LIBRARY 
 
 ANNEX 
 
 2 
 
 Mk 
 
 ! 
 
 m 
 
 ^ 
 
 r:<#«r! 
 
 1/^ 
 
 IS' 
 
 mi 
 
 -h 
 
BOUGHT WITH THE INCOME 
 EROM THE 
 
 SAGE ENDOWMENT FUND 
 
 THE GIFT OF 
 
 Hetirg M. Sage 
 
 1891 
 
 A.nV5.S. islucllA... 
 
 5931 
 
QL 831.T47""' ""'"""•y "-'"rary 
 MlllilflMUil?Lil!!U!},S,,.P.S>v><: floor 
 
J^l 
 
 Cornell University 
 Library 
 
 The original of this book is in 
 the Cornell University Library. 
 
 There are no known copyright restrictions in 
 the United States on the use of the text. 
 
 http://www.archive.org/details/cu31924024786935 
 
THE MYOLOGY 
 
 OF THE 
 
 PE^LVIC FLOOR. 
 
 \ Contribution to Human and Comparative ' Anatomy. 
 
 BY 
 
 PETER THOMPSON, M.D. 
 
 Senior Demonstrator of Anatomy in the 
 Owens College, Manchester. 
 
 iraitb JHustratlons ana JStbUoQtapbB. 
 
 LONDON : 
 
 MCCORQUODALE & CO., LIMITED, PRINTERS — WoRKS, NeWTON. 
 
THE MYOLOGY 
 
 OF THE 
 
 PELVIC FLOOR. 
 
 A Contribution to Human and Comparative Anatomy. 
 
 BY 
 
 PETER THOMPSON, M.D. 
 
 Senior Demonstrator of Anatomy in the 
 Owens College, Manchester. 
 
 mitb Jllustrations an& asibltograpbg. 
 
 LONDON : 
 
 MCCORQUODALE & Co., Ll.MITED, PRINTERS— WOKKS, NeWTON. 
 IS99. 
 
CONTENTS. 
 
 Introduction - 7 
 Part I. :— 
 
 Muscles derived from the primitive sphincter cloaca 11 
 
 A. Superficial Perineal Muscles ib. 
 
 (1) Sphincter ani externus- ib. 
 
 (2) Transversus perinei superficialis 22 
 
 (3) Bulbo-oavernoBus (Male) 29 
 
 (4) Bulbo-cavernosus (Female) 37 
 
 (5) Ischio-cavernosus (Male) 50 
 
 (6) Ischio-cavernosus (Female) 58 
 
 E. Muscles detween.the two layers of the triangular 
 
 UGAMEN'T 60 
 
 (1) Constrictor urethree (Male) ib. 
 
 (2) Constrictor urethrse (Female) 63 
 
 (3) Transversus perinei profundus 64 
 
 (4) Ischio-pubicus 65 
 Part II. :— 
 
 Muscles derived from the primitive flexors and abductors 
 
 OF THE caudal DIVISION OF THE VERTEBRAL COLUMN 68 
 
 (1) Levator ani ib. 
 
 (2) Coccygeus 102 
 
 Bibliography- 103 
 
INDEX TO ILLUSTRATIONS. 
 
 FIGURE 
 1.- 
 
 3. 
 4. 
 
 5.— 
 
 6.— 
 
 7.— 
 
 8.- 
 
 9.— 
 
 10.- 
 
 11.— 
 
 12.— 
 
 13.- 
 
 14.- 
 
 15.- 
 
 FACINy 
 PAGE 
 
 16. 
 
 18. 
 19. 
 20.- 
 
 21. 
 
 22. 
 23.- 
 
 24.- 
 
 -Sagittal section of the pelvis to show the pelvic diaphragm and external 
 
 sphincter ani 
 ■Muscles of the male perineum ... 
 
 ■Sphincter Muscle in the Koala, showing the dififerentiation into two layers 
 ■Arrangement of the great skin muscle at the pelvic outlet in the Hedgehog 
 -Ventral view of the same from the right side... 
 
