, qr^ :>3 c.qia, Columbia (init>ersttp V.^ Collese o{ J^itvsidms anii ^urseoniS Eibrarp Digitized by tine Internet Arciiive -in 2010 witii funding from Columbia University Libraries http://www.archive.org/details/manualofpractica1912cunn MANUAL OF ANATOMY .PUBLISHED BY THE JOINT COMMITTEE OF HENRY FROWDE AND HODDER & STOUGHTON AT THE OXFORD PRESS WAREHOUSE, FALCON SQUARE, LONDON, E.C. MANUAL OF Practical Anatomy BY The Late D. J. CUNNINGHAM M.D. (eDIN. ET duel.), D.SC, LL. D. (ST. AND. ET GLAS.), D.C.L. (OXON.), F.R.S. LATE PROFES%OR OF ANATOMY IN THE UNIVERSITY OF EDINBURGH Fl FTH EDITION EDITED BY ARTHUR ROBINSON PROFESSOR OF ANATOMY IN THE UNIVERSITY OF EDINBURGH VOLUME SECOND THORAX; HEAD AND NECK WITH 236 ILLUSTRATIONS NEW YORK WILLIAM WOOD AND COMPANY MDCCCCXII cm 2. \l- 2- PREFACE TO FIFTH EDITION The main object of this preface is to thank those who have so kindly assisted me in the production of the book. At the same time, it may be pointed out that the reasons for the adoption of the Basle nomenclature were fully stated in vol. i., and that the alterations which have been made in the plans of dissection in vol. ii. are not less numerous than those made in vol. i. The alterations include changes in the method of dissecting the face, the posterior triangle, and the deeper parts of the neck. Two plans of dissection to display the middle ear and its surroundings are described. They can be carried out on opposite sides of the head, and the steps of the second method are those followed by the surgeon operat- ing for the relief of mastoid and middle ear disease. The dissection of the thorax has been very largely re-arranged with the object of giving the dissector an opportunity of studying the relative positions of the organs in the medi- astinum whilst they are practically undisturbed. The various plans of dissection described were decided upon, after many trials, as those best adapted to give the student a clear idea of the relative positions of important structures ; and I am greatly indebted to my first and second assistants. Dr. E. B. Jamieson and Mr. T. B. Johnston, and to Professor R. B. Thomson of Cape Town, for the trouble they have taken and the help they have given in devising, modifying, and testing new plans of work. I am indebted also to Dr. Jamieson for dissections of the brain and heart ; to Mr. Johnston for the dissections of the parotid gland ; to Mr. W. W. Carlow for a dissection of the mediastinum ; and to Messrs. M. Barseghian, R. C. Rogers, V vi PREFACE TO FIFTH EDITION and F. M. Halley for other dissections upon which they have expended time and skill, and which have been used in the preparation of the new illustrations. I wish also to thank Professor Arthur Thomson for per- mission to use the illustrations of his beautiful dissections of the eye ; Professor A. M. Paterson for permission to use two diagrams illustrating the connections of some of the cranial nerves ; and Dr. Logan Turner for the loan of the specimens from which the illustrations of the dissection of the mastoid region and middle ear were made. All the new illustrations are from drawings made by Mr. J. T. Murray. They are characteristic of his excellent work, and I am indebted to him for the care and skill he has ex- pended on their production. The new indices and the glossary are the work of Mr. J. Keogh Murphy, F.R.C.S. I believe they will prove to be of great service ; and I desire to thank him not only for the time and trouble he has spent upon them, but also for many useful suggestions which he has made during the progress of the work. ARTHUR ROBINSON. Edinburgh, July 1912. CONTENTS THORAX. Introductory, Thoracic Wall, Thoracic Cavity, Thoracic Joints, PAGE I 3 TO 112 HEAD AND NECK. Face and Frontal Region of Head, Side of the Neck, Posterior Triangle, The Scalp and the Superficial Structures of the Temporal Region, .... The Dissection of the Back, . Removal of the Brain, . . . The Anterior Part of the Neck, Temporal and Infratemporal Regions, Submaxillary Region, .... Otic Ganglion and Tensor Palati, . The Great Vessels and Nerves of the Neck, The Lateral Part of the Middle Cranial Fossa, Dissection of the Orbit, Prevertebral Region, . The Joints of the Neck, Mouth and Pharynx, Carotid Canal, Nervus Maxillaris, Nasal Cavities, 117 142 142 152 161 200 222 265 279 292 294 325 •^ '-* ■-> 350 356 364 385 386 389 Vlll CONTENTS Spheno - Palatine Ganglion Artery, The Larynx, The Tongue, AND Internal Maxillary 402 406 429 ENCEPHALON— THE BRAIN. Membranes and Blood Vessels of the Brain, Base of Brain, ..... The Cerebrum, ..... The Mesencephalon, .... Basal Ganglia of the Cerebral Hemispheres, The Parts of the Brain which lie in the Posterior Cranial Fossa, ...... 439 452 459 506 512 520 THE AUDITORY APPARATUS. External Meatus, ..... Membrana Tympani, ..... Tympanic Cavity or Middle Ear, Auditory Ossicles, ..... Auditory Tube, . . . . Intrapetrous Part of the Facial Nerve and the Acustic Nerve, ....... -Vestibulum, ...... Canales Semicirculares Ossei, The Cochlea, ...... 547 549 550 555 559 562 566 567 567 BULBUS OCULL General Structure of the Eyeball, The Sclera, The Cornea, Tunica Vasculosa Oculi, The Retina, The Vitreous Body, Lens Crystallina, Chambers of the Eyeball, 571 572 573 574 579 581 583 584 INDEX, 585 A GLOSSARY OF THE INTERNATIONAL (B.N.A.) ANATOMICAL TERMINOLOGY GENERAL TERMS. Terms indicating Situation and Direction. Longitudinalis Longitudinal Verticalis Vertical Anterior Posterior Ventral Dorsal Cranial Caudal Superior Inferior Proximalis Distalis Sagittalis Frontalis } Referring to the long axis of the body. /-Referring to the position of the long I axis of the body in the erect posture. /' Referring to the front and back of the \ body or the limbs. ^Referring to the anterior and posterior aspects, respectively, of the body, \ and to the flexor and extensor { aspects of the limbs, respectively. /'Referring to position nearer the head I or the tail end of the long axis. "'l Used only in reference to parts of I, the head, neck, or body. Used in reference to the head, neck, and body. Equivalent to cranial and caudal respectively. Used only in reference to the limbs. Proximal nearer the attached end. Distal J '^ Distal nearer the free end, /-Used in reference to planes parallel I with the sagittal suture of the Sagittal -, ^^^^Y, i.e. vertical antero-posterior I planes. rUsed in reference to planes parallel Frontal \ with the coronal suture of the skull, \ i.e. transverse vertical planes. ix Anterior Posterior Ventral Dorsal Cranial Caudal J Superior ^ Inferior j Proximal } 1 GLOSSARY Horizontalis Horizontal Medianus Median Medialis Medial ' Lateralis Lateral J Intermedius Intermediate Superficialis Profundus Externus Superficial \ Deep i External ■- Internus Ulnaris Internal , Ulnar \ Radial is Tibial Radial Tibial ^ Fibular Fibular] Used in reference to planes at right angles to vertical planes. Referring to the median vertical antero-posterior plane of the body. ■Referring to structures relatively nearer to or further away from the median plane. "Referring to structures situated be- tween more medial and more lateral structures. Referring to structures nearer to and further away from the surface. Referring, with few exceptions, to the walls of cavities and hollow organs. JVo^ to be used as synonymous with medial and lateral. Used in reference to the medial and lateral borders of the forearm, respectively. Used in reference to the medial and lateral borders of the leg, re- spectively. THE BONES. B.N. A. Terminology. Vertebrae Fovea costalis superior Fovea costalis inferior Fovea costalis transversalis Radix arcus vertebrae Atlas Fovea dentis Epistropheus Dens Sternum Corpus sterni Processus xiphoideus Incisura jugularis Planum sternale Ossa Cranii. Os frontale Spina frontalis Processus zygomaticus Facies cerebralis Facies frontalis Old Terminology, Vertebrae Incomplete facet for head of rib, upper Incomplete facet for head of rib, lower Facet for tubercle of the rib Pedicle Atlas Facet for odontoid process Axis Odontoid process Sternum Gladiolus Ensiform process Supra-sternal notch Anterior surface Bones of SkulL Frontal Nasal spine External angular process Internal surface Frontal surface GLOSSARY XI B.N. A. Terminology. Os parietale Lineae temporales Sulcus transversus Sulcus sagittalis Os occipitale Canalis hypoglossi Foramen occipitale magnum Canalis condyloideus Sulcus transversus Sulcus sagittalis Clivus Linea nuchse suprema Linea nuchce superior Linea nuchae inferior Os sphenoidale Crista infratemporalis Sulcus chiasmatis Crista sphenoidalis Spina angularis Lamina medialis processus ptery- goids Lamina lateralis processus ptery- goidei Canalis pterygoideus [Vidii] Fossa hypophyseos Sulcus caroticus Conchas sphenoidales Hamulus pterygoideus Canalis pharyngeus Tuberculum sellte Fissura orbitalis superior Os temporale Canalis facialis [Fallopii] Hiatus canalis facialis Vagina processus styloidei Incisura mastoidea Impressio trigemini Eminentia arcuata Sulcus sigmoideus Fissura petrotympanica Fossa mandibularis Semicanalis tubee auditivae Os ethmoidale Labyrinthus ethmoidalis Lamina papyracea Processus uncinatus Old Terminology. Parietal Temporal ridges Groove for lateral sinus Groove for sup. long, sinus Occipital Anterior condyloid foramen Foramen magnum Posterior condyloid foramen Groove for lateral sinus Groove for sup. long, sinus Median part of upper surface of basi occipital Highest curved line Superior curved line Inferior curved line Sphenoid Pterygoid ridge Optic groove Ethmoidal crest Spinous process Internal pterygoid plate External pterygoid plate A^idian canal Pituitary fossa Cavernous groove Sphenoidal turbinal bones Hamular process Pterygo-palatine canal Olivary eminence Sphenoidal fissure Temporal Bone Aqueduct of Fallopius Hiatus Fallopii Vaginal process of tympanic bone Digastric fossa Impression for Gasserian ganglion Eminence for sup. semicircular canal Fossa sigmoid ea Glaserian fissure Glenoid cavity Eustachian tube Ethmoid Lateral mass Os planum Unciform process xu GLOSSARY B.N. A. Terminology. Os lacrimale Hamulus lacrimalis Crista lacrimalis posterior Os nasale Sulcus ethmoidalis Maxilla Facies anterior Facies infra-temporalis Sinus maxillaris Processus frontalis Processus zygomaticus Canales alveolares Canalis naso-lacrimalis Os incisivum Foramen incisivum Os palatinum Pars perpendicularis Crista conchalis Crista ethmoidalis Pars horizontalis Os zygomaticum Processus temporalis Processus fronto-sphenoidalis Foramen zygomatico-orbitale Foramen zygomatico-faciale Mandibula Spina mentalis Linea obliqua Linea mylohyoidea Incisura niandibulse Foramen mandibulare Canalis mandibulse Protuberantia mentalis Old Terminology. Lachrymal Bone Hamular process Lachrymal crest Nasal Bone Groove for nasal nerve Superior Maxillary Bone Facial or external surface Zygomatic surface Antrum of Highmore Nasal process Malar process Posterior dental canals Lacrimal groove Premaxilla Anterior palatine foramen Palate Bone Vertical plate Inferior turbinate crest Superior turbinate crest Horizontal plate Malar Bone Zygomatic process Frontal process Tempora-malar canal Malar foramen Inferior Maxillary Bone Genial tubercle or spine External oblique line Interna] oblique line Sigmoid notch Inferior dental foramen Inferior dental canal Mental process The Skull as a Whole. Ossa suturarum Foveolse granulares (Pacchioni) Fossa pterygo-palatina Canalis pterygo-palatinus Foramen lacerum Choanae Fissura orbitalis superior Fissura orbitalis inferior Wormian bones Pacchionian depressions Spheno-maxillary fossa Posterior palatine canal Foramen lacerum medium Posterior nares Sphenoidal fissure Spheno-maxillary fissure GLOSSARY Xlll Upper Extremity. B.N. A. Terminology. Old Termlnology. Clavicula Clavicle \ Tuberositas coracoidea Tuberositas costalis Scapula Incisura scapularis Angulus lateralis Angulus medialis Humerus Sulcus intertubercularis Crista tuberculi majoris Crista tuberculi minoris Facies anterior medialis Facies anterior lateralis Margo medialis Margo lateralis Sulcus nervi radialis Capitulum Epicondylus medialis Epicondylus lateralis Ulna Incisura semilunaris Incisura radialis Crista interossea Facies dorsalis Facies volaris Facies medialis Margo dorsalis Margo volaris Radius Tuberositas radii Incisura ulnaris Crista interossea Facies dorsalis Facies volaris Facies lateralis Margo dorsalis Margo volaris Carpus Os naviculare Os lunatum Os triquetrum Os multangulum majus Os multangulum minus Os capitatum Os hamatum Impression for conoid ligament Impression for rhomboid ligament Scapula Supra-scapular notch Anterior or lateral angle Superior angle Humerus Bicipital groove External lip Internal lip Internal surface External surface Internal border External border Musculo-spiral groove Capitellum Internal condyle External condyle Ulna Greater sigmoid cavity Lesser sigmoid cavity External or interosseous border Posterior surface Anterior surface Internal surface Posterior border Anterior border Radius Bicipital tuberosity Sigmoid cavity Internal or interosseous border Posterior surface Anterior surface External surface Posterior border Anterior border Carpus Scaphoid Semilunar Cuneiform Trapezium Trapezoid Os magnum Unciform XIV GLOSSARY Lower Extremity. B.N. A. Terminology. Os coxse Linea glutsea anterior Linea glutaea posterior Linea terminalis Spina ischiadica Incisura ischiadica major Incisura ischiadica minor Tuberculum pubicum Ramus inferior oss. pubis Ramus superior oss. pubis Ramus superior ossis ischii Ramus inferior oss. ischii Pecten ossis pubis Facies symphyseos Pelvis Pelvis major Pelvis minor Apertura pelvis minoris superior Apertura pelvis minoris inferior Femur Fossa trochanterica Linea intertrochanterica Crista intertrochanterica Condylus medialis Condylus lateralis Epicondylus medialis Epicondylus lateralis Tibia Condylus medialis Condylus lateralis Eminentia intercondyloidea Tuberositas tibise Malleolus medialis Fibula Malleolus lateralis Old Terminology, Innominate Bone Middle curved line Superior curved line Margin of inlet of true pelvis Spine of the ischium Great sacro-sciatic notch Lesser sacro-sciatic notch Spine of pubis Descending ramus of pubis Ascending ramus of pubis Body of ischium Ramus of ischium Pubic part of ilio-pectineal line Symphysis pubis Pelvis False pelvis True pelvis Pelvic inlet Pelvic outlet Femur Digital fossa Spiral line Post, intertrochanteric line Inner condyle Outer condyle Inner tuberosity Outer tuberosity Tibia Internal tuberosity External tuberosity Spine Tubercle Internal malleolus Fibula External malleolus Bones of the Foot. Talus Calcaneus Tuber calcanei Processus medialis tuberis calcanei Processus lateralis tuberis calcanei Os cuneiforme primum Os cuneiforme secundum Os cuneiforme tertium Astragalus Os calcis Tuberosity of Inner Outer Inner cuneiform Middle cuneiform Outer cuneiform GLOSSARY XV THE LIGAMENTS. Ligaments of the Spine. B.N. A. Terminology. Lig. longitudinale anterius Lig. longitudinale posteiius Lig. flava Membrana tectoria Articulatio atlanto-epistrophica Lig. alaria Lig. apicis dentis Old Terminology. Anterior common ligament Posterior common ligament Ligamenta subflava Posterior occipito-axial ligament Joint between the atlas and the axis Odontoid or check ligaments Suspensory ligament The Ribs. Lig. capituli costfe radiatum Lig. sterno-costale interarticulare Lig. sterno-costalia radiata Lig. costoxiphoidea Anterior costo-vertebral or stellate ligament Interarticular chondro-sternal liga- ment Anterior and posterior chondro- sternal ligament Chondro-xiphoid ligaments Lig. temporo-mandibulare Lig. spheno-mandibulare Lig. stylo-mandibulare The Jaw. External lateral ligament of the jaw Internal lateral ligament of the jaw Stylo-maxillary ligament Upper Extremity. Lig. costo-claviculare Labrum glenoidale Articulatio radio-ulnaris proximalis Lig. collaterale ulnare Lig. collaterale radiale Lig. annulare radii Chorda obliqua Articulatio radio-ulnaris distalis Discus articularis Recessus sacciformis Lig. radio-carpeum volare Lig. radio-carpeum dorsale Lig. collaterale carpi ulnare VOL. II — b Rhomboid ligament Glenoid ligament Superior radio-ulnar joint Internal lateral ligament of elbow- joint External lateral ligament Orbicular ligament Oblique ligament of ulna Inferior radio-ulnar joint Triangular fibro-cartilage Membrana sacciformis Anterior ligament of the radio- carpal joint Posterior ligament of the radio- carpal joint Internal lateral ligament of the wrist joint XVI GLOSSARY B.N. A. Terminology Lig. collaterale carpi radiale Old Terminology. External lateral ligament of the wrist joint Carpal joints Palmar ligaments of the metacarpo- phalangeal joints Lig. capitulorum (oss. metacar- Transverse metacarpal ligament palium) transversa Lig. collateralia Lateral phalangeal ligaments Articulationes intercarpae Lig. accessoria volaria The Lower Extremity. Lig. arcuatum Lig. sacro-tuberosum Processus falciformis Lig. sacro-spinosum Labrum glenoidale Zona orbicularis Ligamentum iliofemorale Lig. ischio-capsulare Lig. pubo-capsulare Lig. popliteum obliquum Lig. collaterale fibulare Lig. collaterale tibiale Lig. popliteum arcuatum Meniscus lateralis Meniscus medialis Plica synovialis patellaris Plicae alares Articulatio tibio-fibularis Lig. capituli fibulae Syndesmosis tibio-fibularis Lig. deltoideum Lig. talo-fibulare anterius Lig. talo-fibulare posterius Lig. calcaneo-fibulare Lig. talo-calcaneum laterale Lig. talo-calcaneum mediale Lig. calcaneo-naviculare plantare Lig. talo-naviculare Pars calcaneo-navicularis "j lig. y bifur- Pars calcaneo-cuboidea j catum Subpubic ligament Great sacro-sciatic ligament Falciform process Small sacro-sciatic ligament Cotyloid ligament Zonular band Y-shaped ligament Ischio-capsular band Pubo-femoral ligament Ligament of Winslow Long external lateral ligament Internal lateral ligament Arcuate popliteal ligament P^xternal semilunar cartilage Internal semilunar cartilage Lig. mucosum Ligamenta alaria Superior tibio-fibular articulation Anterior and posterior superior tibio-fibular ligaments Inferior tibio-fibular articulation Internal lateral ligament of ankle Anterior fasciculus of external lateral ligament Posterior fasciculus of external lateral ligament Middle fasciculus of external lateral ligament External calcaneo-astragaloid liga- ment Internal calcaneo-astragaloid liga- ment Inferior calcaneo-navicular ligament Astragalo-scaphoid ligament Superior calcaneo- scaphoid liga- ment Internal calcaneo-cuboid ligament GLOSSARY xvii THE MUSCLES. Muscles of the Back. Superficial. B.N. A. Terminology. Levator scapulas Old Terminology. Levator anguli scapulee Serratus anterior Muscles of the Chest. Serratus ma^nus Muscles of Upper Extremity. Biceps brachii Lacertus fibrosus Brachialis Triceps brachii Caput mediale Caput laterale Pronator teres Caput ulnare Brachio-radialis Supinator Extensor carpi radialis longus Extensor carpi radialis brevis Extensor indicis proprius Extensor digiti quinti proprius Abductor pollicis longus Abductor pollicis brevis Extensor pollicis brevis Extensor pollicis longus Lig. carpi transversum Lig. carpi dorsale Biceps Bicipital fascia Brachialis anticus Triceps Inner head Outer head Pronator radii teres Coronoid head Supinator longus Supinator brevis Extensor carpi radialis longior Extensor carpi radialis brevior Extensor indicis Extensor minimi digiti Extensor ossis metacarpi pollicis Abductor pollicis Extensor primi internodii pollicis Extensor secundi internodii pollicis Anterior annular ligament Posterior annular ligament Muscles of Lower Extremity. Tensor fascise latoe Canalis adductorius (Hunteri) Trigonum femorale (fossa Scarpse major) Canalis femoralis Annulus femoralis M. quadriceps femoris — Rectus femoris Vastus lateralis Vastus intermedius Vastus medialis M. articularis genu Tibialis anterior Tensor fascise femoris Hunter's canal Scarpa's triangle Crural canal Crural ring Quadriceps — Rectus femoris Vastus externus Crureus Vastus internus Subcrureus Tibialis anticus XVlll GLOSSARY B.N. A. Terminology, Tendo calcaneus Tibialis posterior Quadratus plantae Lig. transversum cruris Lig. cruciatum cruris Lig. laciniatum Retinaculum musculorum nreorum superius Retinaculum musculorum naeorum inferius pero- pero- Old Terminology. Tendo Achillis Tibialis posticus Accessorius Upper anterior annular ligament Lower anterior annular ligament Internal annular ligament External annular ligament Axial Muscles. Muscles of the Back. Serratus posterior superior Serratus posterior inferior Splenius cervicis Sacro-spinalis Ilio-costalis— Lumborum Dorsi Cervicis Longissimus — Dorsi Cervicis Capitis Spinalis — Dorsi Cervicis Capitis Semispinalis — Dorsi Cervicis Capitis Multifidus Serratus posticus superior Serratus posticus inferior Splenius colli Erector spinse Ilio-costalis — Sacro-lumbalis Accessorius Cervicalis ascendens Longissimus — Dorsi Transversalis cervicis Trachelo-mastoid Spinalis — Dorsi Colli Capitis Semispinalis — Dorsi Colli Complexus Multifidus spin£e Muscles of Head and Neck. Epicranius Galea aponeurotica Procerus Pars transversa (nasalis) Pars alaris (nasalis) Auricularis anterior Auricularis posterior Auricularis superior Orbicularis oculi Pars lacrimalis Occipito-frontalis Epicranial aponeurosis Pyramidalis nasi Compressor naris Dilatores naris Attrahens aurem Retrahens aurem Attollens aurem Orbicularis palpebrarum Tensor tarsi GLOSSARY XIX B.N. A. Terminology. Triangularis Quadratus labii superioris — Caput zygomaticum Caput infraorbitale Caput angulare Zygomaticus Caninus Quadratus labii inferioris Mentalis Platysma Sterno-thyreoid Tliyreo-hyoid Old Terminology. Depressor anguli oris Zygomaticus minor Levator labii superioris Levator labii superioris alceque nasi Zygomaticus major Levator anguli oris Depressor labii inferioris Levator menti Platysma myoides Sterno-thyroid Thyro-hyoid Muscles and Fascia of the Orbit. Fascia bulbi Capsule of Tenon Septum orbitale Palpebral ligaments Rectus lateralis Rectus externus Rectus medialis Rectus internus Muscles of the Tongue. Genio-glossus Longitudinalis superior Longitudinalis inferior Transversus linguoe Verticalis linguae Genio-hyo-glossus Superior lingualis Inferior lingualis Transverse fibres Vertical fibres Pharyngo-palatinus INI. uvulae Levator veli palatini Tensor veli palatini Glosso-palatinus Muscles of the Pharynx. Palato-pharyngeus Azygos uvulae Levator palati Tensor palati Palato-elossus Deep Lateral Muscles of Neck. Scalenus anterior Scalenus anticus Scalenus posterior Scalenus posticus Longus capitis Rectus capitis anticus major Rectus capitis anterior Rectus capitis anticus minor Muscles of Thorax. Transversus thoracis Triangularis sterni Diaphragma pars lumbalis Crus mediale "j Crus intermedium - Crus laterale Diaphragm, lumbar part — Crura and origins from arcuate ligaments Arcus lumbo - costalis medialis Ligamentum arcuatum internum (Halleri) Arcus lumbo - costalis lateralis Ligamentum arcuatum externum (Halleri) XX GLOSSARY Muscles of the Abdomen. B.N. A, Terminology. Ligamentum inguinale (Pouparti) Ligamentum lacunare (Gimbernati) Fibrse intercrurales Ligamentum inguinale reflexum (Collesi) Annulus inguinalis subcutaneus Crus superius Crus infehus Falx aponeurotica inguinalis M. transversus abdominis Linea semicircularis (Douglasi) Annulus inguinalis abdominalis Old Terminology. Poupart's ligament Gimbernat's ligament Intercolumnar fibres Triangular fascia External abdominal ring Internal pillar External pillar Conjoined tendon Transversalis muscle Fold of Douglas Internal abdominal ring Perineum and Pelvis. Transversus perinei superficialis M. sphincter urethrae membranacese Diaphragma urogenitale Fascia diaphragmatis urogenitalis superior Fascia diaphragmatis urogenitalis inferior Arcus tendineus fasciae pelvis Ligamenta puboprostatica Fascia diaphragmatis pelvis superior Fascia diaphragmatis pelvis inferior Transversus perinei Compressor urethrae Deep transverse muscle and sphinc- ter urethrse Deep layer of triangular ligament Superficial layer of the triangular ligament White line of pelvis Anterior and lateral true ligaments of bladder Visceral layer of pelvic fascia Anal fascia THE NERVOUS SYSTEM. Spinal Cord. Fasciculus anterior proprius (Flech- sig) Fasciculus lateralis proprius Nucleus dorsalis Pars thoracalis Sulcus intermedius posterior Columnse anteriores, etc. Fasciculus cerebro-spinalis anterior Fasciculus cerebro-spinalis lateralis (pyramidalis) Fasciculus cerebello-spinalis Fasciculus antero- lateralis super- ficialis Anterior ground or basis bundle Lateral ground bundle Clarke's column Dorsal part of spinal cord Paramedian furrow Anterior grey column Direct pyramidal tract Crossed pyramidal tract Direct cerebellar tract Gowers' tract GLOSSARY XXI . C *■ — ^ o ,^ ^ ^^ _o o tn >-. tyj •r; ' f^ _ CO ^ !/3 >-. 3- 'i-i '5^ G s (L) '" N G Q 3 (-1-1 G > o OJ t/j (U -^ >-> 3 k4 > V G .2 £ , 's .2 S .5 c^ c3 I ■L 'oj rt s in -§ Pi (U ^ rt rt Q \ 1 / -its JG H s l-H \ \/ / ^ CJ II ^ s 3 5 73 G 1 1 13 '3 1 X c^ ^ G r^ Pi ^ P4 t/3 ^ Sh g" 0) s o G n Eh ^ OS 0) 0^ ^» .s ~' T3 OJ G — ' ;z5 a; fl 52; 1 <5 c '■^ Sg w II dl w ^ g Sz; § ^ O 1— 1 c3 ^£ <1 a Pm m rt M II ^^ Si o • rH H M e« P3 M pq (4 XXll GLOSSARY Brain. B.N. A. Terminology. Ehombenceplialon Eminentia medialis Ala cinerea Ala acustica Nucleus nervi abducentis Nuclei n. acustici Fasciculus longitudinalis medialis Corpus trapezoideum Incisura cerebelli anterior Incisura cerebelli posterior Sulcus horizontalis cerebelli Lobulus centralis Folium vermis Tuber vermis Lobulus quadrangularis Brachium conjunctivum cerebelli Lobulus semilunaris superior Lobulus semilunaris inferior Cerebrum Pedunculus cerebri Colliculus superior Colliculus inferior Aqueductus cerebri Foramen interventriculare Hypothalamus Sulcus hypothalamicus Massa intermedia Fasciculus thalamo-mammillaris Pars opercularis Thalamus Pallium Gyri transitivi Fissura cerebri lateralis Gyrus temporalis superior Gyrus temporalis medius Gyrus temporalis inferior Sulcus centralis (Rolandi) Sulcus temporalis superior - Sulcus temporalis medius Sulcus circularis Sulcus temporalis inferior Gyrus fusiformis Sulcus interparietalis Sulcus corporis callosi Sulcus cinguli Fissura hippocampi Gvrus cinguli Old Terminology. Eminentia teres Trigonum vagi Trigonum acusticum Nucleus of 6th nerve Auditory nucleus Posterior longitudinal bundle Corpus trapezoides Semilunar notch (of cerebellum) Marsupial notch Great horizontal fissure Lobus centralis Folium cacuminis Tuber valvulae Quadrate lobule Superior cerebellar peduncle Postero-superior lobule Postero-inferior lobule Crus cerebri Anterior corpus quadrigeminum Posterior corpus quadrigeminum Iter e tertio ad quartum ventri- culum, or aqued. of Sylvius Foramen of Monro Subthalmic region Sulcus of Monro Middle commissure Bundle of Vicq d'Azyr Pars basilaris Optic thalamus Cortex cerebri Annectant gyri Fissure of Sylvius First temporal gyrus Second temporal gyrus Third temporal gyrus Fissure of Rolando Parallel sulcus Second temporal sulcus Limiting sulcus of Reil Occipito-temporal sulcus Occipito-temporal convolution Intraparietal sulcus Callosal sulcus Calloso-marginal fissure Dentate fissure Callosal convolution GLOSSARY XXlll B.N. A. Terminology. Stria terminalis Trigonum collaterale Hippocampus Digitationes hippocampi Fascia dentata hippocampi Cohimna fornicis Septum peUucidum Inferior cornu Commissura hippocampi Nucleus lentiformis Pars frontalis capsuk^e internje Pars occipitalis capsular internae Radiatio occipito-thalamica Radiatio corporis callosi Pars frontalis Pars occipitalis Old Termlnology. Taenia semicircularis Trigonum ventriculi Hippocampus major Pes hippocampi Gyrus dentatus Anterior pillar of fornix Septum lucidum Descending horn of lateral ventricle Lyra Lenticular nucleus Anterior limb (of internal capsule) Posteriorlimb (of internal capsule) Optic radiation Radiation of corpus callosum Forceps minor Forceps major Membranes of Brain. Cisterna cerebello-medullaris Cisterna interpeduncularis Granulationes arachnoideales Tela chorioidea ventriculi tertii Tela chorioidea ventriculi quarti Cisterna magna Cisterna basalis Pacchionian bodies Velum interpositum Tela choroidea inferior Cerebral Nerves. N. oculomotorius N. trochlearis N. trigeminus Ganglion semilunare (Gasseri) N. naso-ciliaris N. maxillaris N. meningeus (medius) N, zygomaticus Rami alveolares superiores pos- teriores Rami alveolares superiores medii Rami alveolares superiores an- teriores Ganglion spheno-palatinum N. palatinus medius N. mandibularis Nervus spinosus N. alveolaris inferior N. abducens N. facialis N. intermedius ■N. acusticus Third nerve Fourth nerve Fifth nerve Gasserian ganglion Nasal nerve Superior maxillary nerve Recurrent meningeal nerve Temporo-malar nerve Posterior superior dental Middle superior dental Anterior superior dental Meckel's ganglion External palatine nerve Inferior maxillary nerve Recurrent nerve Inferior dental Sixth nerve Seventh nerve Pars intermedia of Wrisberg Eighth or auditory nerve XXIV GLOSSARY B.N. A. Terminology. Ganglion superius N, recurrens Ganglion jugulare Ganglion nodosum Plexus oesophageus anterior 1 Plexus oesophageus posterior J Nervus accessorius Ramus internus Ramus externus Old Terminology. Jugular ganglion of 9th nerve Recurrent laryngeal nerve Ganglion of root ^ ^ r^ T r ^ 1 /-or vagus Ganglion or trunk j '=' Plexus gulae Spinal accessory Accessory portion of spinal accessory nerve Spinal portion Spinal Nerves. Rami posteriores Rami anteriores N. cutaneus colli Nn. supraclaviculares anteriores Nn. supraclaviculares medii Nn. supraclaviculares posteriores N. dorsalis scapulae Nn. intercosto-brachiales N. thoracalis longus N. thoraco-dorsalis N. cutaneus brachii medialis N. cutaneus brachii lateralis Fasciculus lateralis Fasciculus medialis N. cutaneus antibrachii lateralis N. cutaneus antibrachii medialis Ramus volaris Ramus ulnaris N. cutaneus antibrachii dorsalis N. axillaris N. interosseus volaris Ramus palmaris N. median! Nn. digitales volares proprii Ramus dorsalis manus Ramus cutaneus palmaris N. radialis N. cutaneus brachii posterior N. cutaneus antibrachii dorsalis Posterior primary divisions Anterior primary divisions Superficial cervical nerve Suprasternal nerves Supraclavicular nerves Supra-acromial nerves Nerve to the rhomboids Intercosto-humeral nerve Nerve of Bell Long subscapular nerve Lesser internal cutaneous nerve Cutaneous branch of circumflex nerve Outer cord (of plexus) Inner cord Cutaneous branch of musculo-cuta- neous nerve Internal cutaneous nerve Anterior branch Posterior branch External cutaneous branch of mus- culo-spiral Circumflex nerve Anterior interosseous Palmar cutaneous branch of the median nerve Collateral palmar digital branches of median nerve Dorsal cutaneous branch of ulnar nerve Palmar cutaneous branch of ulnar nerve Musculo-spiral nerve Internal cutaneous branch of musculo-spiral nerve External cutaneous branches of musculo-spiral nerve GLOSSARY XXV B.N. A. Terminology. Ramus superficialis N. interosseus dorsalis Nn. digitales dorsales N. ilio-hypogastricus Ramus cutaneus lateralis Ramus cutaneus anterior N. genito-femoralis N. lumbo-inguinalis N. spermaticus externus N. cutaneus femoris lateralis N. femoralis N. saphenus Ramus infrapatellaris N. ischiadicus N. peronasus communis Ramus anastomoticus pero- nasus N, peronaeus superficialis N. peronseus profundus N. tibialis N. cutaneus sura medialis N. suralis N. plantaris medialis N. plantaris lateralis N. pudendus Old Terminology. Radial nerve Posterior interosseous nerve Dorsal digital nerves Ilio-hypogastric nerve Iliac branch of ilio-hypogastric nerve Hypogastric branch of ilio- hypogastric nerve Genito-crural nerve Crural branch of genito-crural nerve Genital branch of genito-crural nerve External cutaneous nerve Anterior crural nerve Long saphenous nerve Patellar branch of long saph- enous nerve Great sciatic nerve External popliteal nerve Nervus communicans fibularis Musculo-cutaneous nerve Anterior tibial nerve Internal popliteal nerve Nervus communicans tibialis Short saphenous nerve Internal plantar External plantar Pudic nerve THE HEART AND BLOOD-VESSELS. Heart. Atrium Auricula cordis Incisura cordis TrabeculcC carneae Tuberculum intervenosum Sulcus longitudinalis anterior Sulcus coronarius Limbus fossae ovalis Valvula venae cavee Valvula sinus coronarii Auricle Auricular appendix Notch at apex of heart Columnas carneL'e Intervenous tubercle of Lower Anterior interventricular groove Auriculo-ventricular groove Annulus ovalis Eustachian valve Valve of Thebesius XXVI GLOSSARY Arteries. B.N. A. Terminology. Sinus aortae A. profunda linguae A. maxillaris externa A. alveolaris inferior Ramus meningeus accessorius A. buccinatoria A. alveolaris superior posterior Aa. alveolares superiores anteriores Ramus carotico-tympanicus A. chorioidea A. auditiva interna Rami ad pontem A. pericardiaco-phrenica Rami intercostales Truncus thyreo-cervicalis A. transversa scapulge A. intercostalis suprema A. transversa colli A. thoracalis suprema A. thoraco-acromialis A. thoracalis lateralis A. circumflexa scapulae A. profunda brachii A. collateralis radialis A. collateralis ulnaris superior A, collateralis ulnaris inferior Ramus carpeus volaris Ramus carpeus dorsalis Aa. metacarpese dorsales A. volaris indicis radialis Arcus volaris superficialis Arcus volaris profundus A. interossea dorsalis A. interossea recurrens A. interossea volaris Ramus carpeus dorsalis Ramus carpeus volaris Aa. digitales volares communes Aa. digitales volares propriae Arteriae intestinales A. suprarenalis media A. hypogastrica A. umbilicalis A. pudenda interna A. epigastrica inferior Old Terminology. Sinuses of Valsalva Ranine artery Facial artery Inferior dental artery Small meningeal artery Buccal artery Posterior dental artery Anterior superior dental arteries Tympanic branch of int. carotid Anterior choroidal artery Auditory artery Transverse arteries (branches of Basilar artery) Arteria comes nervi phrenici Anterior intercostal arteries Thyroid axis Suprascapular artery Superior intercostal Transversalis colli Superior thoracic artery Acromio-thoracic artery Long thoracic artery Dorsalis scapulae Superior profunda Anterior branch of superior pro- funda Inferior profunda Anastomotica magna Anterior radial carpal Posterior radial carpal Dorsal interosseous arteries Radialis indicis Superficial palmar arch Deep palmar arch Posterior interosseous artery Posterior interosseous recurrent artery Anterior interosseous artery Posterior ulnar carpal Anterior ulnar carpal Palmar digital arteries Collateral digital arteries Intestinal branches of sup. mesen- teric Middle capsular artery Internal iliac artery Obliterated hypogastric Internal pudic artery Deep epigastric artery GLOSSARY XXVll B.N, A. Terminology. A. spermatica externa Aa. pudendte externce A. circumflexa femoris medialis A. circumflexa femoris lateralis A. genu suprema A. genu superior lateralis A. genu superior medialis A. genu media A. genu inferior lateralis A. genu inferior medialis A. malleolaris anterior lateralis A. malleolaris anterior medialis A. peroncea Ramus perforans A. malleolaris posterior lateralis A. malleolaris posterior medialis Rami calcanei laterales Rami calcanei mediales A. plantaris medialis A. plantaris lateralis Aa. metatarseae plantares Aa. digitales plantares Old Tekmlnology. Cremasteric artery Superficial and deep external pudic arteries Internal circumflex artery External circumflex artery Anastomotica magna Superior external articular artery Superior internal articular artery Azygos articular artery Inferior external articular artery Inferior internal articular artery External malleolar artery Internal malleolar artery Peroneal artery Anterior peroneal artery Posterior peroneal artery Internal malleolar artery External calcanean artery Internal calcanean artery Internal plantar artery External plantar artery Digital branches Collateral digital branches Veins. V. cordis magna V. obliqua atrii sinistri Lig. venae cavse sinistras Vv. cordis minimge Sinus transversus Confluens sinuum Plexus basilaris Sinus sagittalis superior Sinus sagittalis inferior Spheno-parietal sinus V. cerebri internae V. cerebri magna V. terminalis V. basalis V. transversa scapulae V. thoraco-acromialis Vv. transversae colli V. thoracalis lateralis V. azygos V. hemiazygos V. hemiazygos accessoria V. hypogastrica V. epigastrica inferior V, saphena magna V. saphena parva Great cardiac vein Oblique vein of Marshall Vestigial fold of Marshall Veins of Thebesius Lateral sinus Torcular Herophili Basilar sinus Superior longitudinal sinus Inferior longitudinal sinus Sinus alae parvas Veins of Galen Vena magna Galeni Vein of the corpus striatum Basilar vein Suprascapular vein Acromio-thoracic vein Transversalis colli veins Long thoracic vein Vena azygos major Vena azygos minor inferior Vena azygos minor superior Internal iliac vein Deep epigastric vein Internal saphenous vein External saphenous vein XXV 111 GLOSSARY Lymphatics. B.N. A. Terminology. Cisterna chyli Old Terminology. Receptaculum chyli THE VISCERA. Digestive Apparatus. Arcus glosso-palatinus Arcus pharyngo-palatinus Gl. lingualis anterior Ductus submaxillaris GI. parotis accessoria Ductus parotideus (Stenonis) Dentes prsemolares Dens serotinus Papillae vallatae Recessus pharyngeus Tela submucosa Plicae circulares Gl. intestinales Valvula coli Columnge rectales Plicae transversales recti Valvula spiralis Noduli lymphatici aggregati (Peyeri) Intestinum jejunum Intestinum ileum Noduli lymphatici lienales (Malpighii) Anterior pillar of fauces Posterior pillar of fauces Gland of Nuhn Wharton's duct Socia parotidis Stenson's duct Bicuspid teeth Wisdom tooth Circumvallate papillae Lateral recess of pharynx Pharyngeal aponeurosis Valvulae conniventes Crypts of Lieberkuhn Ileo-caecal valve Columns of Morgagni Valves of Houston " Valves of Heister Peyer's patches Jejunum Ileum Malpighian corpuscles Respiratory Apparatus. Larynx Prominentia laryngea Incisura thyreoidea superior M. ary-epiglotticus M. vocalis M. thyreo-epiglotticus Appendix ventriculi laryngis Plica vocalis Plica ventricularis Ligamentum ventriculare Ligamentum vocale Glottis Rima vestibuli Cartilago thyreoidea Adam's apple Superior thyroid notch Aryteno-epiglottidean muscle Internal thyro-arytenoid muscle Thyro-epiglottidean muscle Laryngeal sac True vocal cord False vocal cord Superior thyro-arytenoid ligament Inferior thyro-arytenoid ligament Glottis vera Glottis spuria Thyroid cartilage GLOSSARY XXIX B.N. A. Terminology. Membrana hyo-thyreoidea Cartilage corniculata (Santorini) Tuberculum epiglotticum Pars intermembranacea (rimce glottidis) Pars intercartilaginea (rimse glottidis) Conus elasticus (membrane elasticae larynges) Glandula thyreoidea Glomus caroticum Nose Concha nasalis suprema (Santorini) Concha nasalis superior Concha nasalis media Concha nasalis inferior Old Terminology. Thyro-hyoid membrane Cartilage of Santorini Cushion of epiglottis Glottis vocalis Glottis respiratoria Crico-thyroid membrane Thyroid gland Intercarotid gland or body Highest turbinate bone Superior turbinate bone Middle turbinate bone Inferior turbinate bone Urogenital Apparatus. Corpuscula renis Paradidymis Appendix testis Ductus deferens Gl. urethrales Glandula bulbo-urethralis (Cowperi) Folliculi oophori vesiculosi Cumulus oophorus Tuba uterina Epoophoron Appendices vesiculosi Ductus epoophori longitudinalis Orificium internum uteri Orificium externum Processus vaginalis Glandula magna vestibuli Malpighian corpuscles Organ of Giraldes Hydatid of Morgagni (male) Vas deferens Glands of Litlre Cowper's gland Graafian follicles Discus proligerus Fallopian tube Parovarium Hydatids of Morgagni (female) Gartner's duct Internal os (of uterus) External os Canal of Nuck Bartholin's gland Peritoneum. Bursa omentalis Foramen epiploicum Lig. phrenico-colicum Excavatio recto-uterina (cavum Douglasi) Lig. gastro-Iienale Lesser peritoneal sac Foramen of Winslow Costo-colic ligament Pouch of Douglas Gastro-splenic omentum SENSE ORGANS. The Eye. Sclera Lamina elastica anterior (Bowmani) Sclerotic coat Bowman's membrane XXX GLOSSARY B.N. A, Terminology. Lamina elastica posterior (Des- cemeti) Spatia anguli iridis Angulus iridis Zonula ciliaris Septum orbitale Fascia bulbi Commissura palpebrarum lateralis Commissura palpebrarum medialis Tarsus superior Tarsus inferior Lig. palpebrale mediale Raphe palpebralis lateralis Tarsal glands Old Terminology. Descemet's membrane Spaces of Fontana Irido-corneal junction Zonule of Zinn Palpebral ligament Capsule of Tenon External canthus Internal canthus Superior tarsal plate Inferior tarsal plate Internal tarsal ligament External tarsal ligament Meibomian glands The Ear. Canalis semicircularis lateralis Ductus reuniens Ductus cochlearis Recessus sphericus Recessus ellipticus Paries jugularis Paries labyrinthica Fenestra vestibuli Fenestra cochleae Paries mastoidea Antrum tympanicum Paries carotica Processus lateralis Processus anterior External semicircular canal Canalis reuniens Membranous cochlea Fovea hemispherica Fovea hemi-elliptica Floor of tympanum Inner wall Fenestra ovalis Fenestra rotunda Posterior wall Mastoid antrum Anterior wall Processus brevis (of malleus) Processus gracilis MANUAL \ OF PRACTICAL ANATOMY. THORAX. 'T^HE dissection of the thorax is commenced on the thirteenth -*- day^ after the subject has been placed in the dissecting- room. By that time the upper hmbs have been detached from the trunk. In form, the thorax resembles a truncated cone. Anteriorly and posteriorly it is flattened ; laterally it is full and rounded. During life the movements of the thoracic walls produce alterations in the capacity of the chest cavity, and play an essential part in the function of respiration ; these movements the student should study upon himself and his friends. The thoracic cavity is bounded anteriorly by the sternum and costal cartilages ; it is bounded posteriorly by the twelve thoracic vertebrae and the intervening fibro-cartilages, together with the portions of the ribs which extend laterally from the vertebral column as far as the angles \ the lateral boundaries are formed by the bodies of the ribs, from their angles posteriorly to their anterior extremities anteriorly. These parts constitute the framework of the thorax, and can be studied on the skeleton as well as upon the part before the dissection is commenced. The anterior wall of the thorax is shorter than the posterior wall and, during expiration, the upper margin of the sternum ^ Saturdays and Sundays are not counted. VOL. II — 1 THORAX lies opposite the fibro-cartilage between the second and third thoracic vertebrae, whilst the lower end of the body of the sternum corresponds in level with the middle of the body of the ninth thoracic vertebra. The bodies of the thoracic vertebrae project anteriorly into the cavity of the thorax, and greatly diminish its antero-posterior diameter in the median plane ; but the backward sweep of the posterior portions of the ribs produces a deep hollow on either side of the vertebral column, for the reception of the most massive part of the lung. The superior aperture, inlet of the thorax^ is a narrow opening which is bounded by the first thoracic vertebra, the Right vagus nerve Right subclavian artery Right innominate vein Innominate artery- Trachea CEsophagus Left subclavian artery ' Sulcus subclavius Left vagus nerve Left common 'carotid Left innominate vein Fig. I. — Cervical Domes of the Pleural Sacs, and parts in relation to them, first pair of costal arches, and the manubrium sterni. The plane of this opening is very obHque ; it slopes from the first thoracic vertebra anteriorly and downwards. Through the inlet of the thorax the apices of the lungs project upwards into the root of the neck, and, between them, the follow- ing structures pass through it : — the windpipe, the gullet, the vagi, the phrenic nerves, the left recurrent nerve, the ganglion- ated sympathetic trunks, the thoracic duct, and the great arteries and veins which carry blood to and from the head and neck and the upper limbs. The base or inferior end of the thorax is very wide, and is sometimes called the outlet. Anteriorly it is bounded by the xiphoid process, and posteriorly by the twelfth thoracic vertebra. Between these points the lower margin of the thorax presents a curved outline. Starting from the sternum, it passes downwards, laterally, and posteriorly, as far as the tip of the eleventh costal cartilage ; thence it proceeds up- THORACIC WALL 3 wards, posteriorly, and medially to the vertebral column. In the first part of its extent it is formed by the cartilages of the seventh, eighth, ninth, tenth and eleventh ribs, and in the second part by the lower border of the twelfth rib. The lower margin of the thorax gives attachment to the diaphragm, a highly vaulted or dome-shaped musculo-tendinous partition, which intervenes between the cavity of the thorax above and that of the abdomen below\ It forms a convex floor for the thorax, and a concave roof for the abdomen. By its upward projection it greatly diminishes the general vertical depth of the thoracic cavity. But the diaphragm does not form an unbroken partition. It presents three large openings, by means of which structures pass to and from the thorax, viz. — (i) for the aorta, thoracic duct, and vena azygos ; (2) for the oesophagus and vagi nerves ; (3) for the inferior vena cava. Besides these there are other smaller apertures which will be mentioned later. THORACIC WALL. Two days at least should be devoted to the dissection of the thoracic wall. In addition to the osseous and cartilaginous framework, the walls of the chest are built up partly by muscles, and partly by membranes, and in connection with these there are numerous nerves and blood-vessels. i External intercostals. Muscles, . J Internal intercostals. I iransversi thoracis. I^Subcostals. I' Anterior intercostal membranes. Membranes, . . X Posterior intercostal membranes. [Pleural membrane (parietal part). r Intercostal nerves. Nerves and Arteries, J ^^^^^^^ intercostal arteries. hupenor mtercostal arteries. 1^ Internal mammary arteries. Dissection. — Portions of certain of the muscles of the upper limb and of the abdominal wall are still attached to the thoracic wall on each side. Antero- posteriorly the dissector will meet with the pectoralis major, the pectoralis minor, and the serratzis anterior, whilst towards the lower margin of the chest he will recognise the recttis abdomifiis anteriorly, and the obliqtius externus and latissimus dorsi upon its lateral aspect. The rounded tendon of the subclavius may also be seen taking origin from the first costal arch. These remnants must be removed so as to lay bare the costal arches and the intercostal muscles. In detaching the II — ^1 a 4 THORAX serratus anterior and external oblique be careful not to injure the lateral cutaneous nerves which make their appearance in the intervals between their digitations. The anterior ctitaneous nerves and perforating b7'anches of the internal mammary artery must also be preserved ; they pierce the origin of the pectoralis major in the intervals between the costal cartilages, close to the margin of the sternum. Intercostal Muscles and Membranes. — These muscles and membranes occupy the eleven intercostal spaces on each side. In each space there are two strata of muscular fibres — a superficial and a deep. The superficial layer of muscular fibres is called the external intercostal 7nuscle^ and the deep layer the internal intercostal muscle. The external intercostal muscles are already exposed, and very little cleaning is necessary to bring out their connections. Note that entering into their constitution there is a large admixture of tendinous fibres, and that these, as well as the muscular fibres, are directed obliquely downwards and anteriorly from the lower border of the rib above to the upper border of the rib below. They do not extend farther anteriorly, in the various spaces, than the region of union of the bony with the cartilaginous parts of the costal arches. In many cases, especially in the upper spaces, they do not reach so far. When the muscular fibres stop, the tendinous fibres are prolonged onwards to the sternum in the form of a membrane, which is called the anterior intercostal 77tem- brane. The external intercostal muscles of the two lower spaces are exceptions to this rule. They extend anteriorly to the extremities of the spaces. Posteriorly the muscles ex- tend as far as the tubercles of the ribs, but this is a point which can be satisfactorily demonstrated only after the thorax has been opened. Dissection. — To bring the internal intercostal muscles into view it is necessary to reflect the external intercostal muscles, and also the anterior intercostal membranes. Divide them along the lower border of each space, and throw them upwards. In effecting this dissection, care must be taken of the intercostal vessels, which lie between the two muscular strata, and of the lateral branches of the intercostal nerves. The internal intercostal muscles^ thus laid bare, will be seen to be similar in their constitution to the external muscles. The fibres, however, run in the opposite direction — viz., from above, obliquely downwards and posteriorly. Superiorly, each is attached to the inner surface of the upper rib, immediately above the costal groove ; inferiorly, it is attached upon the THORACIC WALL 5 inner surface of the lower rib, close to the upper margin. The internal intercostal muscles are prolonged anteriorly to the sternum. Posteriorly they extend to the angles of the ribs. The posterior i?itercosial 7nembra?ies extend from the spine to posterior borders of the internal intercostals where they become continuous with the fascial layer between the external and internal intercostal muscles. They will be seen when the thorax is opened. If the internal oblique muscle of the abdomen has not been removed, the dissector should note that the anterior fibres of the lowest two internal intercostal muscles become continuous with the fibres of that muscle. Sternum / / / i M. transversus thoracis / / / Internal mammary artery ' / Anterior intercostal membrane \ Anterior cutaneous nerve ■ // &^ •■ Vv Jk^^^ ■■■• ''' >^^^ Internal inter- C^^^^'ii^^^<\^^^>^ — "Itf!