the jaw to serve the double 
 
 27. ^Tooth-germ, Premolar, Emuryo Lamb. X 4°- 
 
 function of the future tooth sac and alveolodental membrane; and, 
 third, the thickened epithelium with the underlying tissue push- 
 ing into it. 
 
 Although the germ for the second tooth may be observed at 
 a period somewhat prior to this, a study of some of its charac- 
 teristics is best made at this time. The fact has already been 
 referred to that this interesting phenomenon occurs soon after or 
 
478 
 
 EMBRYOLOGY. 
 
 even simultaneously with that for the first tooth, a portion of the 
 primitive cord for the latter persisting as the germ for the 
 former. 
 
 In figure 329 the cells forming the primitive germ for the 
 enamel organ of one of the permanent teeth are shown highly 
 magnified. It will be observed that they are of the sim- 
 
 FiG. 328. — Section throuch J.wv of Embryo Lamb, in a District not Occupied by 
 A Tooth-germ. X 4°- 
 
 plest epithelial character, and that they are derived directly 
 from the enamel organ of the pre-existing tooth, on the one 
 hand, while, on the other, they communicate with the surface by 
 a narrow band of cells. In this way it is for a time dependent 
 upon both of these parts for continuance and growth, but after 
 
TOOTH DEVELOPMENT. 479 
 
 a time it, too, like its predecessor, severs its connection with the 
 surface, but remains intact with the epithelial cells of the former 
 enamel organ until these cells begin to atrophy. 
 
 The cells which make up this primitive germ are of three 
 varieties : the inner layer, or those derived from the epithelium 
 of the enamel organ of the first tooth, being small and spheroidal ; 
 those of the outer layer, which spring from the surface epithe- 
 
 FiG. 329. — Primitive Bud for Enamel Organ of Permanent Tooth, Human 
 Embryo. X lOo. 
 
 lium, being proportionately larger and cylindrical or oblong; 
 while those which intervene are markedly irregular in outline. 
 In this respect — that is, in the character of the early cell layers 
 — the tooth-germs for the permanent teeth differ from those of 
 the deciduous. 
 
 The question of the origin of those teeth which have no pre- 
 decessors is one upon which there has always been more or less 
 discussion, some writers contending that they are derived 
 
48o EMBRYOLOGY. 
 
 directly from the oral epithelium by a special generation of cells 
 for each tooth, while others are of the opinion that as the jaw 
 grows backward certain changes take place which result in the 
 establishment of an epithelial fold or lamina, in every particular 
 corresponding to the tooth band of the deciduous teeth. With 
 these two conflicting opinions in mind, a number of sections were 
 made through the extreme distal end of the jaw. The result 
 favored the latter theory, for here the tooth band is seen similar 
 in form and location to that observed in the jaw in those locations 
 from which succedaneous teeth result. 
 
CHAPTER VII. 
 
 ANOMALIES OF THE TEETH. 
 
 It has always been conceded that the dental organs of man are 
 susceptible of much variation in form and structural arrange- 
 ment, and that frequently this variation is so positive that the 
 organ is pronounced anomalous in character. Just where the 
 line of distinction between the normal and abnormal should be 
 drawn is a subject worthy of some consideration. Some au- 
 thorities define the word anomaly as a marked deviation from 
 the normal, while, in the opinion of others, a much broader 
 meanino^ is accorded it; and we find all those conditions which 
 
 Fig. 330. — Anomalous Teeth. 
 
 are in themselves an irregularity from the typical structure or 
 occurrence included in this category. Under the first definition 
 a given structure or organ is accorded a wide field ior its normal 
 existence, while under the latter but slight deviation is necessary 
 to classify it among the abnormal. 
 
 Upon first thought it would appear that the ability or inability 
 of a tissue or an organ to perform its special function should, in 
 a measure, decide the question of the nature of its being, and 
 no doubt to a certain extent this is true ; but while the action of 
 an organ or a part of the body may, by observation, appear en- 
 tirely satisfactory, it is only so at the expense of other organs 
 31 4S1 
 
482 ANOMALIES. 
 
 or tissues, and these in the course of time, by this extra exer- 
 tion, become hypertrophied or in other ways pathologic. 
 
 While this is especially applicable to those organs or tissues 
 which have a wide range of function, it may with a good deal of 
 force be applied to the dental organs and their immediate envi- 
 ronments. Anomalous conditions in the teeth may originate 
 in, or be confined to, one or more of the tooth tissues, in any 
 of which the structural disarrangement may eventually result 
 in the death or degeneracy of the part. Enamel malformation 
 is of such a character that it may be observed upon the surface 
 either in the form of a multiplication of cusps, or by an extra 
 development of the various ridges formed by pronounced folds 
 of this tissue. But probably the most disastrous anomaly of 
 the enamel, and one frequently responsible for the downfall of 
 this tissue, is found in some defect of its structural arrangement 
 other than those just referred to. In some instances the enamel 
 rods of a given district, instead of being normally distributed 
 by assuming a direction principally at right angles to the long 
 axis of the tooth crown, are arranged without regard to the base 
 or periphery of the tissue, 'and we have as a result an anomaly 
 of structure. The question of normal and abnormal rod 
 distribution now presents itself, because in certain locations 
 — ?'. e., the summits of the cusps — an arrangement of the rods 
 similar to that referred to is so common that it may be con- 
 sidered a normal condition, while, if a like distribution was 
 found in other locations, the tissues should properly be con- 
 sidered abnormal. 
 
 Malformed teeth, in respect to the number and forms of the 
 cusps present, are not alone confined to the enamel, but also to 
 the dentin which first records the tooth form on its periphery. 
 