 ■Muscles of the perineum in the female 
 
 -Muscles forming the perineal triangle in the male 
 Bulbo-cavernosus in the male 
 
 ■Root of the penis in the Koala 
 
 -Bulbo-cavernosus and superficial transverse muscles in the female 
 -Crura of penis and ischio-cavernosi muscles ... 
 
 -Clitoris and ischio-cavernosi muscles 
 
 -Muscles between the two layers of the triangular ligament in the male . 
 
 -Flexor muscles of the tail in a monkey (Macacus rhesus) 
 
 -Sagittal section of the pelvis to show the pelvic diaphragm and external 
 
 sphincter ani (same as fig. 1) 
 -Pubo-coccygeus, ilio-coccygeus, and coccygeus muscles in the female 
 -Flexor muscles of the tail in a young Kangaroo, seen from the front, and 
 
 slightly from the left side, after wide separation of the symphysis . 
 
 •Flexor muscles of the tail in Echidna 
 
 -Flexor muscles of the tail in the Hedgehog 
 
 ■Pelvic diaphragm in a negro, seen from above after removal of the rectum 
 
 and separation of the pubic bones 
 
 -Muscles at the pelvic outlet in the Leopard . . . 
 Ischio-anal and coccygeus muscles in the Camel 
 
 •Perineal muscles of the Camel 
 
 Muscles of the pelvic cavity in the Wombat, from the front after wide 
 
 separation of the symphysis ... 
 
 10 
 ib. 
 18 
 ib. 
 ib. 
 22 
 30 
 32 
 36 
 38 
 54 
 58 
 62 
 70 
 
 72 
 
 74 
 
 ib. 
 
 77 
 78 
 
 ib. 
 87 
 94 
 ib. 
 
 102 
 
INTRODUCTION. 
 
 In view of the supreme importance of a precise and accurate 
 knowledge of the anatomy of the pelvic floor to the gynaecologist and 
 obstetrician, it is perhaps not surprising that special attention should 
 hitherto have been chiefly directed rather to its topographical 
 anatomy in the human subject, and particularly in the female, than 
 to its morphology and comparative anatomy. It is, however, none 
 the less remarkable that amidst the numerous and indeed almost 
 exhaustive observations which have been made in comparative 
 myology, the muscles of the pelvic floor have received but scant 
 consideration. 
 
 The pelvic floor, as so well pointed out by Dr. Berry Hart and 
 Professor Johnson Symington, is a thick compact mass traversed by 
 " clefts " or " faults " the walls of which are normally in contact, 
 but which open up for the passage of material through them. It 
 includes the whole of the soft structures that close the outlet of the 
 pelvis. 
 
 In the human subject, in whom the erect posture necessitates 
 special modifications, the functions which the pelvic floor is called 
 upon to perform are widely different from those in animals in which 
 the long axis of the body is horizontal. In most mammals the weight 
 of the abdominal viscera is largely borne by the ventral wall of the 
 abdomen, but in man the weight is sustained mainly by the floor 
 of the pelvic cavity, and this is accordingly specially modified to give 
 active support to the burden which has been transferred to it. 
 
 In all mammals the closure of the " clefts " or " faults " in the 
 pelvic floor, through which the rectal and genito-urinary canals are 
 transmitted, is brought about by the action of muscular fibres, and 
 the compact mass forming the floor of the pelvis is therefore, even 
 in its simplest form, partly muscular ; the rest is made up of 
 
8 
 
 connective tissue and integuraent. The muscular fibres, which form a 
 distinct layer in the pelvic floor, surround the canals which traverse 
 the "clefts," and they control or guard these canals at their outlet; 
 in other words, the layer is largely sphincteric in action. It is obvious 
 that a pelvic floor so constituted is not specially adapted for support. 
 
 But a great difference in the architecture of the pelvic floor is 
 apparent in those mammals in which the long axis of the body is 
 either absolutely or approximately vertical. In them the floor is 
 further modified for the support of abdominal viscera, and, in 
 addition to the layer of muscle controlling the clefts, another 
 layer is developed in the form of a well-marked diaphragm, which 
 constitutes a muscular sheet attached on all sides to the walls of the 
 pelvic cavity. In the human subject this sheet includes the levatores 
 ani and coccygei muscles. 
 