^^^^ costal muscle Trunk of thoracic nerve -'TI /' N' ^^'^^^^IWMSS^^^ Anterior branch of thoracic Posterior branch {]/ / > I nerye (intercostal) ' / External intercostal muscle Anterior costo-transverse ligament ' Posterior intercostal membrane Fig. 2. — Diagram of one of the Upper Intercostal Xer\-es. Intercostal Nerves. — The intercostal nerves are altogether out of sight in the present stage of the dissection. They are hidden by the lower borders of the ribs which bound the intercostal spaces superiorly. By gently pulling upon their lateral cutaneous branches they can be drawn downwards, and they are then seen to lie between the two muscular strata as far anteriorly as a point midway between the vertebral column and sternum. There they sink into the substance of the in- ternal intercostal muscles, amidst the fibres of which they may be traced to the anterior extremities of the bony parts of the ribs, where they reach the deep surface of internal 6 THORAX intercostal muscles and are carried medially, first anterior to the pleura, and then anterior to the transversus thoracis muscle. Lastly, they cross anterior to the internal mammary artery and turn anteriorly, at the side of the sternum, as the anterior cutaneous nerves of the pectoral region. Each nerve, before it reaches the surface, pierces — (a) the internal inter- costal muscle ; (^) the anterior intercostal membrane ; ic) the origin of the pectoralis major; and {d) the deep fascia (Fig. 2). This description holds good for the upper five inter- costal nerves only. The lower six nerves leave the anterior ends of the intercostal spaces and run into the abdominal wall. As they leave the thoracic wall the upper four of the six pass posterior to the upturned costal cartilages, and all six pass between the interdigitating slips of the diaphragm and the transversus abdominis muscles. The intercostal nerves are the anterior branches of the upper eleven thoracic nerves. As they traverse the thoracic wall they give off — {a) the lateral cutaneous branches, {f) twigs to the intercostal, subcostal, and transversus thoracis muscles. The terminal extremities of the upper five become the anterior cutaneous nerves of the thorax. (For the abdominal distribution of the lower six see Vol. I., p. 394.) The lateral cutaneous branches arise midway between the vertebral column and the sternum. They pierce the external intercostal muscles, and pass between the digitations of the serratus anterior. The first intercostal nerve does not give a lateral branch, and it does not become cutaneous anteriorly. The lateral cutaneous branch of the second intercostal nerve is the so- called intercosto-brachial nerve. It is not necessary to make a dissection of the intercostal nerves in more than two or three of the spaces. Intercostal Vessels. — The intercostal arteries should be dissected in spaces in which the nerves have not been traced, and in which, therefore, the internal intercostal muscles are still entire. It is only in a well-injected subject that a satisfactory view of these vessels can be obtained. In each intercostal space one artery is found passing dorso-ven- trally ; and in each of the upper nine intercostal spaces, two anterior intercostal arteries run vent7'o-dor sally. THORACIC WALL 7 In the upper two spaces the vessels which run dorso- ventrally are derived from the superior intercostal division of the costo-cervical branch of the subclavian artery; in the lower nine spaces they spring directly from the aorta, and are called the aortic i?itercostal arteries. The anterior intercostal arteries of the upper six spaces proceed directly from the internal mammary, whilst those of seventh, eighth, and ninth spaces arise from the musculo- phrenic artery. The intercostal vessels are distributed for the most part between the two muscular strata. From the angles of the ribs onwards to a point midway between the vertebral column and sternum, the aortic intercostal arteries lie under shelter of the lower margins of the ribs which bound the spaces superiorly, and at a higher level than the corresponding nerves. Then each divides into two branches, which pass ventrally in relation to the upper and lower margins of the intercostal space. They give off small branches which accompany the lateral cutaneous nerves. The lower two aortic intercostal arteries are carried onwards into the abdominal wall. The branches of the superior intercostal artery are disposed in a manner similar to the aortic intercostal vessels. The anterior intercostal arteries are two in number for each space, except the last two. At their origins they lie under cover of the internal intercostal muscles, and they run later- ally in relation to the upper and lower margins of the ribs bounding the spaces. After a short course they pierce the internal intercostal muscles, and end by anastomosing with the aortic and superior intercostal arteries. Dissection. — The dissector should next proceed to remove the intercostal muscles. This dissection must be done with great care, for immediately subjacent to the internal intercostals and the ribs is the delicate pleural membrane which lines the inner surface of the chest wall. The membrane must not be injured or detached from the deep surfaces of the ribs during this stage of the dissection. As the internal intercostal muscles are removed, the anterior perforating branches of the internal mammary and musculo- phrenic arteries, and the anterior cutaneous nerves must be preserved. When the muscles are removed the internal mammary arter}' with its two accompanying veins will be seen behind the costal cartilages, about half an inch from the side of the sternum. Clean these arteries in the intervals between the cartilages and note the small lymph glands which lie beside them. Each internal mammary artery ends by dividing into superior epigastric and musculo -phrenic terminal branches in the interval between the sixth and seventh rib cartilages. Most likely this space will be so narrow that a view of the bifurcation cannot be obtained. If this is the case, pare away the edges of the cartilages over the artery, or, 11—16 8 THORAX if necessary, remove the medial part of the sixth cartilage completely. The muscle posterior to the internal mammary artery is the transversus thoracis (O.T, triangularis sterni). Endeavour to define its slips in the intervals between the costal cartilages. The dissector should note, as an important practical point, that towards the lower margin of the thorax the pleural sac is not prolonged downwards to the lowest limit of the recess between the diaphragm and the costal arches. Indeed, in the axillary line, it will be found to fall considerably Sterno-hyoid -~:4^v Sterno-thyreoid — |'A ^/||/ Transversus thoracis Intercostal nerve and artery \ Internal mammary artery Sternal glands Transversus oracis Musculo- phrenic artery Musculo- \>, phrenic artery Fig. 3.- — Dissection of the posterior surface of the Anterior Wall of the Thorax. short of this. Consequently the dissector will come down directly upon the diaphragm, when the internal intercostal muscles are removed from this portion of the chest wall. The fibres of the diaphragm correspond somewhat in their direction with those of the internal intercostal muscles, and it is no uncommon occurrence for the student to remove them, and thus expose the peritoneum, under the impression that he has simply laid bare the pleura. When the dissection is properly executed a strong fascia will be seen. It passes from the surface of the diaphragm to the surface of the costal pleura and holds the latter in position. Preserve this mem- brane for further examination. THORACIC WALL 9 Arteria Mammaria Interna. — This vessel arises, in the root of the neck, from the first part of the subclavian. It enters the thorax by passing downwards, posterior to the sternal end of the clavicle and the cartilage of the first rib, and it descends to the interval between the sixth and seventh costal cartilages, where it ends by dividing into the superior epigastric and the musculo-phrenic branches. Placed anterior to the internal mammary artery are the upper six costal cartilages, with the intervening internal inter- costal muscles and anterior intercostal membranes. The inter- costal nerves cross anterior to it before they turn forwards to gain the surface. Posterior to the upper part of the artery is the pleura ; and the transversus thoracis intervenes between the lower part of the artery and the pleural sac. In addition to its two terminal branches, a large number of small collateral twigs proceed from the internal mammary — 1. The anterior intercostal, .^ - .1 .v • • ^ rr., r ,- ' > to the thoracic parietes. 2. The perforating, . . J ^ 3. The pericardio-phrenic, 4. Mediastinal and thymic, 5. Superior epigastric, 6. Musculo-phrenic, \ to parts in the interior of the thorax. \ the terminal branches. The anterior intercostal arteries are supplied to the upper six intercostal intervals, and have been dissected already (p. 6). Two are given to each space : frequently these arise by a common trunk. The perforating arteries accompany the anterior cutaneous nerves, and reach the surface by piercing the internal inter- costal muscles, the anterior intercostal membranes, and the pectoralis major muscle. One, or perhaps two, are given off in each intercostal space. In the female those of the second, third, and fourth spaces attain a special importance, inasmuch as they constitute the principal arteries of supply to the mammary gland. The superior epigastnc artery passes between the sternal and costal origins of the diaphragm and enters the sheath of the rectus muscle of the abdominal wall. The musculo-phrenic artery turns laterally and downwards, along the costal origin of the diaphragm and behind the rib- cartilages. Opposite the eighth costal cartilage it pierces the diaphragm and terminates on its abdominal surface. It gives off the anterior intercostal arteries to the seventh, eighth, and ninth intercostal spaces (p. 7). lo THORAX Musculus Transversus Thoracis (O.T. Triangularis Sterni). - — This is a thin muscular layer placed on the deep surface of the sternum and costal cartilages. It is continuous below with the transversus abdominis, and arises from the posterior surface of the xiphoid process, the lower part of the body of the sternum, and from the medial ends of the fifth, sixth, and seventh costal cartilages. Its fibres radiate in an upward and lateral direction, in the form of five slips, which are inserted into the deep surfaces and lower borders of the second, third, fourth, fifth, and sixth costal cartilages, close to their junction with the ribs (Fig. 3). In many cases the muscle is feebly developed, and does not show such wide connections. Upon its anterior aspect are placed the internal mammary artery and some of the intercostal nerves. It is only a partial view of the muscle which is obtained in the present dissection, but it is not advisable to remove the costal cartilages to expose it further, as this would materially interfere with the subsequent display of other more important structures in their proper relations. THORACIC CAVITY. Before the dissection of the interior of the thorax is com- menced it is necessary that the- dissectors should have some general knowledge of the cavity and its contents. The shape and the boundaries have been studied already (p. i), and it must now be understood that the cavity is divided into two lateral parts by a median septum called the Jiiediastinmn^ which extends from the sternum anteriorly to the vertebral column posteriorly, and from the upper aperture of the thorax above to the diaphragm below. The mediastinum is formed by the heart, enveloped in a fibro-serous sac called the pericardium ; the great vessels passing to and from the heart, i.e. the pulmonary artery and veins, the aorta, and the vena cava superior ; the oesophagus ; the trachea and the commencements of the bronchi ; the thoracic duct ; the azygos, hemiazygos and accessory hemi- azygos veins ; the vagi and phrenic nerves ; numerous lymph glands ; and the areolar tissue in which these structures are embedded and by which they are bound together. For con- venience of description the mediastinum is divided into a superior and an inferior portion^ by an imaginary plane which passes from the lower border of the manubrium sterni anteriorly, to the lower border of the fourth thoracic vertebra THORACIC CAVITY II posteriorly ; and the inferior mediastinum is subdivided into anterior, middle, and posterior portions. The anterior mediasti7ium is the part anterior to the pericardium, the posterior viediastijium the part posterior to the pericardium, whilst the pericardium and the heart with the great vessels and the phrenic nerves with their accompanying vessels form the middle inediastifium. It is customary, however, to speak of the mediastinum as if it were a space, and to say that the various viscera, vessels, etc., lie in the mediastina (Fig. 19, p. 44). The lateral portions of the thoracic cavity are known as Costal part of parietal pleura Pleural cavity Visceral pleura Costal part of parietal pleura Pleural cavitj' Visceral pleura Fig. 4. — Diagrammatic representation of a cross section through the Thorax. the pleural spaces ; each contains the corresponding lung surrounded by an invaginated serous membrane called the pleural sac. There are therefore two pleural sacs, and each is so disposed that it not only lines the chamber in which the lung lies, but is also reflected over the surface of the lung, so as to give it an external covering which is intimately connected with the pulmonary substance. Consequently, the wall of each pleural sac is separable into two portions, an investing or visceral part which covers the surface of the lung, and a lining or parietal part which clothes the inner surfaces of the boundary of each lateral part of the thoracic cavity. It must be clearly understood, however, that the two terms are merely applied to indicate different portions of a continuous membrane. 12 THORAX Each lung lies free in the pleural space except along its medial surface, where it is attached to the heart by the pulmonary vessels, to the corresponding bronchial tube, and by a fold of pleura to the side of the pericardium. The dissection which has already been made shows the pleura lining the deep surfaces of the costal arches and the internal intercostal muscles. This part is called the costal pleura, and it is part of the parietal pleura, but before it can be more fully investigated and before the remaining parts of the pleurae and the lungs can be examined, further dissection is necessary. Dissection. — The pleural membrane previously exposed by the removal of the contents of the intercostal spaces must now be carefully separated from the inner surfaces of the ribs by the gentle pressure of the fingers. The separation should be carried anteriorly to the junction of the ribs with their cartilages and posteriorly as far as possible. When this has been done the ribs, from the second to the sixth inclusive, must be divided, with bone forceps, at their junctions with their cartilages, and at the same time any fibres of the transversus thoracis which may be attached to them must be cut. The first and the seventh and those below the seventh vnist not be interfered with. Afterwards the ribs must be divided as far dorsally as possible and the separated portions removed. After the separ- ated parts of the ribs are detached, remove any sharp spicules of bone from the cut ends of the remaining portions. The outer surface of the costal part of the parietal pleura will be exposed in the area from which the ribs have been removed, and the dissector should notice that it has the appearance of a fibrous membrane with a rough surface, the roughness being due to fragments of the connective tissue (endothoracic fascia) which connect it with the adjacent parts. After he has examined the outer surface of the pleura, the dissector should divide it by a vertical incision about midway between the anterior and posterior borders of the area exposed. At each end of the vertical incision a transverse incision must be made. One of the two flaps so formed must be thrown anteriorly, and the other posteriorly. The pleural sac is now opened and the lateral surface of the lung, covered with the visceral portion of the pleura, is exposed. The cavity of the sac and its relations to the mediastinal septum, the diaphragm, and the root of the neck can be explored with the fingers ; and the borders, surfaces, and the root of the lung can be examined. The Pleural Sacs are two in number, a right and a left. They are serous sacs, and are therefore closed. After opening into the interior, the dissector should notice the difference between the rough outer surface of the wall of the sac and its smooth and ghstening inner surface, and in order that he may thoroughly understand the relationship of the wall of the sac to the lung, the mediastinum and the wall of the thoracic cavity, he should follow the wall of the sac, with his fingers, at three different levels — (i) at the level of the THORACIC CAVITY 13 manubrium sterni ; (2) at the level of the third intercostal space ; and (3) at the level of the fifth costal cartilage. He must trace the wall of the sac in the vertical plane also. Commencing at the level of the third intercostal space, he should place his fingers on the surface of the lung and follow it anteriorly and medially until, behind the sternum, he reaches the sharp anterior border, which should be pulled laterally ; then, turning from the lung to the parietal pleura, he should place his fingers on the inner surface of the anterior flap and follow it medially. He will find, at a certain point posterior to the sternum, and to the left of the median plane, that his fingers cease to pass towards the opposite side but are carried posteriorly, along the lateral boundary of the medi- astinum, until they come to the big blood vessels and the air tube of the lung which collectively form its root. Along the front of the vessels his fingers will now pass laterally, following the reflection of the pleura on the front of the vessels, to the medial surface of the lung, and then anteriorly to its anterior border. Round the anterior border they will arrive at the lateral surface of the lung ; along this they will pass to the posterior border and thence anteriorly along the posterior part of the medial surface to the posterior surface of the root, where they will feel, distinctly, the hard outline of the bronchus. Following the posterior surface of the root medially, they will reach the posterior part of the lateral boundary of the mediastinum, along which they will pass posteriorly to the vertebral column, and thence laterally along the posterior parts of the ribs, and finally anteriorly along the inner surface of the posterior flap to its anterior margin. If the dissector has followed the above instructions he cannot fail to have recognised that the pleural sac is in- vaginated by the lung, which in its growth laterally from the mediastinal septurh has invaginated and expanded a part of the medial wall of the sac. The dissector should now examine a transverse section of a hardened thorax, or if that is not available, the diagram on p. 11. The study of either will convince him that the lung carrying the in- vaginated part of the wall of the pleural sac on its surface has expanded until it has practically obliterated the cavity of the sac, and he will find that the invaginated pleura on the surface of the lung, which is called the visceral pleura^ is everywhere in close apposition with the non -invaginated 14 THORAX portion which is termed the parietal pleura ; all that inter- venes between the two portions being a thin stratum of fluid, sufficient to lubricate the surfaces and prevent friction during the movements of the lung and the chest wall. After he has grasped the facts noted above the dissector should follow the inner surface of the pleura in the transverse plane at the level of the fifth costal cartilage, that is, below the level of the root of the lung. At that level he will find that the parietal pleura covering the lateral surface of the mediastinal septum is connected with the visceral pleura on the medial surface of the lung by a thin fold, the pulmonary ligament (O.T. ligamentum latum pulmonis). This consists of an anterior and a posterior layer, which correspond, respectively, with the layers on the front and the back of the root of the lung, but are in contact with each other at the level of the fifth rib, on account of the absence of the great blood vessels and air tube of the lung. The pulmonary ligament extends laterally from the mediastinum to the medial surface of the lung, and from the root of the lung above, to within a short distance from the diaphragm below. Its medial, lateral, and upper borders are attached respectively to the mediastinal septum, the lung, and the lower border of the lung root, and are continuous with the pleura covering each, but its lower border is free. When he has satisfied himself regarding the nature and the attachments of the pulmionary ligament, the dissector should trace the pleura in the hori- zontal plane at the level of the manubrium sterni, that is, above the level of the root of the lung. There he will find that the medial wall of the sac is not reflected on to the lung, but that it passes posteriorly along the lateral surface of the mediastinal septum from the sternum anteriorly to the vertebral column posteriorly, and thence laterally and anteriorly to the sternum in an unbroken circle. In the same way he will be able to trace the visceral pleura in a similar but smaller unbroken circle around the upper part of the lung. Having traced the pleura in three horizontal planes the dissector must next trace it in the vertical plane, first around the lung, and then around the wall of the thorax. Commencing with the lung, the fingers should be passed along the anterior border to the apex, thence, down the thick posterior border, to the base, and anteriorly, across the concave base, to the anterior border. By doing this he will again demonstrate to himself THORACIC CAVITY 15 the fact that the lung is ensheathed in visceral pleura. Next, placing his fingers on the inner surface of the parietal pleura behind the costal cartilages, he should carry them upwards towards the head, and he will find that they pass upwards into the root of the neck for a distance of from one to two inches above the level of the anterior part of the first rib, but, on account of the oblique position of the rib, only to the level of its neck posteriorly. The apex of the sac, therefore, lies in ~ Sternum Discus articularis Clavicle Internal mammary First rib - Phrenic nerve Right subclavian vein Right vertebral vein Ansa subclavia Right subclavian artery- Eighth cervical nerve Anterior branch of first thoracic nerve Anterior branch of second intercostal nerve Lateral branch of second intercostal nerve Cut lower edge of pleura Third rib artery Innominate artery Right innominate vein Trachea Right vagus Right recurrent nerve First thoracic sj'^m- pathetic ganglion Superior intercostal artery Third thoracic vertebra Second intercostal nerve Fig. 5. — Structures in relation with the apex of the pleural sac, seen from below. the root of the neck, and by carefully palpating its inner surface the dissector will be able to distinguish the subclavian artery which passes across its anterior surface below the highest point, and, possibly, he may be able to locate the internal mammary and costo-cervical arteries (O.T. superior inter- costal). The first descends from the subclavian trunk anterior to the apex of the sac, and the second passes first upwards to the apex and then posteriorly above it. After the dissector has examined the position and relations of the 1 6 THORAX apex of the sac he should follow its posterior wall downwards, just lateral to the line of the vertebral column, and, if he is dealing with a subject in good condition, he will find that he can pass his fingers downwards to the lower border of the twelfth rib, where they will be carried anteriorly on to the diaphragm and over its surface to the anterior wall of the thorax. If the dissector carries out the examination of the pleural sac in a thorough manner, and if he has appreciated the significance of the arrangements found at different levels, he will have repeatedly convinced himself that the lung, carrying the blood vessels and air tube with it, has invaginated a portion of the lower part of the medial wall of the pleural sac, and has then expanded anteriorly, posteriorly, upwards and, to a certain extent, downwards beyond the margins of the aperture of invagination, whose position is indicated by the root of the lung and the line of attachment of the pulmonary ligament. The portion of the wall of the pleura which is invaginated by the lung is represented by (i) the visceral pleura, (2) the layers covering the root of the lung, and (3) the pulmonary ligament. Before each lung is removed the dissectors should note that its anterior margin does not extend so far anteriorly, and the inferior margin does not extend so far downwards, as the corresponding part of the pleura. The portions of the pleura unoccupied by the lung are called the pleural sinuses. The sinus along the anterior margin of the pleura is the costo-mediastinal sinus^ and that along the lower margin, the phrenico-costal sinus. The walls of the sinuses are separated by a capillary space filled with pleural fluid, and the margins of the lungs enter into the sinuses and recede from them during inspiration and expiration, respectively. In the event of the lungs not having been hardened in situ by formalin injection the dissectors may, with the consent of the dissectors of the head and neck, introduce the nozzle of the bellows into the cervical part of the trachea and inflate the lungs with air. A truer conception of these organs will thus be obtained, and a demonstration will be afforded of their high elasticity, and of their connection with the wind-pipe. After the dissector has completed the general examination of the walls of the pleural sac, he should pull the anterior margin of the lung laterally to expose its medial surface, the front of the root and the front of the pulmonary ligament ; then he should divide the root and the pulmonary ligament, from above downwards, close to the medial surface of the THORACIC CAVITY 17 lung. The lung, thus set free, is to be removed from the thorax, wrapped in a cloth damped with preservative solution, and placed aside for future study. When the lung has been removed the margins of the pleural sac must be examined, and their positions relative to the chest wall noted. This cannot be done to the best advantage until both lungs have been removed. When this has been done the dis- sector should introduce one hand into each pleura, and placing an index finger in each apex, he should note that the apex is situated about one inch above the junction of the lateral two-thirds with the medial third of the clavicle, a fact which he can demonstrate with the aid of his partner on the opposite side, who should hold two macerated clavicles in their proper posi- tions. The apices of opposite sides, there- fore, are some distance apart, and are separ- ated from each other by the structures occu- pying the median part of the neck ; i.e. the air tube, the gullet, and the great arteries passing upwards to the head. As the anterior margins of the pleurae are traced down- wards from the apices they will be found to converge, passing behind the sterno-clavicular joints and coming into apposition at the lower border of the manubrium sterni, immediately to the left of the median plane. Traced further downwards the anterior margins remain in apposition, the right frequently over- lapping the left and both inclining slightly to the left, to the level of the fourth costal cartilages. From the fourth cartilage VOL. II — 2 P'iG. 6. — Diagram to show the relation of the lungs and the pleural sacs to the anterior thoracic wall. The lungs are depicted in red, and the pleural sacs in blue. 1 8 THORAX the anterior margin of the right sac continues to descend, still with a slight inclination to the left, till it reaches the xiphoid process, where it becomes continuous with the inferior margin. This turns laterally, passing behind the xiphoid process and the cartilage of the seventh rib ; it then crosses the junction Cervical dome of pleura Left subclavian artery Left common carotid artery Internal mam- '''^^ mary artery Anterior margin of right pleural sac Intercostal nerve Pericardium Transversus (J thoracis Diaphragm Left innominate vein Fig. 7. — Diagram to show the parts which He anterior to the pericardium and heart. The outline of the heart is indicated in red by a dotted line, and the anterior margins of the pleural sacs are represented by blue lines. of the bone and cartilage of the eighth rib and reaches the level of the tenth rib in the mid-axillary line ; turning posteriorly, it crosses the eleventh and twelfth ribs, and just below the middle of the latter it becomes continuous with the posterior margin, which ascends along the line of the angle of the ribs to the apex. On the left side, at the level of the fourth costal cartilages, the anterior margin of the left pleura turns away from the median plane, for a variable distance, THORACIC CAVITY 19 passing behind the fifth costal cartilage at the margin of the sternum, or even an inch more laterally; it then descends to the lower border of the sixth cartilage, where it becomes Ollsophagus Left subclavian artery Left common carotid artery ^ Left superior intercostal vein \ \ \ Left innominate vein Cut edge of parietal pleura Pericardium Cut edge of parietal pleura Aortic arch Pulmonarj- arterj' Bronchus Lower pulmon- ary vein Oesophagus Diaphragmatic pleura Fig. 8. — Left Pleural Sac, of a subject hardened by formalin injection, opened into by the removal of the costal pleura. The left lung also has been removed so as to display the mediastinal pleura. The line along which the pleura is reflected from the diaphragm on to the thoracic wall is exhibited. continuous with the lower margin of the pleura, which passes laterally and posteriorly along the lower border of the sixth cartilage, across the medial end of the sixth space, and across the seventh cartilage to the junction of the cartilage and II — la 20 THORAX bone of the eighth rib. The remainder of its course and the posUion of Its posterior margin are the same as on the right Cervical dome of pleura Cut edge of parietal pleura' Trachea Vena azygos Eparterial branch of bronchus Pulmonary artery Bronchus (hyparterial part) Pulmonary veins Inferior vena cava Cut edge of parietal pleura Right innominate vein Left innominate vein Superior vena cava Aorta within the pericardium Cut edge of parietal pleura Phrenic nerve Pericardium Diaphragmatic pleura Stn^^i ^i K '"°''^^ °^ '^" '°''^^ P^^* °^ *^ P^^i^tal pleura. Th^ Not tSinrnf ? .'" '"^^^'^ '° ""''^'^y '^' ^^^^^ mediastinal pleura. iNote the line of diaphragmatic reflection of the pleura. The Student should mark out the margins of the pleural sacs on the livmg body, using himself and his friends for the purpose, until he can indicate them correctly, judging from the contour of the body alone and without feeling for the Skeletal pomts. THORACIC CAVITY 21 After the dissector has made himself thoroughly conversant Thoracic sym- pathetic trunk Intercostal ^ vessels and nerve ~T /f Vena azj^gos ~~j^ ^ Pulmonarjf \i ^ artery Eparterial branch of nAtM/f right bronchus O'^ Hyparterial ;ijjy part of ~^ * ' bronchus Scalenus anterior Brachial nerves Right subclavian artery Right subclavian vein Right innominate vein Internal mammary artery rachea Right vagus nerve Left innominate vein Ascending aorta Superior \ ena cava Internal mam- mary artery Phrenic nerve and accom- panying artery Pericardium and heart Diaphragm Fig. 10. — The Right Pleural Chamber opened up by the removal of its lateral wall. The lung has been taken away so as to expose the mediastinal wall of the pleural chamber. Several of the structures in the medias- tinal septum are seen shining through the mediastinal pleura. II— 2 & 2 2 THORAX with the limits of the pleural sacs, he should examine the cut section of the root of the lung, and should endeavour to recognise, through the mediastinal part of the parietal pleura, the positions of the main constituent parts of the mediastinum. As these vary on the opposite sides, each side must be con- sidered separately, and each dissector must make himself well acquainted with the conditions on both sides. On the right side, in the posterior part of the face of the section of the lung root, at least two parts of the bronchial tube will be seen ; an upper, which is the so-called eparterial bronchus, and a lower, the main stem of the right bronchus. Anterior to and between the two bronchi is the pulmonary artery, and more anteriorly, and at a slightly lower level, the upper pul- monary vein. The lower pulmonary vein lies in the lowest part of the root, below and slightly posterior to the main bronchus. If the specimen is well injected, branches of the right bronchial artery may be distinguished on the posterior faces of the air tubes ; and anterior to and between the great blood vessels, and between them and the bronchi, are a number of bronchial glands, which are easily distinguished by the black pigment deposited within them. In the posterior part of the root of the lung, on the left side, the dissectors will see the cut section of the left bronchus, and, in many cases, a section of its first ventral branch also. The left pulmonary artery is above the bronchus, and its anterior wall is on a slightly anterior plane. The upper left pulmonary vein is anterior to the bronchus, and the lower left pulmonary vein is below the bronchus. In a well in- jected specimen the two left bronchial arteries may be seen on the posterior wall of the bronchus, and a number of bronchial glands will be found between and around the large blood vessels and the bronchus. Turning next to the mediastinal pleura oit the right side, the dissectors will note, anterior to and below the root of the lung, a large bulging, due to the heart and pericardium, which lie in the middle mediastinal area. Continuous with the upper and lower ends of the posterior part of this bulging they will see two longitudinal elevations. The upper, from the level of the third costal cartilage to the lower margin of the first rib, is due to the superior vena cava and above that level, to the right innominate vein. The lower elevation is very short, and is caused by the upper part of the inferior THORACIC CAVITY 23 vena cava. A secondary ridge, formed by the phrenic nerve and the accompanying blood vessels, descends along the elevation caused by the superior vena cava, crosses anterior to the root of the lung, runs down along the posterior part of the bulging due to the heart, and the anterior border of the inferior caval elevation. Arching over the root of the lung is a curved ridge, due to the upper part of the vena azygos, as it passes anteriorly to join the superior cava. Above the vena azygos and posterior to the superior cava, the right lateral surface of the trachea, or main air tube, may be seen or felt in the superior mediastinal region, and, descending obliquely across it, from above downwards and posteriorly, the right vagus nerve can be palpated or seen. Posterior to the root of the lung and to the bulging due to the heart, the oesophagus may be recognised in the posterior mediastinal area, either by touch or sight, or both. Somewhat posterior to the oesophagus the margin of the ascending portion of the vena azygos may be noted, and still further posteriorly are the bodies of the vertebrae and the posterior parts of the ribs. Crossing the bodies of the vertebrae trans- versely the right intercostal vessels may be visible or they may be felt, and, descending along the line of the heads of the ribs, the ganglionated trunk of the sympathetic can be recognised by touch, if not by sight. The dissectors should examine next the mediastinum and the posterior wall of the thorax on the left side (see Figs. 8, II, and 13). By inspection and palpation they will easily recognise the positions of the larger and more important structures. Below and anterior to the root of the lung the mediastinal pleura is bulged much more laterally on the left than on the right side by the heart covered by the pericardium. Arching posteriorly and to the left, over the root of the lung, in the superior mediastinal area, is the arch of the aorta, and from its posterior end the descending aorta runs downwards, in the posterior mediastinal area, first posterior to the root of the lung, and then posterior to the heart but separated, in part, from the latter by the cesophagus, which diverges towards the left side in the lower part of the thorax. Above the arch of the aorta the left common carotid and subclavian arteries and the oesophagus can be distinguished in the above order antero - posteriorly. A long slender secondary ridge, pro- ^4 THORAX duced by the left phrenic nerve and the accompanying vessels Scalenus anterior p j Brachial nerves i Left subclavian artery Left subclavian vein Left subclavian artery- Left vagus nerve __/_^ Left common carotid artery / Left innominate vein ^ Internal mammary artery Phrenic nerve and accompanying artery Pulmonary artery Heart and pericardium 1 horacic duct ("Fsophagu* K( current nerve \ortic arch Left pulmon- ary artery Left bronchus Left pulmon- ary veins Cut edge of parietal pleura Descending thoracic aorta Ligamentum pulmonis (cut) (Esophagus Diaphragm Fig. II. — The Left Pleural Chamber opened up by the removal of its lateral wall. The lung has been taken away and a window has been made into the superior mediastinum by the removal of a portion of the medias- tinal pleura. Several of the structures which form the mediastinal partition are seen shining through the mediastinal pleura which is in situ. THORACIC CAVITY 25 descends along the line of the common carotid artery, crosses the arch of the aorta, and then continues along the side of the pericardium. Above the aortic arch, and posterior to the ridge caused by the phrenic nerve, the left vagus nerve can be seen or felt, as it runs downwards along the anterior border of the subclavian artery, and then downwards and posteriorly across the arch of the aorta, to disappear posterior to the root of the lung. Posterior to the descending aorta the sympathetic trunk of the left side can be seen or palpated as it descends along the line of the heads of the ribs. Anterior to the pericardium and the aortic arch and its branches, the mediastinal pleura passes forwards to the back of the sternum in contact with the pleura of the opposite side. When the inspection and palpation of the structures lying in relation with the mediastinal and posterior parts of the costal pleura is satisfactorily completed, the greater part of the pleura should be removed on both sides. Dissection. — Make a longitudinal incision through the mediastinal pleura immediately anterior to the phrenic nerve and a similar incision posterior to the nerve. From the anterior longitudinal incision an incision should be carried anteriorly, at the level of the middle of the root of the lung, and from the posterior longitudinal incision another cut should be carried posteriorly to the front of the root of the lung and then along its anterior surface. Then the root of the lung should be turned anteriorly and an incision should be made on its posterior surface parallel with that already made on the anterior surface. This incision should be carried posteriorly from the root of the lung across the posterior part of the wall of the mediastinum, and then laterally, across the posterior wall of the thorax. When the incisions are completed four flaps will be marked out, two anterior and two posterior. The upper anterior flap on the right side must be turned anteriorly to the level of the anterior border of the superior vena cava, where it may be cut away, the portion of the pleura extending from the superior vena cava to the sternum being left in situ. The upper anterior flap on the left side should be turned anteriorly to the anterior part of the arch of the aorta and the anterior surface of the upper part of the pericardium where it should be cut away, the part extending further forwards to the sternum being left in position. The lower anterior flap on each side must also be turned anteriorly till the anterior part of the pericardium is reached. There it may be cut away, but the portion of pleura extending from the peri- cardium to the sternum should not be interfered with at present. The posterior flaps on each side should be completely removed, care being taken to avoid injury to any of the structures which they cover. When the pleura has been removed, both dissectors should study care- fully the structures exposed on each side, commencing with the right side. 2 6 THORAX Contents of the Mediastinum and the Structures of the Posterior Wall of the Thorax seen from the Right Side. — After the pleura has been removed from the right side of the thorax and the extra-pleural tissue has been dissected away, the following structures are exposed. Below and anterior to the root of the lung is the pericardium. Entering the peri- cardium below and posteriorly is the thoracic part of the inferior vena cava, and entering the upper part is the superior vena cava. The upper end of the superior vena cava is continuous with the right innominate vein, which lies posterior to the sternal end of the first costal cartilage. Arching over the root of the lung, to join the superior vena cava, is the terminal part of the azygos vein. Above the azygos vein and posterior to the superior vena cava are parts of the trachea, the right vagus nerve, and the oesophagus. On the posterior surface of the root of the lung is the posterior pulmonary plexus, formed by the vagus nerve, and posterior to the lung root is the vena azygos. At a lower level, posterior to the pericardium, the right margin of the oesophagus will be found anterior to the vena azygos. Lateral to the vena azygos, on the sides of the bodies of the vertebrae, lie the right aortic intercostal arteries, the accompanying veins, and the splanchnic nerves. Still more laterally, on the line of the heads of the ribs, runs the sympathetic trunk, and beyond the sympathetic trunk are the intercostal spaces and their contents. After the various parts mentioned above have been located and defined, the dissectors should thoroughly clean the sympathetic trunk and its branches and communications. In the upper part of the thorax the trunk runs along the heads of the ribs, but in the lower part it attains a more anterior position. The Thoracic Portion of the Sympathetic Trunk. — This is continuous above with the cervical portion and below with the abdominal portion. It has the appearance of a knotted cord. The knots are ganglia, which consist of nerve cells and fibres. The intermediate parts of the trunk consist of nerve fibres alone. There are usually eleven ganglia, and, as a rule, each ganglion lies opposite the head of a rib, but the first is opposite the medial end of the first intercostal space, or anterior to the neck of the first rib, and, as the trunk inclines anteriorly below, one or two of the lower ganglia lie on the bodies of the lower thoracic vertebrae. THORACIC CAVITY 27 Branches. — These may be divided into two groups- (i) Lateral; (2) Medial Scalenus niedius Scalenus anterior Brachial plexus Cut edge of costal part of parietal pleura Second right aortic intercostal artery Vena azj'gos Sympathetic trunk End of right bronchial vein Branch of pul- monary artery Eparterial branch of bronchus Posterior pul- monary plexus Hyparterial part of bronchus Lower right pul- monary vein Sulcus terminalis of right atrium Great splanchnic , nerve Inferior vena cava Smjill splanchnic nerve Right phrenic nerve Right common carotid artery Right subclavian artery Right subclavian vein H — First rib (Esophagus Trachea - Right vagus nerve Right phrenic nerve Cut edge of costal part of parietal pleura Superior vena cava Internal mam- mary artery Cut edge of peri- cardial part of parietal pleura Cut edge of peri- cardium Right atrium Diaphragm Fig. 12.