 Anomalies in the general contour of the tooth crown are 
 usually confined to the incisors and third molars, both the dentin 
 and the enamel contributing to the deformity. Here the defect 
 is usually so pronounced that but little difficulty is experienced in 
 properly classifying the organ. One of the most frequent varia- 
 tions in form met with in these locations is found in the peg- 
 shaped or cone-shaped crown. If it were possible it would be in- 
 teresting to trace the development of Such a malformation ; but 
 
LACK OF DENTITION. 483 
 
 with our present knowledge of this process in general, there is 
 little doubt as to its origin, the enamel organ failing to fulfil its 
 early and primary function of molding the tooth crown in the 
 dentin papilla, the responsibility for this resting in the special 
 cells composing it, as well as the so-called stellate reticulum, 
 which, it is believed, exerts a controlling influence over the form 
 of the enamel cap. 
 
 While the organic defects of tooth crowns are numerous and 
 varied, those which are confined to the roots are most frequent, 
 in many instances interfering to some extent with the function 
 of the organ. When a given peculiarity is confined to this por- 
 tion of the tooth, it is frequently difificult to discriminate between 
 the normal and the abnormal. Certain teeth are recognized as 
 normal when either a single root or two roots are present, and 
 the acceptance of this fact increases the difficulty of a proper 
 classification of its peculiarities. 
 
 In very rare instances do we find the roots of the cuspidate 
 teeth more or less crooked ; yet, at the same time, many deci- 
 dedly crooked roots are considered within the natural law ; 
 while, on the other hand, roots with but little more deflection are 
 classed as anomalous. 
 
 Marked flexions of roots or crowns, cases of fusion or con- 
 crescence, are usually so positive in character that an anomalous 
 condition is at once acknowledged. While tooth anomalies are 
 usually referred to as external, or as belonging to the hard 
 tissues of the organ, they are not infrequently found in the pulp 
 or pulp cavity. This cavity, normally following the external con- 
 tour of the tooth, is subject to much variation in outline and 
 capacity, regardless of those changes which are incident to the 
 continuous process of dentinification. 
 
 Among these are a complete division of the pulp chamber ; 
 horn-like processes penetrating the dentin in the direction of the 
 occlusal surface in locations where they would be least expected ; 
 an unusual number, or a peculiar distribution of the canals, etc. 
 
 Lack of Dentition. — Cases in which there is a total absence 
 of teeth have been reported. Guilford reports the case of a man 
 fifty years of age who never had teeth, the jaws not differing in 
 appearance or form from those of a person whose teeth have 
 
484 ANOMALIES. 
 
 been extracted. The mother of the subject had the usual 
 number of teeth, but the grandmother and an uncle were both 
 edentulous and hairless from birth. J. Tomes mentions two 
 cases having been reported to him, and Linderer mentions one. 
 
 On the other hand, instances of a third dentition have been 
 reported, but there is great possibility of such observation being 
 erroneous. Teeth belonging to the permanent set which may 
 have remained unerupted for years could readily be mistaken 
 as predecessors of a third set, when in after years they make 
 their appearance. 
 
 Supernumerary Teeth. — All teeth appearing in the mouth 
 in addition to the normal number are designated as super- 
 numerary teeth. These are divided into two classes, those 
 normal in size and form and those abnormal in size and form. 
 The first-named are most likely to be of the simple class, in- 
 cisors and cuspids, and they may occupy a regular position in 
 the arch or may be found inside the arch closely associated with 
 teeth of the same type. Supernumerary bicuspids and molars 
 are sometimes present either in regular position in the arch or 
 inside of it. When the jaws are long enough to accommodate 
 them, an additional molar may appear back of the third molar, 
 making four molars instead of three, and cases in which two 
 extra molars were thus placed have occasionally been met with. 
 
 Supernumerary teeth of the second class or those which are 
 abnormal in size and form are usually inclined to be cone-shaped 
 and small in size, this in respect to the root as well as the crown. 
 Supernumerary teeth of this character are usually found in the 
 incisor region, but it occasionally happens that they are found 
 in the molar district, but here, instead of having a single cone 
 for the crown, they are mostly made up of a number of smaller 
 cones resembling many small cusps on the occlusal surface. 
 The number of supernumerary teeth may vary from one to eight 
 or ten. In the latter instance they are usually scattered through 
 the entire alveolar border of the hard palate. As many as ten 
 or twelve teeth thus located have been reported. 
 
 Again, certain teeth are frequently missing from the arch. 
 This may be occasioned by delayed eruption, or it may be 
 the result of improper activity within the tooth-germ itself, 
 
SUPERNUMERARY TEETH. 485 
 
 SO that the tooth may have failed to develop. The teeth 
 most frequently missing are the upper lateral incisors. The 
 probable reason for this lies in the fact that the germs for 
 these teeth are located very near the surface of the bone, 
 and in some instances they are not even protected by a 
 thin layer of bone over the follicle. Being thus situated, they 
 are more or less exposed to violence sufficient to destroy the 
 germs and thus render development of the teeth impossible. 
 Lack of certain teeth in the mouth appears to be to some 
 extent an hereditary feature, the condition being transmitted 
 from parent to child. Anomalies as to the size of individual 
 teeth are frequently noticed. When this is the case, it does not 
 usually include the entire set, but is confined to one or two, 
 usually to the same teeth on each side. Teeth that are above 
 the usual size are generally found in persons of large build, but 
 if all the teeth are proportionate in size they can not be included 
 within the abnormal class. The upper incisors are most fre- 
 quently affected in this way. Cases have been reported in 
 which the central incisors in the upper jaw have been fully twice 
 the size which they should normally have been, and all the re- 
 maining teeth in the mouth perfect as to shape and size. Ac- 
 companying the abnormal condition it is usual to find the teeth 
 thus affected more or less abnormal in outline, but, notwithstand- 
 ing this, retaining their form sufficiently well to permit their 
 proper classification. 
 