 The more highly differentiated pelvic floor, therefore, .consists of 
 a compact mass in which two distinct layers of muscles may be 
 recognised, the arrangement and functions of which are in striking 
 contrast. The upper layer, designed for purposes of support, forms 
 a more or less complete "pelvic diaphragm"; the inferior layer, 
 designed for purposes of control, forms sphincters for the openings 
 of the canals which perforate tlie floor to reach the exterior. 
 
 The two layers are not only functionally but morphologically 
 different. The sphincter muscular layer is derived from the primitive 
 sphincter cloacse, and though the muscles differentiated from it vary 
 in the lower and higher types of mammals they follow a general plan 
 of organisation. 
 
 As regards the pelvic diaphragm it is interesting to find, that 
 although it contributes to the support of viscera, the muscles which 
 constitute it are derived from the flexors and abductors of the caudal 
 end of the vertebral column. In tailed mammals this group of 
 muscles passes from the side wall of the pelvis to the tail and moves 
 that structure. But coincident with the assumption of the upright 
 posture not only is the number of caudal vertebrfe reduced but 
 the muscles which move them undergo similar retrogressive changes. 
 This group is now available for other functions, and it eventually 
 nndergoes sucli modifications as to form the diaphragm, which 
 is such an essential feature of the pelvic floor in some of the 
 primates. 
 
The two muscular layers of the pelvic floor described above, can 
 be recognized in anthropoid apes and man, and although in dissecting 
 the perineum of the latter, the number of muscular layers may be 
 greater, the increase is due, not to the presence of a third layer 
 differing in function or origin from the two described above, 
 but to modifications affecting the lower layer in such a way, that 
 its various muscles are arranged in two chief planes or strata. 
 
 In this thesis an attempt is made to describe in detail the two 
 fundamental muscular layers of the pelvic floor ; to trace the origin 
 and development of the muscles forming each, and to compare these 
 in the different groups of mammals; and finally to establish their 
 homologies. 
 
 The work is divided into two parts. The first part deals with 
 the muscles derived from the primitive sphincter cloacae and since 
 these in their most differentiated form are arranged in two planes, 
 the part is further sub-divided into two, one including the superficial 
 perineal muscles, the other, the muscles between the two layers of 
 the triangular ligament. In the former the sphincter ani externus, 
 the transversus perinei superficialis, the bulbo-cavernosus, and the 
 ischio-cavernosus are described, whilst included in the interval 
 between the two layers of the triangular ligament are the constrictor 
 urethrse, the transversus perinei profundus, and the rudimentary 
 ischio-pubicus. 
 
 In the second part of the work those muscles which form 
 the pelvic diaphragm are described. It includes the primitive 
 flexors and abductors of the caudal part of the vertebral column, viz., 
 the coccygeus, and the ilio-and pubo-coccygei, which together 
 constitute the levator ani. 
 
 The ilio-sacralis, an accessory muscle of this layer, is a represen- 
 tative of the dorsal fibres of the ilio-coccygeus in lower animals, the 
 ilio-coccygeus representing only the ventral fibres of that muscle. 
 It is invariably found in front of the coccygeus. 
 
 The pelvic diaphragm — first so-named by Meyer — is somewhat 
 funnel-shaped but much deeper behind than in front. According 
 to Dr. Dickinson, it resembles a horse-shoe attached by its anterior 
 extremities to the pubes and encircling the rectum behind, and 
 perhaps this description is calculated to convey a more correct idea of 
 itfl shape. Through the anterior part of the diaphragm are trans- 
 
10 
 
 mitted the rectum and urethra in the male; the rectum, vagina, 
 and urethra in the female. 
 
 My observations on the muscles of the pelvic floor have been 
 made on the following animals: — 
 
 MoJiotrema ^«.^Echidna hystrix. 
 
 Marsupialia. — Macropus major, Phascolomys "Wombat, Thy- 
 lacinus cynocephalus. 
 
 Edentata. — Dasypus sexcinctus. 
 
 Ungulata. — Camelus dromedarius, Equus caballus, and Bos 
 taurus. 
 
 Rodentia — Lepus cuniculus, and Cavia cobaya (several 
 specimens). 
 