— Dissection of Thorax from right side showing the constituent parts of the middle, superior, and posterior mediastina. (i) Lateral Branches. — From each gangUon two branches pass laterally into the adjacent intercostal space, where they 2 8 THORAX join the corresponding intercostal nerve. One of these branches, called the white root of the ganglion, contains medullated fibres which are passing from the medulla spinalis (O.T. spinal cord) through the intercostal nerve to the ganglion. The other, the grey root, consists of non-medullated fibres which are passing from the cells of the ganglion to the nerve. Some of these fibres are distributed with the branches of the nerve, and others run medially, along the intercostal nerve, to the spinal nerve trunk, whence some are distributed by the posterior branch and others pass more medially to the membranes of the medulla spinalis. (2) Medial Branches. — (a) Pulmonary ; {h) Aortic ; (c) Splanchnic. {a) The pulmonary branches arise from the second, third, and fourth ganglia. They run anteriorly to the posterior surface of the root of the lung. There they com- municate with branches of the vagus, forming a plexus called the posterior pulmonary plexus, {b) The aortic branches are fine filaments which arise from the upper five ganglia and pass to the coats of the aorta ; the dissector will rarely be able to trace them in an ordinary dissection, {c) The splanchnic branches arise from the sixth to the last ganglion, and they run together to form three distinct nerves — the greater, the lesser, and the lowest splanchnic nerves, which are all destined for the abdominal viscera. Nervus Splanchnicus Major. — This nerve is formed by the union of four or five roots derived from the sixth to the tenth ganglia, or from the portions of the trunk between. It passes downwards, on the bodies of the vertebrae, pierces the diaphragm, and terminates in the coeliac (O.T. semilunar) ganglion of the same side in the abdomen. Opposite the last thoracic vertebra there is frequently a small ganglion upon the greater splanchnic nerve, or connected with it ; from this ganglion branches are distributed to the aorta, where they communicate with their fellows of the opposite side. Nervus Splanchnicus Minor. — The small splanchnic nerve arises by two roots either from the ninth and tenth, or from the tenth and eleventh ganglia. It also pierces the crus of the diaphragm and ends in the coeliac ganglion. Nervus Splanchnicus Imus. — The lowest splanchnic nerve is a minute branch which springs from the last thoracic ganglion. It is frequently absent, but when it is present it pierces the crus of the diaphragm and ends in the renal plexus. THORACIC CAVITY 29 Dissection. — When the study of the thoracic portion of the sympathetic trunk and its branches is completed the posterior parts of the inter- costal spaces should be cleaned and examined. The internal intercostal muscles will be seen passing as far medially as the angles of the ribs. In some cases fibres with the same direction as those of the internal intercostal muscles will be found descending from one rib to the second or third below, across the pleural surfaces of the intermediate ribs. Such fibres constitute the subcostal /iiicscles, which are very variably developed in different subjects. Sometimes they form an almost complete lining for the posterior part of the thoracic wall, and in other cases they are represented by a few scattered fibres, or they are entirely absent. The Posterior Intercostal Membranes are medial to the internal intercostal muscles and on a more posterior plane. Each is attached, medially, to the anterior costo-transverse ligament, which passes from the neck of the rib below to the lower border of the transverse process of the vertebra above. Laterally, it is continuous with the fascial layer between the internal and external intercostal muscles, and above and below, it is attached to the adjacent ribs. On the pleural surface of the posterior intercostal membrane, in each space, lie the corresponding intercostal nerve and vessels (see Figs. 12 and 13). These pass laterally, on the internal surface of the membrane, and disappear posterior to the border of the internal intercostal muscle. When the membranes are removed the posterior fibres of the external intercostal muscles will be exposed, passing medially as far as the tubercles of the ribs. After the posterior parts of the intercostal spaces and their contents have been fully considered the vena azygos should be studied. If it is traced downwards, from above the root of the lung, it will be found to disappear gradually posterior to the right margin of the oesophagus, which must be raised to display its lower portion. The Vena Azygos. — This vein enters the thorax through the aortic aperture of the diaphragm, to the right of the aorta and thoracic duct, the lower parts of which will be displayed as the vein is cleaned. After entering the thorax the vein ascends, along the right side of the aorta, from which it is separated by the thoracic duct. A short distance above the diaphragm it passes more or less completely behind the right border of the oesophagus. At the lower border of the root of the lung it emerges from behind the cesophagus, passes posterior to the lung root, turns anteriorly above its superior border, at the level of the fifth thoracic vertebra, and terminates in the posterior wall of the superior vena cava, immediately above the point where the latter enters the pericardium, 30 THORAX at the level of the second costal cartilage (see Fig. 12). As it turns anteriorly the vein lies immediately to the right side of the oesophagus, trachea and vagus nerve. The tributaries of the vena azygos are : (i) The right superior intercostal vein which drains blood from the greater part of the second and third intercostal spaces. (2) The eight lower intercostal veins and the subcostal vein of the right side. (3) The vena hemiazygos, and frequently (4) the vena hemiazygos accessoria. Both the latter enter it from the left. In many cases the accessory azygos vein joins the hemiazygos vein. (5) Two or more bronchial veins from the right lung. (6) Some veins from the oesophagus. (7) Some minute pericardial veins. The vena azygos commences in the abdomen where it anastomoses either with one of the upper lumbar veins or directly with the inferior vena cava. Thus it forms a more or less direct anastomosis between the two venae cavse. The intercostal veins and the accompanying arteries and nerves, on both sides, and the hemiazygos and accessory azygos veins will be studied at a later period of the dissection (see p. 108). Contents of the Mediastinum and the Structures of the Posterior Part of the Left Half of the Thorax seen from the Left Side. — After the removal of the four pleural flaps described on p. 25 the following structures are visible on the left side of the thorax (see Fig. 13). Below and anterior to the root of the lung is the pericardium, covering the left ventricle, the left atrium, the conus arteriosus of the right ventricle and the pulmonary artery. Above the root of the lung is the arch of the aorta. The arch of the aorta terminates posteriorly in the descending aorta, which passes downwards posterior to the root of the lung and the pericardium, but it is separated from the lower part of the posterior wall of the pericardium by the oesophagus, which, at this level, is passing towards the left side. On the left and anterior aspect of the aortic arch, from behind forwards, lie the left vagus nerve, the superior cervical cardiac branch of the left sympathetic trunk, the inferior cervical cardiac branch of the left vagus, and the left phrenic nerve with its accompanying vessels. Crossing the arch obliquely, from behind forwards and upwards, is the left superior intercostal vein, which passes lateral to the vagus and medial to the phrenic nerve. Above THORACIC CAVITY 31 the arch of the aorta are the lower parts of the left common Thyreoid gland Left common carotid artery Scalenus anterior Left subclavian arterj' Left subclavian vein First rib Left innominate vein Left common carotid artery Left subclavian artery Left phrenic nerve Left vagus nerve Cut edge of pleura Cut edge of peri- cardium and pleura Pulnionarj' artery Conus arteri- osus of right ventricle nter\'entricular branch of left :oronarj' arterj- Cut edge of pleura Cut edge of pericardium Left ventricle Brachial plexus Thoracic duct First left aortic intercostal artery Qisophagus Sympathetic trunk Left superior intercostal vein Arch of aorta Left pulmonary artery Upper left pulmonarj- vein Left bronchus Left auricle (O.T. auricular appendage) Lower left pulmonary vein Circumflex branch of left coronary artery Great splanchnic Diaphragm Fig. 13. — Dissection of Thorax from left side showing the constituent parts of the superior, middle, and posterior mediastina. carotid and left subclavian arteries, and posterior to the latter lies the oesophagus, with the thoracic duct running along its left lateral border. 32 THORAX Posterior to the descending aorta are the left aortic inter- costal arteries, the accompanying veins, and the splanchnic nerves ; and still more posteriorly and laterally lie the sympathetic trunk of the left side and the left intercostal spaces and their contents. Dissection. — After the structures exposed by the removal of the left pleura have been located, the dissectors should direct their attention to the sympathetic trunk and its branches and communications. The arrange- ment of these is exactly similar to that already described on the right side (see p. 26), When the dissectors have confirmed this statement they should turn to the left subclavian artery, which is the most posterior of the three great branches which spring from the arch of the aorta. Clean this vessel without disturbing the vagus nerve, which descends along its anterior border. Afterwards clean the part of the aortic arch which lies posterior to the vagus nerve, and the descending aorta. Whilst cleaning the arch avoid injuring the left superior intercostal vein, and, as the descending aorta is being cleaned, endeavour to preserve any of the aortic branches of the sympathetic which may have been found previously during the examination of the sympathetic trunk. As the aorta is cleaned the left border of the lower part of the oesophagus will be brought more clearly into view, but the dissector must not attempt to clean the oesophagus at this stage. After the descending portion of the aorta is cleaned, the left aortic intercostal arteries should be examined. They are nine in number ; they emerge from the posterior aspect of the aorta, and they all pass medial to the sympathetic trunk as they approach the intercostal spaces. The upper arteries ascend very obliquely to gain their proper spaces. Accompanying the arteries are the corresponding veins. The lower veins pass, posterior to the aorta, to their terminations in the hemiazygos and accessory hemiazygos veins, and will be more fully studied at a later stage ; but the veins from the second and third spaces unite into a trunk called the left superior intercostal vein. The Left Superior Intercostal Vein. — This vein is formed by the intercostal veins from the second and third intercostal spaces of the left side, and it not uncommonly receives a communication from the first and fourth spaces. It descends along the medial border of the first left aortic intercostal artery to the posterior end of the aortic arch, there it turns anteriorly, along the left side of the aortic arch, and, passing at the same time obliquely upwards, it crosses lateral to the left vagus and medial to the left phrenic nerve. At a later period of the dissection it will be traced to its termination in the left innominate vein. Dissection. — After the left superior intercostal vein has been secured and studied, the dissectors should clean the region posterior to the left subclavian artery, and expose thoroughly the left border of the oesophagus, as that tube lies in the superior mediastinum, and the upper part of the thoracic portion of the thoracic duct, which runs along the border of the oesophagus. THORACIC CAVITY 33 After this stage of the dissection is completed, the dissectors should examine the triangular interval between the left phrenic and left vagus nerves in the upper part of the thorax. Com- mencing above, they should follow the vagus nerve down- wards ; just before it reaches the lower border of the aortic arch, it gives off a very distinct branch which turns round the lower border of the arch. This is the important recurrent nerve which supplies the majority of the intrinsic muscles of the larynx of the same side. Immediately anterior and medial to the point where the recurrent nerve turns beneath the arch, a very distinct fibrous cord must be defined. It connects the arch with the upper border of the left pulmonary artery close to its origin. This is the Ugamentiim arferiosu7n, and it is the remains of the ductus arteriosus, through which blood passed from the pulmonary artery to the aorta during foetal life. When this has been secured the areolar tissue between the phrenic and vagus nerves must be carefully removed. In this tissue two small nerves wall be found which run downw^ards, parallel with the vagus, across the arch of the aorta. The one next the vagus is the superior cervical cardiac branch of the left sympathetic, and the one next the phrenic is the inferior cervical cardiac branch of the left vagus. When these nerves are followed downwards they will be found to end in the superficial cardiac plexus, which lies in the areolar tissue below the aortic arch and to the right of the hgamentum arteriosum. Dissection. — After the pericardium has been cleaned, incisions should be made through it on each side, and the flaps formed should be turned aside so that the dissectors may make themselves familiar ^\dth the relation- ships of the heart to the mediastinal portions of the pleural sacs. Two longitudinal incisions must be made on each side, one anterior and one posterior to the longitudinal strip of pleura left on the lateral surface of the phrenic nerve (see Pigs. 12 and 13). On the right side the incisions should commence at the level of the upper pulmonary vein. On the left side the anterior incision should begin at the lower border of the aortic arch and the posterior at the level of the left pulmonary artery (see Fig. 13). On both sides the longitudinal incisions must descend to the lower border of the pericardium. On both sides incisions should be carried anteriorly from the upper and lower ends of the anterior longitudinal incision to the line along which the mediastinal pleura was left attached to the anterior surface of the pericardium (see Figs. 12 and 13). From the upper end of the posterior longitudinal incision on the right side a cut should be made downwards and posteriorly along the anterior aspect of the root of the lung to the upper end of the inferior vena cava (see Y\g. 12). From the upper end of the posterior longitudinal incision on the left side an oblique cut must be made downwards and posteriorly, along the line of VOL. II — 3 34 THORAX the anterior surface of the root of the left lung. When the incisions have been made, the anterior flaps can be turned anteriorly and the posterior flaps downwards. None of the flaps must be removed, for it will be necessary to replace them in position at a later stage of the dissection. When the flaps marked out by these incisions are turned aside the dissectors will find that, on the right side, they have exposed the greater part of the right atrium (see Fig. 12). They should note that the area of the atrium which is exposed is separated into two parts by a vertical sulcus, the stdcus ter??tinalis, which runs from the anterior face of the cardiac end of the superior vena cava to the anterior aspect of the terminal part of the inferior vena cava. This sulcus divides the atrium into a posterior part, the sinus venosus, and an anterior part, the atrium proper, whose upper and anterior part is prolonged medially to the anterior surface of the heart. On the left side the greater part of the heart exposed by the reflection of the pericardial flaps is the left ventricle, but in the upper part of the area the auricle (O.T. auricular appendage) of the left atrium is seen. Anterior to it lie the stem of the pulmonary artery and the upper part of the anterior portion of the right ventricle. A line of fat, in which lie the interventricular branch of the left coronary artery and the accompany- ing vein, indicates the position of the septum between the left and right ventricles (Fig. 13). After the dissection is completed and the dissectors have carefully noted the relative positions of the various structures which have been exposed, they should proceed to study the phrenic nerves, which have been retained in position by the strips of pleura on their lateral surfaces (see Figs. 12 and 13). Nervi Phrenici. — Each phrenic nerve arises in the neck from the cervical plexus, receiving fibres from the third, fourth, and fifth cervical nerves. It descends on the scalenus anterior muscle and, at the root of the neck, passes anterior to the subclavian artery and posterior to the corresponding vein, but on the left side, as it leaves the scalenus anterior, it lies anterior to the subclavian artery and posterior to the commencement of the innominate vein. As it enters the upper aperture of the thorax it crosses the internal mammary artery, passing from its lateral to its medial side, then it descends along the lateral border of the mediastinum, anterior to the root of the lung, to the diaphragm where it breaks up into branches. The majority of the branches pass between the muscular fibres of the diaphragm and, after communicating with the abdominal sympathetic nerve fibres which form the diaphragmatic plexus, they are distributed to the muscle from its lower surface. The re- lations of the phrenic nerves in the thorax are different on the two sides, and the left phrenic nerve, as a whole, is on a plane somewhat anterior to the right. The right phrenic nerve descends along the lateral borders of the right innominate vein and the superior vena cava to the point where the latter enters the pericardium, then along THORACIC CAVITY 35 the side of the pericardium, which separates it from the venous sinus of the right atrium (see Fig. 12). The Left Phrenic Nerve. — In the upper part of the thorax the left phrenic nerve runs downwards between the left common carotid and the left subclavian arteries and, whilst lying between them, it crosses anterior to the left vagus and posterior to the left innominate vein. In the lower part of .the superior mediastinum it passes lateral to the arch of the aorta and the left superior intercostal vein, then, descending into the middle mediastinum, it lies at first anterior to the root of the left lung, and afterwards it runs downwards along the side of the pericardium, which separates it from the anterior part of the left atrium and from the lateral part of the left ventricle of the heart. The left phrenic nerve is longer than its fellow of the right side, partly on account of the lower position of the diaphragm, and partly on account of the greater projection of the heart on the left side. Branches of the Phrenic Nerves. — The main distribution of the phrenic nerves is to the diaphragm, but some minute sensory twigs are given off by each nerve to the pericardium and to the pleura. The student should note the great import- ance of the phrenic nerves. They are the nerves of supply to the diaphragm, which is the chief muscle of respiration. Pulmones. ^-Before proceeding to the further dissection of the constituent parts of the mediastinum, the dissectors should study the lungs which they previously removed. The lungs are two soft, comparatively light, spongy organs placed one on either side of the mediastinum. The weight of the right lung, when it is filled with an average amount of blood, is 22 oz. and that of the left 20 oz. When the thorax is opened the lungs collapse to about one-third of their original bulk (unless they have been hardened in situ), and it is difficult for the student to realise their proper size and shape until they are distended to their original dimensions with the aid of the bellows (see p. 16). When healthy and sound, the lungs lie free within the cavity of the chest, and are attached only by their roots and by their pulmonary ligaments. It is rare, however, that a healthy lung is seen in the dissecting-room, for adhesions be- tween the visceral and parietal portions of the pleura, due to pleurisy, are generally present. Each lung is accurately adapted to the space in which it lies, and, when hardened II — 3 a 36 THORAX in situ, it bears on its surface impressions and elevations which are an exact counterpart of the inequahties of the structures with which its surfaces are in contact at the moment of fixation. In the natural condition each lung resembles half a cone, and it presents for examination an apex^ a base, a costal surface, a medial surface. An anterior and a posterior border separate the medial from the lateral surface ; and an inferior or basal border separates the base from the medial and lateral Trachea Subclavian sulcu Groove caused by the first nb Subclavian sulcus Groove caused by the first rib Lower lobe Cardiac notch Lower lobe Fig. 14. — The Trachea, Bronchi, and Lungs of a Child, hardened by formalin injection. surfaces. The apex rises into the root of the neck for one and a half inches above the level of the anterior part of the first rib, and it is crossed by the subclavian artery, which makes a groove upon the anterior border, a short distance below the summit, although the artery is separated from the lung by the membranous cervical diaphragm (Sibson's fascia), and by the pleura. The base of each lung has a semilunar outline and is adapted to the upper surface of the diaphragm. Consequently it is deeply hollowed out, and, as the right cupola of the THORACIC CAVITY 37 diaphragm ascends higher than the left, the basal concavity of the right lung is deeper than that of the left lung. The lateral and posterior parts of the basal margin of the lung are thin and sharp and extend downwards into the phrenico- costal sinus of the pleura, which intervenes between the diaphragm and the wall of the thorax. This margin reaches a much lower position posteriorly and laterally than anteriorly, but in all situations it falls considerably short of the bottom of the sinus. The mediastinal part of the basal margin, which lies along the lower border of the pericardium, is more rounded. The diaphragm separates the base of the right lung from Right vagus nerve Righ subclavian artery Right innominate vein Fig. -Cervical Domes of the Pleural Sacs, and parts in relation to them. the upper surface of the right lobe of the liver, and the base of the left lung from the left lobe of the liver, the stomach, the spleen, and, in some cases, from the left extremity of the transverse colon. The costal surface of the lung is very extensive and convex. It lies in relation with the costal pleura, which separates it from the ribs and intercostal muscles, the transversus thoracis and the sternum, and it bears the impressions of the costal arches. The medial surface is separable into an 2intQnor ox mediastinal portion and a posterior or vertebral portion. The vertebral portion lies against the sides of the bodies of the vertebra. The mediastinal part is applied against the mediastinal partition and presents markings which are the exact counter- parts of the inequalities of the corresponding lateral surface II— 3 & 38 THORAX of the mediastinum. Thus, it is deeply hollowed out in adaptation to the pericardium upon which it fits. The pericardial concavity occupies the greater part of the mediastinal surface, and, owing to the greater projection of the heart to the left side, it is much more extensive in the left lung than in the right lung. Groove for arch of aorta Left pulmonary artery Upper left pulmonary vein Left bronchus Lower left pulmonary vein Pulmonary ligament Groove for oesophagus Groove for left subclavian artery Groove for left innominate vein Groove for first rib Groove for tissue in mediastinum, thymus, etc. V Groove for conus arteriosus Depression for left ventricle Cardiac notch Fig. i6.— Medial of a Left Lung hardened in situ. At the upper and posterior part of the pericardial area is the hilus of the lung. This is a wedge-shaped depressed area through which the bronchus and the pulmonary artery enter and the pulmonary veins and lymphatics leave the lung. It is surrounded by the pleura which is reflected from its margin on to the root of the lung, and the layer of reflected pleura round the hilus is continuous, below, with the pulmonary ligament. The portion of the pericardial area anterior to the upper part of the hilus of the left lung corresponds with the THORACIC CAVITY 39 position of the conus arteriosus and the stem of the puhnonary artery, and the same portion of the pericardial area on the right side corresponds with the position of the lower part of the superior vena cava posteriorly and with the ascending aorta anteriorly (Fig. 17). Below and posterior to the lower Groove for right subclavian artery .^ Groove for lower end of internal — ^ jugular vein Groove for ist rib Groove for superior vena cava Groove for ascending aorta Depression for right atrium - QEsophageal area Tracheal area Groove for azygos vein Groove for az^^'gos vein Groove for oesophagus Groove for in- ferior vena cava Pulmonary ligament Fig. 17. — The Medial Surface of a Right Lung hardened in situ. and posterior part of the pericardial area on the right lung is a secondary depression due to the upper part of the inferior vena cava. Posterior to the pericardial area and the hilus there is a narrow strip of the mediastinal surface of the lung which is in relation with the lateral wall of the posterior mediastinum. On the right lung this portion of the surface presents a longitudinal depression which corresponds with the right border of the oesophagus, and more posteriorly at the upper part there may be a groove caused by the vena 40 THORAX azygos. The left lung in the corresponding situation is marked by a deep longitudinal groove which is produced by the contact of the lung with the descending thoracic aorta ; and, close to the base, a small triangular area, anterior to the aortic groove, lies in relation with the left border of the lowest part of the thoracic portion of the oesophagus. The portion of the mediastinal surface which lies above the hilus and pericardial hollow is applied to the lateral aspect of the superior mediastinum and the markings upon it are different on the two sides. On the left side a broad deep groove, caused by the aortic arch, curves over the hilus and becomes continuous posteriorly with the aortic groove on the posterior mediastinal area. From this arched groove a sharply cut sulcus, caused by the left subclavian artery, ascends on the medial side of the apex and, turning laterally above, it crosses the anterior border of the apex a short distance below the summit. Immediately anterior to the subclavian sulcus the medial surface of the apex is occasion- ally marked by a shallow sulcus caused by the lateral margin of the left innominate vein, and more inferiorly its anterior margin is depressed by the first rib. That portion of the surface which lies posterior to the subclavian sulcus is separated by areolar tissue from the oesophagus. On the right lung also a curved sulcus arches over the hilus. It is caused by the vena azygos, as it passes anteriorly to join the superior vena cava. This groove is much narrower and less distinct than the sulcus on the left lung due to the aortic arch. From the anterior end of the sulcus for the azygos vein a broad shallow sulcus passes upwards to the lower and anterior part of the apex. This is produced by the superior vena cava and the innominate vein, and in some cases it is prolonged to the upper part of the apex by a slight longitudinal depression due to the pressure of the internal jugular vein. Arching laterally, across the upper part of the anterior aspect of the apex, there is a shallow groove produced by the right subclavian artery. Posterior to the sulcus for the innominate vein, the medial surface of the apex lies in relation with the right side of the trachea, and still further posteriorly it is either in relation with the right lateral border of the superior mediastinal part of the oesophagus, or it is separated from it by a mass of areolar tissue. The anterior and posterior borders of the lung are in THORACIC CAVITY 41 marked contrast with each other. The anterior is compara- tively short and thin and it extends medially into the costo- mediastinal sinus of the pleura, which lies posterior to the sternum and the costal cartilages. It commences at the apex, curves downwards, anteriorly and medially, posterior to the sterno-clavicular articulation, to the lower border of the manubrium sterni, and then it descends vertically to the base. Immediately below the highest point of the apex it is grooved by the subclavian artery on each side, and on the left side it presents a cardiac notch at the levelof the fifth costal cartilage. The posterior border is rounded and indistinct. It descends from the apex to the base, along the line of the articulations of the heads of the ribs with the bodies of the vertebras, and it is much longer than the anterior border. Lobes of the Lungs. — The left lung is divided into two lobes by a long, deep oblique fissure which penetrates its substance to within a short distance of the hilus. This fissure begins above at the posterior border, about tw^o and a half inches below the apex, at the level of the vertebral end of the third rib, which corresponds wdth the medial end of the spine of the scapula. It is continued on the lateral surface, in a somewhat spiral direction, downwards and anteriorly till it cuts the inferior margin opposite the lateral part of the costal cartilage. The upper lobe of the lung lies above and anterior to this cleft. It is conical in form, with an oblique base. The apex and the whole of the anterior border belong to it. The lower lobe, somewhat quadrangular, is more bulky than the upper, and Hes below and posterior to the fissure ; it comprises the entire base and the greater part of the thick posterior border. In the right lung there are two fissures subdividing it into three lobes. The oblique fissure is very similar in its position and relations to the fissure in the left lung, but it is more vertical in direction. It separates the lower lobe from the upper and middle lobes. The second cleft, the horizontal fissure, begins at the anterior border of the lung at the level of the fourth costal cartilage and extends horizontally till it joins the oblique fissure. The middle or intermediate lobe, thus cut off, is wedge-shaped in outhne. It lies between the oblique and horizontal fissures. Differences between the two Lungs. — The dissectors should particularly note the following differences between the two 42 THORAX lungs : — (i) The right lung is slightly larger than the left, in the proportion of ii to lo. (2) The right lung is shorter and wider than the left lung. This difference is due to the great bulk of the right lobe of the liver, which elevates the right cupola of the diaphragm to a higher level than the left cupola, and also to the heart and pericardium, which project more to the left than the right, and thus diminish the width of the left lung. (3) The anterior sharp margin of the right lung is more or less straight ; the corresponding margin of the left lung presents, in its lower part, a marked angular ■ deficiency {incisura cardiacd) for the EPARTERIAL BRANCH Of right y Bronchus Reflection / of pleura Pulmonary veins amentum pulmonis Fig. 18. — The two Pulmonary Roots transversely divided close to the hilus of each lung. reception of the heart and the pericardium. (4) The right lung is subdivided into three lobes, and the left lung into two. Radix Pulmonis. — The root of the lung is formed by a number of structures which enter the lung at the hilus or slit on its mediastinal surface. The structures which form the root are held together by an investment of pleura, and they constitute a pedicle which attaches the lung to the contents of the mediastinum. The pleura has already been removed from around them, and now a more detailed examination of the constituent parts of the root and of its relations must be made. The portion of the root still THORACIC CAVITY 43 attached to the mediastinum should be used for this purpose. Dissection. — Commence with the vagus nerve and follow it downwards from a point just above the vena azygos on the right side, and from the arch of the aorta on the left, looking carefully for small branches which spring from its anterior border and pass to the anterior surface of the root, where they communicate with the twigs from the sympathetic ganglia, and from the deep cardiac plexus, to form the anterior ptdmonary plextis, from which branches are distributed to the walls of the air tube and the blood vessels. On the left side a few twigs may be found passing from the super- ficial cardiac plexus to the anterior pulmonary plexus. After the branches of the vagus to the anterior pulmonary plexus have been identified, the trunk of the vagus, on each side, must be followed down to the posterior surface of the root of the lung, where it breaks up into branches which unite with twigs from the corresponding sympathetic trunk to form the posterior pulmonary plexus (see p. 28). The posterior pulmonary plexuses of opposite sides are connected together by strong branches, which pass both anterior and posterior to the oesophagus, and each gives branches to the walls of the bronchial tube and the blood vessels of the root of its own side. These various branches must be found and identified. After the posterior pulmonary plexuses are satisfactorily displayed the bronchial blood vessels should be found and cleaned. Arterise Bronchiales. — As a rule, two bronchial arteries are distributed to the left lung and one to the right lung. The two left bronchial arteries spring from the descending aorta. The right bronchial artery is a branch either of the first right aortic intercostal artery or of the upper left bronchial artery. The bronchial arteries and their branches run along the posterior surfaces of the bronchi and their branches, and are the proper nutrient vessels of the lungs. Part of the blood which they convey to the lungs is returned by the pul- monary veins to the left atrium of the heart, but the remainder is returned by bronchial veins, which open on the right side into the vena azygos, and on the left side into the vena hemiazygos accessoria, or into the left superior intercostal vein. Dissection. — After the bronchial vessels have been traced, the dissector should separate the great vessels and the air tube from each other. \Vhilst attempting this, he will find that his work is greatly impeded by the hardened and pigmented bronchial glands. The relative positions of the constituent parts of the roots of the lung have been noted already (p. 22). The Relations of the Roots of the Lungs. — Anterior to the root of each lung are the phrenic nerve, with its accompanying vessels, and the anterior pulmonary plexus ; behind it, the posterior pulmonary plexus, and below it, the ligamentum pulmonis. In addition, in front of the root of the right lung 44 THORAX is the superior vena cava, and above and behind it, the vena azygos. Whilst above the root of the left lung is the aortic arch, and behind it, the descending aorta (Figs. 12 and 13). Bronchi. — There are two primary bronchial tubes, one for each lung. They spring from the termination of the trachea, and each passes downwards and laterally, in the root of the corresponding lung, to the hilus, through which it enters the lung. After passing through the hilus it descends, in the substance of the lung, to the base, lying nearer the posterior than the anterior border. In the root of the lung the bronchus is crossed anteriorly by the pulmonary artery. First thoracic verteb Fourth thoracic vertebra Posterior mediastinum Superior mediastinum Manubrium sterni Anterior mediastinum Middle mediastinum Fig. 19. — Diagram of the Mediastina. which afterwards descends on the posterolateral aspect of the intra-pulmonary part of the bronchial tube. The relations of the bronchi are considered later (p. 96). The Mediastinum and its Contents. — It has been pointed out already that the mediastinum is the interval which extends from the sternum to the vertebral column between the two pleural sacs ; that it is occupied by some of the most important viscera, vessels and nerves in the body. I.e. the heart enclosed in the pericardium ; the aorta and its great branches ; the great vessels which carry the blood to and from the heart ; the oesophagus and trachea ; the vagi and phrenic nerves ; and the thoracic duct. It was THORACIC CAVITY 45 noted further that the mediastinum is separated, for descrip- tive purposes, into two main parts, the superior and the inferior mediastinum^ by an imaginary plane which passes from the lower border of the manubrium anteriorly to the Trachea Vertebral artery Inferior thyreoid artery Transverse cervical artery Trunk common to trans, cervical and trans, scap. arts. ".I^SSTSTV Phrenic nerve Right common carotid - Right innominate vein Pericardiac vein Internal mammary N;^^ w^^ vessels •'" vSyj' Cut margins of right -'',^'mF' \l f pleura and of j^ {ft pericardium jT j - Right lung .,..,... Nfej M p ^jB Right coronary /^F ^'^ artery /j /|P Cut margin of _^ ~~„„^-s^- right pleura -^ Mifcter lU Cut margin of pericardium TlBwy '■tftti **§£ Left common carotid Inferior thj^reoid artery - Phrenic nerve ( Trunk of trans, cervical ( and trans, scap. arteries Scalenus anterior Left innominate vein Internal mammary artery Left lung Cut margin of left pleura Ascending aorta Cut margin of pericardium Right ventricle Fig. 20. — Dissection of the Anterior Part of the Thorax. The sternum and costal cartilages were replaced in position after the dissection had been made. The right scalenus anterior is cut away from its insertion up to the level of the upper border of the subclavian arter)^ lower border of the fourth thoracic vertebra posteriorly ; it has been noted also that the inferior mediastinum is separable into three parts: (i) the a7iterior mediastimwi^ anterior to the pericardium, (2) the posterior 7?iediastinu?Ji, posterior to the pericardium, and (3) the middle 7nediasti7iU7n occupied by the pericardium, the heart, the great vessels immediately adjacent 46 THORAX to the heart, and the phrenic nerves with their accompanying vessels. These sections of the mediastinum and their con- tents must now be examined in detail. Dissection. — The remains of the anterior part of the mediastinal pleura must be divided longitudinally immediately posterior to the sternum, from the lower end of the thorax to the apices of the pleural sacs. The sternal extremities of the first ribs must be then cut through, close to the manu- brium sterni, and, at the same time, the sternal heads of the sterno-mastoid muscles must be separated from the manubrium, if that has not already been done by the dissector of the head and neck. After the sterno- mastoid muscles and the first ribs are divided, the sterno-hyoid and sterno- thyreoid muscles must be cut through transversely, as close to the upper margin of the manubrium as possible. Next, the body of the sternum must be separated from the xiphoid process and the tips of the seventh costal cartilages. The sternum vi^ith the attached costal cartilages may then be removed and placed aside, but it must be carefully preserved for future use. When the sternum is removed the mediastinum is exposed from the front. As seen from the front, the superior mediastinum, v^hich lies posterior to the manubrium, is a relatively vi^ide triangular area, w^ith its apex below^. The anterior mediastinum, on the other hand, is merely a narrow cleft between the adjacent anterior margins of the pleural sacs, except opposite the anterior end of the left fifth costal cartilage where the left pleural sac deviates slightly to the left and the anterior mediastinum becomes slightly wider (Fig. 20). The anterior parts of both the superior and the anterior mediastina are occupied by areolar tissue in which, as far down as the third or fourth costal cartilages, remains of the thymus gland may be found. Thymus. — The thymus gland is a bilobed organ, developed from the third visceral clefts. It is well developed in the foetus and in the child until the end of the second year. Then it frequently undergoes atrophy, but it may persist even until old age. Dissection. — All the remains of the mediastinal pleura and the thymus gland should now be taken away, and the anterior surface of the pericardium and the contents of the superior mediastinum should be thoroughly cleaned. When this has been done the right and left innominate veins and their tributaries will be exposed. The innominate veins should be traced to their union with the superior vena cava. To the left of the superior vena cava and below the left innominate vein lie the upper part of the ascending portion of the aorta, and the anterior part of the aortic arch. When these contents of the upper part of the mediastinum have been thoroughly cleaned, the various structures found in the mediastinum must be studied in detail. Vense Anonymse. — The innominate vein of each side is formed posterior to the sternal end of the corresponding clavicle by the union of the internal jugular and subclavian veins of the same side, and it ends, at the lower border of the right first costal cartilage, by uniting with its fellow of the opposite side to form the superior vena cava. The right innominate vein is short and its course is THORACIC CAVITY 47 almost vertical. It is accompanied on its medial side by the innominate artery, on its lateral side by the right phrenic nerve, and posteriorly by the right vagus nerve. Antero-laterally it is in relation with the anterior margin of the right pleura. The left i7ifiominate vein is much longer than the right. Fig. Spinal medulla Trachea CEsophagus 4th thoracic vertebra Innominate artery Left common carotid ft innominate vein ^lanubrium sterni Synchondrosis sternalis Right pulmonary artery •Pericardial cavity Left atrium Aortic valve Body of sternum Right atrio- ^•entricular valve Wall of right ^■entricle CEsophagus Diaphragm Descending aorta Xiphoid process •^ f T- -m— ^--Liver 21. — Sagittal section of the Thorax of an old man. The upper border of the manubrium sterni and the bifurcation of the trachea are lower than in the averagje adult. It passes obliquely to the right and downwards, posterior to the upper half of the manubrium sterni ; it lies posterior to the re- mains of the thymus gland and the lower ends of the sterno-hyoid and thyreoid muscles, and anterior to the three great branches of the aortic arch and the left phrenic and vagus nerves. Tributaries. — These are (i) the internal jugular vein, (2) the subclavian vein, (3) the vertebral vein, (4) the internal mammary vein, and frequently (5) the inferior thyreoid vein 48 THORAX of the same side. In addition, the right innominate vein receives the right lymph duct, or lymph vessels from the head and neck, the upper extremity and the right half of the thorax of the same side ; and the left innominate vein receives (a) the left superior intercostal vein, (d) some peri- cardiac and thymic veins, and (c) the thoracic duct. Dissection. — After the innominate veins and their tributaries have been studied the left vein may be pushed aside, or, if necessary, it may be cut in order to display the three great branches of the arch of the aorta. artery Recurrent nerve Left innomi- nate vein Innominate artery ^ . Phrenic nerve -f ■'V Left common carotid artery *♦ ' " _. v ^ Vagus nerve - f ^^^ \ ^^^V\i Left subclavian ^, ^ 'V ^^ J% Mediastinal . '' j"^Lar- pleura f \ 7"-* Thoracic duct , \ Cartilage of , i^ first rib ^\ Internal mam- mary vessels Right innomi- nate vein Phrenic nerve Trachea Vagus CEsophagus Mediastinal pleura Fig. 22. — Transverse section through the Superior Mediastinum at level of the third thoracic vertebra. Arteria Anonyma. — The innominate artery is the largest of the three great branches of the aortic arch. It com- mences, from the upper border of the arch, posterior to the centre of the manubrium, passes upwards and to the right, and terminates, posterior to the upper border of the right sterno- clavicular articulation, by dividing into the right common carotid and the right subclavian arteries. Anterior to it are the manubrium sterni, with the attachments of the sterno- hyoid and thyreoid muscles, the right sterno-clavicular joint, the remains of the thymus gland, and the left innominate vein. THORACIC CAVITY 49 Posterior to its lower part is the traciiea, but as the artery passes upwards and to the right it gains the side of the trachea and has the upper part of the lung and pleura posterior to it. To its left, at its commencement, is the left common carotid artery, and at a higher level the trachea. On its right side is the right innominate vein, which separates it from the right phrenic nerve and the pleura. As a rule it gives off its terminal branches only, but occasionally a small artery, called the thyreoidea i?na, springs from it. The Thyreoidea Ima. — This artery is frequently absent. \Yhen it is present it springs from the innominate artery, or from the arch of the aorta, and runs upwards, anterior to the trachea, to the thyreoid gland. Arteria Carotis Communis Sinistra. — The left common carotid artery springs from the arch of the aorta immediately to the left of, and slightly posterior to, the innominate artery. It passes upwards, through the superior mediastinum and posterior to the left sterno-clavicular joint, into the neck. Its anterior relations in the thorax are similar to those of the innominate artery. Posterior to it, from below upwards, are the trachea, the left recurrent nerve, the oesophagus and the thoracic duct, and, on a plane somewhat more to the left, the left phrenic and vagus nerves, and the subclavian artery. To its right lie first the innominate artery, and then the trachea ; and to its left is the left pleura. It gives off no branches in the thorax. Arteria Subclavia Sinistra. — The left subclavian artery springs from the posterior part of the aortic arch, posterior to the left common carotid. It passes vertically upwards, through the superior mediastinum and posterior to the sternal end of the clavicle, into the root of the neck. Anterior to it are the left phrenic and vagus nerves, which separate it from the left common carotid artery. Posterior, and to its left side, it is in relation with the left mediastinal pleura and the lung. To its right side are the trachea and the left recurrent nerve, and, at a higher level, the oesophagus and the thoracic duct. It gives off no branches in the thoracic part of its course. Dissection. — The lateral walls of the pericardium have already been exposed and opened (see p. 33) ; the flaps then made should be replaced and fixed in position. When this has been done, the outline of the sac will be fully displayed, and the dissectors can then study its relations to adjacent organs. VOL. II — 4 50 THORAX The Pericardium. — This is a fibro-seioiis sac which occupies the middle mediastinum. It surrounds the heart and the roots of the great vessels which enter and leave the heart. llic Fibrous Faicardiiim, — The fibrous or outer part of the pericardium is conical in form. Its base rests upon the diaphragm, principally on the central tendon but also upon the muscular ]H:>rtion, particularly upon the left side. Near the median plane it is blended with the central tendon, and can be separated from it only by the aid of the edge of the scalpel ; more laterally the areolar tissue which connects the pericardium and the diaphragm is easily broken down by the handle of the knife. The diaphragm separates the pericardium mainly from the upper surface of the liver, but also, towards the left and anteriorly, from the fundus of the stomach, llie apex of the fibrous sac blends with the outer coats of the aorta, the pulmonary arteries and the superior vena cava. The anterior surface lies behind the body of the sternum and the cartilages of the ribs from the second to the sixth inclusive, but it is separated from them by the lungs and pleurae, except (i) in the median plane of the anterior medi- astinum, where condensations of the areolar tissue of the medi- astinum, called the superior and inferior sterno-pe7'icardiac li^amcnts^ connect the anterior surface of the fibrous sac to the upper and lower ends of the body of the sternum respectively, and (2) in the region of the sternal extremity of the left fifth costal cartilage, where the left pleura retreats somewhat towards the left side, and the pericardium comes into direct relation with the sternum and the left transversus thoracis muscle. This portion of the pericardium is the so-called bare area. It is usually of small extent, and iVeciuently it does not extend beyond the margin of the sternum, but it is of importance because through it the surgeon attempts to tap the pericardium when the sac is distended with fluid. The lateral ivalls of the pericardium are in relation with the mediastinal pleura, the phrenic nerve and the pericardiaco- phrenic vessels intervening (O.T. comes nervi phrenici). The posterior surface lies anterior to the descending aorta and the cxjsophagus medially, whilst laterally it is supported posteriorly by the lungs and pleunxi. At the junction of the upper parts of the lateral and posterior surfaces, on each side, two pulmonary veins enter the pericardium and receive sheaths from its fibrous wall. THORACIC CAVITY 5» Diner t ion. — When the relations and prolongations of the fibrous peri- cardium have been studied, the two anterior flaps already made in the lateral walls of the sac (see p. 33) should \yt connected together and c<'>n- verted into one large anterior flap. This can be done by a transverse cMi^ passing across the median plane just above the diaphragm. The large triangular flap thus formed should be thrown upwards towards the apex of the pericardium. Left common carotid artery Left vagus nerve— I>eft subclavian artery Left innominate vein Trachea Left pulmonary artery I^eft bronchu'S Left pulmonary veins Right vagus ner Diaphragmatic surface of heart Innominate artery _CRiV>phagus _ Right vagoA nerve Superior vena cava Vena azygos Right posterior pulmonary plexus Right pulmonary artery Right bronchus Right pulmonary veins ("Esophageal plexus Portion of peri- cardium I/cft vagus nerve Inferior vena cava Fig. 23. — Posterior Aspect of the Heart with the Descending Aorta, the Trachea and Bronchi, and the QEsophagus. The Serous Pericardium. — The serous pericardium is a closed and invaginated sac which lines the inner surface of the fibrous sac and envelops the heart and the roots of the great vessels passing to and from the heart. The uninvaginated portion of the wall of the serous sac, 52 THORAX which Hnes the inner surface of the fibrous sac, is called the parietal layer, and the invaginated portion, which envelops the heart, is the visceral portion. The inner surface of the sac is fined by a flat endothefium, and, during health, is smooth and Inferior thyreoid veins Right common carotid artery / ', Left common carotid artery Right internal jugular vein --j-» Right subclavian artery — *H Right subclavian vein --^^* Left internal mammarj' vein ' Right internal mammary. vein Cut edge of filarous pericardium Superior vena cava.. Cut edge of serous Ji_ pericardium Aorta Division of pul- monary' arterj' Right pulmonary artery Superior vena cava Upper right pulmonary vein Lower right pu monary vein Cut edges of serous pericardium Inferior vena cava Left internal jugular vein Thoracic duct 'limm Left subclavian artery Left subclavian vein - Left phrenic nerve -Left vagus Left superior intercostal vein Left recurrent nerve Ligamentum arteriosum Left pulmonary artery Arrow in transverse sinus Left bronchus Upper left pulmonary vein Lower left pulmonary vein Fibrous pericardium Serous pericardium Fig. 24. — The Pericardium and Great Vessels of the Heart. The thoracic organs were hardened in situ by formalin injection. The pericardium having been opened by the removal of its anterior wall, the great vessels were divided and the heart removed. gfistening. The parietal and visceral layers are separated, during health, merely by a thin layer of serous fluid, which prevents friction between the two surfaces as they move over each other during the contractions and expansions of the heart. THORACIC CAVITY 53 The Sterno- costal Surface of the Heart. — Before the dissectors disturb the heart, which has been exposed by the reflection of the anterior wall of the pericardium, they should note carefully not only the parts of the heart which are visible, but also their relations to the anterior wall of the thorax. The latter they can easily do by replacing the sternum and costal cartilages in position from time to time. They will find that the sterno-costal surface is divided into an upper, right, or atrial portion and a lower, left, or ventricular portion by an oblique sulcus, the corojiary sulcus (O.T. auriculo-ventricular), which is quite distinct below and on the right, but is masked above and to the left by the roots of the pulmonary artery and the aorta. The position of this sulcus can be indicated on the surface by a line extending obliquely downwards and to the right, from the sternal end of the third left to the sternal end of the sixth right costal cartilage. Below and to the left of the sulcus is the ventricular part of the sterno-costal surface, termi- nating on the left and below in the apex of the heart, which lies posterior to the fifth left intercostal space, three and a half inches from the median plane. The ventricular area of the sterno-costal surface is divided by the anterior longitudinal sulcus (O.T. anterior interventricular sulcus) into a right two-thirds, formed by the right ventricle, and a left third, formed by the left ventricle. The anterior longitudinal sulcus terminates on the lowxr border of the sterno-costal surface, to the right of the apex, in a slight notch, the mcisura cordis. The apex, therefore, is formed entirely by the left ventricle. The lower margin of the sterno-costal surface lies on the diaphragm. It is formed chiefly by the lower border of the right ventricle, and only to a small extent by the apical part of the left ventricle. The upper and right portion of the sterno-costal surface is formed by the atria, which are to a large extent concealed by the pulmonary artery and the ascending part of the aorta. Above and to the right is the right atrium, continuous above with the superior vena cava and below with the inferior vena cava, whilst its auricular portion (O.T. auricular appendage) curves upwards and to the left, along the line of the coronary sulcus, to the root of the pulmonary artery. Crossing the front of the right atrium, immediately below the lower end of the superior vena cava, is a sulcus, the sulcus 54 THORAX terjninalis. If the heart is pulled a little over to the left this sulcus can be traced downwards, along the lateral aspect of the right atrium, to the anterior aspect of the upper end of the inferior vena cava. It indicates the separation between Right common carotid artery Opening of right internal jugular vein ■> Right subclavian artery- Right subclavian vein A Innominate artery Superior vena cava Right phrenic nerve Eparterlal branch of right bronchus iPulmonary artery Upper right pulmonary' vein Right auricle (O.T. appendix) Left common carotid artery End of left internal jugular vein Left subclavian artery Left subclavian vein Infer Right atrium lor vena cava // /' Left phrenic nerve Cut edge of peri- cardium Ascending aorta , Root of pulmonary artery y.'