 There are likewise teeth that are deficient in size. This does 
 not refer to teeth all relatively small, as frequently found in per- 
 sons of small frame and stature. This anomalous condition is 
 often present in the upper lateral incisors and in the third 
 molars. Teeth that are deficient in size generally possess their 
 normal shape. 
 
 While the crowns of the teeth are susceptible to the above 
 variations, the roots appear to be anomalous much more 
 frequently and to a more marked extent than are the crowns. 
 Most important among these may be mentioned flexions of 
 the roots. Curvatures in the roots may be found either in 
 single-rooted teeth or in multirooted teeth, and the point of 
 flexion may be located either at the center of the root or 
 
486 ANOMALIES. 
 
 near its apex, or both of these points may be affected. 
 Flexions in the roots of the teeth present a great variety 
 in form. A single curve in one direction may be present 
 or a number of curvatures in different directions. In multi- 
 rooted teeth the roots may be so flexed that they will en- 
 twine about each other, and the overlapping portions may be 
 or may not be fused. Probably the most important cause for 
 the flexions of the roots of the teeth is delayed eruption, this 
 being particularly true if some positive force prevents the prog- 
 ress of the organ. The roots of the teeth are frequently anom- 
 alous in regard to number. These may have the same general 
 form and the same approximate length as the normal root or 
 
 Fig. 331. — Anamolous Roots. 
 
 roots would be, but they are proportionately smaller in diameter. 
 Cases are on record in which the incisor teeth have had two dis- 
 tinct roots, but probably the most frequent location for the mul- 
 tiplicity of roots is found in connection with the third molar. 
 While this tooth when normally developed as to crown is usu- 
 ally supported by three roots, it sometimes possesses five or six 
 smaller roots. 
 
 It not infrequently happens that the roots of the teeth are 
 less in number than they should normally be. This is usually 
 brought about by the blending of the roots, which occurs 
 during the developmental stage. This may be of two distinct 
 kinds. In the first place, it may be the result of the conversion 
 of two or more pulp canals into one, or the individual roots 
 
FUSION AND CONCRESCENCE. 
 
 487 
 
 may be united by a body of cementum being interposed between 
 them. In the former instance a single pulp canal is mostly 
 found within the blended roots, while in the latter the number 
 of canals is usually normal. With this blending there is 
 generally a line of demarcation between the individual roots 
 as they should normally exist, in the way of longitudinal 
 depressions extending through the entire root from cervical 
 
 Fig. 332. — Fusion of Molars. 
 
 Fig. 333. — Fusion and Concrescence. 
 
 line to apex. This anomaly, like that of the multiplicity of 
 roots, is principally confined to the third molars, and is more 
 frequent in the upper jaw than in the lower. 
 
 Fusion and Concrescence. — The union of two or more 
 teeth is known as fusion or concrescence, and may occur either 
 during the development of the organ or after this process has 
 been completed, When union takes place during development, 
 
ANOMALIES. 
 
 it is characterized as fusion ; wlien it takes place after the com- 
 pletion of this process, it is known as concrescence. There 
 seems to be but little doubt that fusion of the teeth occurs 
 through some irregularity in the tooth-germ or germs, the be- 
 ginning of the developmental process taking place generally 
 between two germs and continuing together until the complete 
 calcification of the organs. Teeth thus united may have an in- 
 ternal anatomy corresponding in nearly every respect to two 
 separate teeth, and, on the other hand, they may possess but a 
 single pulp chamber and canal. Fusion may take place in the 
 
 Fig. 334.— Fusion and Concrescence. 
 
 roots of the teeth alone, when it is called partial fiision ; but 
 when it is confined to the roots and crowns alike, it is classified 
 as complete fusion. The teeth most likely to be affected in this 
 way are the upper incisors and the second and third molars. 
 Some distinction must be made between those teeth which are 
 united by a layer of cementum, and those of true fusion, the 
 latter existing only when there has been a union between dentin 
 and dentin. 
 
 Concrescence. — In concrescence, the roots of the teeth only 
 can be affected, as the union takes place after the complete de- 
 velopment of the organ. The roots of one tooth become 
 united to the roots of another through an additional growth of 
 
GEMINOUS TEETH. 
 
 489 
 
 cenientum, this growth being sufficiently extensive to cause ab- 
 sorption of the alveolar septa by pressure. Following this 
 there is a resorption of the pericementum. The cemental tissues 
 of the teeth are then brought in contact, and coalescence gradu- 
 ally takes place. Concrescence may take place not only 
 between the roots of two teeth, but between the various roots 
 of an individual tooth, this resulting in the same manner as 
 above described by the destruction of the septa within the tooth 
 socket. When concrescence takes place, the process is usually 
 confined to the apices of the roots, although they may become 
 coalesced throughout their entire length.* The teeth most com- 
 monly affected by concrescence are the molars and bicuspids. 
 
 Fig. 335. — Geminous Tooth. 
 
 from the fact that the alveolar walls, particularly the septa about 
 these teeth are especially thin, owing to the form and relative 
 location of the roots. 
 
 Geminous Teeth (Fig. 335). ^It occasionally happens that 
 two separate germs are confined within a single sacculus, and 
 from this results two teeth, either similar or dissimilar in size and 
 form. One of the pair may be normal as to form and size, while 
 the other may be much below the normal size, but more or less 
 perfect in outline. Geminous or twin teeth may be united or en- 
 tirely separate. This condition is most frequently found in the 
 molar teeth, although cases in which the bicuspids and incisors 
 have been thus affected are recorded. Teeth thus formed must 
 not be confounded with those in which fusion is the anomaly. 
 
ANOMALIES. 
 
 In geminous teeth a single sac contains two tooth-germs from, 
 which result two similarly formed teeth ; in fusion two follicles 
 coalesce, each of which contains its own eerm. 
 
 Fig. 336. 
 
 Fig. 337. 
 