 Carnivora. — FeUs leopardus, Felis catus, Canis familiaris, 
 Phoca vituHna, and Herpestes mungo. 
 
 Insectivora. — Erinaceus europseus (several specimens). 
 Chiroptera. — Pteropus medius, Vesperugo noctula (Schreber), 
 Cynonycteris aegyptiaca (Geoff.). 
 
 Primates. — Simla satyrus, and Macacus rhesus. 
 
 Many of these were obtained from the stores of the Anatomical 
 Department of the Owens College, kindly placed at my disposal by 
 Professor Young. I have also to express my indebtedness to 
 Dr. N. H. Alcock for several chiroptera and for the Phoca vitulina, 
 and to Professor Hickson for the specimen of Macacus rhesus. Some 
 of the carnivores and ungulates, and the insectivores I obtained 
 from other sources. 
 
 Further, I specially desire to express my thanks to Professor 
 Young for suggesting the subject of this investigation and for much 
 kindly help and criticism during the progress of the work ; also to 
 Professor Windle for his kindness in undertaking the examination 
 of several carnivores. 
 
M o.fl. 
 
 L.S. 
 
 - JC. 
 
 cv. 
 
 T E- BriGHAM . 
 
 oa. 
 
 ( O 3 3 - 
 
 Fig. 1. — iSaoittiil Kfction of tlie pelvis to sliow the pelvic (liaplii'ati'iii ami 
 external sphinctei- ani. S., saevuin ; M.iS.A., middle sacral artery ; L.S., 
 li2'am(,ntum sacro-coccyg-eum antcrius ; I.C, coccygcus ; C.V., coccygeal vciteljra' ; 
 Il.C, ilio-coccj'geus : T.l'.J'.C, tendinous aponeurosis of puljo-coccygeus ; In.C"., 
 raplii- formed liy ilio-coccyg'ci ; 8.R., sphincter recti; S.A.S'., S.A.S"., spliincter 
 ani externiis sulicutaneus and superficialis ; H.A.I'., spliincter rni externus 
 profundus; K., rectum; A'., vagina; U., mctlua; V.V., pulic-coccj'gens ; O.F., 
 olitiUMtoi' canal; >S.P., s_\ mpljysis pidi^s. 
 
(L C. 
 
 S.L. 
 
 T.E.BlNbHMM 
 IB97. 
 
 Fig. 2. — Muscles of tlje nialf perineiiiii. P.L., roiij);iit's ligament ; I.Cav., 
 iscliio-caverncsiis; B.C., l:nill)0-C'a\"e]nosvis : T.P.S., tr'ansversiis j>erinei supei'Hcialis ; 
 Ir..C, ilio-coccyj^'-eus ; S.L., great S:icro-sciatic ligament: P.C, i)iibo-coccygeus ; 
 S.A.S'., S.A.S"., spliinetei' arii e.xtenuis .suKientaneus and su])eitieialis ; S.A.P., 
 sphincter ani exteiims ]aofim(ius ; T.U., triangular ligament; P., jjulii.s. 
 
PART I. 
 
 fluscles derived from the Primitive Spliincter 
 
 Cloacas. 
 
 A. Superficial Perineal Muscles. 
 
 [Sphincter ani extemus, transversus perinei, bulbo-eavernosus, 
 and ischio-cavernosus.] 
 
 (1) Sphincter ani externus. 
 
 The external sphincter ani is a muscular band about an inch deep 
 which encircles the anal canal. It consists of layers of superimposed 
 fibres, and along with the pubo-rectal portion of the levator ani, it 
 forms a muscular cylinder by which the rectum is guarded at its outlet. 
 The external sphincter muscle is elliptical in shape. In its most 
 differentiated form three layers' are distinguishable, but in some cases, 
 and particularly in the female, there are only two separate layers. 
 The three layers usually existing are appropriately named — 
 
 (1) Sphincter ani externus subcutaneus. 
 
 (2) Sphincter ani externus superficialis. 
 
 (3) Sphincter ani externus profundus. 
 