/ Coronary sulcus (O.T. auriculo- ventricular) Right ventricle Anterior longi- tudinal sulcus Left ventricle' Cut edge of pericar- dium Fig. 25.— Dissection of the Middle and Superior Parts 01 tlie Mediastinum from the anterior aspect. the venous sinus of the atrium, into which the great veins open, and the cavity of the atrium proper. The whole of the right border of the heart is formed by the right atrium. Its position can be indicated on the surface by a Hne, convex to the right, which commences at the level of the third right costal cartilage, half an inch from the THORACIC CAVITY 55 sternum, and terminates opposite the sixth right cartilage at the same distance from the right margin of the sternum. At the upper and left corner of the atrial area is the apex of the left auricle (O.T. auricular appendage), and between the two auricles are the roots of the pulmonary artery and the aorta, the former anterior to the latter. The rounded portion of the upper part of the right ventricle, immediately below the pulmonary artery, is the co}ms arteriosus. If a finger is introduced into the cleft betw^een the aorta anteriorly and the superior vena cava posteriorly, it can be passed across, from the right to the left side of the pericardial cavity, through a passage, called the transverse sinus of the pericardium (Figs. 24 and 27). This sinus lies anterior to the superior vena cava and the atria, and posterior to the ascending aorta and the stem of the pulmonary artery. The upper border of a finger placed in the sinus will indicate the position of the upper border of the heart. This border is formed to a slight extent by the upper border of the right atrium, but mainly by the upper border of the left atrium. Its position can be in- dicated, on the anterior surface of the body, by a line com- mencing half an inch from the side of the sternum at the lower border of the second left costal cartilage, and ending at the same distance from the sternum on the upper border of the third right cartilage. Whilst a finger is kept in the transverse sinus a pointer should be introduced into the right pulmonary artery through its cut end in the root of the right lung. The dissector will note, as the pointer traverses the right pulmonary artery, that it passes first posterior to the superior vena cava and then along the upper border of the transverse sinus, that is along the upper border of the heart where that border is formed by the left atrium ; therefore the position of the right pulmonary artery may be indicated, on the anterior surface of the body, by the right two-thirds of the line which marks the position of the upper border of the heart. The left border of the anterior surface of the heart is formed, to a slight extent, by the left atrium, but mainly by the left ventricle. It is convex to the left and its position is marked, on the surface of the body, by a line which com- mences above at the lower border of the left second costal cartilage, half an inch from the sternum, and terminates below at the apical point in the fifth left intercostal space. Before proceeding further the dissector should summarise 56 THORAX the information he has gained regarding the relationship of the apex of the heart and the borders of the sterno-costal surface of the heart to the anterior wall of the thorax. The upper border is formed by the atria, and as the heart lies in situ it is concealed to a great extent by the aorta and the Fig. 26. — The relations of the Heart and of its Orifices to the Anterior Thoracic Wall. (Young and Robinson.) I to VII. Costal cartilages. A. Aorta. Ao. Aortic orifice. C. Clavicle. LA. Left atrium. LV. Left ventricle. M. Mitral orifice. P. Pulmonary orifice. RA. Right atrium. RV. Right ventricle. SVc. Superior vena cava. T. Tricuspid orifice. pulmonary artery. Its position is marked on the surface by a line extending from the lower border of the second left to the upper border of the third right costal cartilage, commencing and terminating about half an inch from the border of the sternum. The right border is formed entirely by the right atrium, and its position is indicated on the sur- THORACIC CAVITY 57 face by a line, convex to the right, commencing above at the lower border of the right second costal cartilage, half an inch from the side of the sternum, and terminating below at the sixth right cartilage half an inch from its junction with the sternum. More than two-thirds of the lower border are formed by the right ventricle, and the remainder by the apical portion of the left ventricle, and the two parts may be separated by a distinct notch, the incisura cordis. This border is slighdy concave downwards, in correspondence with the upward convexity of the diaphragm on which it rests, and it has a slight inclination downwards and to the left. It is marked, on the surface of the body, by a line extending from the sixth right costal cartilage, near the sternum, to the apical point, which lies in the left fifth intercostal space from 3 J to 3 J inches from the median plane. The left border, which is formed mainly by the left ventricle and only to a slight extent by the left atrium, extends from the apex to a point on the lower border of the left second costal cartilage half an inch from the margin of the sternum. The coronary sulcus, which indicates the plane of union of the atria and ventricles and, therefore, the plane of the atrio -ventricular and aortic and pulmonary orifices of the heart, can be indicated, on the surface, by a line extending from the sternal end of the third left costal cartilage to the sternal end of the sixth right cartilage. Posterior to the left extremity of this line, at the level of the upper part of the third left costal cartilage, is the orifice of the pulmonary artery. The aortic orifice is a litde low^er and slightly to the right, posterior to the sternum at the level of the low^er border of the third left cartilage. Immediately below the aortic orifice, posterior to the left margin of the sternum, at the level of the upper part of the fourth left cartilage, lies the mitral orifice ; and the tricuspid orifice is situated posterior to the middle of the sternum, opposite the fourth intercostal spaces. The positions of the great orifices cannot be confirmed at this stage of the dissection, and they will be noted again at a later period when the heart is opened. After the sterno-costal aspect of the heart, the boundaries of the transverse sinus, and the general position of the heart have been studied, the dissectors should turn the apex of the heart upwards and to the right, and examine the inferior and posterior surfaces whilst the heart is still in situ. They 58 THORAX will find that the inferior or diaphragmatic surface^ which rests upon the diaphragm, is slightly concave; that it is formed entirely by the ventricles, and mainly by the left ventricle, which forms the left two -thirds, the separation between the ventricles being indicated by the inferior longi- tudinal sulcus. As the apex of the heart is held upwards and to the right, the dissector should note that a recess of Innominate artery Aortic arch — Pulmonary artery ._ Pulmonary valve Conus arteriosus Pericardial cavity Ascending aorta Aortic valve .. Aortic sinus ., Left common carotid Superior vena cava Vena azygos Right — pulmonary artery > Right pulmonary artery Trans verse sinus eft pencaraium " Qbliq^ue sinus of pericar3Tum Upper right pulmonary vein Left atrium Lower left pulmonary vein Base of anterior cusp of mitral valve Obl ique sinus of pericardium Coronary sinus Fig. 27. — Sagittal Section of Heart. the pericardial cavity ascends posterior to the base or posterior surface of the heart. This recess is the oblique sinus of the pericardium. Its orifice is below, where it is bounded to the right and below by the upper end of the inferior vena cava, and to the left and above by the left inferior pulmonary vein. The posterior boundary of the sinus is the pericardium; and the pericardium separates the cavity of the sinus from the oesophagus, which, at this level, is lying between the pericardium and the descending part of the thoracic portion of the aorta. Both the oesophagus and the aorta can be THORACIC CAVITY 59 palpated through the posterior wall of the sinus. The anterior wall of the oblique sinus is the posterior wall of the left atrium (Fig. 27). If the dissector passes his left index finger into the transverse sinus and the middle and index fingers of his right hand into the oblique sinus, he will be able to convince himself that the left atrium is the only structure which intervenes between the cavities of the two sinuses. When he has satisfied himself regarding this point, he should note that the lower and posterior part of the coronary sulcus of the heart extends across the lower part of the base between the posterior end of the left ventricle and the lower end of the left atrium, and that it is occupied by the coronary blood sinus, which opens into the right atrium immediately to the left of the upper end of the in- ferior vena cava. A complete examination of the base of the heart cannot be made until the heart is removed from the thorax at a later stage of the dissection, and the dissectors should pass now to a consideration of the relation of the serous layer of the pericardium to the great vessels which are entering or leaving the heart (see Fig. 24). They have previously noted (p. 51) that the visceral layer of the serous portion of the pericardium covers almost every portion of the heart, the only part left uncovered being the upper border of the left auricle, which is in contact wdth the lower border of the right pulmonary artery. Along this border the visceral part of the serous layer of the pericardium, ascending on the anterior aspect of the left atrium, becomes continuous with the parietal layer which passes anteriorly, in the roof of the transverse sinus, on the lower wall of the right pulmonary artery, to the posterior surface of the ascending part of the aorta, where it becomes continuous with the visceral layer which descends on the posterior surface of the aorta, in the anterior wall of the transverse sinus. Along the same border the visceral part of the serous pericardium is reflected posteriorly in the roof of the oblique sinus, to become continuous with the parietal layer on the posterior wall of the pericardial sac. The fact that he can pass his finger through the transverse sinus posterior to the aorta and the pulmonary artery, but cannot insinuate it between the two vessels, will indicate to the student that the two great arteries are enclosed in a tubular sheath of the visceral part of the serous membrane. An 6o THORAX examination of the venae cavse will show that the lower inch of the superior vena cava lies within the fibrous pericardium and that it is ensheathed, except along its postero-medial border, by a covering of the serous layer, whilst the inferior vena cava can scarcely be said to have any intra-pericardial course, for it joins the lower and posterior part of the right atrium immediately after piercing the fibrous layer, but the margin of the orifice by which it enters is surrounded by the serous layer except along a narrow line posteriorly. The left pulmonary veins are covered by the serous layer on their superior, anterior, and inferior aspects, but not posteriorly ; and the right pulmonary veins, which enter the left auricle as soon as they have pierced the fibrous pericardium, are in rela- tion with the serous layer merely along the medial and lateral borders of the orifices in the fibrous layer through which they enter. Dissection. — After the examination of the reflections of the serous layer of the pericardium is completed, the dissectors should study the vessels and nerves which supply the walls of the heart. They are the coronary arteries and the cardiac veins and nerves, and they lie in the coronary and longitudinal sulci of the heart, which have been noted already. To display them the visceral pericardium superficial to them must be cut and turned aside, the fat which lies in the sulci around the vessels must be removed, then the main vessels can be traced to their origins and terminations, and an endeavour should be made to preserve the fine nerves which accompany the vessels. Arterise Coronarise. — The coronary arteries are the nutrient vessels of the heart. They spring from dilatations of the com- mencement of the aorta which are called the sinus aortce. (Valsalva). There are three sinuses of the aorta, an anterior and two posterior, and only two coronary arteries, a right and a left ; the right artery springs from the anterior sinus, and the left from, the left posterior sinus. The right coronary artery passes anteriorly from the anterior aortic sinus, between the pulmonary artery and the right auricle ; turns downwards and to the right, in the coronary sulcus, to the lower part of the right margin of the heart, round which it curves. Then it proceeds to the left, in the posterior part of the coronary sulcus, till it reaches the posterior end of the inferior (posterior) longitudinal sulcus, where it divides into a small transverse and a large interventricular branch. The transverse branch continues to the left till it anastomoses with the circumflex branch of the left coronary artery. The interventricular (descending) branch runs anteriorly in the THORACIC CAVITY 6i inferior longitudinal sulcus on the diaphragmatic surface of the heart, and it anastomoses with the interventricular or descending branch of the left coronary artery at the cardiac notch on the lower margin of the heart. In addition to its terminal branches, the right coronary artery supplies branches to the roots of the pulmonary artery and the aorta, and to Left pulmonary artery Pulmonary artery Interventricular branch of left coronary artery Left posterior sinus of aorta Circumflex branch of left coronary artery Anterior cusp of mitral valve Posterior cusp Ligamentum arteriosum Pulmonary artery -Aorta Right pulmonary' artery Conus arteriosus Right coronary artery jl^ Right posterior sinus of aorta Anterior cusp of tricuspid valve Inferior cusp Medial cusp Marginal branch Interventricular branch of right coronary artery Fig. 28. — The Base of the Ventricular Part of the Heart from which the Atria have been removed. The detached atria are depicted in Fig. 31, The specimen was hardened in situ. the walls of the right atrium and the right ventricle, the larger and more numerous branches being given to the ventricle. One of the latter, the marginal branch, passes along the lower margin of the heart towards the apex ot the ventricle (see Fig. 29). The left corona?y artery, as it springs from the left posterior aortic sinus (Fig. 28), lies posterior to the pulmonary artery. For a short distance it runs to the left, then it turns anteriorly, between the pulmonary artery and the left auricle. 62 THORAX and divides into a descending or interventricular, and a circumflex branch. The interventricular branch passes down the sterno-costal surface of the heart, in the anterior longitudinal sulcus (Fig. 29), and turning round the lower border, in the cardiac notch, it anastomoses with the interventricular branch Right innominate vein Innominate artery Superior vena ca^•c Serous pericardium Apex of right auricle (O.T. appendix) Coronar> Marginal branch of right coronary artery Right ventricle- Left common carotid Left subclavian Left innominate vein Aortic arch Ligamentum arteriosum Left pulmonary artery Pulmonary artery Left auricle (O.T. appendix) Conus arteriosus Anterior interven- tricular furrow with the interventricular branch of the left coro- nary artery and the great cardiac vein Left ventricle Apex of heart Fig. 29. — Sterno-costal Surface of the Heart. of the right coronary artery. The circumflex bra?ich runs to the left, in the coronary sulcus, turns round the left border of the heart (Fig. 28) and anastomoses, on the posterior surface, with the transverse terminal branch of the right coronary. From the stem of the artery twigs are given to the roots of the pulmonary artery and the aorta, and its terminal branches supply the walls of both ventricles and the walls of the left atrium. Venae Cordis. — The cardiac veins are: (i) the coronary THORACIC CAVITY 63 sinus; (2) the great cardiac vein; (3) the inferior (posterior) ventricular vein ; (4) the middle cardiac vein ; (5) the oblique vein; (6) the small cardiac vein; (7) the anterior cardiac veins ; and (8) the venae minimae cordis. The coronary si?tus lies at the base of the heart, in the posterior part of the coronary sulcus, between the left atrium and the left ventricle. It can be displayed when the apex of the heart is turned upwards and to the right. Its right extremity opens into the right atrium, immediately below and to the left of the orifice of the inferior vena cava. At its left Oblique vein Coronarj' sinus ^■^ Great cardiac vein I Small cardiac Middle cardiac vein Inferior ventricular \ein Great cardiac vein Fig. 30. — The Coronarj^ System of Veins on the Surface of the Heart. (Diagram. ) extremity it receives the great cardiac vein. The great cardiac vein ascends along the anterior longitudinal sulcus (Fig. 29), where it lies in relation with the interventricular branch of the left coronary artery. At the upper end of the interventricular sulcus it turns round the left border of the heart, with the circumflex branch of the left coronary artery, and it ends in the left extremity of the coronary sinus. The inferior (posterior) ventricular veiti or veins, from the diaphragmatic surface of the left ventricle, and the middle cardiac vein, which runs posteriorly in the inferior longitudinal sulcus, end in the lower border of the coronary sinus. The oblique vein descends 64 THORAX on the posterior wall of the left atrium and ends in the upper border of the sinus; and the small cardiac vein (O.T. right coronary) runs along the lower margin of the heart with the marginal branch of the right coronary artery, curves round the right border of the heart, in the coronary sulcus, ends in the right extremity of the coronary sinus. The anterior cardiac — Superior vena cava Reflection of serous pericardium Right atrio- ventricular openins; Right auricle Interatrial furrow Left atrium Left auricle Crista terminalis Fossa ovalis Valve of inferior vena cava Inferior vena cava Left atrio- ventricular opening Coronary sinus Fig. 31. — The Anterior Aspect of the Atrial Part of the Heart. The atria have been removed from the ventricles. The ventricular portion of the same heart is depicted in Fig. 28. The specimen was hardened in situ. veins are small vessels which ascend along the anterior surface of the right ventricle and terminate directly in the lower and anterior part of the right atrium. The vencB cordis mini7n(E are small veins which pass from the substance of the heart, and more particularly from the walls of the right atrium and ventricle, and open, by small orifices, into the cavity of the right atrium. The orifice through which the great cardiac vein opens into the coronary sinus is usually provided with a valve ; the orifice of the small cardiac vein may be provided THORACIC CAVITY 65 with a valve, but the orifices of the other tributaries of the sinus are generally devoid of valves. Cardiac Nerves. — The coronary plexuses, from which the nerve supply of the heart is directly derived, are offshoots of the superficial and deep cardiac plexuses, which will be dissected later (pp. 85 and 100). The nght coronary plexus is formed by twigs from the superficial cardiac plexus which descend along the pulmonary artery, and by additional fibres from the deep cardiac plexus. It is distributed along the course of the right coronary artery. The left coronary plexus^ which accompanies the artery of the same name, is derived from the deep cardiac plexus. The nerves do not slavishly follow the arteries ; they soon leave the vessels, and are ultimately lost in the substance of the heart. Here and there ganglia are developed in connection with them. Dissection. — The chambers of the heart and the great vessels which communicate with them should now be examined, as far as possible whilst the heart is still m situ, so that the relations of the various orifices to the sternum and costal cartilages can be verified. Examine first the right atrium and the venae cavae, then the right ventricle and the pulmonary- artery, and afterwards the left ventricle and the ascending part of the aorta, which springs from it. The examination of the left atrium, and the terminations of the pulmonary veins, cannot be conveniently undertaken until the heart and the pericardium have been removed from the body (see p. 89). Atrium Dextrum (O.T. Right Auricle). — Open the right atriu?fi by means of the following incision. Enter the knife at the apex of the auricle (O.T. auricular appendix) and carry it posteriorly, close to the upper border of the auricle, across the sulcus terminalis and through the lateral wall of the atrium, to the posterior border of the lower end of the superior vena cava; then downwards, posterior to the sulcus terminalis, to the inferior vena cava ; and finally anteriorly, across the lower end of the sulcus terminahs and above the anterior aspect of the lower end of the inferior vena cava, to the coronary sulcus. Throw the flap thus formed anteriorly, and clean the interior of the cavity with a sponge. As the flap is turned anteriorly a vertical muscular bundle will be noted on its inner surface. This is the crista terminalis^ which corresponds in position with the sulcus terminalis on the outer surface. It marks the boundary between the anterior part, the atrium, and the posterior part, which is known as the venous sinus because the great veins of VOL. II — 5 66 THORAX the body and heart open into it. These two parts of the cavity differ, however, not only in position and their relations to the great veins, but also in the characters of their walls. The whole of the interior of the atrium presents a poHshed glossy appearance, due to the endocardial Hning; but whilst the wall of the venous sinus is smooth, the rest of the wall of the atrium is rendered rugose by a large number of muscular ridges Aorta Superior vena cava I jbwk m M^' ^^^^^tr^T^ J^y^'V *M^^M^Kkt. Crista Upper right, ,i.,„ ,^ ,J ..j^M^Bm^rilf^' f < €jPWky terminalis pulmonarj' vein Lower right ^ pulmonary vein Limbus fossse ovalis Fossa ovalis \ Tricuspid orifice Opening of coronary sinus Inferior vena cava Valve of the inferior vena cava (Eustachian) Valve of the coronary sinus (Thebesian) Fig. 32. — The Right Atrium. Part of the posterior wall and the whole of the right lateral and anterior walls have been thrown anteriorly. which commence at the crista terminalis and run anteriorly to the right margin of the atrium. These bundles, on account of their somewhat parallel arrangement, are called the musculi pectinati. The veins which open into the right atrium are the (i) superior vena cava, (2) inferior vena cava, (3) coronary sinus, (4) anterior cardiac veins, and (5) venae cordis minimse. The aperture by which the blood leaves it is the tricuspid orifice. The orifice of the superior vena cava is in the upper and posterior part of the atrium, at the level of the third right costal THORACIC CAVITY 67 cartilage. It is entirely devoid of any valvular arrangement. Immediately below it on the posterior wall of the atrium, in a well -fixed heart, will be found a rounded prominence, the interve?ious tubei-cle (Lower), which tends to throw the Pericardium Superior vena cava Musculi pectinati Crista terminalis Diaphragm Vena az>- gos Right bronchus Right ^hi^_^ pulmonary artery Bronchial gland Pulmonary veins Venous sinus of right atrium Inferior vena cava Hepatic vein Pig. 33. — Sagittal section through the Right Atrium of the Heart and the Root of the Right Lung. Stream of blood entering the atrium by the superior vena cava downwards and anteriorly into the atrio-ventricular orifice. The orifice of the ijiferior vena cava is in the lower and posterior part of the atrium, at the level of the sixth right costal cartilage and the lower border of the eighth thoracic vertebra. Running along its anterior margin, and intervening between it and the atrio-ventricular opening, is the remnant of a valve, the valve of the vena cava (Eustachian). It terminates, to the left, in the lower end of a muscular ridge, limbus fosses ovalis 68 THORAX Orifice of superior vena cava (O.T. annulus ovalis), which lies on the inter-atrial septum and forms the anterior and upper boundary of a shallow fossa, the fossa ovalis. At the upper end of this fossa there was, during foetal life, a foramen, tht foramen ovale, through which the two atria Superior vena cava COmmunicatcd with each other. The g^ Right auricle (O.T. appendix) objCCt of the ValvC of the vena cava, which in foetal life was much more perfect, was to di- rect the oxygenated inferior caval blood through the fora- men ovale into the left atrium, whence it was passed into the left ventricle, and was then dis- tributed, by the aorta, throughout the whole system. During foetal life it would have been use- less to pass the blood through the lungs, which were inactive and devoid of air. At the same time, had the oxygenated blood been passed through the Crista terminalis Intervenous tubercle Limbus ovalis Fossa ovalis Left atrio- ventricular orifice Opening of coronary sinus Coronary valve Inferior caval valve (Eustachian) Cut edge of atrial wall Inferior vena cava Fig. 34. — Interior of Right Atrium as seen by the removal of the anterior wall, or that wall op- posed to the base of the Ventricles. This is a part of the same specimen that is depicted right atrium into the in Fig. 31. right ventricle, it would have failed to reach the head and the upper extremities, for, leaving the right ventricle by the pulmonary artery, it would have entered the aorta through the ductus arteriosus beyond the origin of the left subclavian artery and, therefore, beyond the innominate and left common carotid arteries. In many cases a small part of the foramen ovale persists in the adult. If it is present it will be found on the left of the upper curved end of the limbus ovalis. The opening of the coronary sinus lies to the left of the lower end of the limbus ovalis and directly posterior to the tricuspid orifice. On its right margin lies a valvular fold, the valve of THORACIC CAVITY 69 the coronary siiius (O.T. Thebesian), which turns the blood, flowing from left to right in the sinus, anteriorly into the atrio- ventricular orifice. The venae minimae cordis and the anterior cardiac veins open directly into the atrium by small orifices scattered irregularly over the walls. The tricuspid orifice is in the lower and anterior part of the atrium. It opens anteriorly into the lower and posterior part of the cavity of the right ventricle, and is sufficiently large to admit the tips of three fingers. It is bounded by a fibrous ring to which the cusps of the right atrio-ventricular valve are attached. These cusps will be examined when the right ventricle is opened. Pulmonary' artery Aorta ^ j^== ::r^~,.^ I Right end of transverse sinus Left coronary ^^^^jg^ ' ^'^^^ coronary artery arterj- ./j1^^^BBl''''i5?^s3^^ auricle Left end of transverse sinus Left auricle Left atrium ^ Right atrium T . , -''^ ■ — "^ Transverse sinus Inter-atrial septum Fig. 35. — Transverse section through the Upper Part of the Heart. The Septum Atriorum and the Fossa Ovalis. — The inter- atrial septum is a fibro-muscular partition which intervenes between the right and left atria. In the foetus it is pierced by an obliquely directed foramen, the foramen ovale, already referred to ; and in the adult it is marked on the lower and posterior part of its right side by a shallow depression, the fossa ovalis^ which is bounded anteriorly and above by a muscular ridge, the limbus ovalis^ whilst below and posteriorly it fades away into the orifice of the inferior vena cava. The floor of the fossa ovalis is very thin ; it marks the situation of the lower part of the foramen ovale of the foetus, and is formed by a portion of the inter-atrial wall which, during foetal life, acted as a flap valve and prevented regurgi- tation of blood from the left to the right atrium. The Vena Cava Superior. — The superior vena cava returns to the right atrium the blood from the head and neck, the II — ha 70 THORAX upper extremities, the wall of the thorax, and the upper parts of the walls of the abdomen. It commences, by the union of the right and left innominate veins, at the level of the lower border of the sternal end of the right first costal cartilage ; and it terminates, in the upper and posterior part of the right atrium, at the level of the right third costal cartilage, about half an inch from the right border of the sternum. It lies partly in the superior and partly in the middle mediastinum, and its lower half is within the fibrous pericardium and is partly ensheathed by the serous pericardium. Tributaries. — The tributaries of the superior vena cava are the two innominate veins, by whose junction it is formed, and the vena azygos, which enters it immediately before it pierces the fibrous pericardium, at the level of the second right costal cartilage. Relations. — The superior vena cava lies to the right of, and somewhat posterior to, the ascending aorta. Posterior to its upper part are the right pleura and lung on the right, and the right vagus and the vena azygos on the left, and, at a lower level, the right bronchus, the right pulmonary artery, and the upper right pulmonary vein. Anteriorly and on the left it is overlapped by the ascending aorta, and on the right by the right pleura and lung. On its left side above is the lower end of the innominate artery, and below is the ascending aorta ; and on the right side is the right pleura, with the right phrenic nerve and the accompanying vessels intervening. The Thoracic Part of the Inferior Vena Cava. — Only a small portion, about three-quarters of an inch, of the inferior vena cava is found in the thorax. It ascends from the diaphragm along the mediastinal surface of the right pleura and lung, pierces the pericardium anterior to the lower border of the right ligamentum pulmonis, and immediately * ends in the lower and posterior angle of the right atrium. Relations. — Anterior to it is the diaphragm ; posterior to it the vena azygos, the splanchnic nerves and the thoracic duct ; and to its right the phrenic nerve with its accompanying vessels and the right pleura and lung (see Fig. 12). Ventriculus Dexter. — The cavity of the right ventricle should be opened by three incisions. The first should be made transversely across the upper end of the conus arteriosus, immediately below the commencement of the pulmonary artery. It should begin a little to the right of the upper THORACIC CAVITY 71 end of the anterior longitudinal sulcus and terminate a little to the left of the coronary sulcus. The second must commence at the right end of the first and pass obliquely downwards and to the right, along the left margin of the coronary sulcus, to the lower border of the heart. The third commences at the left end of the first, follows the line of the anterior inter-ventricular sulcus, lying a little to its right side, Superior vena cava ^^ Innominate artery Left subclavian artery Left common carotid artery Aortic arch Serous pericardium Ascending a6rta Pulmonary artery Right auricle (O.T. appendix) Left anterior pulmonary sinus (Valsalva) Pulmonary valve Conus arteriosus Anterior segment of tricuspid valve Medial segment Anterior papillary muscle - Moderator band Inferior vena cava Inferior segment of tricuspid valve Fig. 36. — The Interior of the Right Ventricle. and also terminates at the lower margin of the heart. After the triangular flap thus formed is turned downwards and to the right, the cavity of the ventricle should be cleaned with the aid of sponge and forceps. If the moderator band of muscle fibres, which connects the anterior wall of the ventricle with the inter-ventricular septum, interferes with the necessary displacement of the flap, it must be divided. - The cavity of the right ventricle has a triangular outline. The atrio-ventricular orifice opens into the lower and posterior angle, the pulmonary artery springs from the upper and II— 5 & 72 THORAX anterior angle, and between the two orifices is a strong and rounded muscular ridge, the supra -ventricular ridge. This projects into the cavity converting it into a U-shaped tube which commences posterior to and below the supra-ventricular ridge, runs anteriorly and to the left, towards the apex, and turns upwards and anteriorly, along the anterior part of the inter-ventricular septum and anterior to the supra-ventricular ridge, to the orifice of the pulmonary artery. On transverse section the cavity of the right ven- tricle is semilunar in outline, in consequence of the thick inter - ventricular septum, which forms the left and posterior wall, bulging into the cavity (Fig. 37). Its walls are much thicker than the walls of the right Fig. 37.— Transverse section through atrium, but much thinner the Ventricular Part of the Heart than the walls of the left seen from above. (From Luschka. ) ventricle (Fig. 41). The reason for these differences is obvious : the auricle has merely to force the blood through the wide atrio- 6. Inferior longitudinal (inter -ven- yCntricular OrificC iutO the tricular) sulcus with middle cardiac • i . , • i j . i • ^ ^ vein and inferior branch of right I^^g^t VCntricle, and the right coronary artery. VCntriclc haS Only tO SCud 7. Anterior longitudinal (inter -ven- ^l^g bloo(^ thrOUgh the luUgS tricular) sulcus with great cardiac U i f ' U u vein and anterior branch of left ^O the IClt atriUm ', but the coronary artery. left VCntriclc haS tO forCC the blood through the whole of the body, the head and neck, and the limbs; and the muscular strength of the walls of the cavities of the heart is proportional to the work they have to do. The portion of the right ventricle which ascends to the orifice of the pulmonary artery is the conus arteriosus. Its walls are smooth and devoid of projecting muscular bundles, but the inner surface of the walls of the remaining part of the ventricle is rendered extremely irregular by the projection of a lace-work of fleshy ridges called trabeculce. carnece. Some of the trabeculse are merely ridges raised in relief upon the Cavity of right ventricle. Cavity of left ventricle. Ventricular septum. Thick wall of left ventricle. Thinner wall of right ventricle. THORACIC CAVITY 73 surface ; others are attached to the wall at each extremity, but are free in the rest of their extent. The cavity of the ventricle is invaded, however, not only by the trabeculae carneae, but also by a number of conical muscular projections, the viusculi papillares. These are attached by their bases to the walTof the ventricle, whilst their apices are connected, by a number of tendinous strands, to the margins and the ventricular surfaces of the cusps of the atrio-ventricular valve. As a rule there is one large anterior papillary muscle attached to the anterior wall, a large inferior papillary muscle attached to the inferior wall, and a number of smaller papillary muscles attached to the septal wall. Occasionally the anterior and inferior muscles are represented by a number of smaller projections. It must be noted that the chordae tendineae from each papillary muscle, or group of papillary m.uscles, gain insertion into the margins and ventricular surfaces of two adjacent cusps of the valve. The result of this arrange- ment is, as the papillary muscles contract simultaneously with the contraction of the general wall of the ventricle, that the chordae tendineae hold the margins of the cusps together and prevent them being driven backwards into the atrium. One of the trabeculae carnea3, which is usually strong and well marked, passes across the cavity from the septum to the base of the anterior papillary muscle. This is the juoderator band. It tends to prevent over-distension of the cavity of the ventricle, by fixing the more yielding anterior w^all of the ventricle to the more solid septum. There is one opening of entrance into the right ventricle, the atrio-ventricular, and one opening of exit, the pulmonary orifice. Each is guarded by a valve. The right atrio-ventricular orifice lies at the lower and posterior part of the right ventricle, its centre being behind the middle of the sternum at the level of the fourth intercostal space. It is about one inch in diameter, and is surrounded by a fibrous ring. It admits the tips of three fingers, and it is guarded by a valve possessing three cusps, an anterior, a medial, and an inferior. The anterior cusp intervenes between the atrio-ventricular orifice and the conus arteriosus. The medial cusp lies in relation with the septal w^all ; and the inferior cusp with the inferior wall of the ventricle. The bases of the cusps are attached to the fibrous ring 74 THORAX round the margin of the orifice. Their apices, margins, and ventricular surfaces are attached to the chordae tendinese. Their auricular surfaces, over which blood flows as it enters the ventricle, are smooth, and their ventricular surfaces are more or less roughened by the attachment of the chordae tendinese, but the roughening is less marked on the ventricular surface of the anterior cusp over which the blood flows as it passes through the conus arteriosus to the pulmonary orifice. Pulmonary artery Posterior cusp of pulmonary valve Aorta Supra- ventricular crest , Pars nrembranacea septi Right auricle Left segment of atrio-ventricular bundle I Right segment of atrio-ventricular bund Moderator band Base of anterior papillary muscle Fat in sulcus longl- tudinalis anterior Left ventricl Coronary sulcus Coronary valve Opening of coronary sinus Base of medial cusp of tricuspid valve Medial cusp of tricuspid valve Atrio-ventricular bundle Fig. 38. — Dissection of the Right Ventricle showing the Atrio- ventricular Bundle. The Atrio-ventricular Btmdle. — The atrio-ventricular bundle is a small bundle of peculiar muscle fibres, of pale colour, which forms the only direct muscular connection between the walls of the atria and the ventricles (see p. 92). To expose this bundle, the anterior part of the medial cusp of the tricuspid valve must be detached from the fibrous atrio-ventricular ring. When this has been done, the pars membranacea, or upper fibrous part of the inter-ventricular septum will be exposed, and the atrio-ventricular bundle will be found running along its posterior and lower border to the upper end of the muscular part of the septum, where it divides into right and left branches. The right branch runs along the right side of the septum to the moderator band, along which it passes to the anterior papillary muscle. The left branch passes between the pars membranacea THORACIC CAVITY 75 and the upper end of the muscular part of the septum, and then descends along the left side of the septum. Both branches send off numerous rami- fications which are distributed to the various parts of the walls of the ventricles. The pulmonary orifice lies at the upper, anterior, and left part of the ventricle, at the apex of the conus arteriosus. Its centre is behind the third left costal cartilage immediately to the left of the left border of the sternum, and its margin is surrounded by a thin fibrous ring to which the bases of the three semilunar cusps of the pulmonary valve are attached. Dissection. — Note that immediately above its commencement the wall of the pulmonary artery shows three distinct bulgings ; these are the pulmonary sinuses (Valsalva) of which two are anterior, and the third is situated posteriorly. Make a transverse incision across the wall of the pulmonary artery immediately above the dilatations, and from each end of the transverse incision make a vertical incision upwards towards the arch of the aorta ; raise the flap so formed and examine the cusps of the valve from above. The Pulmonary Valve. — Each cusp of the valve is of semi- lunar form. • Its upper or arterial surface is concave, its lower or ventricular surface is convex ; and it consists of a layer of fibrous tissue covered, on each surface, by a layer of endothelium. The fibrous basis of the cusp is not equally thick in all parts. A stronger band runs round both the free and the attached margin. The centre of the free margin is thickened to form a small rounded mass — the 7iodulus of the valve — and the small thin semilunar regions on each side of the nodule are called the hmulcB of the valve. When the ventricular contraction ceases, and the elastic reaction of the wall of the pulmonary artery forces the blood backwards towards the ventricle, the cusps of the valve are forced into apposition ; the nodules meet in the centre of the lumen -, the ventricular surfaces of the lunulse of adjacent cusps are com- pressed against each other, and their free margins project upwards into the cavity of the artery, in the form of three vertical ridges which radiate from the nodules to the wall of the artery. Regurgitation of blood into the ventricle is thus effectually prevented. The dissector may readily demonstrate the general appear- ance of the cusps and their relationship to each other by packing the concavity of each cusp with cotton wool. Arteria Pulmonalis. — -The pulmonary artery lies within the fibrous pericardium, and is enclosed, with the ascending 76 THORAX part of the aorta, in a common sheath of the serous pericardium. It commences at the upper end of the conus arteriosus, posterior to the sternal extremity of the third left costal cartilage. It is about two inches long, and it runs up- wards and posteriorly into the concavity of the aortic arch, where it bifurcates into two branches. The bifurcation takes place posterior to the sternal end of the left second costal cartilage. Relatio7is. — At its commencement it is placed anterior to the lower end of the ascending aorta, but as it runs upwards and posteriorly it passes to the left side of the latter vessel, and lies anterior to the upper part of the anterior wall of the left atrium, from which it is separated by the transverse sinus of the pericardium. Anterior to it is the upper part of the anterior wall of the pericardium, which separates it from the anterior part of the mediastinal surface of the left pleura and lung. To its right side, below, are the right coronary artery and the apex of the right auricle, and above is the ascending aorta. To its left side lie the left coronary artery and the anterior end of the left auricle. Dissection. — Cut away the anterior wall of the pulmonary artery up to the level of its bifurcation and pass probes into its right and left branches. Note that the right branch runs transversely to the right, and that the left branch runs posteriorly and to the left. The right pulmonary artery commences at the bifurcation of the pulmonary stem, below the arch of the aorta. As it runs to the right, towards the hilus of the right lung, along the upper border of the left atrium and the transverse sinus (Figs. 2 1 and 27), it passes posterior to the ascending aorta and the superior vena cava, and anterior to the oesophagus and the stem of the right bronchus. It enters the hilus of the lung below the eparterial branch of the bronchus, above and posterior to the upper right pulmonary vein, and it descends, in the substance of the lung, on the postero-lateral side of the stem bronchus, and between its ventral and its dorsal branches, where it will be dissected at a later period (p. 98). Branches. — As it enters the hilus of the lung it gives oif a branch which accompanies the eparterial bronchus, and as it descends in the substance of the lung it gives off branches which correspond with the branches of the stem bronchus (see p. 98). The left pulmonary artery runs posteriorly and to the THORACIC CAVITY 77 left, across the anterior aspect of the descending aorta and the left bronchus, to the hilus of the left lung. It is covered an- teriorly and on the left by the anterior part of the mediastinal surface of the left pleural sac. As it descends in the sub- stance of the lung it lies along the postero-Iateral aspect of the stem bronchus and between its ventral and dorsal branches (p. 98). Branches. — Except that it has no branch corresponding with that which accompanies the eparterial bronchus on the Left common carotid artery^ Left innominate vein Right auricle Stem