 Besides the foregoing, the roots of the teeth are subject to 
 anomalies in size, in some instances being abnormally small, 
 in others abnormally large. In the former they may nearly 
 
GEMINOUS TEETH. 49' 
 
 always be characterized as anomalous, but this is not always 
 true of the latter. When the roots are abnormally large, it is 
 somewhat difficult to discriminate between an anomalous and a 
 pathologic condition, the latter usually being the case when the 
 roots of individual teeth are affected. Roots, to be considered 
 anomalous in size, should in a measure retain their normal form, 
 cases of hypertrophy (hypercementosis) usually resulting in the 
 destruction of the normal contours (Figs. 336 and 2)37)- 
 
NDEX, 
 
 Accessory palatal foramina, 34 
 Adipose tissue, 349 
 Alveolar process, 60-74 
 
 development of, 64 
 Alveoli, 61 
 
 Alveolodental membrane, 12S-446 
 blood supply to, 130 
 cells of, 448 
 fibers of, 450 
 histology of, 446 
 ■ interfibrous elements of, 453 
 nerve supply to, 130 
 Amelification, 401 
 Ameloblasts, 289, 400, 402, 403 
 Anatomic element, 344 
 Angular artery, 29 
 Anomalies of the teeth, 481 
 Anterior palatal foramen, 34 
 nerve, 35 
 
 superior dental nerve, 121 
 Antrum of Highraore, 65 
 Apical foramina, description of, 238 
 Areolar tissue, 34S 
 Artery, deep facial, 34, 49 
 inferior dental, 119 
 internal maxillary, 34, 115 
 lingual, 49 
 ranine, 50 
 sublingual, 50 
 Azygos uvulte, 39 
 
 B. 
 
 Bicuspid, lower first, 217 
 second, 221 
 upper first, 163 
 second, 175 
 Blastoderm, 457 
 cells of, 457 
 layers of, 457 
 Blood, course of, from heart to cheeks, 30 
 from heart to hard palate, 35 
 from heart to lips, 24 
 from heart to soft palate, 39 
 from heart to tongue, 50 
 Blood supply to the teeth, 115 
 Bone, 351 
 
 canaliculi of, 352 
 
 cells of, 352 
 
 Haversian canals of, 352 
 
 histologic examination of, 353 
 
 byoid, 42, 80 
 
 inferior maxillary, 71 
 
 lacunae of, 352 
 
 Bone, marrow of, 354 
 matrix of, 351 
 osteoblasts of, 354 
 palate, 67 
 periosteum of, 354 
 Sharpey's fibers of, 354 
 superior maxillary, 51 
 
 Bones, of the mouth, 51 
 superior maxillary, 51 
 
 Brown striase of Retzius, 396 
 
 Buccal cavity, 457 
 
 embryology of, 457 
 glands, 131, 378 
 orifice, iS 
 
 Buccinator muscle, 25 
 
 Calcification, beginning of, 318 
 
 of cementum, 333, 439 
 
 of dentin, 318, 418 
 
 on enamel, 401 
 Calciform papilte, 43 
 Canal, inferior dental, 76 
 
 infra-orbital, 52 
 
 posterior palatal, 55 
 Canaliculi, 352 
 Canals, Haversian, 352 
 
 pulp, 23S 
 Canine eminence, 53 
 
 fossa, 53 
 Capsular ligament, 85 
 Cartilage, 349 
 
 cells of, 349 
 
 elastic, 350 
 
 fibro-, 350 
 
 hyaline, 350 
 
 matrix of, 349 
 
 Meckel's, 79 
 
 permanent, 351 
 
 temporary, 351 
 
 varieties of, 350 
 Cell, essential parts of, 345 
 
 general description of, 345 
 
 nucleolus of, 346 
 
 nucleus of, 345 
 
 protoplasm of, 345 
 Cells, ciliated, 347 
 
 columnar, 346 
 
 epithelial, 347 
 
 fat, 349 
 
 gland, 349 
 
 pigment, 349 
 
 plasma, 349 
 
 squamous, 347 
 
INDEX. 
 
 494 
 
 Cement corpuscles, 434 
 
 fibers, 436 
 Ceraentification, 333, 439 
 Cementoblasts, 333, 44^ 
 Cementum, 427 
 
 calcification of, 333, 439 
 canaliculi of, 427 
 fibers of,' 436 
 histology of, 412 
 lacunae of, 427 
 lamellae, 431 
 matrix of, 427 
 Central incisor, lower, 209 
 
 upper, 136 
 Cervical line, 99 
 Cheeks, 24 
 
 blood supply to, 29 
 external covering of, 25 
 glands of, 25, 131, 378 
 integument of, 25 
 internal covering of, 2$ 
 mucous membrane of, 25, 367 
 muscles of, 25 
 muscular tissue of, 385 
 nerves of, 30 
 substance of, 25 
 Circumvallate papillfe, 43 
 Concrescence of teeth, 487 
 Condyle, neck of, 77 
 Condyloid process, 77-5^3 
 
 forms of, 83 
 Connective tissue, cells of, 346, 347 
 classification of, 347 
 fibrous, 347.348 
 intercellular substance of, 347 
 tissues, 347 
 Coronoid process, 77 
 Crowns, anomalous, 485 
 Cuspid, lower, 214 
 upper, 153 
 
 D. 
 