 (1) Sphincter ani externus subcutaneus. — This division of 
 the muscle is situated immediately beneath the skin. Its fibres 
 surround the anal aperture and decussate in front of and behind that 
 opening. Posteriorly, the fibres fail to reach the coccyx, but anteriorly 
 they may be prolonged forwards to the scrotum, forming a rudi- 
 mentary retractor scroti as described by Straus-Durckheim in the cat, 
 and by Paulet in the tiger. In the female, in whom the subcutaneous 
 
12 
 
 sphincter is usually more strongly developed than in the male, the 
 anterior fibres also pass forwards in many oases and become con- 
 tinuous with the innermost fibres of the sphincter vaginse of the 
 same side or of the opposite side. 
 
 (2) Sphincter ani bxteenus superficialis.— As the superficial 
 sphincter is the only layer which is attached to the coccyx, it is 
 convenient to refer to it as the coccygeal part of the muscle. This 
 connection with the caudal end of the vertebral column represents 
 the primitive arrangement of the whole mass ; in the case of the other 
 layers the attachment has disappeared. It arises chiefly by means of a 
 fibrous aponeurosis from the dorsal aspect of the terminal piece of ithe 
 coccyx, though in some subjects the muscular fibres arise directly 
 from the bone, and also, according to Testut; from the ano-coccygeal 
 raphfe. 
 
 Passing forwards the muscle increases in size and at the posterior 
 margin of the anus it divides into two halves which come into contact 
 on either side with the lower part of the anal canal. 
 
 At their insertion some of the fibres become tendinous in the 
 central point of the perineum, others pass superficially towards the 
 skin, whilst many are continuous with the bulbo-cavernosus in the 
 male or the sphincter vaginae in the female. Not infrequently the 
 layer extends' outwards as far as the tuber ischii, and a few fibres then 
 terminate in the dense fibrous tissue covering that bony prominence. 
 
 In certain carnivores this stratum of the external sphincter 
 becomes considerably modified to form a muscular envelope for the 
 anal pouches. Straus-Durckheim and Paulet have both observed 
 this arrangement of the muscle in the cat and tiger respectively, and 
 it is also found in the leopard. To the muscular envelope Straus- 
 Durckheim has given the name of M. constricteur de la poche anale. 
 
 (3) Sphincter ani externus profundus. — The deep division 
 forms an annular band of some thickness in contiguity with 
 the pubo-rectal fibres of the levator ani. Its upper margin is not 
 sharply defined, because the fibres intermingle to a certain degree 
 with those of the levator ani, and the fibres of the two sides are con- 
 tinuous behind the rectum without being attached to the coccyx. 
 The disposition of the fibres in front of the anus deserves special con- 
 sideration. I have examined some thirty subjects, including both 
 sexes, with the special object of noting the relations between tlie deep 
 
13 
 
 sphincter an(i the other perineal muscles. In sixteen of these the 
 fibres of the deep division passed over to the opposite side in front of 
 the anus, and were attached to the ascending ramus of the ischium. 
 In the remainder, however, the fibrous tissue constituting the perineal 
 body extended into the layer, and separated those fibres passing to the 
 ischium from those in contact with the rectum. Thus, in about half 
 the cases examined the fibres were uninterruptedly continuous. The 
 fibres passing to the ischial ramus represent the transversus perinei, 
 and obviously this muscle is closely connected with the deep layer of 
 the external sphincter, a fact which will be referred to at greater 
 length in discussing the morphology of the transversus perinei. The 
 continuity has been noticed by many writers, especially by Theiie 
 and Velpeau. 
 