of pulmonary artery Pulmonary valve Upper left pulmonary vein Left auricle -- Right innominate vein Innominate artery Left subclavian artery , Arch of aorta Vena azygos Aorta ~- Ductus arteriosus Left pulmonary artery Lower left pulmon- ary vein Descending aorta Inferior vena cava Fig. 39. — Dissection of the Heart and Great Vessels of a Foetus, showing the angular junction of the Ductus Arteriosus with the Aorta. right side, the branches of the left pulmonary artery are similar to those given off by the right pulmonary artery. Ligamentum Arteriosum. — The ligamentum arteriosum is a strong fibrous band which connects the commencement of the left pulmonary artery with the lower surface of the arch of the aorta. It is the remains of the walls of a wide channel, the ductus arteriosus^ which united the left pulmonary artery with the aorta throughout the whole period of pre-natal life. During foetal life the lungs had no aerating function ; therefore the right puhnonary artery and the part of the left pulmonary artery beyond the origin of the ductus arteriosus were small, for they had merely to convey sufficient blood to maintain the life and growth of the non-functional lungs. At this period, therefore, the blood which had entered the right ventricle, 7 8 THORAX ' » through the superior vena cava and the right auricle (see p. 68), was ejected, by the ventriclCj into the pulmonary artery and the greater part of it passed through the ductus arteriosus into the aorta, which it entered beyond the origin of the left subclavian artery, and there mingled with the more oxygenated blood from the placenta, the lower part of the body, and the lower limbs, which passed from the inferior vena cava through the right atrium and the foramen ovale to the left atrium, and thence to the left ventricle by which it was pumped into the aorta. It is obvious that the passage of blood from the pulmonary artery into the aorta could take place only so long as the pressure in the pulmonary artery was greater than the pressure in the aorta. At birth, when the blood rushed through the rajDidly enlarged right and left pulmonary arteries into the lungs, as they expanded with the first respiratory efforts, the pres- sure in the pulmonary artery and the ductus arteriosus was reduced below that in the aorta, and the blood in the aorta would have flowed into the ductus arteriosus had it not been that the angle of union between the ductus arteriosus and the aorta had become more and more acute during the latter part of foetal life, with the result that the upper and right margin of the orifice of communication attained a position overhanging the lower and left margin (Fig. 39) ; and as soon as the blood pressure in the aorta exceeded that in the ductus arteriosus, this margin, acting as a flap valve, was driven against the left and lower margin, closing the orifice effectually. After this occurred the utility of the ductus arteriosus terminated, and it was converted into a fibrous cord — the ligamentum arteriosum. Note that the left recurrent nerve curves round the lower surface of the aortic arch on the left side of the upper end of the ligamentum arteriosum, and that the superficial cardiac plexus lies below the aortic arch immediately to the right of the ligament. In a few cases the ductus arteriosus remains patent for several years of life after birth, and occasionally it is patent throughout the whole of life. Dissection. — Cut through the remains of the upper part of the conus arteriosus immediately below the bases of the cusps of the pulmonary valve, and carefully dissect the upper part of the conus and the lower part of the pulmonary artery away from the front of the commencement of the ascending aorta. When this has been done, turn the lower end of the pulmonary artery upwards and pin it to the arch of the aorta (see Fig. 40). The upper part of the anterior wall of the left ventricle and the commencement of the aorta are now exposed, and the dissector should note three bulgings at the commencement of the aorta — the three aortic sinuses. One of the three sinuses lies anteriorly, and the right coronary artery springs from it. The other two, a right and a left, lie posteriorly, and the left coronary artery springs from the left sinus. Make a transverse incision across the upper end of the left ventricle, a short distance below the base of the anterior aortic sinus. On the right side extend the incision into the upper part of the inter-ventricular septum and carry it downwards and anteriorly in the septum to the apex of the heart. From the left extremity of the upper transverse incision carry an incision downwards and anteriorly through the left lateral border of the anterior surface of the left ventricle, parallel with the incision already made in the septum, towards the apex. As this incision is made pull the anterior THORACIC CAVITY 79 wall of the left ventricle forwards till the base of a large papillary muscle which springs from its internal surface is exposed ; carry the incision anterior to this and then onwards to the apex, and remove the anterior wall of the left ventricle and the anterior part of the inter-ventricular septum. The cavity of the left ventricle and the mitral valve, which guards the left atrio-ventricular orifice, are now exposed (Fig. 40). Ventriculus Sinister. — The cavity of the left ventricle is longer and narrower than that of the right ventricle. It reaches to the apex, and when exposed from the front it appears to be of conical shape. In cross section it has a circular or broadly oval outline, and its walls are very much thicker than those of the right ventricle (Fig. 37). When the interior has been cleaned with the aid of a sponge and forceps, the dissector will note that its walls are covered with a dense mesh-work of trabeculae carneae, which are finer but much more numerous than those met with in the right ventricle. The network is especially complicated at the apex and on the inferior wall of the ventricle, whilst the surface of the septum and the upper part of the anterior wall are, comparatively speaking, smooth. But whilst the trabeculae carneae in the left ventricle are slighter and more numerous than those in the right, the musculi papillares, on the other hand, are less numerous and much stronger; indeed, as a general rule there are only two papillary muscles in the left ventricle, an anterior and an inferior, the former attached to the anterior wall and the latter to the inferior wall of the cavity. The chordae tendineae from the papillary muscles pass to the margins and to the ventricular surfaces of the two cusps of the mitral valve, which guards the left atrio-ventricular orifice, the chordae tendineae from each papillary muscle gaining attachment to the adjacent margins of both cusps. Dissection. — Detach the anterior papillary muscle from the anterior wall of the ventricle and note that its chordse tendineae go to the anterior and left margins of the cusps of the mitral valve. Introduce the blade of a scalpel between the anterior margins of the cusps and carry it downwards between the groups of chordae going to the apex of the papillary muscle ; then split the papillary muscle from its apex to its base leaving each half connected with a corresponding group of chordae tendineae. The cusps of the mitral can now be separated from each other, and the atrio-ventricular orifice and the cavity of the ventricle can be more completely examined. The Orifices of the Left Ventricle. — There are two orifices of the left ventricle — one of entrance, the left atrio-ventricular orifice, and one of exit, the aortic orifice. The Left Atrio - ventricular Orifice, — The left atrio- 8o THORAX ventricular orifice lies in the lower and posterior part of the ventricle posterior to the left margin of the sternum at the level of the fourth left costal cartilage. It is somewhat smaller than the right atrio-ventricular orifice and admits the tips of two fingers only, a fact which will be better appreciated when the orifice is examined from the left atrium at a later period. It is guarded by a bicuspid valve, called the mitral valve, which prevents' regurgitation of blood from the left ventricle into the left atrium. The Mitral Valve. — The mitral or left atrio-ventricular valve consists of two cusps, a large anterior and a small posterior. Occasionally, however, as on the right side, small additional cusps are interposed between the bases of the main cusps. The bases of the cusps are attached to a fibrous ring which surrounds the atrio-ventricular orifice and their apices project into the cavity of the ventricle. To their apices, margins, and ventricular surfaces are attached the chordae tendinese from the papillary muscles, which hold the margins of the cusps together and prevent the valve being driven backwards into the atrium during the contraction of the ventricle. The dissector should note, however, that the chordae tendinese spread less over the ventricular surface of the anterior than over that of the posterior cusp, and he should associate this fact with the circumstance that blood flows over both surfaces of the large anterior cusp, which intervenes between the atrio-ventricular and the aortic orifices. By means of this large anterior cusp of the mitral valve the cavity of the ventricle, which has, on the whole, a somewhat conical form, is converted into a bent U-shaped tube, one limb of the tube lying below and to the left, and the other anteriorly and to the right. The blood enters the ventricle below and posteriorly through the atrio-ventricular orifice. It runs anteriorly to- wards the apex of the cavity along the inferior surface of the anterior cusp of the mitral valve, then, as the ventricle contracts, it is driven upwards, anteriorly, and to the right, to the aortic orifice, along the anterior surface of the large anterior cusp of the mitral valve. The portion of the cavity of the left ventricle which lies directly below the aortic orifice is known as the aortic vestibule (Fig. 40). Its walls con- sist mainly of fibrous tissue ; therefore they remain quiescent during the contraction of the ventricle and, as a result, the rapid closure of the aortic valve is not interfered with when THORACIC CAVITY 8i the ventricular contraction ceases and the elastic reaction of the walls of the aorta tends to force blood back into the ventricle. The aortic orifice lies at the upper, right, and anterior part of the cavity, posterior to the left margin of the sternum at Trachea- Innominate artery Right innonriinate vein-i Left innominate vein Superior vena cava-- Ascending aorta, - Upper right pulmonary' vein Ria;ht auricle Anterior aortic sinus Right coronary' artery- Moderator band Anterior , papillary muscle Tricuspid orifice - Moderator band-" Left subclavian artery Left common carotid artery Left internal jugular vein Left subclavian vein Arch of aorta Pulmonary' artery' turned upwards Left pulmonary artery Front of left atrium Left auricle Left coronarj' artery Left posterior aortic sinus Aortic vestibule Anterior cusp of mitral valve Mitral orifice Anterior papillary muscle Posterior papillajy muscle Interventricular septum Fig. 40. — Dissection of the Heart from the anterior aspect. the level of the third intercostal space. Its left and inferior margin is separated from the atrio-ventricular orifice by the anterior cusp of the mitral valve. It is guarded by a valve, the aortic valve, which prevents regurgitation from the aorta into the ventricle. This valve, like the pulmonary valve, consists of three semilunar cusps, but in contradistinction to VOL. II — 6 82 THORAX the pulmonary valve, one of the cusps is placed anteriorly and the other two posteriorly. The cusps of the aortic valve are stronger than the cusps of the pulmonary valve described on p. 75, but correspond with them in all details of structure. Before terminating his examination of the left ventricle the dissector should note that the muscular wall of the cavity is thickest a short distance from the atrio-ventricular Opening of coronary sinus Interatrial septum Right atrium ; ! ^ . , • r.i. Musculi pectinati ....-SSSsK^ ! / Part of right sinus of the aorta Lower left , pulmonary vein Central fibrous mass 7^. Fibrous ring of /' tricuspid orifice"? Inferior cusp of |^ tricuspid valve Medial cusp of tricuspid valve j Trabeculacarnea -. Interventricular septum Wall of left 'atrium Central fibrous mass _,., , Pars mem- ^ "^fi"'" branacea septi lj{t-_/ Great cardiac vein *- jT Fibrous ring of f- mitral orifice Posterior cusp of mitral valve Anterior cusp of mitral valve -- Wall of left ventricle Fig. 41. — Section of the Heart showing the Interventricular and Inter- auricular Septa and the Fibrous Rings round the Orifices. orifice and thinnest at the apex, and he should examine the inter-ventricular septum. TAe Inter-ventricular Septum. — The inter-ventricular septum is a musculo-membranous partition which separates the left ventricle not only from the right ventricle, but also from the lower part of the right auricle. In the greater part of its extent the septum is thick and muscular, and is thickest below and anteriorly, where it springs from the lower border of the heart immediately to the right of the apex and opposite the THORACIC CAVITY 83 cardiac notch. The muscular part becomes gradually thinner as it passes upwards and posteriorly and, a short distance from the atrio-ventricular orifices, it terminates in a fibrous membrane, the pars inembranacea sepfi, which connects the muscular part of the septum with the fibrous rings which surround the atrio-ventricular orifices and the orifices of the pulmonary artery and the aorta. The pars membranacea is the thinnest part of the septum. Occasionally it is deficient in whole or in part, and in such cases a communication exists between the two ventricles, and, in some rare cases, between the left ventricle and the right auricle. The pars membranacea was exposed from the right side when the anterior part of the medial cusp of the tricuspid valve was removed during the dissection of the atrio-ventri- cular bundle (see p. 74). Finally the dissector should note that the inter-ventricular septum is placed obliquely, so that its anterior border lies to the left and its inferior border to the right ; and that its right lateral surface, which looks anteriorly and to the right, bulges towards the cavity of the right ventricle (Fig. 37). The Aorta. — The aorta is the great arterial trunk of the body. It commences from the upper, anterior and right portion of the left ventricle, at the level of the third inter- costal spaces and posterior to the left margin of the sternum. It terminates at the level of the lower border of the fourth lumbar vertebra, to the left of the median plane, where it divides into the right and left common iliac arteries. It is described as consisting of three main parts: (i) the ascend- ing part, (2) the arch, and (3) the descending part. The descending part is divided into {a) thoracic and {b) abdominal portions. The first two parts and the thoracic portion of the third part are met with in the dissection of the thorax. The Ascending Part of the Aorta. — The ascending aorta commences at the aortic orifice of the left ventricle and runs upwards to the right and slightly anteriorly, posterior to the first piece of the body of the sternum, to the level of the sternal end of the right second costal cartilage, where it becomes the arch of the aorta. It lies in the middle mediastinum, is enclosed in the fibrous sac of the pericardium, and is en- sheathed by a covering of the serous sac which is common to it and the stem of the pulmonary artery. The lumen of this portion of the aorta is not of uniform diameter ; on the II — 6 a 84 THORAX contrary it presents four dilatations, three at the commence- ment, the aortic sinuses (Valsalva), and one along the right border, the great sinus of the aorta. The latter is merely an indefinite bulging along the right border of the vessel. Relatiofis. — The lower part of the ascending aorta lies posterior to the upper part of the conus arteriosus and the lower Internal Pericardium ii!!^-_'J' Ascending aorta r^^/t'^ Right phrenic Left phrenic nerve Thoracic duct Vena hemiazygos accessoria _Right pulmon- ary artery Bifurcation of trachea — ^ Right vagus Xc \ nerve Bronchial artery Vena azygos Intercostal artery Sympathetic trunk Fig. 42. -Transverse section through the Mediastinal Space at the level of the fifth dorsal vertebra. part of the stem of the pulmonary artery ; but the upper part is in direct relation with the anterior wall of the pericardium, which separates it from the anterior part of the mediastinal surface of the right pleura and lung. Posterior to the ascend- ing aorta, from below upwards, are the left atrium, the right pulmonary artery and the right bronchus. To the right are the right auricle below and the superior vena cava above ; and THORACIC CAVITY 85 to the left lie the left auricle below, and the upper part of the stem of the pulmonary artery above. Branches. — Only two branches are given off from the ascending part of the aorta ; they are the right and left coronary arteries. The right springs from the anterior aortic sinus and the left from the left posterior sinus. Their distribution has been described already (p. 60). The Superficial Cardiac Plexus. — Before the arch of the aorta is studied, the position, connections and relations of the superficial cardiac plexus should be defined. It lies below the arch of the aorta, above the bifurcation of the stem of the pulmonary artery, and between the ascending aorta on the right and anteriorly, and the ligamentum arteriosum to the left and posteriorly. The positions of the superior cervical cardiac branch of the left sympathetic trunk, and the inferior cervical cardiac branch of the left vagus, on the left side of the arch of the aorta, have been defined already (p. 33). Trace these nerves to the plexus, clear away the areolar tissue from around the plexus, and trace branches posteriorly and upwards from it towards the deep cardiac plexus, which lies posterior to the arch of the aorta. Other branches which spring from the superficial part of the cardiac plexus descend along the pulmonary artery and form the right coronary plexus, which is distributed with the right coronary artery. The Arch of the Aorta. — The aortic arch commences at the termination of the ascending part of the aorta, at the level of the second costal cartilage, and posterior to the right margin of the sternum, from which it is separated by the anterior part of the mediastinal portion of the right pleura and lung, or by the remains of the thymus gland (see Fig. 43). It runs posteriorly, to the left, and slightly upwards, through the middle mediastinum and round the left margins of the trachea and oesophagus (see P'igs. 13 and 43), to the level of the lower border of the left side of the fourth thoracic vertebra, where it becomes continuous with the descending part of the aorta. It is curved in both the vertical and the horizontal planes, and as it passes posteriorly and to the left it forms a convexity upwards, and also a convexity which is directed anteriorly and to the left. Its lower border is connected with the left pulmonary artery by the ligamentum arteriosum, and from its upper border arise the three great vessels which supply the head, neck, and upper extremities. 86 THORAX Relations. — Above, the left innominate vein runs along its upper border immediately anterior to the origins of the in- nominate artery, the left common carotid artery and the left subclavian artery, which spring from its upper border ; the first arises from the apex of the convexity, posterior to the centre Internal mammary vessels Superior vena erve CEsophagus Thoracic duct Sympathetic trunk Phrenic nerve t^^W^A:^ Aortic arch ^»r^ J nerve ^^ Left superior , intercostal vein ' Fig, 43. — Transverse section through the Superior Mediastinum at the level of the fourth dorsal vertebra. of the manubrium sterni ; the second arises close to, and some- times in common with the first, whilst the origin of the subclavian is a little more posterior and to the left, separated by a distinct interval from the left common carotid (Figs. 20 and 24). Be/ow the arch lie (i) the bifurcation of the pulmonary artery and portions of its right and left branches ; (2) the liga- THORACIC CAVITY 87 mentum arteriosum, which connects the left pulmonary artery with the arch ; (3) the superficial part of the cardiac plexus immediately to the right of the ligamentum arteriosum ; (4) the left recurrent nerve on the left side of the Hgament ; and (5) still further to the left, the left bronchus passes beneath the arch on its way to the hilus of the left lung. To the right of the arch are the trachea, the oesophagus, the left recurrent nerve, and the thoracic duct. The nerve lies in the angle between the oesophagus and the trachea, and the thoracic duct is pos- terior to and to the left of the oesophagus (Fig. 43). The left side of the ar^h is overlapped by the posterior part of the media- stinal surface of the left pleura and lung, but intervening between the pleura and the arch are (1) the left phrenic nerve, (2) the inferior cervical cardiac branch of the left vagus, (3) the superior cervical cardiac branch of the left sympathetic, (4) the left vagus, and (5) the left superior intercostal vein. The vein passes upwards and anteriorly, lying to the left of the vagus and the cardiac nerves, and to the right of the phrenic nerve (Fig. 13). Dissection.— X>vj'\^& the right coronary artery close to its origin. ^ Cut through the anterior wall of the ascending part of the aorta on each side of the anterior aortic sinus ; extend the incisions upwards to the commencement of the aortic arch, and examine the aortic valve. Note that it is formed by three semilunar cusps which are much stronger than the semilunar cusps of the pulmonary valve (p. 75), but are exactly similar in structure and attachments. Note further that one cusp lies anteriorly, and the other two posteriorly. Examine the aortic sinuses and note that the right coronary artery springs from the anterior sinus, and the left coronary from the left posterior sinus. Note further that the orifices of the coronary arteries, as a rule, lie immediately above the level of the upper margins of the semilunar cusps. Replace the stem of the pulmonary artery in position, and note the relative positions of the pulmonary, aortic, and atrio-ventricular orifices. Topography of the Great Orifices of the Heart. — Replace the sternum in position and note the relations of the cardiac orifices to that bone. The pulmonary orifice is highest. It lies to the left of the margin of the sternum at the level of the third costal cartilage. The aortic orifice is a little lower, and more to the right, posterior to the left margin of the sternum, at the level of the third left intercostal space. Below the aortic orifice is the left atrio-ventricular orifice, posterior to the left margin of the sternum at the level of the left fourth costal cartilage. Still lower and more to the right is the right atrio- ventricular orifice, posterior to the centre of the sternum at the level of the fourth intercostal spaces (Fig. 44). 88 THORAX Dissection. — Divide the phrenic nerves immediately above the diaphragm ; then, with the handle and the edge of the scalpel, detach the lower part of the pericardium from the diaphragm. The attachment of the peri- cardium to the muscular part of the diaphragm is not close, and can easily be broken down. The attachment to the central tendon is much more firm and, as the median plane is approached, the aid of the edge of the knife will probably be necessary before a separation can be effected. Fig. 44. — The relations of the Heart and of its Orifices to the Anterior Thoracic Wall. (Young and Robinson. ) I to VII. Costal cartilages. A. Aorta. Ao. Aortic orifice. C. Clavicle. LA. Left atrium. LV. Left ventricle. M. Mitral orifice. P. Pulmonary orifice. RA. Right atrium. RV. Right ventricle. SVc. Superior vena cava. T. Tricuspid orifice. Divide the right innominate vein and the right phrenic nerve, immediately above the upper end of the superior vena cava, and as the division is made take care not to injure the right vagus posterior to the vein. Then divide the vena azygos just posterior to its entrance into the superior vena cava. Cut the inferior thyreoid veins, the innominate artery, and the left common carotid artery, immediately above the upper border of the left innominate vein, and then divide the left innominate vein, in the interval between the left common carotid and the left subclavian arteries. Cut the left phrenic THORACIC CAVITY 89 nerve, the superior cardiac branch of the left sympathetic, and the inferior cervical cardiac branch of the left vagus, immediately above the upper border of the aortic arch. Next divide the aortic arch. Enter the knife at the upper border of the arch, between the left common carotid and left subclavian arteries and anterior to the left vagus and the left recurrent nerve, and cut from above downwards, completing the division of the arch at the lower border, immediately to the left of the upper end of the ligamentum arteriosum. The left superior intercostal vein will be divided at the same time, but care must be taken not to injure the left recurrent nerve, which is curving round the arch from the front to the back. When the incisions are completed, pull the anterior part of the aortic arch, with the superior vena cava and the lower parts of the innomi- nate veins, anteriorly, and separate them from the lower part of the trachea and from the bronchi. As the separation proceeds, keep the edge of the knife turned towards the aortic arch, to avoid injury to the deep part of the cardiac plexus, which lies anterior to the bifurcation of the trachea. When the lower border of the arch is reached, the twigs which connect the superficial with the right half of the deep part of the cardiac plexus will be exposed, and must be divided. When this has been done detach the posterior surface of the pericardium from the front of the oesophagus and the descending aorta, taking care to avoid injury to the plexus formed by the vagi nerves on the anterior aspect of the oesophagus. As soon as the separation is completed, the heart, with the remains of the pericardium and the lower parts of the phrenic nerves, can be removed from the thorax, and the investigation of the left atrium and the structure of the heart can be proceeded with ; but, before this is done, the dissector should note that the posterior wall of the pericardium intervenes between the posterior wall of the left atrium and the anterior surfaces of the oesophagus and the descending part of the aorta, as the latter structures lie anterior to the middle four thoracic vertebrse (Fig. 21). After the heart and the roots of the great vessels have been removed from the thorax, fasten the left vagus and the recurrent nerve to the part of the arch left in situ by one or two points of suture ; then cut away the remains of the pericardium from the heart, leaving only those portions of it which mark the lines of reflection of the parietal to the visceral portions of the serous sac. Note, as the posterior wall of the pericardium is removed, that it forms the posterior boundary of the oblique sinus (p. 21). The Left Atrium. — The left atrium, like the right, is separable into two parts — a larger main portion, the atrium proper or body ; and a long narrow prolongation, the auricle (O.T. auricular appendage), which runs from the left margin of the body anteriorly and to the right. The four pulmonary veins, two on each side, open into the left atrium. They enter close to the upper ends of the lateral borders of the posterior surface, and not uncommonly the right or the left pair may fuse into a common trunk at the point of entrance. It has been noted previously that the left atrium forms the greater part of the base of the heart, a small part of the anterior or sterno-costal surface, and a still smaller part of the left border. The only part which can be seen from the front, when the heart is in situ, is the apical portion of the 90 THORAX auricle (appendage), for the portion which enters into the formation of the sterno-costal surface is hidden by the roots of the aorta and the pulmonary artery (Fig. 35). The posterior wall of the left atrium is of quadrangular outUne. Along its superior border lie the pulmonary arteries. It is bounded inferiorly by the posterior part of the coronary Left common carotid Aorta Ligamentiim arteriosum Left pulmonary artery- Reflection of serous pericardium Left pulmonary Left atrium Oblique vein Left ventricle. Coronary sulcus (O.T. Auriculo ventricular groove; Coronary sinu; Inferior surface ventricular of heart - Innominate artery Right innominate vein Vena azygos Superior \ ena cava Right pulmonary irtery Right pulmonary Sulcus terminalis Right pulmonary vein Interatrial sulcus Right atrium Inferior vena cava Fig. 45. — Posterior or Basal Aspect of a Heart hardened in situ by formalin injection. sulcus, in which lies the coronary sinus, and on the right by an indistinct inter-atrial sulcus, which indicates the position of the posterior border of the inter-atrial septum. Descending obliquely across the posterior wall of the left atrium, from the lower border of the left inferior pulmonary vein, down- wards and to the right to the coronary sinus, is the oblique vein (Marshall), which is the remains of the left duct of THORACIC CAVITY 91 Cuvier of the foetus. Occasionally it becomes the lower end of a left superior vena cava. Dissection. — Open the left atrium by three incisions — one horizontal and two vertical. The horizontal incision must run from side to side along the lower border of the atrium, immediately above the coronary sulcus ; and the vertical incisions must ascend from the extremities of the horizontal to the upper border of the posterior surface, each passing to the medial side of the terminations of the corresponding pulmonary veins. When the incisions have been made the posterior wall of the atrium must be turned upwards whilst the cavity is being examined. Aorta Left pulmonary veins Pulmonary artery Left auricle (O.T. appendix Mitral _ _ / ' orifice '^ ^ ,' Right pul- Imonary veins sition of fossa ovalis in right atrium Coronary sinus Fig. 4^. — The Left Atrium opened from behind. The greater part of the posterior wall has been thrown upwards. The inner surface- of the wall of the left atrium is smooth and generally devoid of muscular bundles, but the inner surface of the wall of its auricle (O.T. auricular appendage) is covered with musculi pectinati, a fact which can be demon- strated by carrying an incision anteriorly into it. As this incision is made, the dissectors should note that, in a formalin hardened heart, a strong muscular ridge descends along the left border of the cavity anterior to the orifices of the left pulmonary veins, entirely concealing them from view when the cavity is examined from the front. On the right or septal wall of the left atrium the position 92 THORAX of the valve of the foramen ovale is marked by one or more small semilunar depressions situated between slender muscular ridges. The portion of the septal wall which lies below and posterior to these depressions forms the floor of the fossa ovalis, and is the remains of the valve of the foramen ovale of the foetus. The Orifices of the Left Atrium. — The orifices of the left atrium are the openings of the four J)ul7?ionary veins, which convey to it the oxygenated blood from the lungs ; a number of minute openings which are the mouths of the vencs cordis minimcB ; and the left atrio-ventricular orifice through which blood passes from the left atrium to the left ventricle. The openings of the pulmonary veins are situated in the posterior wall, nearer the upper than the lower part, and close to the lateral borders, two on each side. They are entirely devoid of valves. The orifices of the venae cordis minimae, which are scattered irregularly, are also valveless ; but the left atrio-ventricular orifice, which lies in the lower part of the anterior wall of the atrium, is guarded by a bicuspid valve, the mitral valve, which has been described already (p. 79). This orifice is smaller than the corresponding orifice on the right side, and admits the tips of two fingers only. The Structure of the Walls of the Heart. — The last step in the dissection of the heart consists in the examination of the structure of its walls. On the outside the walls are covered with the epicardium, which is the visceral part of the serous pericardium ; and on the inside they are lined with the smooth and glistening endocardmm, which plays a large part in the formation of the flaps of the valves, and is continuous, through the orifices, with the inner coats of the arteries and veins. Between the epicardium and the endocardium lies the muscular tissue of the heart, which is termed the myocardium. The muscular fibres of the myo- cardium are disposed in layers, in each of which the fibres take a special direction. The arrangement of the various layers of the myocardium cannot be displayed in an ordinary dissecting-room heart, in which the continuity of the fibres has been destroyed by the incisions made to display the cavities, but the arrangement of the layers is practically the same in the hearts of all mammals. Therefore, for the purpose of studying the layers, the dissector should obtain a sheep's heart. This should be filled with a paste made of flour and water ; then it should be boiled for a quarter of an hour. The boiling expands the paste, softens the connective tissue, and hardens the muscular fibres. After the boihng is finished the heart should be placed for a time in cold water. After it has cooled, first the epicardium and then the muscular fibres should be gradually torn off. The atrial fibres are difficult to dissect. They consist of three groups : (i) A superficial group running more or less transversely and common to both atria. They are best marked near the coronary sulcus. (2) A deep group special to each auricle. The extremities of these fibres are connected THORACIC CAVITY 93 with the fibrous atrio-ventricular rings, and they pass over the auricles from front to back. (3) The third group consists of sets of annular fibres surrounding the orifices of the veins which open into the atria. The fibres of the ventricles are more easily dissected. They consist, for the main part, of two groups — the superficial and the deep. The fibres of each set are common to both ventricles, and the dissectors should note the remarkable spiral or whorled arrangement of the superficial fibres which occurs at the apex, where they pass into the deeper parts of the wall. The superficial fibres spring mainly from the fibrous atrio-ventricular rings. Those which are attached to the right ring turn inwards at the apex and become continuous with the papillary muscles of the left ventricle, whilst the fibres which spring from the left ring pass in the same way to the papillary muscles of the right ventricle. The deeper fibres form an (y^-shaped layer, one loop of the CO surrounding the right and the other the left ventricle. The fibrous rings of the atrio-ventricular orifices intei^vene between the atrial and the ventricular muscle fibres, but the two groups are brought into association with each other by the atrio-ventricular bundle described on p. 74. It has been assumed that the impulses which regulated the movements of the ventricles were conveyed to them from the atria by the fibres of this bundle, but it has been shown recently that numerous nerve fibrils are intimately intermingled with the fibres of the atrio- ventricular bundle. It is possible, therefore, that the connection between the atria and the ventricles is neuro-muscular. The Action of the Heart. — The differences between the various parts of the heart, i.e. the thinness of the walls of the atria as contrasted with the thickness of the walls of the ventricles, and the greater thickness of the walls of the left as contrasted with those of the right ventricle, are associated with the functions of the various chambers, and with the action which the heart plays in the maintenance of the circulation of the blood. The heart is a muscular pump, provided with receiving and ejecting chambers. It has three phases of action : (i) a period of atrial contraction ; (2) a period of ventricular contraction, which immediately succeeds the atrial con- traction ; (3) a period of diastole or rest. During the period of diastole or rest the chambers, previously con- tracted, dilate, as the muscular fibres of the heart relax. The dilatation is aided by the respiratory movements of the thorax. As the dilatation pro- gresses blood flows into the right atrium from the superior vena cava, the inferior vena cava, and the coronary sinus ; and into the left atrium through the four pulmonary veins. The atrial contraction commences with the contraction of the circular fibres which surround the mouths of the veins entering the atria, and thus the blood is prevented from passing back into the veins. As the contraction extends to the general fibres of the atria the blood is forced onwards into the ventricles, which become distended. Then the ventricular contraction commences, the atrio-ventricular valves close, and, as the contraction proceeds, the blood is driven out of the ventricles through the arterial orifices, that in the right ventricle being ejected into the pulmonary artery, and that in the left ventricle into the aorta. ^Yhen the ventricular contraction is completed the period of diastole commences ; and, as long as the heart remains alive, the cycle is repeated. The work of the atria is merely to force the blood through the widely open atrio-ventricular orifices into the ventricles and to expand the dilating walls of the ventricles. For this purpose no great force is required, there- fore the walls of the atria are thin. The work of the ventricles is much more severe, therefore their walls are thicker, but the right ventricle has only to exert sufficient force to drive the blood through the lungs to the left 94 THORAX auricle, that is, through a comparatively short distance and against a com- paratively small resistance ; therefore its walls are thin as compared with the walls of the left ventricle, which has to be sufficiently strong to force the blood through the whole of the trunk, the head and neck, and the upper and lower limbs. The Topography of the Heart. — Before proceeding to the study, of the trachea, the dissectors should replace the heart in position and revise their knowledge of its relations to the surface. Its position can be indicated on the anterior wall of the thorax by the following four lines: — (i) A line com- mencing at the lower border of the second left costal cartilage, half an inch from the left border of the sternum, and ending at the upper border of the third right costal cartilage, half an inch from the right border of the sternum. This line indicates the position of the upper border of the heart, which is formed by the atria. (2) A line from the upper border of the third right costal cartilage to the sixth right costal cartilage. This line should commence and end half an inch from the border of the sternum, and should be slightly convex to the right. It indicates the right border of the heart, which is formed by the right atrium alone. (3) A line from the sixth right costal cartilage to the apex, which lies behind the fifth left intercostal space three and a half inches from the median plane. This line marks the position of the lower border of the sterno-costal surface, which is formed, in the greater part of its extent, by the right ventricle, the left ventricle entering into its constitu- tion only in the region of the apex. (4) A line from the apex to the lower border of the second left costal cartilage. This line should be convex upwards and to the left ; the point of greatest convexity should coincide with the lower border of the fourth left costal arch, and the upper extremity should be situated half an inch from the left margin of the sternum. It marks the position of the left border of the heart, which is formed in four-fifths of its length by the left ventricle and in the remaining fifth by the left atrium. A line from the upper border of the sternal end of the third left costal cartilage to the lower border of the sternal end of the sixth right cartilage indicates the anterior part of the coronary sulcus. The points indicating the positions of the arterial and atrio-ventricular orifices must be placed below and to the left of the line of the coronary sulcus in the following order from above downwards ; pulmonary orifice^ THORACIC CAVITY 95 aortic orifice^ mitral orifice^ tricuspid orifice. The centre of the pulmonary orifice is posterior to the third left costal cartilage at the margin of the sternum. The aortic orifice lies posterior to the left half of the sternum opposite the third inter- Right common carotid artery Orifice of right internal jugular vein \ Right subclavian artery Right subclavian vein Innominate artery Left common carotid artery I End of left internal jugular \'ein Left subclavian artery Left subclavian vein Right superior inter- costal vein Vena azygos Eparterial branch of right bronchus Stem of right bronchus Right vagus nerve Right intercostal vein Right aortic intercostal artery Right great splanchnic nerve Right sympathetic trunk Inferior vena cava Trachea Termination of aortic arch Left bronchus Left vagus nerve Descending thoracic aorta (Esophageal plexus Fig. 47. — Dissection of tlie Posterior Mediastinum and the posterior part of the Superior Mediastinum from the anterior aspect. costal spaces. The mitral orifice is posterior to the left border of the sternum at the level of the fourth left costal cartilage ; and the centre of the tricuspid orifice is posterior to the middle of the sternum at the level of the fourth intercostal spaces. The Thoracic Portion of the Trachea. — The thoracic portion of the trachea, like the cervical portion, is a wide 96 THORAX tube kept constantly patent by a series of cartilaginous rings embedded in its walls. Posteriorly the rings are deficient and in consequence the tube is flattened behind (Fig. 43). It enters the thorax at the upper aperture, posterior to the upper border of the manubrium, and it terminates, at the level of the lower border of the manubrium and the upper border of the fifth thoracic vertebra, by dividing into a right and a left bronchus. It lies, therefore, in the superior mediastinum. Trachea Right bronchus Eparterial branch First ventral branch First dorsal branch First ventral branch Stem of bronchus Left bronchus First ventral branch First dorsal branch Stem of bronchus Fig. 48. — Drawing of a Stereoscopic Skiagraph of the Trachea and Bronchi injected with starch and red lead. and its median axis is in the median plane, except at the lower end where it deviates slightly to the right. Relations. — Posteriorly^ it is in contact with the oesophagus, which separates it from the vertebral column ; and in the angle between its left border and the anterior surface of the oesophagus is the left recurrent nerve (Fig. 43). Anteriorly^ it is in relation below with the arch of the aorta, the deep part of the cardiac plexus intervening; and at a higher level with the innominate and left common carotid arteries, the left innominate vein and the inferior thyreoid veins. More superficially lie the remains of the THORACIC CAVITY 97 Thyreoid cartilage Crico-thyreoid ligament Cricoid cartilage Part of trachea covered by isthmus of thyreoid gland Common carotid artery Left subclavian artery thymus, and still more superficially the manubrium sterni with the origins of the attached muscles. On the rights it is in relation with the upper part of the mediastinal surface of the right pleura and lung (Fig. 43), the right vagus nerve, and the arch of the azygos vein (Fig. 12). It is also in relation, on its right side, near its lower end and more anteriorly, with the superior vena cava, and at a higher level with the innominate artery. Its left lateral relations are the arch of the aorta below and the left sub- clavian and left common carotid arteries above. The Bronchi. — Each bronchus passes down- wards and laterally first to the hilus of the corre- sponding lung and thence downwards in the sub- stance of the lung to its lower end. It can, therefore, be divided into an extra-pul- monary and an intra- pulmonary portion. The extra-pulmonary part, like the trachea, is kept permanently open bythe presence of cartilaginous rings in its walls ; and as the rings are defi -Aortic arch Left bronchus Left pulmonary artery First ventral branch of left bronchus Eparterial bianch of right bronchus Hyparterial branch of I right bronchus Right pulmonary artery Fig. 49. — The Trachea and Bronchi. The dotted Hne gives the outline of the thyreoid gland. cient posteriorly, the extra-pulmonary part of each bronchus presents a flattened posterior surface similar to that of the trachea. The lumina of the intra-pulmonary parts of the bronchi are kept patent by cartilaginous plates which are irregularly distributed in the substance of the walls. VOL. II — 7 98 THORAX Relations of the Extra-puhjionary Part of the Right Bronchus. — The right bronchus is much more vertical than the left (Fig. 48), and, as the ridge which separates the orifices of the two bronchi at their origins, lies to the left of the median line of the trachea, the right bronchus is the direct continuation of the trachea, and foreign bodies, which have entered the windpipe, pass more frequently into it than into the left bronchus. It passes downwards and laterally from the upper border of the fifth thoracic vertebra to the level of the upper part of the sixth thoracic vertebra, where it enters the hilus. Anterior to the extra-pulmonary part of the right bronchus are the ascending part of the aorta, the lower part of the superior vena cava, and the right pulmonary artery. Above it is the arch of the azygos vein ; d^wd, posterior to it are the azygos vein, the posterior pulmonary plexus, and the right bronchial artery. This part of the right bronchus gives off one branch, which arises close to the hilus and is called the eparterial bronchus, because it originates immediately above the point where the right pulmonary artery crosses anterior to the stem bronchus. Relations of the Extra-pulmonary Part of the Left Bronchus. — The extra-pulmonary part of the left bronchus commences and ends at the same level as the corresponding part of the right bronchus, but it has further to go, because the hilus of the left lung is further from the median plane than the hilus of the right lung ; therefore it is longer and less vertical than the right bronchus. It gives off no branches. Anterior to it are the left pulmonary artery, and the upper and left part of the pericardial sac which separates the bronchus from the left auricle. Above it is the arch of the aorta, and posterior to it are the descending aorta, the posterior pulmonary plexus, the left bronchial arteries, and the oeso- phagus. Dissection. — The intra- pulmonary parts of the bronchi and the intra- pulmonary parts of the pulmonary arteries and veins should now. be dissected. The dissectors must commence at the hilus of the lung and follow the bronchus and the vessels into the interior of the lung, cutting away the lung substance, but avoiding injury to the main branches of the bronchus and of the artery, and the main tributaries of the veins. Relations of the Intra-pulmonary Parts of the Bronchi, the Pul- monary Arteries and the Pulmonary Veins. —After passing through the hilus each bronchus descends, in the substance of the lung, to the lower end of the lung, lying nearer the medial than the lateral surface, and nearer the posterior than the anterior border. As it descends it gives off two sets of THORACIC CAVITY 99 branches : (i) ventral, which run towards the anterior border of the lung, and (2) dorsal, which pass posteriorly to the thick posterior border. As these branches are given off below the point where the pulmonary artery crosses anterior to the bronchus they are called Jiyparterial branches. The hyparterial branches arise alternately, first a ventral and then a dorsal branch, and, in addition, a number of small accessor}' branches are given off from the stem bronchus in some of the intervals between the dorsal and ventral branches. On the right side, the eparterial bronchus, which is given off from the extra-pulmonary part of the right stem bronchus, supplies the upper lobe of the right lung. The first ventral hyparterial branch supplies the middle lobe, and all the remaining branches are distributed to