 Decalcification, 341 
 Deciduous lower central incisor, 279 
 cuspid, 280 
 first molar, 275, 281 
 lateral incisor, 273, 279 
 second molar, 278, 283 
 teeth, decalcification of, 341 
 detail description of, 271 
 enamel organs for, 305 
 general description of, 26S 
 occlusion of, 270 
 pulp chambers and canals of, 2S4 
 upper central incisor, 271 
 upper cuspid, 274 
 Deep facial artery, 34, 39 • 
 
 branches of, 39 
 Dendrites, 360 
 Dental arch, 99 . 
 
 arrangement of teeth m, loi 
 curve described by, 104 
 influence of temperament on, 104 
 follicle, 289, 307, 315 
 formula, 97 
 
 Dental furrow, 313 
 pulp, 440 
 sacculus, 307 
 Dentin, 94, 408 
 
 calcification of, 418 
 cells, 305, 307 
 chemical analyses of, 410 
 exposed by dissection, 315 
 fibers of, 409, 413 
 histology of, 40S 
 matrix of, 409 
 organ, 288, 304 
 papillte, 316, 41S 
 tubules of, 409, 410 
 Dentinal fibers, 413 
 sheaths, 409, 412 
 tubules, 409, 410 
 walls of, 412 
 Dentinification, 418 
 Dentition, completion of, 343 
 
 lack of, 483 
 Depressor anguli oris, 28 
 labii inferioris, 23 
 labii superioris, 22 
 Development of enamel, 397 
 of permanent teeth, 326 
 of teeth, 286, 470 
 Digastric fossa, 74 
 Duct, parotid, 134 
 sublingual, 135 
 submaxillary, 135 
 
 Elastic cartilage, 350 
 Elementary organism, 345 
 Embryology, general, 455 
 
 of mouth and teeth, 455 
 Enamel, 94, 3S9 
 
 ameloblasts of, 400 
 brown stria: of, 396 
 calcification of, 401 
 cells, 289, 400 
 chemic composition of, 390 
 cuticle of, 445 
 development of, 397 
 histology of, 389 
 organ, 288, 289, 398 
 cells of, 289, 297 
 external epithelium of, 289, 299 
 form of, 2S9, 292 
 internal epithelium of, 289, 399 
 stratum intermedium of, 289, 399 
 stellate reticulum of, 289, 399 
 prisms of; 390 
 rods, formation of, 404 
 Endomysium, 356 
 Epithelial tissues, 346 
 Eruption of the teeth, 334 
 External maxillary artery, 29 
 oblique line, 72 
 pterygoid, 92 
 
 Facial angle, in 
 artery, 29 
 
495 
 
 Facial artery, branches of, 29 
 
 nerve, 30 
 
 branches of, 30 
 Fat cells, 349 
 Fauces, anterior pillars of, 36 
 
 isthmus of, 36 
 
 pillars of, 36 
 
 posterior pillars of, 36 
 Fibers, dentinal, 413 
 
 Sharpey's, 354 
 Fibroblasts, 449 
 Filoro-cartilage, 350 
 Fibrous connective tissue, 347 
 
 cells of, 348 
 Fifth nerve, 120 
 
 division of, 120 
 Filiform papillae, 43 
 Floor of the mouth, boundaries of, 41 
 embryology of, 460 
 framework of, 40 
 Follicle, dental, 289, 307, 315 
 Foramen, anterior palatal, 34 
 
 apical, description of, 238 
 
 CKCum, 43 
 
 incisive, 59 
 
 infra-orbital, 52, 54 
 
 mental, 73 
 Foramina, accessory palatal, 34 
 
 posterior palatal, 34 
 Fossa, glenoid, 8;} 
 Frenn; of the mouth, 125 
 Fungiform papillse, 43 
 Fusion of teeth, 487 
 
 and concrescence, 4S7 
 
 complete, 488 
 
 partial, 488 
 
 Ganglion, Gasserian, 120 
 
 Meckel's, 35 
 
 sphenopalatal, 25 
 Geminous teeth, 489 
 Genial tubercles, 73 
 Geniohyoglossus, 46 
 Germs for permanent molars, 306 
 Gingiva;, 33 
 Gingival border, 33 
 
 margins, outlines of, 125 
 Gland cells, 349 
 
 follicles, 376 
 
 parotid, 133, 382 
 
 saccular, 376 
 
 tubular, 376 
 
 sublingual, 135, 382 
 
 submaxillary, 134, 3S2 
 Glands and ducts of the mouth, histology of, 
 376 
 
 buccal, 131, 378 
 
 excretory ducts of, 377 
 
 labial, 131, 377 
 
 Ungual, 132, 379 
 
 molar, 378 
 
 of the cheeks, 37S 
 
 of the hard palate, 379 
 
 of the mouth, 130,376 
 
 Glands of the soft palate, 132, 379 
 
 palatal, 132, 379 
 
 salivary, 132,381 
 Glenoid fossa, S3 
 Gomphosis, 96 
 Groove, infra-orbital, 52 
 Gubernaculum, 322 
 
 foramina of, 328 
 Gums, 124 
 
 epithelium of, 369 
 
 fibrous tissue of, 369 
 
 general description of, 124 
 
 mucous membrane of, 125, 369 
 
 H. 
 
 Hard palate, 31 
 
 arch of, ^j 
 
 blood supply to, 34 
 
 bones of, 31 
 
 covering of, 31 
 
 formation of, 31 
 
 glands of, 31, 379 
 
 mucous membrane of, 31, 370 
 
 nerves of, 35 
 Haversian canals, 352 
 Highmore, antrum of, 65 
 Histology, 344 
 Hyaline cartilage, 350 
 Hyoglossus, 45 
 Hyoid bone, 40 
 Hypoblast, 457 
 
 I. 
 