 Action and Neeve-Sdpply. — By the tonic contraction of the 
 three layers of the sphincter ani externus both the anus and the 
 anal canal are kept closed. Although this action is carried out 
 involuntarily, the muscle is under the control of the will, and 
 the canal may be forcibly occluded if necessary. In this action the 
 muscle is assisted by the pubo-rectalis and the internal sphincter, 
 though the latter is only to a very slight degree controlled by the will. 
 Thus, by a voluntary act the expulsive force exerted by the walls 
 of the rectum can be resisted, but only up to a certain point. 
 When the pressure above becomes very great the strongest voluntary 
 efforts directed to the contraction of the external sphincter may be over- 
 come. An oppositeaction of the muscle may be brought into play at the 
 last stage of defaecation. After inhibition of the reflex action 
 of the sphincters, the pressure above forces the contents of the rectum 
 through the anal canal. To^rards the end of this movement the 
 external sphincter along with the pubo-rectalis may be forcibly con- 
 tracted, so that the muscle now assists and completes the action of the 
 circular fibres of the rectum, that is to say, instead of retarding the 
 progress of the contents of the bowel it assists in their extrusion. 
 While this action is more apparent in the case of constipation, it may 
 be carried out to a greater or less degree in every act of defaecation. 
 When the anal canal is closed the external sphincter attains its 
 greatest depth, and further, it is flattened from side to side so that its 
 length much exceeds its breadth. When the canal is dilated the muscle 
 becomes more flattened in a vertical direction, and also more circular. 
 
 The external sphincter derives its nerve-supply from two sources — 
 
14 
 
 the internal pudic and the perineal branch of the fourth sacral. The 
 1 xtter supplies the coccygeal part of the muscle, whilst the pudic, through 
 the inferior haemorroidal, gives branches chiefly to the two layers 
 which have no attachment to the coccyx. The branches from the 
 inferior haemorroidal can usually be found by raising the outer border 
 of the superficial division of the muscle, and twigs can be traced 
 through it into the subcutaneous layer. 
 
 In the numerous descriptions which have been given of the 
 Sphincter ani exteknus, authors are by no means agreed as to the 
 number of divisions which may be recognised. Whilst most writers 
 describe one, others — notably Cruveilhier, Luschka, and Theile — have 
 described two. Bourgery also describes two layers, a superficial 
 sphincter and a deep sphincter, and the latter he names the rectal 
 sphincter. Santorini was the first to indicate the division into three 
 layers, and more recently Holl has figured and described a like 
 number. Paulet also describes three layers in the tiger, and this 
 arrangement also exists in the camel and leopard. My observations 
 support the view taken by Holl, and I am satisfied that the trilaminar 
 arrangement of the fibres of the muscle is the most common. 
 
 The separation of the muscle into its constituent parts is well 
 shown by distinct connective tissue septa, which Holl refers to "as 
 prolongations from a fibro-elastic membrane, in close contact with the 
 longitudinal muscular fibres of the intestine, to the skin of the anus." 
 
 That the trilaminar condition of the muscle is both fundamental 
 and primitive is furthur shown by phylogenetic considerations. The 
 primitive ventral muscle, from which, as I hope to show, the three 
 layers of the sphincter ani externus are derived, is differentiated into 
 three chief planes or strata, viz., the external oblique, internal oblique, 
 and transversalis. The trilaminar arrangement of the external sphincter 
 ani simply repeats this division, so that each of the three layers arises 
 from the corresponding stratum of the primitive ventral muscle. 
 
 From the external oblique stratum there arises, according to 
 Humphry, a superficial layer more or less completely segmented 
 from the remainder, and which, retaining its connection with the skin, 
 furnishes the group of subcutaneous muscles. 
 
 In some animals, notably the hedgehog, the great skin muscle 
 {pannicuhiB carnosus) comes into close association at the outlet of the 
 pelvis with the end of the digestive tract, somewhat similar to the 
 
15 
 
 arrangement of the muscle at the opposite end of the alimentary 
 canal and the face generally. In the highest mammals the skin 
 muscle has undergone a striking reduction so that it is now 
 represented in man, for example, by the platysma myoides and the 
 cutaneous facial muscles. I venture to associate with this group the 
 subcutaneous layer of the external sphincter. As the great skin 
 muscle has undergone a process of shrinking, a rudiment has 
 remained behind at the pelvic outlet immediately surrounding the 
 anal aperture. In accordance with this view the sphincter ani 
 externus subcutaneus must be considered as a derivative from the 
 primitive external oblique stratum. 
 