the lower lobe. On the left side, the first ventral branch goes to the upper lobe of the left lung, and all the other branches go to the lower lobe. The intra-pidmo7iary part of each pzdvionary a7ieiy descends along the postero-lateral aspect of the intra-pulmonary part of the stem bronchus, between the ventral branches anteriorly and the dorsal branches posteriorly, and it gives off branches which correspond with the branches of the main bronchus. The vein from the upper lobe, on the right side, runs along the antero- medial aspect of the eparterial bronchus to the hilus, where it joins the vein of the middle lobe, which lies along the antero-medial border of the first ventral hyparterial bronchus, to form the upper right pulmonary vein. The vein from the lower lobe ascends along the antero-medial border of the intra-pulmonary part of the stem bronchus. On the left side, the upper left pulmonary vein accompanies the first ventral bronchus, and the lower accompanies the intra-pulmonary part of the stem bronchus ; each vein lies along the ventro-medial aspect of the bronchus which it accompanies. The Thoracic Portions of the Vagi Nerves. — The thoracic parts of the vagi nerves, which are still in position, should now be examined. Both vagi enter the thorax at the upper aperture. The right vagus descends, through the superior mediastinum, posterior to the right innominate vein and the superior vena cava, passing obliquely downwards and pos- teriorly (Fig. 12) along the side of the trachea, and between the trachea medially, and the right pleura laterally, to the arch of the azygos vein. Next it passes between the trachea medially, and the arch of the azygos vein laterally, and reaches the posterior aspect of the root of the right lung, where it breaks up into a number of branches which unite with branches of the sympathetic trunk to form the posterior pulmonary plexus. It emerges from the plexus as a single trunk which runs downwards and medially, in the posterior mediastinum, to the front of the oesophagus. On the oesophagus it breaks up into branches which unite with branches of the left vagus to form the oesophageal plexus (Fig. 47). At the lower end of the thorax the right vagus again becomes distinct ; it passes to the posterior aspect of the oesophagus and enters the abdomen through the oesophageal orifice of the diaphragm. II — la loo THORAX Thoracic Branches of the Right Vagtis. — Whilst the right vagus is in the superior mediastinum it gives off a thoracic cardiac branch, which goes to the right half of the deep cardiac plexus, and some anterior pulmonary branches to the front of the root of the right lung, where they join with branches of the cardiac plexus to form the anterior pul- monary plexus. As it passes posterior to the root of the lung it gives branches to the bronchi and the lung ; and in the posterior mediastinum it gives branches to the oesophagus, and to the posterior part of the pericardium and pleura. The Left Vagus. — As the left vagus descends through the superior m.ediastinum it lies at first between the left common carotid artery and the left phrenic nerve anteriorly, and the left subclavian artery posteriorly, and then on the left side of the arch of the aorta. In the latter situation it is crossed laterally by the left superior intercostal vein. Below the lower border of the aortic arch it passes posterior to the root of the left lung, where it breaks up into branches which enter into the formation of the posterior pulmonary plexus. At the lower border of the root of the left lung it emerges from the plexus as two trunks, which descend, into the posterior mediastinum, to the oesophagus, where they unite with branches of the right vagus to form the oesophageal plexus. At the lower end of the thorax the left vagus again becomes a single trunk which passes through the oesophageal orifice of the diaphragm on the anterior aspect of the oesophagus. Thoracic Branches of the Left Vagus. — In the superior mediastinum, whilst it lies against the left side of the aortic arch, it gives off the left recurrent branch, branches to the upper and anterior part of the pericardium, and branches to the left anterior pulmonary plexus. Posterior to the root of the left lung, it supplies branches to the left bronchus and the left lung ; and during its course through the posterior mediastinum, as it takes part in the oesophageal plexus, it gives branches to the oesophagus, to the posterior part of the pericardium, and to the left pleura. The Thoracic Part of the Left Recurrent Nerve. — The left recurrent nerve springs from the trunk of the left vagus near the lower border of the left side of the aortic arch. It curves round the lower border of the arch, posterior and to the left of the ligamentum arteriosum, and passes upwards, posterior and to the right of the arch. THORACIC CAVITY loi through the superior mediastinum, in the angle between the left border of the trachea and the oesophagus, and posterior to the left common carotid artery. As it turns round the arch it gives branches to the deep cardiac plexus, and, as it ascends along the left border of the trachea, it gives offsets to the trachea and to the oesophagus. The Deep Cardiac Plexus. — The deep cardiac plexus lies between the arch of the aorta and the bifurcation of the trachea. It is more or less distinctly separable into right and left parts, and the right part is connected with the superficial cardiac plexus. The right part of the plexus receives (i) three cardiac branches from the cervical part of the right sympathetic trunk; (2) the two cervical cardiac branches of the right vagus ; (3) the cardiac branch of the right recurrent nerve ; (4) the thoracic cardiac branch of the right vagus. It is connected \vith the superficial cardiac plexus and gives branches to (i) the right anterior pulmonary plexus; (2) the right atrium; (3) the right coronary plexus. The left part of the deep cardiac plexus receives (i) the middle and low^er cervical cardiac branches of the left sympathetic trunk ; (2) the upper cervical cardiac branch of the left vagus ; (3) the cardiac branches of the left recurrent nerve. It gives branches to (i) the left anterior pulmonary plexus; (2) the left atrium ; (3) the left coronary plexus. Dissection. — Cut through the right and left bronchi, close to their origins from the trachea ; then divide the trachea at the upper aperture of the thorax and remove its thoracic portion, but avoid injury to the vagi and the left recurrent nerves. The extra-pulmonary parts of the bronchi will be retained in position by the bronchial arteries and the branches of the pulmonary plexuses ; and the thoracic part of the oesophagus will be fully exposed. The Thoracic Part of the CEsophagus. — The thoracic part of the oesophagus enters the thorax at the upper aperture, passes downwards, through the superior and posterior mediastina, and leaves, at the level of the tenth thoracic vertebra, by passing through the oesophageal orifice of the diaphragm into the epigastric region of the abdomen. As it enters the superior mediastinum it lies somewhat to the left of the median plane, but as it descends it passes medially, gains the median plane at the level of the fifth thoracic vertebra, and continues downwards in that plane to the level of the seventh thoracic vertebra. There it passes forwards II— 7 & I02 THORAX and to the left, across the anterior aspect of the descending aorta and posterior to the pericardium (Figs. 12 and 21). Posterior Relations. — In the superior mediastinum it is an- terior to the left longus colli muscle and the vertebral column. In the upper part of the posterior mediastinum it is separated from the vertebral column by (i) the posterior part of the oeso- phageal plexus, (2) the upper six right aortic intercostal arteries, (3) the thoracic duct, (4) the vena azygos, (5) the vena hemi- azygos and the accessory hemiazygos vein; and in the lower part by (6) the oesophageal plexus and (7) the descending aorta. Anterior Relations. — Anterior to it, in the superior ??iedia- stinum, lie the trachea, the left recurrent nerve, the upper part of the left common carotid artery, the left subclavian artery, the arch of the aorta, and the structures which lie anterior to those already mentioned. As it passes from the superior to the posterior mediastinum its anterior relations are first the commencement of the left bronchus and then the right pulmonary artery.^ In the posterior mediastinmn, the oesophageal plexus is on its anterior surface, intervening between it and the posterior wall of the pericardium, which separates both the plexus and the oesophagus from the posterior wall of the left atrium ; and at a lower level the oesophagus lies posterior to the diaphragm (Fig. 21). Right lateral Relations. — In the superior mediastimwi, it is in relation with the right pleura and lung and with the arch of the vena azygos (Figs. 12 and 22), and in the posterior mediastinum with the oesophageal plexus and right pleura and lung, until it passes anteriorly and to the left, anterior to the descending aorta. left latei-al Relations. — In the siperior mediastinum, it is in relation on the left side with the thoracic duct, the left subclavian artery, the left pleura and lung, and the termination of the arch of the aorta. Frofn the fifth to the seventh thoracic vertebra its left lateral relations are the oesophageal plexus and the descending aorta ; and at its lower end, as it Hes anterior to the descending aorta, it comes again into relation with the left pleura and lung. The dissector should note (i) that, after death, the oesophagus is somewhat compressed antero- posteriorly by the structures between which it fies. It probably has a similar form during Hfe when empty and flaccid, but becomes 1 Verify this statement by replacing the heart in situ. THORACIC CAVITY 103 more circular when solids or fluids are passing along it ; and (2) that it is somewhat constricted at the level of the left bronchus. An inch or more of the upper part of the posterior mediastinal portion of the tube should be removed and dis- sected under water in a cork-Hned tray. It will be found to possess from without inwards the following coats: (i) an external fibrous sheath; (2) a muscular coat; (3) a sub- mucous coat ; and (4) a mucous internal hning. The submucous coat forms a loose connection between the muscular and mucous coats ; consequently, when the muscular — Vena cava inferior Pericardium CEsophagus Thoracic duct .Vena azygos Pleura Thoracic aorta Pleura Fig. 50. — Tracing of section through the Posterior Mediastinum at the level of the eighth thoracic vertebra, coat is contracted the mucous Hning is thrown into longi- tudinal folds. The muscular coat consists of an external layer of longitudinal fibres and an internal layer of circular fibres. Aorta Descendens. — The descending aorta commences at the termination of the aortic arch, at the lower border of the left side of the fourth thoracic vertebra. It passes down- wards, through the posterior mediastinum, and it leaves the thorax by passing through the aortic aperture of the diaphragm, opposite the lower border of the twelfth thoracic vertebra. Its length is about seven inches. In the upper part of its extent it lies to the left of the vertebral column ; but in the lower part it lies anterior to the column, in the median plane. Branches. — Branches spring from both the anterior and the posterior aspects of the descending aorta. Those from the anterior aspect are the two left bronchial arteries, four II— 7 c I04 THORAX oesophageal branches, and some small and irregular media- stinal and pericardial branches. The posterior branches are nine pairs of aortic intercostal arteries and one pair of sub- costal arteries. Relations. — Anterior to the thoracic part of the descending aorta, from above downwards, are the root of the left lung; the upper part of the posterior wall of the pericardium, separating the aorta from the left atrium ; the oesophagus, separating the aorta from the lower part of the posterior wall of the pericardium ; and the crura of the diaphragm, which separate the lower portion of the thoracic aorta from the Pericardium Diaph -Diaphragm CEsophagus Thoracic aorta Left pleura ,.- Thoracic duct Right pleura Vena azygos Fig, 51. — Tracing of a section through the lower part of the Posterior Mediastinum, where its anterior wall is formed by the diaphragm. omental bursa of the peritoneum and from the posterior surface of the caudate lobe (O.T. Spigelian) of the liver. Posteriorly are the vertebral column, its own intercostal and subcostal branches, the hemiazygos and accessory hemiazygos veins ; and it is overlapped posteriorly in the upper part of its extent by the left pleura and lung. Along its right side, in its whole length, are the thoracic duct and the vena azygos, and anterior to them, from the fifth to the lower part of the seventh thoracic vertebra, lies the oesophagus. At a lower level a mass of areolar tissue separates the aorta from the right pleura and lung. On its left side it is in relation with the left pleura and lung. Dissection. — Turn the remains of the lower part of the oesophagus down- wards towards the diaphragm. Clean the thoracic duct, the right aortic intercostal arteries, and the hemiazygos and accessory hemiazygos veins, which lie posterior to the oesophagus. Then trace the thoracic duct in the THORACIC CAVITY 105 Thoracic Duct and its Tributaries, Lumbar veins. Left renal vein. Right renal artery. Inferior vena cava. Suprarenal gland. Cisterna chyli. Thoracic duct. Descending thoracic lymph trunk. Vena azj'gos. ^Mediastinal lymph vessel. Superior intercostal vein. Subclavian vein. Subclavian artery. Clavicle. Scalenus anterior muscle. Phrenic nerve. Thyreo-cervlcal trunk. Internal jugular vein. Vertebral artery. Common carotid artery Trachea. Thyreoid gland. Qilsophagus. Common carotid artery. 25. Internal jugular vein. 26. Vertebral artery. 27. Thyreo-cervical trunk. Common lymph trunk from head and upper limb. Scalenus anterior muscle. Subclavian arte^>^ Superior intercostal vein Bronchial lymph vessel. Vena hemiazygos accessoria. Aorta. Vena hemiazj'gos. 36. CEsophagus. 37. Descending thoracic Ij-mph trunk. Inferior phrenic artery. Suprarenal gland. Ccfiliac artery. Superior mesenteric artery. Common intestinal lymph trunk. Renal arterj-. Renal vein. Common lumbar lymph trunk. To6 THORAX whole of the thoracic portion of its course, and arrange with the dissector of the head and neck to display the cervical portion of its course. The Thoracic Duct. — The thoracic duct is a vessel of small calibre but of great importance, for it conveys, to the left innominate vein, the whole of the lymph from the lower extremities, the abdomen (except that from part of the upper surface of the liver), the left side of the thorax, including the left lung and pleura and the left side of the heart, the left upper extremity, and the left side of the head and neck. It is the upward prolongation of a dilated sac, the cisterna chyli, which lies between the right crus of the diaphragm and the bodies of the first and second lumbar vertebrae. It enters the thorax through the aortic orifice of the diaphragm, lying between the aorta on the left and the vena azygos on the right. It continues upwards through the posterior mediastinum, lying between the descending aorta and the vena azygos, anterior to the right aortic intercostal arteries and the hemiazygos and accessory hemiazygos veins, and posterior to the right pleura below and the oesophagus above. At the level of the fifth thoracic vertebra it crosses to the left of the vertebral column, and then ascends, through the superior mediastinum, along the left border of the oesophagus, in contact, on the left, with the left pleural sac, and separated posteriorly from the left longus colli muscle by the mass of areolar tissue. Anterior to the thoracic duct, in the superior mediastinum, are the termination of the aortic arch, the left subclavian, and the left common carotid arteries, in that order from below upwards. At the upper end of the thorax the thoracic duct enters the root of the neck, and, at the level of the seventh cervical vertebra, it turns laterally, posterior to the left common carotid artery, the left vagus nerve, and the left internal jugular vein, and anterior to the vertebral artery and veins, the thyreo-cervical trunk or inferior thyreoid artery, and the phrenic nerve. Then, turning downwards, anteriorly and medially, on the anterior aspect of the scalenus anterior, it crosses anterior to the transversa colli and transversa scapulae arteries, and terminates in the upper end of the innominate vein, in the angle of junction of its internal jugular and sub- clavian tributaries. Immediately before its termination it receives the left common jugular and subclavian lymphatic trunks, unless they end separately in one or other of the three large veins. When the thoracic duct is distended it THORACIC CAVITY 107 has a beaded or nodulated appearance on account of the numerous valves which lie in its interior. The terminal valve is usually situated a short distance from the point of entrance of the duct into the left innominate vein. Clavicular head of -. sterno-mastoid "* Stemo-thj'reold — Th>Teoid gland - — _, . Phrenic nerve '- Vagus"" '' Sternal head of_ sterno-mastoid Stemo-hyoid . External jugular vein / . Platysma reflected with skin /--» Nervus cutaneus colli Internal jugular vein Supra-clavicular nerves Omo-hyoid Transverse cervical vein Brachial plexus Scalenus anterior Trans. cer%'ical artery Trans, scapular artery External jugular vein Subclavius Cephalic vein Axillarj^ vein Anterior jugular vein Cla^icular facet on sternum Left common carotid Left innominate vein ! \ First rib \ \ Dome of left pleura \ Thoracic duct Internal mammary artery Phrenic nerve Fig. 53- -Dissection of the Root of the Neck showing the termination of the Thoracic Duct. The Right Lymphatic Duct. — From the point where the thoracic duct turns from the front to the left of the vertebral column a small lymphatic vessel, which frequently communicates with the thoracic duct, may be traced upwards along the front of the column to the root of the neck. io8 THORAX where it ends in the commencement of the right innominate vein. This is the right lymphatic duct. Immediately before its termination it may be joined by the right common jugular and right subclavian lymphatic trunks, but, as a rule, the two latter vessels open separately into the sub- clavian, the internal jugular, or the innominate veins (Parsons). The right lymphatic duct conveys lymph from the upper part of the right lobe of the liver, the right side of the thorax, including the right pleura and lung and the right half of the heart, and, if it is joined by the jugular and subclavian trunks, the lymph from the right upper extremity and the right side of the head and neck also. Lymphoglandulse Thoracales. — During the dissection of the thorax the dissector will have noted certain groups of lymph glands. These are of considerable importance, for their enlargement in disease is not infrequently the cause of serious thoracic trouble ; but whilst some, such as the bronchial glands, are quite obvious, others are frequently so small that they escape notice. The following are the chief groups: — (i) Two chains of minute glands which are placed in relation to the anterior thoracic wall and follow the course of the internal mammary vessels. They are termed sternal lymph glands, and are joined by lymphatic vessels from the anterior thoracic wall, the mammary glands, the anterior part of the diaphragm, and the upper part of the anterior wall of the abdomen. (2) Two chains of glands on the posterior thoracic wall — one on either side of the vertebral column in relation to the vertebral extremities of the ribs. These are very minute ; afferents to them accompany the intercostal vessels ; therefore they are called the intercostal lymph glands, and they receive the lymphatics of the posterior thoracic wall. (3) Anterior mediastinal lymph glands, two or three in number, which receive lymphatics from the diaphragm and upper surface of the liver. They occupy the lower open part of the anterior mediastinum. (4) Posterior mediastinal lymph glands, which follow the course of the thoracic aorta, and are joined by lymphatics from the diaphragm, pericardium, and oesophagus. (5) Superior inedia- stinal lymph glands, an important group, eight to ten in ntimber, and placed in relation to the aortic arch and the bifurcation of the trachea. The lymphatics of the heart, pericardium, and thymus enter these. (6) Bronchial lymph glands, continuous above with the preceding, and massed chiefly in the interval between the two bronchi. They are also prolonged into the roots of the lungs. The lymphatic vessels of the lungs pour their contents into them. In the adult, they are generally dark in colour, and sometimes quite black. Dissection. — Cut through the descending aorta immediately above the diaphragm. Detach its upper end from the left vagus and the left recurrent nerve which were previously fastened to it, then draw it forwards and divide the intercostal and subcostal arteries, which arise from its posterior surface, close to their origins and remove it. Arterise Intercostales. — There are eleven pairs of inter- costal arteries. The upper two pairs are derived indirectly THORACIC CAVITY 109 from the subclavian arteries ; the remaining nine pairs are branches of the thoracic part of the descending aorta. The Aortic Intercostal Arteries. — The nine pairs of aortic intercostal arteries spring from the posterior surface of the descending aorta, either separately or by a series of common trunks, one for each pair. The right arteries are longer than the left because the aorta lies to the left of the median plane ; and, since the descending aorta commences only at the level of the lower border of the fourth thoracic vertebra, the four or five highest pairs have to ascend to gain the level of the spaces to which they are distributed. The right aortic intercostal arteries run across the anterior aspects of the bodies of the vertebrae, lying posterior to the thoracic duct and the vena azygos; then they turn posteriorly, between the sides of the bodies of the vertebrcC and the parietal pleujra ; and, finally, immediately before they enter the inter- costal spaces, they pass between the sides of the bodies of the vertebrae medially and the sympathetic trunk laterally. The shorter left aortic intercostal arteries run posteriorly, first between the left pleura and the bodies of the vertebrae, and then between the sympathetic trunk and the vertebral bodies. As each artery enters the space to which it belongs it gives off a dorsal branchy which passes posteriorly, between the vertebral column medially and the anterior costo-transverse ligament laterally \ it gives off a spinal twig, which enters the verte- bral canal through the corresponding intervertebral foramen ; then it divides into a medial and a lateral branch which accompany the medial and lateral divisions of the posterior branch of the corresponding thoracic nerve. After giving off the dorsal branch, the trunk of the artery runs laterally, along the upper border of the space to which it belongs, at first anterior to the posterior intercostal membrane, and then between the internal and external intercostal muscles. Its further course has been described already (p. 6). As it passes along the upper border of the intercostal space, in the shelter of the subcostal groove of the rib, it is situated between the intercostal vein above and the anterior branch of the thoracic nerve below. The Subcostal Arteries. — The subcostal arteries are the last pair of branches which spring from the posterior aspect of the thoracic part of the descending aorta. They enter the abdomen, by passing beneath the lateral lumbo-costal no THORAX arches, and they run, in company with the last thoracic nerves, along the lower borders of the last pair of ribs. Arteriae Intercostales Supremae. — The superior intercostal arteries, which supply the upper two intercostal spaces on each side, are derived from the costo-cervical branches of the subclavian arteries (Fig. 5). Each superior intercostal artery commences at the level of the upper border of the neck of the first rib. It descends anterior to the neck of the rib, posterior to the parietal pleura and between the first thoracic ganglion of the sympathetic trunk medially and the first thoracic nerve ; which is passing upwards to the brachial plexus, laterally (Fig. 5). At the lower border of the neck of the first rib it gives off the posterior inter- costal artery to the first intercostal space ; then it crosses anterior to the neck of the second rib, and, turning later- ally, it becomes the posterior intercostal artery of the second space. Nervi Intercostales. — The intercostal nerves are the anterior branches of the thoracic nerves. They pass laterally in company with the arteries. The twigs which connect them with the sympathetic ganglia have been noted already (p. 26). Each nerve lies at a lower level than the corre- sponding artery, and is at first placed between the posterior intercostal membrane and the pleura, and then between the two muscular strata. The further course of the nerves is described on p. 5. The first thoracic nerve runs upwards, anterior to the neck of the first rib, to join the brachial plexus. It gives a small branch to the first intercostal space, but this nerve, although it is disposed after the manner of an intercostal nerve, does not furnish, as a rule, a lateral cutaneous or an anterior branch. The second intercostal nerve, as a rule, sends a branch upwards, anterior to the neck of the second rib, to join that portion of the first thoracic nerve which enters the brachial plexus. This communicating twig is usually minute and in- significant, but sometimes it is a large nerve ; when this is the case, the intercosto -brachial nerve (O.T. intercosto- humeral), or lateral cutaneous branch of the second intercostal nerve, is very small or altogether absent. Venae Intercostales. — The intercostal veins differ in their arrangement upon the two sides of the body. On the right side they terminate in three different ways : — THORACIC CAVITY m 1. The intercostal vein of the first or highest space joins the right innominate vein (sometimes the vertebral vein). 2. The intercostal veins of the second and third spaces (and sometmies that of the fourth space) unite into a common trunk, termed the Hght superior intercostal vein, which joins the upper part of the vena azygos. 3. The intercostal veins of the lower eight spaces join the vena azygos. On the left side of the body four modes of termination may be recognised : — 1. The intercostal vein of the first space joins the /^// innominate vein (sometimes the vejiebral vein). 2. The intercostal veins of the second and third spaces (and sometimes that of the fourth space) converge and by their union form a single trunk, termed the left stipeHor intercostal vein, which crosses the arch of the aorta and joins the left innominate vein independently of the first intercostal vein. The union with the left innominate vein may be absent, and then the trunk formed by the veins of the second and third spaces joins the accessory hemiazygos vein. 3. The intercostal veins of the fourth, fifth, sixth, seventh, and eighth spaces terminate in the accessory hemiazygos vein (O.T. vena azygos minor superior), which crosses posterior to the aorta and joins the hemiazygos vein, or it ends directly in the vena azygos. 4. The intercostal veins of the ninth, tenth, and eleventh spaces join the hemiazygos vein (O.T. vena azygos minor infeHor). Vena Azygos (O.T. Vena Azygos Major). — This has already been studied, but 'should now be revised (p. 29), and then the dissector should examine the hemiazygos and accessory hemiazygos veins. Vena Hemiazygos Accessoria. — The accessory hemiazygos vein is formed, on the left side of the body, by the union of the intercostal veins of the fourth, fifth, sixth, seventh, and eighth spaces. It communicates above with the left superior inter- costal vein, which carries the blood from the second and third intercostal spaces to the left innominate vein ; and it receives the left bronchial veins. At the level of the seventh thoracic vertebra it crosses to the right, posterior to the aorta and thoracic duct, and ends by joining either the hemiazygos vein or the vena azygos. In addition to the intercostal veins it receives the left bronchial veins. Vena Hemiazygos (O.T. Vena Azygos Minor Inferior). — This vein takes origin within the abdomen as the left ascendi?ig lumbar vein. It enters the thorax by piercing the left crus of the diaphragm, and is continued upwards, upon the vertebral column, as far as the eighth or seventh thoracic vertebra. At this point it turns to the right, and. 112 THORAX crossing posterior to the aorta and the thoracic duct, it joins the vena azygos. Before it terminates it may receive the accessory hemiazygos vein. The thoracic tributaries of this vein are the intercostal veins of the lower three spaces of the left side and the left subcostal vein. In the abdomen it receives the upper two left lumbar veins. The Anterior Intercostal Veins. — The blood is drained from the anterior part of the thoracic .wall by veins which accompany the intercostal branches of the internal mammary arteries. They terminate in the internal mammary veins. The veins of the thoracic parietes are extremely variable, and the description given above must be looked upon as representing merely their more usual arrangement. THORACIC JOINTS. The dissector should now complete the dissection of the thorax by an examination of the various thoracic joints. Dissection. — When the portion of the sternum with the cartilages of the ribs, which was laid aside, is studied, the following joints will be noted : inter-sternal, costo-sternal, and inter-chondral. Very little dissection is necessary. After the ligaments have been defined, the dissector should remove a thin slice from the anterior aspect of each articulation, in order that the interior of the joint may be displayed. Synchondrosis Sternalis. — The joint between the manu- brium and the body of the sternum is a synchondrosis. The opposing surfaces of bone are covered with a layer of hyaline cartilage, and are united by intermediate fibro-cartilage. The joint is supported by some anterior and posterior longitudinal fibres which are developed in connection with the strong and thick periosteum. The posterior ligament is the stronger of the two. The joint between the body of the sternum and the xiphoid process is also a synchondrosis till middle life, at which period the two parts become ossified together. Sterno-chondral Articulations. — Seven ribs articulate with each side of the sternum by means of their cartilages. The articulations of the first and the sixth are peculiar, inasmuch as they articulate with single pieces of the sternum, viz. with the manubrium and the lowest piece of the body, respectively ; whereas each of the cartilages of the other true ribs articulates with two segments of the sternum. The cartilage of the first rib is implanted upon the side of the manubrium THORACIC JOINTS 113 without any synovial membrane, or other material, intervening. The second costal cartilage is usually separated from the sternum by two synovial cavities, between which an interarticular ligament is developed. In the case of the other joints it is more common to find a single synovial cavity and no interarticular ligament. There is, however, considerable variety in these articulations, and a synovial membrane is very frequently wanting altogether in the sterno-chondral joint of the seventh costal cartilage. With the exception of the first, which is a synchondrosis, the sterno-chondral joints belong to the diarthrodial variety. They are provided with anterior and posterior ligaments, and also, in those cases where the joint presents a double synovial cavity, with an interarticular ligament. A?itenor and posterior ster?io-costal radiate ligaments. These are strong, flattened bands of fibres which radiate from the extremities of the rib-cartilages and blend with the periosteum on the anterior and posterior surfaces of the sternum. The intera7iicular liga?nejits are feeble bands which pass from the tips of'the rib-cartilages to the sternum, and divide the articu- lations in which they exist into an upper and a lower com- partment, each of which is lined with a synovial stratum. Inter-cliondral Articulations. — Interchondral joints are formed between the adjacent margins of the ribs from the sixth to the tenth. The joint cavities are surrounded by ordinary capsular ligaments, each of which is lined internally with a synovial stratum ; they are, therefore, diarthrodial joints. Costo-vertebral Articulations. — The costo-vertebral joints are separable into two groups, capitular and costo-transverse. The capitular articulations are the joints between the heads of the ribs and the bodies of the vertebras and the interverte- bral fibro-cartilages ; they are diarthrodial joints. With the exceptions of the first and the last three ribs, the head of every rib articulates with the bodies of two adjacent vertebrae and the intervening intervertebral . fibro-cartilage, and it is connected with them by an articular capsule and an inter- articular ligament. The interarticular ligament connects the intervertebral fibro-cartilage with the ridge which separates the two facets on the head of the rib. It is united, anteriorly and posteriorly, with the capsule, and separates the joint cavity into an upper and a lower compartment. The anterior part of the capsule is specialised into three radiating bands which form the 7-adiate ligament. The upper and lower bands go VOL. II S 114 THORAX to the corresponding vertebrae, whilst the intermediate band is attached to the intervertebral fibro-cartilage. The capitular joints of the first, and the tenth, eleventh, and twelfth ribs are each formed between the head of the rib and the correspond- ing vertebra. The interarticular ligament is absent; therefore each joint possesses only one cavity. The anterior parts of the capsules of these joints are not, as a rule, specialised into radiate bands. The Costo-transverse Articulations are the joints formed Anterior longitudinal ligament Rib Three slips I of radiate-! ^ ligament I ^ Anterior costo-transverse ligament Fig. 54. — Anterior aspect of the Costo-vertebral Joints ; also Anterior Longitudinal Ligament of Vertebral Column. between the necks and the tubercles of the ribs and the trans- verse processes of the vertebrae. The tubercle of each rib, with the exception of the eleventh and twelfth, articulates with the tip of the transverse process of the vertebra of the same number, by a circular articular facet which is surrounded by an articular capsule lined with a stratum synoviale. The joint is, therefore, a diar- throdial joint and the upper and posterior part of the capsule is greatly thickened, and is called the ligament of the tubercle (O.T. posterior costo-transverse Ugameni). In addition to the capsule and its posterior thickening there are three accessory THORACIC JOINTS 115 costo-transverse bands, the anterior and posterior costo-trans- verse ligaments and the Ugament of the neck of the rib. The anterior costo - transverse ligament ascends from the anterior margin of the upper border of the neck of the rib to the lower border of the transverse process above. The posterior costo-transverse ligament passes upwards from the posterior part of the upper border of the neck of the rib to the junction of the lamina and the transverse process of the vertebra above ; and the ligament of the neck of the rib (O.T. middle costo-transverse ligament^ connects the posterior aspect of the neck of the rib with the anterior aspect of the transverse process of the vertebra of the same number. In the case of the eleventh rib the costo-transverse hga- ments are rudimentary or absent, and in the case of the twelfth rib they are usually entirely absent. Intervertebral Articulations. — The bodies of the vertebrae are held together by a series of synchondrodial joints, sup- ported anteriorly by an anterior longitudinal ligament, and posteriorly by a posterior longitudinal ligament. The vertebral arches^ by means of the articular processes, form a series of diarthrodial joints surrounded by capsular ligaments, each capsule being lined with a synovial stratum. Certain ligaments pass between different portions of the vertebral arches and their processes, viz., the ligamenta flava between adjacent laminae, the inter-transverse, the inter-spinous, and the supra-spinous ligaments. The laminae and the spinous processes of the vertebrae have been removed by the dissector of the head and neck in opening up the vertebral canal to display the spinal medulla. Consequently, the ligamenta flava, the inter-spinous and supra-spinous ligaments, cannot be seen at present. The anterior longitudinal liga?}ie?it (O.T. a?iterior common Ugament) is situated anterior to the bodies of the vertebrae, and extends from the atlas vertebra above to the first piece of the sacrum below. It consists of stout glistening fibrous bands, which are firmly attached to the margins of the verte- bral bodies and to the intervertebral fibro-cartilages. The most superficial fibres are the longest, and extend from a given vertebra to the fourth or fifth below it. The deeper fibres have a shorter course, and pass between the borders of two, three, or four adjacent vertebrae. The dissector cannot fail to notice that the origin of the longus colli muscle is inseparably connected w^ith this ligament. II — 8 a ii6 THORAX Root of arch (cut) (O.T. pedicle) Posterior longitudinal ligament The posterior longitudinal ligament (O.T. posterior co7nmon ligament) is placed on the posterior aspects of the vertebral bodies, and therefore within the vertebral canal. It is firmly connected to the margins of the vertebral bodies and to the intervertebral fibro-cartilages, but is separated from the central parts of the bodies by some loose connective tissue and by a plexus of veins. It is constricted where it covers this venous plexus, but widens out opposite the fibro-cartilages. It there- fore presents a scalloped or denticulated appearance. The intervertebral fibro- cartilages are a series of discs of white fibro-car- tilage, thicker anteriorly than posteriorly, which are interposed between the bodies of adjacent vertebrae. The peripheral part of each disc, annulus fibrosus, is tough and fibrous ; the central portion, nucleus pulposus, is soft and pulpy. The discs increase the elasticity of the spine, and tend to restore it to its natural curvature after it has been deflected by muscular action. The intervertebral fibro - cartilages constitute the main bond of union between the bodies of the vertebrae, but, except in old people, they are not directly attached to the bone. A thin layer of en- crusting hyaline cartilage coats the opposing vertebral surfaces. Vertical and horizontal sections must be made through two or more of the fibro-cartilages, in order that their structure may be displayed. The intertransverse ligaments are feeble bands which pass between the tips of the transverse processes. In the lower part of the thoracic region they are intimately blended with the intertransverse muscles : in the middle and upper parts of the thoracic region they entirely replace the muscles. Inter- vertebral fibro- cartilage Fig. 55. — Posterior Longitudinal Liga- ment of the Vertebral Column. The vertebral arches have been removed from the vertebras. FACE AND FRONTAL REGION OF HEAD 117 HEAD AND NECK. The dissectors of the Head and Neck begin work as soon as the subject is brought into the room. During the first three days, whilst the body is in the lithotomy posture, they dissect the face, the anterior part of the eyelids, the superficial part of the nose, and the anterior part of the scalp. During the following five days, when the body is lying on its back, they dissect the posterior triangle, and complete the dissection of the scalp. It is only by dissecting the face at this period, whilst the parts are in good condition, that the dissector can gain any satisfactory idea of its component parts ; and it is essential that the contents of the posterior triangle, which is such an important surgical region, should be displayed before the dissector of the arm has disturbed its posterior boundary. The first day should be devoted to the examination of the anterior part of the frontal region of the head and the face, the study of the surface anatomy of the ocular appendages, the reflection of the skin, and the clean- ing of the superficial muscles of the face and anterior part of the scalp. On the second day the dissectors should display the superficial surface of the parotid gland ; they should also find and clean the superficial vessels and nerves, and trace them to their terminations. On the third day the superficial muscles must be reflected, and the deeper vessels and nerves must be exposed and cleaned, and the auricle should be examined and dissected. On the fourth day, when the body has been placed upon its back, the dissectors should commence the dissection of the posterior triangle of the neck, and should complete that part of the dissection in three days. On the seventh day they should complete the examination of the scalp. The eighth day should be devoted to a final study of the brachial plexus in association with the dissectors of the upper extremity. FACE AND FRONTAL REGION OF HEAD. The dissectors should commence the study of the face and frontal region by an examination of the bony prominences and ridges in the area to be dissected. In the centre of the facial area is the prominent outer portion of the nose, consisting of a lower mobile part formed mainly by skin and cartilage, and an upper rigid portion formed by the nasal bones and the frontal processes of ii8 HEAD AND NECK the maxillge. On either side of the nose are the sockets for the eyeballs, each of which is bounded above by the supra-orbital margin of the frontal bone and below by the orbital margins of the maxilla and the zygomatic bone (O.T. malar). The supra- and infra-orbital margins meet laterally in the region of the cheek bone (zygomatic). From the posterior part of the zygomatic bone, the zygomatic arch, formed partly by the zygomatic and partly by the temporal bone, extends posteriorly to the ear. Above the zygomatic arch is the region of the temporal fossa, which is bounded superiorly by the temporal line. The line terminates anteriorly in the lateral part of the supra-orbital margin. Above the medial part of the supra-orbital margin the superciliary arch can be felt, and at a higher level, above the lateral part of the supra-orbital margin, lies the frontal tuber. The region above the nose and between the medial ends of the superciliary arches is the glabella. Below the zygomatic arch lies the ramus of the mandible covered by the masseter muscle ; and extending anteriorly from the lower end of the ramus is the body of the mandible. A line dropped vertically through the junction of the medial third with the lateral tw^o-thirds of the supra-orbital margin, will cut through the supra-orbital notch of the frontal bone, the infra-orbital foramen of the maxilla, and the mental foramen of the mandible, all three of which may be felt if firm pressure is made in the proper situations. The first, which lies in the supra-orbital margin, transmits the supra-orbital vessels and nerve. The second is placed about half an inch below the infra-orbital margin. It transmits the infra-orbital vessels and nerve. The third lies midway between the second premolar tooth of the mandible and the lower border of the mandible ; it transmits the mental branches of the inferior alveolar vessels and nerve. After the bony points of the region have been studied, the surface anatomy of the ocular appendages should be examined. Under this head are included (i) the eyebrows; (2) the eyelids; (3) the conjunctiva. The eyebrows are two curved tegumentary projections placed over the supra-orbital arch of the frontal bone ; they intervene between the forehead above and the ocular regions below. The short stiff hairs which spring from the eyebrows have a lateral inclination. FACE AND FRONTAL REGION OF HEAD 119 The eyelids (palpebrae) are the semilunar curtains provided for the protection of each eyeball. The upper lid is the longer and much the more movable of the two. When the eye is open, the margins of the two lids are slightly concave and the interval between them, riJiia palpebrarum^ is elliptical in outline. When the eye is closed, and the margins of the lids are in apposition, the rima palpebrarum is reduced to a ^Margin of the upper eye- lid with openings of ducts of tarsal glands Papilla lacrimalis with punctum lacrimale on the summit Plica semilunaris Caruncula lacrimalis Papilla lacrimalis — Opening of tarsal glands Tarsal glands shining through the conjunctiva Fig. 56.