 Incisive foramen, 59 
 
 fossa, 53, 72 
 Incisor crest, 59 
 
 lower central, 209 
 
 lateral, 213 
 upper central, 136 
 lateral, 146 
 Inferior coronary artery, 23, 29 
 vein, 30 
 dental artery, 119 
 
 incisive branch of, 119 
 mental branch of, 1 19 
 canal, 76 
 meatus, 57 
 nerve, 120 
 lingualis, 4S 
 maxillary bone, 71 
 body of, 72 
 development of, 78 
 facial surface of, 72 
 internal surface of, 73 
 muscles attached to, 78 
 vertical portion of, 76 
 palatal vein, 35 
 turbinated crest, 54, 58 
 Infra-orbital canal, 52 
 foramen, 52 
 groove, 52 
 Intercellular substance, 346 
 Interglobular spaces, 147 
 
496 
 
 Internal maxillary artery, 34, 115 
 
 infra-orbital branch of the. 1 17 
 superior maxillary branch of 
 the, 115 
 oblique line, 73 
 pterygoid, 92 
 Interproximate spaces, 106 
 Involuntary muscular tissue, 355 
 Isthmus of fauces, 36 
 
 Labial glands, 131, 377 » 
 
 Lacrimal canal, 54 • 
 
 tubercle, 55 
 Lacunae, 352 
 Lateral incisor, upper, 146 
 
 lower, 213 
 Layer, granular, 
 
 Malpighi's, 474 
 Levator alseque nasi, 21 
 anguli oris, 27 
 labii inferioris, 22 
 labii superioris, 21 
 palati, 38 
 Lines of Schreger, 395 
 Lingual artery, 49 
 glands, 132, 379 
 vein, 50 
 Lips, 18 
 
 blood supply to, 23 
 external covering of, 19 
 frense of, 19, 125 
 glands of, 19, 131, 377 
 integument of, 19 
 internal covering of, 19 
 raucous membrane of, 19, y6 
 muscles of, 20 
 muscular tissue of, 385 
 nerves of, 24 ; 
 
 substance of, 19 
 Lower bicuspid, first, 217 
 
 buccal surface of, 219 
 calcification of, 217 
 cusps of, 218 
 distal surface of, 220 
 lingual surface of, 219 
 measurements of, 217 
 mesial surface of, 219 
 neck of, 220 
 occlusal surface of, 21S 
 pulp cavity of, 264 
 root of, 220 
 second, 221 
 
 buccal surface of, 222 
 calcification of, 221 
 distal surface of, 224 
 lingual surface of, 223 
 measurements of, 221 
 . mesial surface of, 223 
 neck of, 224 
 'occlusal surface of, 221 
 root of, 224 
 bicuspids, general description of the, 217 
 
 pulp cavities of, 264 
 cuspid, 214 
 
 Lower cuspid, calcification of, 214 
 
 cusp of, 216 
 
 distal surface of, 215 
 
 labial surface of, 214 
 
 lingual surface of, 215 
 
 measurements of, 214 
 
 mesial surface of, 215 
 
 neck of, 216 
 
 root of, 216 
 cuspids, pulp cavities of, 263 
 incisor, central, 208 
 
 calcification of, 208 
 cervical margin of, 212 
 incisor, cmtting-edge of, 212 
 
 distal surface of, 211 
 
 labial surface of, 209 
 
 lingual surface of, 210 
 
 mesial surface of, 210 
 
 neck of, 212 
 
 root of, 212 
 incisors, pulp cavities of, 262 
 lateral incisor, general description of, 
 
 213 
 molar, first, 224 
 
 buccal surface of, 228 
 calcification of, 224 
 cusps of, 226 
 distal surface of, 230 
 lingual surface of, 229 
 measurements of, 224 
 mesial surface of, 229 
 neck of, 230 
 occlusal surface of, 225 
 roots of, 230 
 
 second, 231 
 
 buccal surface of, 233 
 calcification of, 231 
 distal surface of, 233 
 lingual surface of, 233 
 measurements of, 231 
 mesial surface of, 233 
 occlusal surface of, 231 
 roots of, 234 
 
 third, calcification of, 235 
 
 general description of the, 235 
 roots of, 236 
 types of the, 237 
 molars, pulp cavities of, 265 
 
 M. 
 
 Malpighi's layer, 474 
 Mandible, 71 
 
 evolution of. 310 
 Masseter, 26, 89 
 Mastication, muscles of, 89 
 
 active organs of, 1 7 
 Maxillary bones, development of, 309 
 
 sinus, 65 
 
 superior, 51 
 Meckel's cartilage, 78, 310, 466 
 
 ganglion, 35 
 Median raphe, 1 27 
 Membrana eboris, 305 
 
 prreformativa, 403 
 
 propria, 349 
 
497 
 
 Mental foramen, 73 
 
 protuberance, 72 
 Mesoblast, 457 
 Middle meatus, 57 
 
 superior dental nerve, 121 
 Molar glands, 378 
 lower, first, 224 
 second, 231 
 third, 235 
 upper, first, 177 
 second, 191 
 third, 200 
 Mouth, 17 
 
 angles of, 18 
 bones of, 51 
 boundaries of, 1 7 
 contents of, 17 
 dissection of, 31 
 divisions of, 31 
 entrance to, 17 
 epithelium of, 364 
 floor of, 3 1 , 40 
 frense of, 125 
 general description of, 17 
 glands of, 130 
 inferior portion of, 40 
 interior of, 31 
 lateral walls of, 24 
 mucous membrane of, 126, 364 
 muscular tissues of, 385 
 posterior boundary of, 37 
 roof of, 31 
 situation of, 17 
 submucosa of, 365 
 superior portion of, 31 
 tunica propria of, 365 
 vestibule of, 17 
 walls of, 24 
 Mucous membrane of the cheeks, histology of, 
 367 
 of gums, histology of, 369 
 of lips, histology of, 366 
 of mouth, 126, 364 
 
 blood supply to, 365 
 histology of, 364 
 nerve supply to, 365 
 of tongue, histology of, 371 
 Muscle, external pterygoid, 92 
 internal pterygoid, 92 
 masseter, 26, 89 
 temporal, 91 
 Muscles, angular series, 37 
 of mastication, 89 
 of soft palate,. 37 
 of tongue, 44 
 Muscular tissue, 355 
 
 tissues of cheek, 386 
 
 endomysium of, 356 
 involuntary, 355 
 of lips, 38s 
 
 perimysium of, 356 
 
 sarcolerama of, 357 
 
 sarcoplasm of, 357 
 
 of mouth, histology of, 3S5 
 
 non-striated. 355 
 of soft palate, 386 
 
 32 
 
 Muscular tissues of soft palate, striated, 356 
 of tongue, 3S7 
 
 voluntary, 357 
 Mylohyoid ridge, 73 
 Myrtriform fossa, 53 
 
 N. 
 
 Nasal crest, 59 
 
 spine, 59 
 Nasmyth's membrane, 445 " 
 
 Nerve, anterior palatal, 35 
 cell, 359 
 cells, 363 
 corpuscles, 362 
 fiber, axis cylinder of, 362 
 
 neurilemma of, 362 
 fibers, 362 
 
 medullated, 362 
 non-medullated, 362 
 inferior dental, 122 
 inferior maxillary, 122 
 middle superior dental, 121 
 posterior superior dental, 121 
 process, 360 
 superior dental, 121 
 superior maxillary, 120 
 Nerves, 362 
 
 endoneurium of, 362 
 epineurium of, 362 
 funiculi of, 362 
 medullary sheath of, 362 
 perineurium of, 362 
 of tongue, 50 
 system of, 362 
 Nervous tissue, 358 
 Neumann's sheath, 412 
 Neurilemma, 362 
 Neuroblasts, 359 
 Neurocyte, 359 
 Neuron, 359 
 Non-striated muscular tissues, 355 
 
 Occlusion of the teeth, loS 
 of the deciduous teeth, 270 
 
 Odontoblastic cells, 316 
 
 Odontoblasts, 305, 306, 419, 441 
 processes of, 442 
 
 Oral cavity, 458 
 
 embryology of, 45S 
 
 Orbicularis oris, 20 
 
 Osteoblasts, 354, 447 
 
 Osteoclasts, 449 
 
 Overbite, III 
 
 Palatal glands, 132, 379 
 raphe, 32, 127 
 ruga:, 33, 127 
 Palate, bone, articulation of, 70 
 
 attachment of muscles to, 70 
 blood supply to, 70 
 development of, 70 
 
INDEX. 
 
 Palate, bone, horizontal plate of, 67 
 vertical plate of, 68 
 bones, 67 
 hard, 31 
 soft, 36 
 Palatoglossus, 37 
 Palatomaxillary suture, 34 
 Palatopharyngeus, 37 
 Papilla: of the tongue, 43 
 Parotid duct, 134 
 
 gland, 133, 382 
 Perichondrium, 350 
 Perimysium, 356 
 Periosteum, 354 
 
 Permanent incisors, papills for, 329 
 molars, germs for, 306 
 teeth, 95 f <; 
 
 preparation for development 01, 320 
 advance of, 342 
 Pigment cells, 349 
 Pillars of fauces, 36 
 Plasma cells, 349 
 Posterior foramina, 34 
 palatal canal, 55 
 superior dental nerve, 12I 
 Primitive dental furrow, 313 
 Process, alveolar, 60 
 condyloid, 77 
 coronoid, 77 
 Pulp, blood-vessels of, 443 
 canals, 238 
 
 cavities, description of, 238 
 dissections to show, 238 
 horns of, 239 
 of deciduous teeth, 284 
 of lower teeth, 262 
 of teeth, 238 
 of upper teeth, 240 
 cells of, 440 
 histology of, 44° 
 nerves of, 444 
 odontoblasts of, 441 
 
 QuADRATUS menti, 23 
 
 R. 
 
 Ranine artery, 50 
 ■ Raphe, 32, 127 
 Retzius, brown stnse of, 390 
 Ridge, mylohyoid, 73 
 Risorius muscle, 28 
 Roots, anomalous, 485 
 
 formation of, 333 
 Rugae, 33, 127 
 
 S. 
 
 Sacculus, dental, 307 
 Salivary glands, 132, 381 
 
 blood-vessels of, 383 
 nerves of, 383 
 
 Sarcolemma, 351 
 Sarcoplasm, 352 
 Schreger, lines of, 395 
 Schwann, sheath of, 362 
 
 white substance of, 362 
 Seventh nerve, 30 
 Sharpey's fibers, 354 
 Sheath, medullary, 362 
 
 of Schwann, 362 
 Simple saccular glands, 376 
 
 tubular glands, 376 
 Soft palate, 36 
 
 blood supply to, 39 
 glands of, 379 
 muscles of, 37 
 muscular tissue of, 387 
 nerves of, 39 
 substance of, 36 
 Spaces, interglobular, 417 
 
 interproximate, 106 
 Sphenomaxillary ligament, 86 
 Sphenopalatal ganglion, 35 
 Stellate reticulum, 399 
 Stenson, foramen of, 59 
 Stratum intermedium, 289, 399 
 Striated muscular tissue, 356 
 Styloglossus, 46 
 Stylomaxillary ligament, 85 
 Sublingual artery, 50 
 duct, 135 
 fossa, 74 
 gland, 135 
 Submaxillary duct, 135 
 fossa, 74 
 gland, 134 
 Submucosa, 365 
 Supernumerary teeth, 484 
 Superior coronary artery, 23, 29 
 vein, 30 
 lingualis, 48 
 
 maxillary bone, articulation of, 62 
 alveolar process of, 60 
 blood supply to, 63 
 development of, 63 
 facial surface of, 52 
 malar process of, 58 
 muscles attached to, 62 
 nasal process of, 57 
 orbital surface of, 51 
 palatal process of, 54, 5^ 
 proximal surface of, 54 
 sinus of, 55 
 tuberosity of, 56 
 zygomatic surface of, 56 
 bones, 51 
 nerve, 120 
 meatus, 57 
 palatal vein, 35 
 turbinated crest, 58 
 Suture, palatomaxillary, 34 
 Symphysis, 72 
 