— Eyelid slightly everted to show the Conjunctiva (enlarged). nearly horizontal line. Owing to the greater length and mobility of the upper Hd, the rima, in this condition, is placed below the level of the cornea or clear part of the eyeball. At the extremities of the rima palpebrarum the eyelids meet and form the palpebral co7nmissures, and immediately lateral to the medial commissure the rima expands into a small triangular space called the lams lacrifnalis. If the dissector now examines the free margins of the Uds he will note that to the lateral side of the lacus lacrimalis they I20 HEAD AND NECK are flat, and that in each case the eyelashes project from the anterior border, whilst the tarsal glands open along the posterior border, a distinct interval intervening between the cilia and the mouths of the glands. On the other hand, the small portion of the margin of each eyelid which bounds the lacus lacrimalis is more horizontal in direction, somewhat rounded, and destitute both of eyelashes and of tarsal glands. At the very point where the eyelashes in each eyelid cease, and the palpebral margin becomes rounded, a minute emi- nence with a central perforation will be seen. The eminence is the papilla lacrimalis^ whilst the perforation, called the punctum lacrimale, is the mouth of the lacrimal duct, which conveys away . the tears. Endeavour to pass a bristle into each of the orifices. The upper duct at first ascends, whilst the lower one descends, and then both run horizontally to the lacrimal sac. The conjunctiva is the membrane which lines the deep surfaces of the lids, and is reflected from them on to the anterior aspect of the eyeball. At the margins of the lids it is continuous with the skin, whilst, through the puncta lacri- malia and the lacrimal ducts, it becomes continuous with the lining membrane of the lacrimal sac. The line of re- flection of the conjunctiva from the lids on to the eyeball is termed the fornix conjunctiv(B. Owing to the greater depth of the upper lid, the conjunctival recess between the upper lid and the eyeball is of greater extent than that of the lower lid. The conjunctiva is loosely connected with the eyelids on the one hand, and with the sclera of the eyeball on the other. Over the cornea the membrane becomes thinned down to a mere epithelial covering, which is closely adherent. In connection with the conjunctiva, the plica semilunaris and the caruncula lacrimalis must be examined. The caruncula is the reddish fleshy -looking elevation which occupies the centre of the lacus lacrimalis. From its surface a few minute hairs project. The plica semilunaris is of interest because in the human eye it is the rudimentary representative of the membrana nictitans, or third eyelid, found in many animals. It is a small vertical fold of conjunctiva, which is placed immediately to the lateral side of the caruncula, and it slightly overlaps the eyeball at this point. Dissection. — Distend the eyelids slightly by placing a little tow or cotton wool steeped in preservative solution in the conjunctival sac ; then stitch FACE AND FRONTAL REGION OF HEAD 121 the margins of the lids together. Distend the cheeks and lips slightly by placing tow or cotton wool steeped in preservative solution in the vestibule of the mouth— that is, between the cheeks and lips externally and the teeth and gums internally ; then stitch the red margins of the lips together. Reflect the skin by means of three incisions, a median longitudinal and two transverse. Commence the median incision midway between the root of the nose and the external occipital protuberance, carry it anteriorly to the forehead and then downwards along the median line of the forehead, the nose and the lips, to the tip of the chin. Commence the upper horizontal incision at the level of the rima palpebrarum ; carry it laterally from the longitudinal incision to the medial commissure, then round the margins of the rima to the lateral commissure, and, finally, posteriorly to the ear. The lower horizontal incision should run from the angle of the mouth to the posterior border of the ramus of the mandible. Reflect the upper and middle flaps and leave them attached posteriorly. Reflect the lower flap downwards to the lower border of the mandible. Note, whilst reflecting the skin, that many of the superficial fibres of the facial muscles are implanted into its deep surface. It is these fibres which tend to displace the margins of wounds of the face, and necessitate the application of numerous and firmly tied sutures in order to secure quick and accurate union. Whilst reflecting the skin the dissector must be careful to keep his knife playing against its deep surface ; otherwise he is certain to injure the sphincter muscle of the eyelids, and the superficial extrinsic muscles of the ear which lie in the temporal region. After the skin is reflected the superficial muscles must be cleaned. That which will first attract attention is the orbicu- laris oculi around the orbit. Above the orbicularis oculi is the frontalis belly of the epicranial muscle. To the medial side of the orbicularis oculi Ue the muscles of the nose, and below it the muscles of the upper lip pass downwards to the orbicularis oris. Passing anteriorly and upwards, over the posterior part of the lower border of the mandible, are the upper and posterior fibres of the platysma, and more medially are the muscles of the lower lip. Commence with the Orbicularis Oculi (O.T. Orbicularis Palpebrarum). — Pull the eyelids laterally and note a prominent cord-like band which extends from the frontal process of the maxilla to the medial commissure, where it becomes continuous with both eyeUds ; this is the medial palpebral ligament (O.T. internal tarsal ligament). A somewhat similar band, the lateral palpebral raphe (O.T. external tarsal ligament), extends from the lateral commissure to the zygomatic bone. After the medial palpebral ligament has been recognised, clean first the thicker orbital part of the orbicularis oculi, which covers the superficial bony boundaries of the orbit, and then the thinner palpebral portion, which lies in the eyelids. The palpebral part is not only thin but also pale, and its fibres, in 1 122 HEAD AND NECK each eyelid, sweep in gentle curves from the medial palpebral ligament to the lateral palpebral raphe, gaining attachment to both. They form a continuous layer of uniform thickness in each eyelid, except near the free margins, where, close to the bases of the eyelashes, there is a more pronounced fasciculus termed the ciliary bundle. The orbital portion of the muscle passes upwards to the forehead, laterally to the temporal region and downwards into the cheek. Its fibres are relatively dark and coarse. They all take origin medially from the medial part of the palpebral ligament, the medial angular process of the frontal bone, and the frontal process of the maxilla, and they sweep laterally round the margin of the orbit in the form of a series of con- centric loops. The pars lacrimalis of the orbicularis oculi (O.T. tensor tarsi) will be described when the eyelids are dissected (p. 140). Musculus Epicranius (O.T. Occipito - Frontalis). — The epicranius is a quadricipital muscle possessing two occipital heads, the occipitales muscles, and two frontal heads, the frontales muscles ; they are all inserted into an intermediate aponeurosis, the galea aponeurotica (O.T. epicranial aponeur- osis)^ which extends from the frontal to the occipital region (p. 158). The lower part of each frontal head blends with the orbicularis oculi, and from its medial border a small muscular bundle, known as the ?nusculus procerus (O.T. pyrafnidalis nasi\ descends to the dorsum of the nose. At present only the frontaUs and the procerus are to be displayed. The Frontalis becomes apparent immediately above the upper border of the orbicularis oculi. As it is cleaned care should be taken to avoid injury to the branches of the supra- orbital nerve which pierce it. It has little or no attachment to bone. Below, its fibres either blend with the fibres of the orbicularis oculi or they are attached to the skin of the eye- brows. Above, they terminate in the galea aponeurotica in the region of the coronal suture. The lateral border is attached to the temporal ridge by aponeurotic fibres, and the medial border blends with its fellow of the opposite side for a short distance above the root of the nose. Above the union the medial fibres of opposite sides diverge, and below it they pass downwards over the nasal bones as the proceral muscles. Musculus Procerus (O.T. Pyramidalis Nasi). — The proceral muscles are often absent; when present, each springs from FACE x\ND FRONTAL REGION OF HEAD 123 the lower and medial part of the corresponding frontalis. It descends over the nasal bone and ends on the dorsum of the nose, where some of its fibres blend with the trans- verse part of the nasalis and others are inserted into the skin. Along the lower and medial border of the orbicularis oculi will be found the muscles of the nose and the upper lip. The proper muscles of the nose are the musculus nasalis and the musculus depressor septi, but the procerus may also be looked upon as partly a nasal muscle, and the angular head of the quadratus labii superioris has a nasal attachment. Musculus Nasalis. — The musculus nasaUs consists of two parts, the pars transversa (O.T. co?7ipressor ?iaris), and the pars alaris (O.T. dilator ?taris). The pars transversa springs from the root of the frontal process of the maxilla, passes across the cartilaginous part of the nose, above the ala, and ends in an aponeurosis which connects it with its fellow of the opposite side. The pars alaris springs from the maxilla, at the side of the lower part of the anterior nasal aperture, and it terminates in the posterior part of the ala and the mobile part of the septum of the nose. The nasalis is partly concealed by the medial fibres of the quadratus labii superioris. Musculus Depressor Septi Nasi. — This small muscle is frequently difficult to display. It springs from the superficial fibres of the upper part of the orbicularis oris, and is inserted into the anterior part of the septum of the nose. It depresses the septum and reduces the anteroposterior diameter of the anterior nasal aperture. After the muscles of the nose have been examined clean the superficial muscles of the mouth and cheek. The Muscles of the Mouth and Cheeks. — The muscles of this group form two layers, a superficial and a deep. Those of the superficial group are the orbicularis oris, quadratus labii superioris, zygomaticus, triangularis, risorius, quadratus labii inferioris ; those of the deeper group are the buccinator, caninus, incisivi and mentalis. x\ll, with the exception of the orbicularis oris, are bilateral. The members of the superficial group must be examined first ; the deeper muscles will be displayed after the superficial vessels and nerves have been dissected. Orbicularis Oris. — The orbicularis oris is the sphincter muscle of the oral aperture. It lies in the substance of the lips, and consists of a deeper layer of fibres which are arranged 124 HEAD AND NECK in concentric ellipsoidal rings, and a series of superficial fibres into which all the other muscles of the lips and cheeks con- verge. The details of its formation cannot be understood until the attachments of the other muscles have been studied. Frontalis Orbicularis oculi Procerus M. quadratus labil superioris angular head M. nasalis pars transversa M. quadratus labii superioris infra-orbital head M. zygomaticub M. caninu Risorius Orbicularis oris Orbicularis oris quadratus labii inferioris ^ Platysma Fig. 57. — The Facial Muscles. Musculus Quadratus Labii Superioris. — The quadratus labii superioris possesses three heads — a zygomatic, an infra- orbital, and an angular. As the muscle is cleaned the dissector should secure the upper part of the anterior facial vein, which crosses its superficial surface. FACE AND FRONTAL REGION OF HEAD 125 The zygomatic head (O.T. zygomaticiis minor) springs from the anterior part of the facial surface of the zygomatic bone, under cover of the lower lateral part of the orbicularis oculi. It runs downwards and anteriorly, and is inserted into the lateral part of the upper portion of the orbicularis oris and into the adjacent part of the skin of the upper lip. TJu Infra-orbital Head (O.T. Levator Labii Superior is Proprius). — This head springs from the whole length of the infra-orbital border, under cover of the orbicularis oculi. It is inserted into the upper lateral part of the orbicularis oris and the skin of the upper lip. The angular head (O.T. levator labii superioris alcEque nasi) springs from the frontal process of the maxilla. It broadens as it descends,, and it is inserted into the ala of the nose and into the upper part of the orbicularis oris. Musculus Zygomaticus. — The zygomaticus (O.T. zygo- maticus major) is a comparatively long, slender muscular band which springs from the facial surface of the zygomatic bone, under cover of the lower lateral fibres of the orbicularis oculi and to the lateral side of the zygomatic head of the quadratus labii superioris. Its fibres pass downwards and medially to the angle of the mouth, where some blend with the orbicularis oris and others are inserted into the skin. The Risorius. — This muscle, when well developed, consists partly of some of the uppermost fibres of the platysma muscle of the neck, which bend anteriorly to the angle of the mouth, and partly of additional fibres which spring from the fascia over the masseter muscle and the parotid gland. Both groups of fibres blend with the fibres of the orbicularis oris at the angle of the mouth. Musculus Triangularis. — The triangularis (O.T. depressor anguli oris) springs from the oblique line on the lateral surface of the body of the mandible. Its fibres converge as they pass anteriorly and upwards, and, at the angle of the mouth, they blend with the orbicularis oris, in which some of them curve past the angle and terminate in the substance of the upper lip (Figs. 57, 58). Musculus Quadratus Labii Inferioris (O.T. Depressor Labii Inferioris). — This muscle springs from the lower part of the superficial surface of the mandible, between the mental tubercle and the mental foramen, its posterior border being overlapped by the triangularis. The fibres pass upwards 126 HEAD AND NECK and medially, some to blend with the orbicularis oris and others to gain attachment to the skin of the lower lip. ' Platysma. — Only the upper part of the broad, flat, quadrangular subcutaneous muscle of the neck is at present visible. The posterior fibres ascend over the lower border of the ramus and the posterior part of the lower border of the body of the mandible, and they have already been seen taking part in the formation of the risorius. The anterior fibres gain direct insertion into the anterior part of the lower M. quadratus labii superloris caput angulare M. quadratus labii superioris caput infraorbitale M. caninus M. triangularis M. quadratus labii inferioris Fig. 58. — Diagram of the Orbicularis Oris Muscle. The fibres which enter it from the buccinator are not represented. border of the body of the mandible. The latter attach- ment is the only bony attachment which the muscle possesses, all its other attachments being either to fascia or to skin. Dissection. — Cut through the posterior half of the platysma along the lower border of the mandible ; detach the risorius from the fascia on the masseter ; then turn the risorius and the detached part of the platysma towards the angle of the mouth. Whilst doing this be careful to avoid injuring the branches of the vessels and nerves of the face. As soon as the platysma and the risorius are reflected search below the level of the ear for branches of the great auricular nerve which ascend over the lower part of the parotid gland. Some of them pierce the parotid and terminate in its substance, others end in the skin of the masseteric region. Find the anterior facial vein and the external maxillary artery at the FACE AND FRONTAL REGION OF HEAD 127 lower and anterior angle of the masseter as they cross the lower border of the mandible. Clean them at this point, but do not trace them towards their terminations at present. At the posterior border of the mandible note the fascia over the super- ficial surface of the parotid gland. It ascends from the fascia of the neck, and is attached above to the zygomatic arch. Note also that at the anterior border of the parotid this fascia blends with the fascia on the superficial surface of the masseter muscle. Cut through the fascia covering the parotid gland immediately anterior to the ear, extending the incision from the zygoma above to the angle of the mandible below ; then raise the fascia from the gland, dissecting carefully anteriorly, upwards, and down- wards. As the extremities and the anterior border of the gland are approached, look carefully for nerves and vessels which emerge from beneath them, and also for the duct of the gland, which appears from under cover of the anterior border about a finger's breadth below the zygoma. The duct has thick walls, is of considerable size, and is easily re- cognised. It runs anteriorly across the masseter and turns round the anterior border of the muscle, bending at right angles to its original course. It pierces, in turn, the fascia covering the buccinator muscle, the buccinator muscle itself and the mucous membrane of the mouth ; and it opens into the vestibule of the mouth, on a small papilla opposite the second molar tooth of the maxilla. Above the duct and below the zygomatic arch find (i) the accessory parotid, a small detached part of the parotid which lies a short distance anterior to the anterior border of the main mass of the gland ; (2) the transverse facial vessels ; and (3) the zygomatic branches of the facial nerve. Below the duct find the buccal and the mandibular branches of the facial nerve. At the upper end of the parotid seek for the superficial temporal vessels. Posterior to them lies the auriculo- temporal branch of the third division of the trigeminal nerve, and an- terior to them, the temporal branches of the facial nerve. From, or from beneath, the lower extremity of the gland emerge (i) the cervical branch of the facial nerve, (2) the posterior facial vein (O.T. anterior division of the temporo-maxillary vein), and (3) the external jugular vein. The Terminal Branches of the Facial Nerve. — The dis- sector should note that there are five terminal branches, or groups of branches, of the facial nerve: (i) temporal; (2) zygomatic; (3) buccal; (4) mandibular; (5) cervical. They all emerge from under cover of the parotid gland, the temporal branches at its upper end, the cervical at its lower end, and the remaining three groups of branches at its anterior border. The temporal branches will be followed when the temporal region and the scalp are being dissected, and the cervical branch when the anterior triangle of the neck is displayed ; but the remaining three groups of branches should now be followed to their terminations. The upper filaments of the zygomatic branch or- bra?2ches run anteriorly, across the zygomatic bone, and terminate, in both the upper and the lower eyelid, in the fibres of the orbi- cularis oculi. If the branches are carefully traced, one of them will be found to communicate with the zygomatico- 128 HEAD AND NECK facial branch of the second or maxillary division of the fifth nerve. This small nerve pierces the zygomatic bone a short distance below the lateral border of the orbit. The lower filaments are larger. They run anteriorly along the lower border of the zygomatic arch, under cover of the musculus zygomaticus and the infra-orbital part of the Supra-orbital Zygomat ico -temporal Y^Supra-trochlear Lacrimal Infra-trochlear , — External nasal Infra-orbital Mental Zygomatico- facial ^uriculo-temporal Posterior auricular Trunk of facial Branch to posterior belly of digastric and stylo-hyoid Buccinator Fig. 59- — Nerves of the Face. The facial nerve is depicted in yellow, the sensory branches of the trigeminal in black, I. Temporal branches. 4. Buccal branch. 2 and 3. Zygomatic branches. 5. Mandibular branch. 6. Cervical branch. quadratus labii superioris, and deep to the latter they com- municate with the infra-orbital branch of the maxillary division of the fifth nerve, forming with it the i7ifra-07'bital plexus. The buccal branch or branchts run towards the angle of the mouth. At the anterior border of the masseter they com- municate, around the anterior facial vein, with the buccinator branch (O.T. jlong buccal) of the third division of the fifth, and they supply the buccinator and the orbicularis oris. Dissection. — ^In order to trace the branches to their terminations and to display fully the infra-orbital plexus, cut through the musculus zygomaticus FACE AND FRONTAL REGION OF HEAD 129 and the quadratus lahii superioris immediately below their origins, and turn them downwards towards the upper lip. When this has been done, clear away the fatty tissue which lies on the deep aspect of the quadratus labii superioris and secure the infra-orbital vessels and nerve, as they emerge from the infra-orbital foramen. The infra-orbital plexus lies deep to the quadratus labii superioris, and on the superficial aspect of the musculus caninus. From the plexus three groups of branches are distributed : (i) palpebral, which pass upwards to the lower eyelid ; (2) nasal, which run medially to the nose ; and (3) labial, which descend to the upper lip. Either by means of these branches, or. more directly, the lower zygomatic twigs of the facial nerve are distributed to the musculus zygomaticus, the muscles of the lower eyelid, muscles of the nose, and the muscles of the upper lip. The mandibular branch or branches run anteriorly along the mandible to be distributed to the muscles of the lower lip. As they pass anteriorly they lie deep to the triangularis, and they communicate, under cover of it, with the mental branch of the inferior alveolar (O.T. dental) nerve. To display this communication the triangularis must be reflected, and the mental vessels and nerves must be found as they emerge from the mental foramen. Arteria Maxillaris Externa (O.T. Facial). — The ex- ternal maxillary artery is a tortuous vessel which enters the face at the lower and anterior angle of the masseter, after turning round the lower border of the mandible and piercing the deep fascia of the neck. From that point it runs anteriorly and upwards to the angle of the mouth and then, assuming a more vertical direction, it is prolonged upwards, as the angular artery, to the medial commissure of the eyelids, in the substance of the angular head of the quadratus labii superioris. Immediately after its entrance into the face it is comparatively superficial, being covered by skin, super- ficial fascia, and platysma, and it is easily compressed against the bone. More anteriorly it lies between the zygomaticus superficially and the buccinator deeply, then between the quadratus labii superioris and the caninus, and, as already stated, its terminal part is usually embedded in the substance of the quadratus labii superioris. Branches. — The branches of the external maxillary artery form two groups, a posterior and an anterior. The branches of the posterior group pass posteriorly and are of small size. They are distributed to the masseteric, buccal, and malar regions where they anastomose with the transverse facial, the buccinator, and the infra-orbital arteries. The branches of the anterior group run anteriorly and re- VOL. II — 9 I30 HEAD AND NECK ceive special names : they are the inferior labial, the superior labial, the lateral nasal, and the angular continuation. The ijiferior labial (O.T. inferior coronary) arises below the level of the angle of the mouth and passes towards the Superficial temporal Frontal branch of ophthalmic artery Supra-orbital branch of ophthalmic artery Middle temporal Transverse facial Angular Lateral nasal Infra-orbital Superior labial S®^)^ Inferior labial A -,^ ^^J inferior labial.) See p. 131 i'luccinator branch of internal maxillary External maxillary Fig. 60. — Arteries of the Face. median plane, under cover of the triangularis, the quadratus labii inferioris, and the orbicularis oris. In the substance of the lip it lies immediately adjacent to the mucous membrane, and it anastomoses in the median plane with its fellow of the opposite side. The superior labial arises about the level of the angle FACE AND FRONTAL REGION OF HEAD 131 of the mouth and runs medially in the upper lip, between the orbicularis oris and the mucous membrane. Before it anastomoses with its fellow of the opposite side, it gives off a branch, the septal artery of the nose, which passes upwards and ramifies on the lower and anterior part of the nasal septum, where it anastomoses with the septal branch of the spheno- palatine artery. The Angular Artery. — This is the continuation of the external maxillary beyond the point of origin of the lateral nasal branch. It runs upwards in the substance of the angular head of the quadratus labii superioris, and it terminates at the medial commissure of the eye by anastomos- ing with the nasal branch of the ophthalmic. The lateral ?iasal branch springs from the external maxillary at the point where it becomes the angular. It ramifies on the side of the nose and anastomoses in the median plane with its fellow of the opposite side. In addition to the branches already noted, a very definite branch is usually given off from the anterior aspect of the external maxillary artery immediately after it crosses the lower border of the mandible. This branch (O.T. inferior labial) runs towards the median plane under cover of the triangularis and the depressor labii inferioris, and it anasto- moses not only with the inferior labial (O.T. inferior coronary) above, and its fellow^ of the opposite side in the median plane, but also with the mental branch of the inferior alveolar artery. Vena Facialis Anterior (O.T. Facial). — The anterior facial vein is a less tortuous vessel than the external maxillary artery to w4iich it corresponds, and it lies posterior, and on a slightly more superficial plane. • It commences as the a?igular vein, which is formed at the medial commissure of the eyelids, by the union of the frontal and supra-orbital veins, which descend from the forehead. It passes down- wards and posteriorly, in a comparatively straight line, to the anterior inferior angle of the masseter, which it crosses immediately behind the external maxillary artery; then it pierces the deep fascia of the neck, and enters the sub- maxillary triangle. In the upper part of the face it lies on the quadratus labii superioris ; then it is situated between the zygomaticus and the risorius superficially and the buccinator deeply ; and as it crosses the anterior angle of the masseter it is covered with the skin, superficial fascia, and the platysma, II — 9 a 132 HEAD AND NECK Tributaries. — In addition to the frontal and supra-orbital veins, it receives external nasal, palpebral, superior liabial, inferior labial, masseteric and superficial parotid tributaries. As it crosses the buccinator muscle it is joined by the deep facial vein, which connects it with the pterygoid plexus of veins in the infra-temporal region. Dissection. — After the branches of the facial nerve, the external maxillary artery and the anterior facial vein have been studied, the dissection of the deeper muscles and the deeper vessels and nerves must be proceeded with ; but the supra-orbital and supra-trochlear nerves, the supra-orbital vessels, and >the corrugator supercilii muscle may be left till the scalp is dissected (p. 156). Musculus Caninus (O.T. Levator Anguli Oris). — The caninus is concealed by the lower part of the orbicularis oculi, the quadratus labii superioris, and the zygomaticus, and it is crossed superficially, near the angle of the mouth, by the external maxillary artery. When the structures superficial to it are turned aside, the muscle will be found springing from the canine fossa below the infra-orbital foramen. It passes downwards to the angle of the mouth, where it blends with the orbicularis oris, some of its fibres passing into the lower lip (Fig. 57). It is an elevator of the angle of the mouth. The Buccinator. — This muscle occupies the interval between the upper and the lower jaws and forms a most important part of the substance of the cheek. Above, it springs from the alveolar border of the maxilla, in the region of the molar teeth. Below, it arises from the alveolar border of the mandible, also in the region of the molar teeth, and, posteriorly, it is attached to the pterygo- mandibular raphe, which forms a bond of union between the buccinator and the superior constrictor of the pharynx. This attachment will be seen to better advantage when the wall of the pharynx is studied (p. 373). Anteriorly, its fibres converge towards the angle of the mouth, where they blend with the orbicularis oris, of which they form a large part. The manner in which the fibres enter the orbicularis must be carefully noted. The upper and lower fibres pass directly to the corresponding lips ; the middle fibres, on the other hand, decussate at the angle of the mouth, so that the lower fibres of the series enter the upper lip, whilst the higher fasciculi reach the lower lip (Fig. 61). The Molar Glands. — The buccinator is covered posteriorly FACE AND FRONTAL REGION OF HEAD 133 by a pad of fat, the suctorial pad, and by a strong layer of fascia which must be carefully removed. As this is being done the dissector will find; both superficial and deep to the fascia, a number of small glands, the molar salivary glands. The ducts of these glands pierce the buccinator and open into the vestibule of the mouth. One or two buccal lymph gkmds also are sometimes found resting on the super- ficial surface of the buccinator. Dissection. — After the dissection of the buccinator and the molar glands is completed, remove the stitches from the lips ; evert the lips and dissect the mucous membrane from the deep surfaces, in order to expose the muscular sHps which attach the orbicularis oris to the alveolar margins of the upper and the lower jaws, and to display the mentalis muscle. As the lips are everted the dissector should note that a fold of mucous membrane, the fremduni iabii, passes from each lip to the gum of the corresponding jaw in Fig. 61. — Arrangement of the Fibres of the Buccinator Muscle at the Angles of the Mouth. the median plane ; and as the mucous membrane is removed a number-'of small labial salivary glands, which lie in the submucous tissue, w^ill be seen. They are readily felt in the living subject by pressing the tip of the tongue against the inner surfaces of the lips. Musculi Incisivi Labii Superioris et Inferioris. — These are four small muscular bundles, two upper and two lower, which attach the deeper part of the orbicularis oris to the alveolar margins of the jaws in the regions of the upper and lower lateral incisor teeth. Musculus Mentalis. — When the incisive muscles of the lower jaw are detached from the bone and the lower lip is further everted, a distinct muscular bundle will be found on each side, springing from the outer surface of the socket of the canine tooth, under cover of the quadratus labii inferioris. The two bundles converge and blend together, between the medial borders of the musculi quadrati labii inferioris, to form a single bundle which is inserted into the skin of the chin. It is an elevator of the skin of the chin. II— 9 & 134 HEAD AND NECK Nervus Buccinatorius (O.T. Long Buccal). — This nerve is a branch of the third division of the trigeminal nerve. It passes anteriorly into the cheek from under cover of the ramus of the mandible. It is a sensory nerve, and it supplies branches to the skin on the outer surface and the mucous membrane on the inner surface of the buccinator muscle. In order to display it at the present stage it may be necessary to make an antero-posterior incision through the middle of the anterior border of the masseter. Eyelids. — The following strata will be exposed in each eyelid as the dissection is carried from the surface towards the conjunctiva. Upper Lid. Lower Lid. I. Integument. I. Integument. 2. Palpebral part of the orbicularis 2. Palpebral part of the orbicularis oculi. oculi. 3. The tarsus, the palpebral fascia, and the expanded ten- •3- The tarsus and the palpebral fascia. don of the levator palpebroe supenoris. 4. Conjunctiva. 4- Conjunctiva. In addition to these structures, two ligamentous bands, named the medial palpebral ligament (O.T. internal tarsal ligament) and the lateral palpebral raphe (O.T. external tarsal ligament), will be noticed. They attach the tarsi to the medial and lateral margins of the orbit. Integument and Orbicularis Oculi. — These strata have been examined already, and the skin has been reflected. Dissedioit. — Separate the palpebral part of the orbicularis oculi from the remainder by a circular incision ; turn the palpebral part towards the rima palpebrarum, and take care, whilst raising the muscle fibres, to preserve the palpebral vessels and nerves, and at the same time to avoid injury to the palpebral fascia. As the dissection is completed the origin of the muscle from the medial palpebral ligament (p. 121) will be displayed. Tarsi. — The removal of the palpebral part of the orbicularis oculi brings into view the palpebral fascia and the tarsi. These lie in the same morphological plane, and they constitute the ground-work of the eyelids. The tarsi are two thin plates of condensed fibrous tissue, placed one in each eyelid so as to occupy an area immediately FACE AND FRONTAL REGION OF HEAD 135 adjoining its free margin. They differ very materially from each other. The superior tarsal plate is much the larger of the two, and presents the figure of a half oval. Its deep surface is intimately connected with the subjacent conjunctiva, whilst its superficial surface is clothed by the orbicularis muscle, and is in relation to the roots of the eyelashes. Its superior border is thin, convex, and continuous with a tendinous expansion of the levator palpebrae superioris. The inferior border of the tarsal plate is thickened and straight, and the integument adheres firmly to it. The inferior tarsal plate is a narrow strip which is similarly placed in the lower lid. Glandulae Tarsales (O.T. Meibomian Follicles). — At this stage the student should examine the tarsal glands, which he will display by everting the eyelids. They are placed on the deep surfaces of the tarsi. To the naked eye they appear as closely placed, parallel, yellow granular -looking streaks, which run at right angles to the free margins of the lids. They are more numerous and of greater length in the upper lid, and, being lodged in furrows on the deep surface of the tarsal plates, they are distinctly visible upon both aspects of these, even while the conjunctiva is in position. Their ducts open upon the free margin of each lid posterior to the eyelashes. The Palpebral Fascia. — The palpebral fascia is a sheet of fibrous membrane which occupies the interval between the tarsi and the margins of the orbit, forming, with the tarsi, a septum between the orbit and the exterior. Its peripheral border is attached to the orbital margin, except at the medial angle of the orbit, where it occupies a more posterior plane, and is attached to the crista lacrimalis, posterior to the medial palpebral ligament and the lacrimal sac. Its central border in the lower lid is connected with the lower border of the lower tarsus. In the upper lid it blends with the expanded tendon of the levator palpebrae superioris, and is attached with it to the anterior surface of the upper tarsus. It is pierced by the supra-orbital, supra-trochlear, and lacrimal branches of the first division of the trigeminal nerve, and by the terminal branches of the ophthalmic artery. Raphe Palpebralis Lateralis. — The lateral palpebral raphe (O.T. external tarsal ligament) is merely a thickening of the palpebral fascia, between the lateral commissure and the II— 9 c 136 HEAD AND NECK medial border of the fronto-sphenoidal process of the zygomatic bone (O.T. malar), to which it connects both the tarsi. Ligamentum Palpebrale Mediale (O.T. Internal Tarsal Ligame?if). — The medial palpebral ligament is a strong fibrous band which connects the medial ends of both tarsi to the frontal process of the maxilla. It lies between the skin anteriorly, and the lacrimal sac posteriorly. By its upper and lower borders it gives attachment to fibres of the orbicularis Tendon of levator palpebrae superioris Palpebral fascia Palpebral branch of \ lacrimal nerve Superior tarsus Raphe palpebralis lateralis Palpebral fascia Supra-orbital nerve Supra-trochlear nerve Superciliary arch Infra-trochlear nerve Lacrimal sac !__]_ Ligamentum palpe- bral mediale Inferior tarsus Infra-orbital nerve Fig. 62. — Dissection of the Right Eyehd. The orbicularis palpebrarum has been completely removed. oculi, and by the lateral part of its posterior surface, to the pars lacrimalis of the orbicularis oculi (O.T. tensor tarsi). Levator Palpebrae Superioris. — Only the anterior expanded tendon of this muscle can be seen at the present stage of the dissection, and that, as a rule, in only a partially satisfactory manner. The muscle arises within the orbital cavity, extends forwards to the upper eyelid, and ends in an expanded tendon which splits into three lamellae ; a superior lamella, which blends with the upper part of the palpebral fascia and is attached with it to the anterior surface of the upper tarsus; an intermediate lamella, which is connected with the upper FACE AND FRONTAL REGION OF HEAD 137 border of the upper tarsus; and an inferior lamella, which gains insertion into the upper fornix of the conjunctiva. It raises the upper eyelid by pulling on the upper tarsus, and at the same time elevates the upper fornix of the conjunctiva. Vessels and Nerves of the Eyelids. — At the medial com- missure two arteries, the palpebral branches of the ophthalmic, pierce the palpebral fascia and run laterally, one in the upper and one in the lower lid. At the lateral margin of the orbit, one or more branches of the lacrimal division of the ophthalmic pierce the palpebral fascia and anastomose with Frontal bone M. orbicularis oculi Palpebral fascia Superior conjunctival fornix Superior tarsus Conjunctival recess — Y^- — \ Inferior conjunctival fornix Palpebral fascia^ Fig. 63. — Diagram of the Structure of the EyeHds. the palpebral arteries. An arterial arch, arms iarseus, is thus formed close to the margin of each eyelid, between the orbicularis muscle and the tarsus. The veins run medially towards the root of the nose and open into the frontal and angular veins. The nerves are more numerous and come from a number of different sources. The motor filaments for the various parts of the orbicularis oculi are derived from the temporal, and zygomatic branches of the facial nerve. They enter from the lateral margins. The sensory twigs for the upper lid come from the lacrimal, supra-orbital, supra-trochlear, and infra-trochlear branches of the first or ophthalmic division of the trigeminal nerve; and the lower Ud is supplied by the 138 HEAD AND NECK infra-orbital branch of the second or maxillary division of the fifth nerve. The lacrimal nerve will be found piercing the palpebral fascia near the lateral part of the upper border of the orbit ; the supra-orbital lies in the supra-orbital notch at the junction of the lateral two-thirds with the medial third of the upper border ; and the supra- and infra-trochlear pierce the palpebral fascia at the medial end of the upper border. The branches of the infra-orbital nerve pass to the lower lid in the palpebral branches of the infra-orbital plexus (p. 128). Apparatus Lacrimalis. — The following structures are in- cluded under this head : (i) the lacrimal gland and its ducts ; (2) the conjunctival sac ; (3) the puncta lacrimalia ; (4) the lacrimal ducts ; (5) the lacrimal sac ; (6) the naso-lacrimal duct; (7) the lacrimal part of the orbicularis oculi. Glandula Lacrimalis. — This lies in the upper and lateral part of the orbital cavity under cover of the zygomatic process (O.T. external angular) of the frontal bone. It can be exposed by cutting through the palpebral fascia at the upper and lateral angle of the orbit, and it will be found that the anterior part of the gland projects slightly beyond the orbital margin and rests upon the conjunctiva as the latter is reflected from the lateral part of the upper lid on to the eyeball. If the anterior border of the gland is raised and the point of the knife carried carefully up and down in the fascia under it, several exceedingly fine ducts will be found passing from the gland into the lateral part of the upper fornix of the conjunctiva. The ducts vary in number, and the secretion which they convey, which constitutes the tears, is carried, by the in- voluntary movements of the upper eyehd, over the exposed surface of the eyeball and is directed towards the medial commissure ; there it passes through the puncta lacrimalia into the lacrimal ducts, and is carried by them to the lacrimal sac, whence it passes by the naso-lacrimal duct into the inferior meatus of the nose. Under ordinary circumstances, the amount of lacrimal secretion is merely sufficient for lubrica- tion, and practically the whole of it is evaporated from the surface of the eyeball ; consequently, when the lacrimal ducts and the lacrimal sac are extirpated, a proceeding which is necessary under certain circumstances, the patient suffers little or no inconvenience from the overflow of tears, so long as the secretion is not excessive. If the amount of secretion is greater than can be removed by evaporation, the excess, FACE AND FRONTAL REGION OF HEAD 139 under ordinary circumstances, passes through the pun eta into the ducts and thence through the lacrimal sac and naso- lacrimal duct to the nose ; and if the secretion becomes so abundant that it cannot be removed by evaporation and drainage, part flows through the rima as tears. Lacrimal gland superior part Temporal muscle 'emporal fascia — Excretory ducts 'V Lacrimal glands', lower part V ifra-orbital nerve Maxillary sinus ■^'~" Buccinalor Conjunctiv^a - — T'superior fornix r Puncta lacrimalla ' Lacrimal ducts Lacrimal sac }iledial palpebral ligament ■ ^ -Naso-lacrimal duct -]\Iiddle concha ~ — '" INluco-periosteum — ^ - Plica lacrimalis Inferior meatus Liferior concha Fig. 64. — Dissection of Lacrimal Apparatus. The Conjunctival Sac. — The conjunctival sac is the potential space between the eyelids and the eyeball. It opens externally through the rima and communicates with the lacrimal sac through the puncta and the lacrimal ducts. The Puncta Lacrimalla. — It has been noted already that the punctum lacrimale of each hd lies at the lateral margin of the lacus lacrimalis (p. 120). Small probes should now be I40 HEAD AND NECK passed through the puncta into the lacrimal ducts and along the ducts into the lacrimal sac (Fig. 64). Saccus Lacrimalis. — The lacrimal sac is the blind upper end of a canal which extends from the orbit to the inferior meatus of the nose. It is lodged in the fossa lacrimalis in the anterior part of the medial wall of the orbit. It lies posterior to the medial palpebral ligament, from which it receives a fibrous expansion, and it is covered on its lateral aspect, and on the lateral part of its posterior aspect, by the pars lacrimalis of the orbicularis oculi. The lacrimal ducts open into its antero- lateral aspect, under cover of the medial palpebral ligament ; and it is continuous below with the naso- lacrimal duct. The anterior wall of the sac should be incised and a probe passed down the naso -lacrimal duct into the nose. Note that as the probe passes along the duct it inclines downwards, laterally and slightly posteriorly. Pars Lacrimalis Orbicularis Oculi (O.T. Tensor Tarsi). — This small special portion of the orbicularis oculi springs from the posterior aspect of the lateral part of the medial palpebral ligament and passes posteriorly and medially, round the lateral part of the lacrimal sac, to the crista lacrimalis of the lacrimal bone, to which it is attached. When it contracts it compresses the lacrimal sac, and so tends to facilitate the flow of the lacrimal secretion into the nose. Ductus Naso -Lacrimalis. — This duct will be seen at a later period of the dissection. It is a bony canal, lined with muco-periosteum, which runs, in the lateral wall of the nose, from the lacrimal sac to the upper and anterior part of the inferior meatus. It is about half an inch long. At the medial side of its lower end is a fold of mucous membrane, the plica lacrimalis^ which serves as a flap valve (Fig. 64). The dissection of the face should be completed by an examination of the nasal cartilages and the external nasal branch of the ophthalmic division of the trigeminal nerve. The nerve will be found emerging between the lower border of the nasal bone and the lateral cartilage. After its emergence it descends to the tip of the nose supplying filaments to the skin. Dissection.— The cartilaginous part of the nose should now be examined by stripping off the nasalis muscle and the remains of the integument. Nasal Cartilages. — In addition to the septal cartilage, FACE AND FRONTAL REGION OF HEAD 141 which will be more appropriately studied in the dissection of the nasal cavities, two cartilaginous plates will be found upon each side. These are : — 1. The lateral cartilage. 2. The cartilage of the ala. The lateral cartilage is a triangular plate which, by its posterior margin, is attached to the lower border of the nasal bone and the upper part of the sharp margin of the nasal notch of the maxilla. In the median plane this cartilage External nasal nerve —Lateral cartilage jSIinor alar cartilages ^Nlajor alar cartilage Fig. 65. — Cartilages of the Nose. becomes continuous with its fellow of the opposite side, and also with the subjacent anterior border of the septal cartilage of the nose. Below, there is a slight interval between the two lateral cartilages, in which is seen the margin of the nasal septal cartilage. The inferior border of the lateral cartilage is connected with the lateral part of the alar cartilage by some dense fibrous tissue. The alar cartilage is bent upon itself and folded round the orifice of the nostril anteriorly and laterally. Posteriorly it is deficient. The lateral part is oval, and does not reach down to the margin of the nostril, nor posteriorly as far as the nasal notch of the maxilla. The interval between it and the bone is filled in by fibrous tissue in which one or two small islands of cartilage (cartilagines minores vel sesa- moidese) appear. A?iteriorly, the bent part of cartilage comes into contact with its neighbour and forms the point of the 142 HEAD AND NECK nose. Medially^ the medial part of the cartilage is in the form of a narrow strip which lies upon the lower part of the septal cartilage, and projects slightly below it so as to support the margin of the nostril upon this side. Its extremity is turned slightly laterally. SIDE OF THE NECK. On the fourth day after the body is brought into the room it is placed upon its back, and the dissectors of the head and neck should examine the side of the neck and commence the dissection of the posterior triangle. The side of the neck is bounded below by the clavicle, above by the lower border of the mandible, the mastoid portion of the temporal bone, and the superior nuchal line of the occipital bone. Anteriorly it extends to the median plane, and posteriorly to the anterior border of the trapezius muscle. It is divided into anterior and posterior parts, the anterior and posterior triangles^ by the sterno- mastoid muscle. If the head is pulled over towards the opposite side, the sterno- mastoid muscle will be seen descending from the mastoid portion of the temporal bone and the superior nuchal line of the occipital bone, to the upper border of the sternal third of the clavicle and the anterior surface of the manubrium sterni. In the lower part of the posterior region, posterior to the sterno -mastoid and above the convex middle third of the clavicle, there is a depression called the fossa supraclavicularis major, to distinguish it from the fossa supraclavicularis minor which lies above the sternal end of the clavicle between the sternal and clavicular heads of the sterno-mastoid. The brachial plexus, the third part of the subclavian artery, and the supra -clavicular lymph glands lie in the region of the fossa supra-clavicularis major, and the fossa supra-clavicularis minor indicates the position of the internal jugular vein near its lower end. POSTERIOR TRIANGLE. Dissection. — To expose the boundaries and contents of the posterior triangle make the following three incisions through the skin, (i) From the back of the auricle along the upper border of the mastoid part of the POSTERIOR TRIANGLE • 143 temporal bone and the superior nuchal line to the external occipital pro- tuberance. (2) From the sternal to the acromial end of the clavicle, following the line of that bone. (3) Join the anterior extremities of i and 2 by a vertical incision passing along the back of the external acustic meatus and then down the middle of the sterno-mastoid muscle. Reflect the flap, thus marked out, from before backwards, and note that the skin is thicker over the upper and posterior part of the triangle than over the lower and anterior part. When the skin is reflected the superficial fascia and the lower part of the platysma muscle will be exposed. The superficial fascia in the region of the posterior triangle is comparatively thin, and embedded in its lower and anterior part is the lower and posterior part of the platysma. The Platysma. — The platysma is a thin sheet of muscle which commences in the superficial fascia of the infra-clavi- cular region, whence it ascends across the clavicle and through the superficial fascia of the side of the neck, to the face where its upper border has been examined already (p. 126). It covers the lower and anterior part of the posterior triangle, and the upper and posterior part of the anterior triangle ; and it is supplied by the cervical branch of the facial nerve, which emerges from the lower end of the parotid gland. Dissection. — Make an incision through the lower part of the platysma along the line of the clavicle, and turn the part above the incision upwards and anteriorly. Whilst making the incision and whilst reflecting the muscle, be careful not to injure the supraclavicular cutaneous nerves and the external jugular vein, which lie directly subjacent to it. After the platysma is reflected, clean the external jugular vein, which emerges from the lower end of the parotid and passes downwards, in- clining posteriorly, to the lower and anterior angle of the posterior tri- angle, where it pierces the deep fascia. Whilst cleaning the vein, avoid injury to the nervus cutaneus colli, which sometimes crosses superficial to the vein about the middle of its length. Secure and clean the posterior auricular vein, which descends behind the auricle and joins the external jugular a little below the level of the angle of the mandible. Next, find and clean the superficial branches of the cervical plexus as they pierce the deep fascia. They are (i) descending branches, the anterior, middle, and posterior supra-clavicular nerves. (2) A transverse branch, the nervus cutaneus colli (O.T. transverse cervical). (3) Ascending branches, the great auricular and the small occipital. The anterior and middle sjipra-clavicular nerves will be found piercing the deep fascia immediately above the clavicle, the anterior at the posterior border of the sterno-mastoid and the middle above the convexity of the clavicle. They descend into the pectoral region as far as the lower border of the second rib and their lower portions will be displayed by the dissector of the arm. The posterior supra-clavicidar nerves pierce the deep fascia at a somewhat higher level. They descend across the lower and anterior part of the trapezius to the acromial region, and to the skin of the arm over the upper part of the deltoid, where they will be exposed by the dissector of the arm. 144 HEAD AND NECK The Deep Fascia. — The deep fascia forms the superficial boundary or roof of the posterior triangle. It is attached below to the upper border of the middle third of the clavicle ; Great occipital nerve ._1 Posterior 'i^^V.. auricular vein "' Small occipital nerve Great auricular nerve 1^.