 Teeth, 94 
 
 anterior, 99 
 
499 
 
 Teeth, apical extremities of, 99 
 
 articulation of, I09 
 
 attachment of, 95 
 
 blood supply to, I15, II9 
 
 classification of, 95, 96 
 
 complex, 95 
 
 deciduous, 268 
 
 description in detail of, 136 
 
 development of, 286, 470 
 
 dissections of, 23S 
 
 division of, 95 
 
 eruption of, 334 
 
 names of, 96 
 
 nerve supply to, 120 
 
 occlusion of, 108 
 
 permanent, 95 
 
 posterior, 99 
 
 pulp cavities of, 238 
 
 roots of, 98 
 
 simple, 95 
 
 surfaces of, 97 
 
 tissues of, 389 
 
 veins from, 119 
 Temporal muscle, 91 
 Temporomandibular aniculation, 82 
 
 movements of, 88 
 Tensor palati, 38 
 Tissue, adipose, 349 
 
 areolar, 348 
 
 muscular, 355 
 
 nervous, 358 
 Tissues of the body, divisions of, 346 
 
 connective, 347 
 
 of the teeth, 389 
 Tongue, 41 
 
 attachment of, 42 
 
 base of, 42 
 
 blood-vessels of, 49 
 
 circumvallate papilla; of, 373 
 
 dorsum of, 42 
 
 embryology of, 46 
 
 filiform papillae of, 371 
 
 frenum of, 43 
 
 function of, 41 
 
 fungiform papilUe of, 372 
 
 glands of, 132, 379 
 
 median raphe of, 43 
 
 mucous membrane of, 371 
 
 muscles of, 44 
 
 muscular tissue of, 3S7 
 
 nerves of, 50 
 
 papilla: of, 43 
 
 post-tip, 42 
 
 prebase of, 43 
 
 shape of, 42 
 
 size of, 42 
 
 substance of, 42 
 Tonsil, 36 
 Tonsillar recess, 36 
 Tooth band, 287 
 
 development, cellular stage of, 286, 
 470 
 saccular stage of, 309, 316 
 
 follicle, walls of, 308 
 
 fundamental parts of a, 94 
 general description of a, 94 
 
 Tooth germs, 288 
 
 roots, preparations for development of, 
 
 332 
 sac, 307 
 
 sacs exposed by dissection, 314 
 sockets, 61 
 
 tissues of a, 94 
 Transverse facial artery, 29 
 
 branches of, 30 
 vein, 30 
 Tunica propria, 365 
 
 U. 
 
 Upper bicuspid, first, 163 
 
 angles of, 169 
 buccal surface of, 166 
 calcification of, 163 
 crown of, 164 
 cusps of, 165 
 distal surface of, 169 
 measurements of, 163 
 mesial surface of, 168 
 neck of, 169 
 lingual surface of, 167 
 pulp cavity of, 248 
 roots of, 170 
 types of, 171 
 
 second, calcification of, 174 
 general description of, 175 
 measurements of, 174 
 pulp cavities of, 251 
 cuspid, 153 
 
 calcification of, 153 
 
 cusp of, 159 
 
 cutting-edge of, 15S 
 
 distal surface of, 157 
 
 labial surface of, 154 
 
 measurement of, 153 
 
 mesial surface of, 157 
 
 neck of, 159 
 
 Ungual surface of, 155 
 
 pulp cavity of, 245 
 
 root of, 160 
 
 types of, 160 
 incisor, centra], 136 
 
 calcification of, 136 
 crown of, 137 
 cutting-edge of, 141 
 distal surface of, 140 
 labial surface of, 137 
 measurements of, 136 
 mesial surface of, 139 
 neck of, 142 
 lingual surface of, 138 
 pulp cavity of, 240 
 root of, 143 
 types of, 143 
 
 lateral, 146 
 
 calcification of, 1 46 
 crown of, 147 
 cutting-edge of, I49 
 distal surface of, 149 
 labial surface of, 147 
 measurements of, 146 
 mesial surface of, 149 
 
500 
 
 Upper incisor, lateral, neck of, 156 
 libgual surface of, 148 
 pulp cavity of, 243 
 root of, 150 
 types of, 151 
 molar, first, 177 
 
 buccal surface of, 184 
 calcification of, 177 
 cusps of, 180 
 distal surface of, 1S7 
 fossEe and grooves of, I S3 
 lingual surface of, 185 
 marginal ridges of, 179 
 measurements of, 177 
 mesial surface of, 186 
 neck of, 187 
 occlusal surface of, 1 78 
 pulp cavity of, 255 
 roots of, 188 
 types of, 189 
 second, igi 
 
 angles of, 198 
 buccal surface of, 196 
 calcification of, 191 
 cusps of, 194 
 distal surface of, 198 
 fossae and grooves of, 195 
 lingual surface of, I96 
 marginal ridges of, 193 
 measurement of, 191 
 mesial surface of, 197 
 
 Upper molar, second, neck of, 198 
 occlusal surface of, 192 
 pulp cavity of, 258 
 roots of, 198 
 third, 200 
 
 buccal surface of, 202 
 calcification of, 200 
 cusps of, 205 
 distal surface of, 202 
 fossss and grooves of, 206 
 lingual surface of, 203 
 measurements of, 200 
 mesial surface of, 201 
 occlusal surface of, 204 
 pulp cavity of, 259 
 types of, 207 
 
 Uvula, 36 
 
 Vein, inferior palatal, 35 
 
 lingual, 50 
 
 superior palatal, 35 
 Voluntary muscular tissue, 356 
 
 Zygomaticus major, 27 
 minor, 23 
 
COLUMBIA UNIVERSITY LIBRARIES (hsl.slx) 
 
 RK 280 B79 1902 C.I 
 
 Analiiiiiv.MC IhMuIduv ni Ihrmniilh and t 
 
 2002354101 
 
 RK280 B79 
 
 1902 
 
 Broomell 
 Anatomy and histology of the mouth