- Splenius capitis Accessory ner\'e Levator scapulae Middle supra- clavicular nerve . Posterior supra- f M\ clavicular nerve " " Scalenus medius ;=' Nervus cutan- eus colli upper branch Nervus cutaneus colli Anterior supra- -- clavicular nerve. Fig. 66. — The superficial branches of the cervical plexus. above, to the superior nuchal line of the occipital bone; anteriorly it is continuous with the fascia of the stern o-mastoid and posteriorly with the fascia of the trapezius. It is pierced by (i) the supra-clavicular branches of the cervical plexus, (2) the external jugular vein, (3) small cutaneous branches of the POSTERIOR TRIANGLE 145 transverse cervical, transverse scapular (O.T. suprascapular), and occipital arteries, and, occasionally, by the occipital artery itself. It is not a very strong layer, and it is frequently difficult to display it as a continuous sheet. Over the upper part of the triangle it forms a single layer, but below, it splits into two lamellae, a superficial and a deep. The superficial layer which is already displayed, is attached to the upper border of the clavicle from the sterno-mastoid anteriorly to the trapezius posteriorly. It is pierced by the external jugular vein and the supraclavicular nerves. Dissection. — Trace the supraclavicular nerves upwards through the deep fascia to the posterior border of the sterno-mastoid ; then, pulHng them aside, cut through the superficial layer of the deep fascia immediately above the clavicle and along the posterior border of the sterno-mastoid, and turn it upwards. Introduce the handle of the scalpel behind the clavicle and note that it can be passed downwards as far as the posterior border of the lower surface of the bone. Its further progress is barred by the attachment of the second layer of the deep fascia to this border, where it blends with the posterior lamella of the costo-coracoid membrane. Pass the handle of the knife forwards behind the sterno-mastoid and note that, without using any great force, it can be pushed medially until it crosses the median plane ; therefore, the space betw^een the two layers of deep fascia in the lower part of the posterior triangle is continuous anteriorly with the space which lies above and posterior to the manubrium sterni, between the first and the second layers of the deep fascia of the anterior part of the neck. Laterally, this space extends as far as the coracoid process, and upwards to a short distance above the posterior belly of the omo-hyoid muscle. Clear away the areolar tissue which lies between the two layers of the deep fascia, and expose a further part of the external jugular vein, and the terminal parts of the transverse cervical and the transverse scapular (suprascapular) veins, as they join the posterior border of the external jugular. Pull the lower part of the external jugular vein posteriorly and expose the termination of the anterior jugular vein in its anterior border. Dissect carefully behind the clavicle and find the transverse scapular (suprascapular) artery. Trace the second layer of the deep fascia upwards and note that it is continuous with the fascia which surrounds the posterior belly of the omo-hyoid muscle ; indeed it is the tension of this portion of the deep fascia which holds the posterior belly of the muscle down in its position. Remove the remaining parts of the deep fascia, first from the upper, and then from the lower part of the triangle, and expose the floor and the remaining contents of the triangle. Commence above, in the region of the junction of the upper third and the lower two-thirds of the posterior border of the sterno-mastoid, and secure the great auricular, the small occipital, the accessory nerve, and the nervus cutaneus colli. The great auricular is most easily found. It turns round the posterior border of the sterno-mastoid, in the region indicated, and runs upwards and anteriorly, parallel with and slightly above and posterior to the external jugular vein. The small occipital will be found hooking round the lower border of the accessory nerve a little above the great auricular ; and the nervus cutaneus colli lies a little below the great auricular. Follow the small occipital and the great auricular nerves to their VOL. II — 10 146 HEAD AND NECK terminations, but the nervus cutaneus colli must be traced only to the point where it crosses either superficial or deep to the external jugular vein. It eventually divides into upper and lower terminal branches, which will be seen when the anterior triangle is dissected. Nervus Occipitalis Minor. — The small occipital is a sensory branch of the second cervical nerve. It emerges from under cover of the sterno-mastoid, and ascends for a short distance along its posterior border, then it passes to the superficial surface of the muscle, pierces the deep fascia, and divides into occipital, mastoid, and auricular branches. The occi- pital and mastoid branches supply the skin in the regions indicated by their names. The auricular is distributed to the skin of the upper third of the cranial surface of the auricle. Nervus Auricularis Magnus. — This consists of cutaneous filaments derived from the second and third cervical nerves. After turning round the posterior border of the sterno-mastoid it runs upwards and anteriorly, towards the angle of the mandible, in the deep fascia on the superficial surface of the sterno-mastoid, and breaks up into three sets of terminal branches, mastoid, auricular, and facial. The mastoid branches go to the skin of the mastoid region. The auricular branches supply the skin of the lower two-thirds of the cranial surface and the lower third of the lateral surface of the auricle. The facial branches^ which have already been seen, ramify in the posterior part of the face, in the parotid and masseteric regions. Some of the filaments enter the substance of the parotid. Dissection. — The accessory nerve, previously found at the junction of the upper third with the lower two-thirds of the posterior border of the sterno-mastoid, must now be traced downwards and posteriorly, through the triangle, to the point where it disappears under cover of the trapezius, at the junction of the upper two-thirds with the lower third of the anterior border of that muscle. As the nerve is cleaned, attempt to secure twigs from the third and fourth cervical nerves which communicate with it in the posterior triangle. Turn next to the posterior belly of the omo-hyoid muscle, which crosses the lower part of the triangle. Note that it divides the triangle into a large upper or occipital portion, and a small lower or subclavian portion. Cut through the fascia on the surface of the muscle, parallel with the muscle fibres, and turn it upwards and downwards ; then turn the upper border of the muscle laterally and find the nerve from the ansa hypoglossi, which emerges from under cover of the sterno-mastoid and enters the deep surface of the omo-hyoid to supply it. Take away the remains of the superficial layer of deep fascia, and the areolar tissue beneath it from the upper part of the triangle. Whilst removing the latter note a number of lymph glands which lie embedded in it along the posterior border of the sterno-mastoid, superficial to the stems and branches of the cervical nerves. At the apex of the triangle look for the occipital artery, which either emerges between the adjacent POSTERIOR TRIANGLE 147 borders of the trapezius and the sterno-mastoid, or pierces the trapezius a little further posteriorly. Between the accessory nerve above and the posterior belly of the omo- hyoid below find (i) the upper -part of the brachial plexus ; (2) its branch to the subclavius ; (3) its suprascapular branch ; (4) its dorsalis scapulae branch; (5) its long thoracic branch; (6) branches from the third and fourth cervical nerves to the levator scapulos ; (7) branches from the third and fourth cervical nerves to the trapezius, and others which communicate with the accessoiy nerve in the posterior triangle ; and (8) the upper and posterior part of the transverse cervical artery. Find the transverse cervical artery as it appears from under cover of the upper border of the omo-hyoid. It runs upwards and posteriorly. Next secure the nerve to the subclavius, which lies under cover of the deep fascia above the omo-hyoid and a short distance behind the sterno-mastoid. Trace it upwards to its origin from the trunk formed by the union of the fifth and sixth cervical nerves. Clean the latter nerves and the upper part of the seventh cervical nerve, which lies immediately below them. Then find the suprascapular nerve, which springs from the lateral border of the trunk formed by the fifth and sixth nerves. It lies immediately above the anterior part of the posterior belly of the omo-hyoid, and disappears under cover of the posterior part. Turn the trunk formed by the fifth and sixth cervical nerves anteriorly and find, posterior to it, the upper roots of the long thoracic nerve, which spring from the fifth and sixth nerves, and are emerging through the fibres of the scalenus medius muscle. The nervus dorsalis scapulae (O.T. nerve to the rhomboids) lies at a slightly higher level than the suprascapular nerve. It springs from the fifth cervical nerve, runs downwards and posteriorly, and disappears, through the floor of the triangle, between the adjacent borders of the levator scapulae above and the scalenus medius below. Above the dorsal scapular nerve are the branches from the third and fourth cervical nerves to the trapezius and the communications to the accessory nerve. When the structures mentioned above have been found and cleaned, proceed to the dissection of the subclavian portion of the triangle. Find the transverse scapular artery (O.T. suprascapular), which lies behind the clavicle, and therefore, strictly speaking, outside the limits of the triangle. Then remove the second layer of deep cervical fascia which binds the posterior belly of the omo-hyoid to the posterior border of the clavicle, and find behind it (i) a further part of the external jugular vein ; (2) a further part of the transverse cervical artery ; (3) the lower part of the nerve to the subclavius ; (4) the upper portion of the third part of the subclavian artery ; (5) the lowest root and the lower parts of the trunks of the brachial plexus ; (6) a part of the long thoracic nerve ; (7) supraclavicular lymph glands. First clean the lower end of the external jugular vein and follow it behind the clavicle to its termination in the subclavian vein. Note the valves near its lower end. Next clean the transverse cervical artery and the nerve to the subclavius. Follow the nerve to the subclavius across the front of the third part of the subclavian artery ; and afterwards clean the lower part of the subclavian artery and the adjacent part of the brachial plexus, which lies behind and above the artery. Note that the artery and the plexus are covered by a layer of deep cervical fascia, the backward prolongation of the prevertebral layer of fascia, which passes on to them from the lateral border of the scalenus anterior, and is prolonged along them to become continuous with the sheath of the axillary artery. As the areolar tissue is cleared from the subclavian portion of the triangle a number of supraclavicular lymph glands may be noted. They receive lymph from the axillary glands, and they transmit it to the large lymph vessels at the root of the neck. II— 10 a 14S HEAD AND NECK After the contents of the lower part of the triangle are thoroughly cleaned, remove the remains of the fascia covering the muscles which form the floor of the triangle. Note that this fascia is continuous anteriorly, round the tips of the transverse processes of the cervical vertebrse with the prevertebral fascia. Posteriorly it blends with the sheaths of the deeper "--Digastric Nerve to thyreo-hyoid Thyreo-hyoid Superior thyreoid artery Omo-hyoid Transverse = capular artery Scalenus anterior Subclavian artery Subclavian vein Suprascapular N Fig. 67. — The Triangles of the Neck seen from the side. The clavicular head of the sterno-mastoid muscle was small, and therefore a considerable part of the scalenus anterior muscle is seen. muscles at the back of the neck ; above it is attached to the superior nvichal line ; and below, as already stated, it is prolonged into the axilla along the axillary vessel? and nerves. Boundaries and Contents of the Posterior Triangle. — The dissection of the triangle should be completed in two days. On the third day the dissector should revise his knowledge of the boundaries and the relative positions of the contents. POSTERIOR TRIANGLE 149 The triangle is bounded anteriorly by the posterior border of the sterno-mastoid ; posteriorly by the anterior border of the trapezius ; below by the upper border of the middle third of the clavicle ; and above by the superior nuchal line of the occipital bone, or by the meeting of the upper ends of the sterno- mastoid and the trapezius. The roof is formed by the deep cervical fascia, which is covered by superficial fascia and skin, and in its lower and anterior part by the platysma, which is embedded in the superficial fascia. It is pierced by (i) the external jugular vein at the lower and anterior angle; (2) the supraclavicular nerves, a short distance above the clavicle ; (3) small cutaneous branches of the transverse scapular, trans- verse cervical, and occipital arteries; (4) lymphatic vessels passing from the superficial structures to the glands in the triangle. It is frequently stated that the small occipital, the great auricular, and the cervical cutaneous nerves also pierce the roof. As a general rule they turn round the posterior border of the sterno-mastoid under cover of the fascia, and pierce the fascia as it lies on the muscle. The floor is formed by the splenius capitis, the levator scapulae, the scalenus medius, and the scalenus posterior muscles, with the addition, occasionally, of a small part of the semispinalis capitis (O.T. complexus) above, and the upper serration of the serratus anterior below ; the latter appears in the area of the triangle only when the clavicle is very fully depressed. The muscles of the floor are covered with a layer of fascia which is the backward continuation of the prevertebral fascia of the anterior cervical region. The contents of the posterior triangle are : — 1. Fatty areolar tissue. 2. The posterior belly of the omo-hyoid muscle. 3. Lymph f Post sterno-mastoid. Glands, ( Supraclavicular. ' Third part of subclavian. {Third part or subclavian. Transverse cervical and its terminal branches. Occipital (sometimes). /"External jugular. I Transverse cervical. 5. Veins, '-^ "1 Transverse scapular (O.T. suprascapular). [Termination of anterior jugular. ■•• The transverse scapular artery (O.T. suprascapular) lies posterior to the clavicle and is not, strictly speaking, in the triangle. ^ The subclavian vein is posterior to the clavicle and therefore is not contained within the triangle. II— 10& ISO HEAD AND NECK > Branches of cervical plexus. 6. Nerves, 'Accessory. Small occipital. Great auricular. Nervus cutaneus colli. To levator scapulae. ,, trapezius. ,, scalenus medius. * ,, ,, posterior. Supraclavicular. To posterior belly of omo-hyoid from ansa hypoglossi. Trunks of brachial plexus. The nervus dorsalis scapulae. ] ,, long thoracic. |_ Branches of the brachial ,, suprascapular. j ,, nerve to the subclavius. j plexus. Some of the contents of the triangle which are now displayed require further consideration. The Posterior Belly of the Omo-hyoid Muscle. — The posterior belly of the omo-hyoid muscle springs from the upper border of the scapula and upper transverse scapular ligament. It enters the posterior triangle, at its lower and posterior angle, and runs upwards and anteriorly, at a variable distance from the clavicle, to the posterior border of the sterno- mastoid. Either immediately behind or under cover of the posterior border of the sterno-mastoid it joins the intermediate tendon which connects it with the anterior belly. Its nerve has already been seen entering its deep surface (p. 146) it divides the posterior triangle into a lower or subclavian portion and an upper or occipital portion. The Accessory Nerve (O.T. Spinal Accessory). — The portion of the accessory nerve which appears in the posterior triangle consists of fibres which arise from the cervical part of the spinal medulla and with them are incorporated some filaments derived from the second cervical nerve. Before appearing in their present situation the spinal fibres entered the cranium through the foramen magnum and left it by pass- ing through the jugular foramen ; then they passed downwards and posteriorly, through the deeper fibres of sterno-mastoid, where they received the communication from the second cervical nerve. As already pointed out, the nerve usually enters the posterior triangle at the level of the union of the upper third with the lower two-thirds of the posterior border of the sterno- mastoid. It runs downwards and posteriorly through the triangle, along the line of the levator scapulae, and disappears POSTERIOR TRIANGLE 151 under the trapezius at the junction of the upper two-thirds with the lower third of its anterior border. As it enters the triangle the small occipital nerve turns round its lower border, and, as it crosses the triangle, it is joined by twigs from the third and fourth cervical nerves. The Branches of the Cervical Plexus. — The dissector should note that whilst many of the branches of the cervical plexus lie within the area of the posterior triangle, the plexus itself is under cover of the upper part of the sterno- mastoid, where it will be exposed and studied when the sterno - mastoid is reflected. The branches which appear in the triangle are the superficial bra?iches — the small occipital, the great auricular, the nervus cutaneus colli, and the supra- clavicular nerves ; and the deep posterior branches^ that is, the nerves to the scalenus medius and posterior, the nerve to the levator scapulae, the branches to the trapezius and the communication to the accessory nerve. The Third Part of the Subclavian Artery. — Only a portion of this part of the subclavian artery is in the triangle ; the lower and lateral part is behind the clavicle. The part in the triangle is situated deeply in the anterior inferior angle and below the omo-hyoid muscle. It is covered zvith the skin, superficial fascia, the platysma, deep fascia, the external jugular vein, the ends of the transverse scapular, and trans- verse cervical veins, and the nerve to the subclavius muscle. Behind it is the lowest trunk of the brachial plexus, which separates it from the insertion of the scalenus medius. Below, it rests upon the first rib, against which it can be compressed, and, more medially, on the cervical pleura. The Brachial Plexus and its Supraclavicular Branches. — Only the upper portion of the brachial plexus lies in the region of the posterior triangle, i.e. the roots, the trunks, and some of the branches ; the remainder lies either posterior to the clavicle or in the axilla. The cervical portion lies in the lower and anterior part of the posterior triangle partly in the occipital and partly in the supraclavicular areas. The detailed study of the plexus should be left till the fifth day after the body has been placed upon its back, when the dissector of the head and neck will assist the dissector of the upper extremity to disarticulate the clavicle and to lay bare the whole of the plexus (p. 160). The fourth day after the body has been placed upon its 152 HEAD AND NECK back should be devoted to the study of the temporal region and the anterior part of the scalp. THE SCALP AND THE SUPERFICIAL STRUCTURES OF THE TEMPORAL REGION. Under the term " scalp " are included the soft structures which cover the vault of the cranium above the temporal ridges and anterior to the superior nuchal line. Its con- stituent parts are arranged in five layers : (i) skin; (2) super- ficial fascia ; (3) the epicranius, consisting of four muscular L- Integument C,«JJ Dura mater Fig. 68. — Section through the Scalp and Cranial Wall. bellies, the two occipitales and the two frontales muscles, and the aponeurosis called the galea aponeurotica, which connects them together; (4) a layer of loose areolar tissue ; (5) the periosteum, which is here called the pericranium. In the temporal region the wall of the* cranium is much more thickly covered than in the scalp area, and it is possible to distinguish eight layers of soft tissues between the surface and the bone : (i) skin; (2) superficial fascia ; (3) extrinsic muscles of the ear ; (4) the thin lateral extensions of the galea aponeurotica ; (5) a thin layer of fascia descending from the temporal ridge to the auricle ; (6) the strong temporal fascia ; (7) the temporal muscle ; (8) periosteum. TAe Scalp. — The scalp and the superficial temporal region are richly supplied with blood vessels and nerves, which all AURICLE 153 enter from the periphery, passing into the superficial fascia after piercing the deep fascia of adjacent regions. As a consequence of this arrangement large flaps of the scalp may be torn from the centre towards the margin, but, so long as they remain attached at the periphery, their sources of vitality are not seriously interfered with, and if they are cleaned and replaced healing occurs rapidly and satisfactorily. Dissection. — The skin has already been removed from the anterior parts of the scalp and the temporal region. A median longitudinal in- cision must now be made through the skin of the posterior part of the scalp as far as the external occipital protuberance, and the flap on either side of the incision must be turned downwards and posteriorly to the superior nuchal line. When this has been done the dissector should ex- amine the auricle of the external ear, and familiarise himself with its various parts before he commences the dissection of its extrinsic muscles. Crus antihelicis Fossa triangularis Tragus Incisura \ intertragica ^l Lobulus -\ w Fig. 69. — The Auricle. Auricle or Pinna. — The auricle consists of a thin plate of yellow fibro-cartilage, covered with integument. It is fixed in position by certain ligaments, and possesses two sets of feeble muscles — viz., one group termed the extrinsic muscles., passing to the cartilage from the aponeurosis of the epicranius and the mastoid process, and a second group in connection with the cartilage alone, and therefore called the iiitrinsic muscles. The concha is the wide and deep fossa which leads into the external meatus ; the antiJielix is the curved prominence w^hich bounds this posteriorly ; the helix is the folded or in- curved margin of the auricle ; and the lobule is its soft dependent part. The concha is partially subdivided into an upper and a lower part by the commencement of the helix, which curves upwards and forwards on its floor to become continuous with the anterior border of the auricle. This portion of the helix is called the crus helicis. A small pro- Intrinsic muscles, - 154 HEAD AND NECK minence anterior to the meatus, and projecting posteriorly so as to overshadow it, is termed the tragus^ whilst a similar eminence posterior to and below the meatus receives the name of the antitragus. The notch between these two prominences is termed the incisura intertragica. But it will be noted that the upper end of the antihelix bifurcates, and in this way two fossae are marked off from each other; one — the fossa of the helix, or scaphoid fossa — is placed between the helix and the antihelix, and the other — the fossa of the antihelix, or triangular fossa — is situated between the two diverging crura of the antihelix. [Anterior. Ligaments, . . . . \ Superior. (^ Posterior. {Auricularis anterior. Auricularis superior. Auricularis posterior. 'Musculus helicis major. "^ Musculus helicis minor. I Upon the lateral face of the Musculus tragicus. j cartilage. Musculus antitragicus. J Musculus transversus. ) Upon the cranial face of , Musculus obliquus. / the cartilage. Dissection. — When the dissector has noted the various parts of the auricle he should endeavour to display its extrinsic muscles ; they are the auriculares anterioi' [O.T. attrahens), stiperior {O.T. attollens), dcnd posterior (O.T. retrahens). The two former spring from a lateral prolongation of the galea aponeurotica into the temporal region. The anterior is inserted into the front of the helix, and the superior into the cranial surface of the auricle. To display them pull the auricle downwards and posteriorly, and carefully remove the superficial fascia and, at the same time, avoid injury to the auriculo-temporal nerve, the temporal branches of the facial nerve, and the branches of the superficial temporal artery which are ascending through the superficial fascia of the temporal region to the scalp. The auricularis posterior arises from the outer surface of the mastoid part of the temporal bone and passes anteriorly to its insertion into the cranial aspect of the concha. To display it pull the auricle anteriorly and remove the fascia from the surface of the muscle, at the same time secure the posterior auricular artery and nerve as these ascend posterior to the external meatus. As this is being done one or more mastoid lymph glands may be seen, and care must be taken to avoid injuring the branch of the posterior auricular nerve to the occipitalis muscle, which passes posteriorly along the lower border of the auricularis posterior or on its deep surface. The auriculares muscles are supplied by the facial nerve ; the anterior and the anterior part of the superior by its temporal branches, and the posterior and the posterior part of the superior by the posterior auricular branch. After the auriculares muscles have been defined remove the skin from the entire extent of the auricle to display the cartilage, the ligaments, and the intrinsic muscles.^ Great care is required to make a successful dissection. ^ In most cases it will be advisable to defer this part of the dissection till the body is turned on its back for the second time (p. 200). AURICLE 155 The auricular cartilage extends throughout the entire auricle, with the exception of the lobule and the portion between the tragus and the helix. These portions are composed merely of integument, fatty tissue, and condensed connective tissue. The shape of the cartilage corresponds with that of the auricle itself. It shows the same elevations and depressions, and by its elasticity it serves to maintain the form of the auricle. But it also enters into the formation of the cartilaginous or lateral portion of the external acustic meatus. By its medial margin this part of the cartilage is firmly fixed by fibrous tissue to the rough outer edge of the auditory process of the temporal bone, but it does not form a complete tube. It is deficient above and anteriorly, and here the tube of the meatus is completed by tough fibrous membrane, which stretches between the tragus and the commencement of the helix. In a successful dissection of the cartilage of the auricle, two other points will attract the attention of the student. The first is a deep slit, which passes upwards so as to separate the lower part of the cartilage of the helix, termed the p7'ocessus helicis caudahis, from the cartilage of the anti- tragus ; the second is a sharp spur of cartilage which projects anteriorly from the helix, at the level of the upper margin of the zygoma. This is termed the spitta helicis. The Ligaments of the Auricle. —The ligaments are three bands of fascia. The anterior passes from the spine of the helix to the root of the zygoma. The superior and posterior are both attached to the cartilage in the region of the concha ; the former blends above with the temporal fascia, and the latter is attached to the mastoid portion of the temporal bone. The Intrinsic Muscles of the Auricle. — The two muscles of the helix, the tragicus and the antitragicus, are placed upon the lateral face of the cartilage. The transversus and the obliquus lie upon the cranial surface of the auricle. The musculus antitragicus is the best-marked member of the lateral group. It lies upon the lateral surface of the antitragus, and its fibres pass obliquely upwards and posteriorly. Some fasciculi can be traced to the processus helicis caudatus. The musculus tragicus is a minute bundle of short vertical fibres situated upon the lateral surface of the tragus. When well developed a slender fasciculus may sometimes be observed to pass upwards from it to the anterior part of the helix, where it is inserted into the spine of the helix. The musculus helicis major is a well-marked band, which springs from the spina helicis, and extends upwards upon the anterior part of the helix, to be inserted into the skin which covers it. The musculus helicis minor is a minute bundle of fleshy fibres which is placed upon the crus helicis as it crosses the bottom of the concha. The musculus transversus auriculce is found upon the cranial aspect of the auricle. It is generally the most strongly developed muscle of the series, and its fibres bridge across the hollow which, on this aspect of the auricle, corresponds to the antihelix. The musculus obliquus aurictdcB is composed of some vertical fasciculi bridging across the depression which corresponds to the eminence of the lower limb of the antihelix. After the auricular muscles and the auricle have been dissected, trace the temporal branches of the facial nerve, the branches of the super- ficial temporal vessels, and the auriculo-temporal nerve upwards, from the point where they emerge from under cover of the upper end of the parotid through the superficial fascia of the temporal region to their termina- tions in the superficial fascia of the scalp. About half an inch behind the zygomatic process of the frontal bone (O.T. external angular process) find 156 HEAD AND NECK the zygomatico-temporal branch of the maxillary nerve. Next pull the auricle anteriorly and trace the posterior auricular ner\^e to its termination in the occipitalis muscle, and in the intrinsic and extrinsic muscles of the auricle, and the posterior auricular artery to its anastomoses with the occipital and superficial temporal arteries. After this part of the dissection is completed, turn to the anterior part of the scalp and find the medial and lateral branches of the supra-orbital nerve. The medial branch pierces the fibres of the frontalis and the lateral branch pierces the galea aponeurotica a little further posteriorly. Trace both branches backwards through the superficial fascia as far as possible ; they extend to the level of the lambdoid suture. Then secure the supra-trochlear nerve, which pierces the frontalis above the medial margin of the orbit, and trace it upwards to its termination. With the branches of the supra-orbital nerve are branches of the supra-orbital arter}', and the supra-trochlear nerve is accompanied by the frontal branch of the ophthalmic arter}\ ^Yhen the ner\-es and vessels in the anterior region have been cleaned, the head should be turned well over to the opposite side, and the branches of the occipital arter\' and the great occipital nerve should be sought for in the posterior region ; they radiate upwards and anteriorly from the upper extremity- of the trapezius. After they have been secured, the occipitalis muscle must be cleaned. It springs from the lateral part of the sviperior nuchal Hne, and after a short course upwards and anteriorly it terminates in the galea aponeurotica. The remains of the superficial fascia should now be removed from the surface of the galea aponeurotica (O.T. epicranial aponeurosis), and then the dissector should make a survey of the vessels and nerves which are met with in the scalp and the superficial fascia of the temporal region. Nerves and Vessels of the Scalp and the Superficial Temporal Eegion. — Branches of ten nerves are found, on each side, in the superficial fascia of the region which lies above the supra-orbital margin, the zygomatic arch and the superior nuchal line. Of these, five lie mainly anterior to the auricle and five posterior to it ; and of each group four are sensory and one is motor. The four sensory nerves anterior to the auricle are all branches of the trigeminal nerve. They are the supra-trochlear and supra-orbital branches of the first or ophthalmic division : the zygomatico-temporal branch of the maxillary or second division; and the auriculo -temporal branch of the mandibular or third division. The motor nerve is the temporal branch of the facial nen'e. The four sensory nerves, distributed mainly to the scalp area behind the auricle, are the great auricular and the sjnall occipital branches of the cervical plexus ; the great occipital^ which is the medial division of the posterior branch of the second cervical nerv^e ; and the smallest occipital^ not yet seen, but which will be displayed when the body is turned on its face. It lies medial to the great occipital, and is the medial division of the posterior branch of the third cervical nerve. XERVE? AND VESSELS OF SCALP 157 The motor nen-e distributed posterior to the auricle is the posterior auricular branch of the facial nerve. The arteries distributed to the scalp are five in number on each side; they anastomose freely, and are derived, either indirectly or directly, from the internal and external carotid arteries. Three are distributed mainly anterior to, and two posterior to the region of the auricle. The three anterior to the auricle are the frontal and supra-orbital branches of the ophthalmic branch of the internal carotid, which accompany the supra-trochlear and supra-orbital nenxs, and the superficial temporal branch of the external carorid. This branch divides into two main branches, an anterior, which accompanies the temporal branches of the facial nerve, and is usually a very tortuous vessel, and a posterior branch, which accompanies the auriculo-temporal nen^e, as it ascends anterior to the auricle towards the vertex of the cranium. The two arteries posterior to the auricle are both branches of the external carotid. They are the posterior auriailar^ which accompanies the posterior auricular branch of the facial nerve to the mastoid region and the posterior part of the parietal region, and the occipital, which is distributed to the occipital area and posterior part of the parietal area. The terminations of the veins wiiich drain the blood from the scalp are as follows. The frontal and supra-orbital veins unite, at the medial border of the orbit, to form the angular vein, which is the commencement of the anterior facial vein already dissected (p. 131;. The blood it conveys passes eventually to the internal jugular vein. The superficial temporal vein accompanies the corresponding arter}-. It unites, immediately above the posterior root of the zygoma, with the middle temporal vein, which pierces the temporal fascia at that point The trunk formed by the union of the superficial and middle temporal veins is the posterior facial vein, which descends through the parotid gland, emerges from under cover of its lower end and terminates immediately below the angle of the mandible by joining with the anterior facial vein to form the common facial vein. \\Tiilst in the gland, it gives oflf the commencement of the external jugular vein. The posterior auricular vein descends posterior to the external meatus and terminates in the external jugular vein. The occipital vein accompanies the occipital artery into the sub- occipital region, and ends in the sub-occipital venous plexus. iS8 HEAD AND NECK In addition to the arteries and veins there are numerous lymph vessels in the scalp, but they cannot be displayed by ordinary dissecting methods. Nevertheless, it is important that the student should remember their usual terminations. The lymph vessels of the anterior area end in small lymph glands which are embedded in the superficial surface of the parotid gland. Those of the posterior area terminate either in lymph glands which lie superficial to the mastoid part of the temporal bone, or in occipital lymph glands, which lie in the neighbourhood of the superior nuchal line. Dissection, — After the vessels and nerves of the scalp have been traced, the dissector should cut through the fibres of the orbicularis oculi and the frontalis over the medial part of the supra-orbital eminence and display the corrugator supercilii muscle. It springs from the medial end of the supra-orbital ridge of the frontal bone and passes anteriorly and laterally, through the fibres of the orbicularis oculi, to its insertion into the skin of the eyebrow. It is supplied by the temporal branch of the facial nerve. Galea Aponeurotica (O.T. Epicranial Aponeurosis). — The galea aponeurotica is fully exposed as soon as the superficial fascia of the scalp is completely removed. It is a strong layer of aponeurosis connected anteriorly with the frontal bellies of the epicranius, posteriorly with the occipital belhes, and between the occipital bellies, with the external occipital protuberance and the medial parts of the superior nuchal lines, or with the supreme nuchal lines when they are present. Laterally it becomes thinner, descends over the upper part of the temporal fascia, and gives origin to the anterior and superior auriculares muscles. It is so closely connected with the superjacent skin, by the dense superficial fascia, that the two cannot be separated, except with the aid of the cutting edge of the scalpel ; but above the supra-orbital ridges, the temporal ridges, and the superior nuchal lines it is only loosely connected to the pericranium by the layer of loose areolar tissue ; therefore the three closely connected superficial layers, the skin, superficial fascia, and the galea aponeurotica, can easily be torn from the pericranium, a circumstance taken advantage of by the Indians who scalped their defeated foes. The looseness of the areolar tissue beneath the galea aponeurotica permits the latter to be drawn forwards and backwards by the alternate contractions of the occipitalis and frontalis muscles, and, as it moves, it carries with it the skin and superficial fascia with which it is so closely blended. SCALP 159 Dissection. — The dissector, after studying the attachments of the galea aponeurotica, and after he has made himself thoroughly conversant with the nerve and vascular supply of the scalp, and has appreciated the fact that every part of its area is supplied by more than one nerve and that the blood vessels anastomose very freely together, should next convince himself of the greater looseness of the areolar layer beneath the galea in the medial area and its greater denseness and closer attachment to the various parts of the superjacent epicranius, and the subjacent pericranium at the margins of the scalp area. He may do this by introducing the handle of a scalpel through a median incision in the galea, and passing it anteriorly and posteriorly and from side to side. The Layer of Loose Areolar Tissue. — This is the fourth layer of the scalp. It is but shghtly vascular and is of loose texture, but is not equally loose over the whole area of the scalp ; on the contrary in the regions of the temporal and supra-orbital ridges it becomes much denser, and, at the same time, much more closely connected with the galea aponeurotica and the frontalis muscles, whilst posteriorly it disappears where the occipitalis muscles and the galea become attached to the superior nuchal lines. It is on account of these peculiarities that effusions of blood or inflammatory exudations in the areolar layer easily raise the greater part of the scalp from the bone, but such effusions do not readily pass from beneath the scalp into either the facial, temporal, or occipital regions. On the fifth day after the body has been placed upon its back, the eighth after it was brought into the room, the dissector of the head and neck must assist the dissector of the upper extremity to display the whole extent of the brachial plexus and the origins of the branches which spring from it ; and he should take the opportunity to revise his own know- ledge of the plexus. Detach the clavicular head of the sterno-mastoid from the clavicle, and displace the sternal head towards the median plane. When this has been done the anterior and upper parts of the sterno-clavicular joint capsule will be fully exposed, for the pectoraHs major, which covered the lower part of the anterior surface, has already been reflected by the dissector of the upper extremity. Dissection. — The sterno-clavicular joint is described on p. 28 of Vol. I. After the dissectors have noted that the fibres of the capsule run medially and downwards from the clavicle to the sternum, the anterior, superior, and posterior portions must be divided close to the sternum, care being taken to avoid injury to the anterior jugular vein, which passes laterally close to the upper and back part of the joint. When the division is completed, elevate the sternal end of the clavicle by depressing the i6o HEAD AND NECK acromial end, introduce the knife into the cavity of the joint, close to the sternum, and carry it laterally below the clavicle, to detach the lower part of the interarticular cartilage from the sternum and the cartilage of the first rib, and to divide the lower part of the capsule and the costo-clavicular ligament, which lies immediately lateral to it. If the subclavius muscle has not already been detached, it also must be divided, and then the clavicle can be displaced laterally, and the whole extent of the plexus will be exposed. The Brachial Plexus. — The brachial plexus is fully described on p. 28, Vol. I., and only a brief resume of the main facts regarding it is given here. The plexus is formed by the last four cervical nerves and the larger part of the first thoracic nerve ; it also receives a communication from the fourth cervical nerve and not uncommonly a small twig from the second thoracic nerve. These various nerves constitute the 7'oots of the plexus. The roots of the plexus emerge from between the scalenus medius and the scalenus anterior, and unite to form three trunks, upper, middle, and lower, which lie superficial to the scalenus medius, the lowest of the three being wedged in between that muscle posteriorly and the third part of the subclavian artery anteriorly. The tipper trunk is formed by the fifth and sixth nerves and the communication from the fourth. The seventh nerve alone forms the middle trunk ; and the lowest trunk is formed by the eighth cervical and first thoracic nerves and the communication from the second thoracic. Almost immediately after their formation the trunks divide into anterior and posterior divisions, and the divisions reunite to form three cords, lateral, medial, and posterior. The lateral cord is formed by the anterior divisions of the upper and middle trunks, the medial cord by the anterior division of the lowest trunk, and all three posterior divisions unite to form Xhe posterior cord. The cords descend behind the clavicle and subclavius muscle, through the cervico-axillary canal, to the level of the coracoid process of the scapula where the plexus terminates and each cord divides into two terminal branches. The terminal branches of the lateral cord are the lateral head of the median nerve and the musculo-cutaneous nerve. Those of the medial cord are the medial head of the median and the ulnar nerve, and the posterior cord divides into the axillary (O.T. circumflex) nerve and the radial (O.T. musculo-spiral). In addition to the terminal branches, collateral branches are given off from the roots, the trunks and the cords ; and the roots are connected with the middle and lower ganglia of the cervical part of the sympathetic trunk by grey rami communicantes. The branches given oft' from the roots are twigs of supply to the longus colli, the scalenus anterior, the scalenus medius, and the scalenus posterior, the roots of origin of the long thoracic nerve, which supplies the serratus anterior (O.T. magnus) and the dorsal scapular nerve (O.T. nerve to the rhomboids). The roots of the long thoracic nerve spring from the fifth, sixth, and seventh nerves ; the upper two pierce the scalenus medius and the lowest passes anterior to that muscle. The three unite, behind the trunks of the plexus, to form the stem of the nerve, which descends behind the cords of the plexus into the axilla. The dorsalis scapulae nerve arises from the lateral border of the fifth nerve ; it disappears under cover of the levator scapulae and supplies the two rhomboid muscles, and, sometimes, the levator scapulae. The branches from the trunks of the plexus are the suprascapular nerve and the nerve to the subclavius. They both spring from the upper trunk. The collateral branches of the three cords of the plexus, are ( i ) from the outer cord : the lateral anterior thoracic nerve ; (2) from the posterior cord : the upper and lower subscapular nerves and the thoraco-dorsal nerve (O.T. long subscapular) ; and (3) from the medial cord : the medial anterior thoracic, the medial cutaneous nerve of the arm (O.T. lesser internal THE DISSECTION OF THE BACK i6i cutaneous) and the medial cutaneous nerve of the forearm (O.T. internal cutaneous). The Position of the Brachial Plexus. — The plexus lies in the lower and anterior part of the posterior triangle of the neck, partly above and partly below the posterior belly of the omo-hyoid ; posterior to the clavicle ; and in the axilla. Above the clavicle it is covered by the skin, the superficial fascia and the platysma, branches of the supraclavicular nerves, the first layer of deep fascia, the external jugTilar vein, and the terminal parts of the transverse cervical and transverse (supra) scapular veins ; the second layer of deep cervical fascia, the transverse cervical artery, the posterior belly of the omo-hyoid, the nerve to the subclavius, and the third part of the subclavian artery. Behind the clavicle it is crossed superficially by the transverse scapular artery (O.T. suprascapular). Below the clavicle it is covered by the skin and superficial fascia, the platysma, the middle supracla\acular nerves, the deep fascia, the pectoralis major, the pectoralis minor, the cephalic vein, the branches of the thoraco-acromial artery, the costo-coracoid membrane, and the axillary arter}^ and vein. Its posterior' relations in the neck are the scalenus medius and the long thoracic nerve. In the axilla the serratus anterior, the fat in the interval between the serratus anterior and the subscapularis, and finally the sub- scapularis itself. After the brachial plexus has been examined, the clavicle must be replaced in position and the skin flap, reflected from the posterior triangle, must be replaced and fixed in position by a few sutures. On the ninth day after the body is brought into the room, that is, on the sixth day after it has been placed on its back, it will be turned upon its face, with the thorax and the pelvis supported by blocks. The body will remain upon its face for five days, and during that period the dissectors of the head and neck must complete the dissection of the posterior part of the scalp ; dissect the muscles, vessels and nerves of the back and the suboccipital region ; and remove and examine the spinal medulla. THE DISSECTION OF THE BACK. Dissection. — Make a median longitudinal incision from the external occipital protuberance to the seventh cervical spine, and a second laterally from the seventh cervical spine to the acromion, and throw the flap laterally. When this has been done the posterior triangle will be exposed from behind, and the dissector should take the opportunity of noting the positions of the contents and the constituent parts of the floor from this aspect. Afterwards he must look for the superficial nerves in the superficial fascia over the upper part of the trapezius. If the great occipital nerve was not found during the dissection of the scalp secure it at once, as it pierces the deep fascia covering the upper end of the trapezius, about midway between the external occipital protuberance and the posterior border of the mastoid portion of the temporal bone ; trace it upwards through the dense superficial fascia of the scalp and clean the branches of the occipital artery which are distributed in the same region. The smallest occipital nerve will be found VOL. II — 11 1 62 HEAD AND NECK in the superficial fascia between the great occipital and the median plane. It is the medial division of the posterior branch of the third cervical nerve, and it supplies the skin of the medial and lower part of the posterior portion of the scalp