 Again, the primitive sphincter cloacte is usually regarded as the 
 layer of muscle from which the external sphincter and other muscles 
 of the perineum arise. Gegenbaur has shown that the original junction 
 of the termination of the rectum with the uro-genital sinus, forming 
 a temporary cloaca, is of great importance in studying the complicated 
 condition of the muscles in the perineum. He takes as the starting 
 point the sphincter cloacae, a muscular ring surrounding the cloaca 
 which is partly attached to the bones at the pelvic outlet. With the 
 disappearance of the cloaca the muscle subdivides into different 
 groups one belonging to the anus, another to the uro-genital canal, and 
 a third the different parts of which, strictly speaking, do not belong 
 to either of the two. 
 
 Although the view that the external sphincter ani is derived 
 from the sphincter cloacae is generally accepted it is probable 
 that only a part of the sphincter arises in this way. This is the 
 external sphincter ani superficialis, and by its attachment to the 
 coccyx it retains the relations of the primitive ventral muscle which 
 extended backwards into the caudal region. According to Humphry, 
 the superficial muscles, viz., those derived from the primitive sphincter 
 cloacae are derived from the internal oblique stratum ; and the super- 
 ficial layer of the external sphincter must in this case be regarded as 
 having the same origin. 
 
 Finally, Lesshaft regards the external sphincter as a part of the 
 levator ani, and in his account of the latter muscle he divides it into 
 
 Ruge, in his monograph on the skin muscles of monotremes, refers to the relations 
 existing between the musculature and the opening of the cloaca in Echidna. A 
 kind of sphincter cloacae is formed, the existence of which seems to be bound up with 
 the primitive marsupium, which is missed in higher mammals. 
 
16 
 
 two parts, the levator ani proprius and the sphincter ani externus. 
 Professor Macalister also describes the superficial sphincter (which he 
 divides into two strata, a superficial and a deep,) as a segmentation 
 from the levator ani. Bearing in mind the origin of the subcutaneous 
 and superficial layers of the external sphincter, it is probable that the 
 division of the. muscle arising from, the transversalis stratum is the 
 sphincter ani externus profundus, but it is not so clear that it is a 
 segmentation of the levator ani. 
 
 Varieties of the Sphincter Ani Externus. — Judging from 
 the numerous illustrations in text-books of anatomy, and from 
 a study of special dissections, specimens are not infrequently seen 
 which do not conform to the description which has been adopted 
 above. This is probably accounted for to a large extent by the 
 variations to which the muscle is liable. The more important varieties 
 follow along well-marked lines and depend upon fusion of two strata 
 of the muscle either wholly or in part. When this occurs, the anal 
 sphincter assumes a characteristic flattened, elliptical form, which is 
 found more frequently in the female than in the male. Indeed, 
 so frequently does the variation occur in the former that one associates 
 the cylindrical form of muscle with the male sex, and the flattened, 
 elliptical form with the female sex. 
 
 It may, therefore, be stated that there are two chief types:0f the 
 external sphincter ani, the male type and the female type. Both 
 are figured in the accompanying illustrations, the former in fig. 2 
 and the latter in fig. 6. As the cylindrical form was the basis of the 
 general description given above, a brief description may now be given 
 of the main features of the second type. 
 
 By referring to fig. 6, a drawing of the external sphincter 
 is seen, in which a common arrangement of the muscular fibres in the 
 female is indicated. The muscle was strongly developed, and 
 measured 4J inches in length, and each half ^^ inch in width. 
 
 Immediately beneath the skin and covered only by a thin layer of 
 subcutaneous tissue was a flat layer of muscle surrounding the lower 
 part of the anal canal. It arose behind by a slender band of muscular 
 fibres from the dorsal aspect of the last piece of the coccyx. The 
 band was IJ inches long, and at the posterior margin of the anus 
 it divided into two parts, which passed forwards on either side to 
 the central point of the perineum. At the place of division the layer 
 was markedly accentuated both in size and strength by a series of 
 
17 
 
 fibres which passed from one side to the other behind the anus. 
 These commissural fibres had no attachment to the coccyx, and 
 appeared to represent the sphincter ani externus subcutaneus. 
 
 Under cover of this layer was a distinct muscular stratum passing 
 around the rectum, and then in front of the anal opening to the 
 ascending ramus of the ischium of the opposite side. It was attached 
 to the bone superficially "to the erector clitoridis and this part 
 represented the transversus perinei. 
 
 The nerve-supply was of special interest. The perineal branch of 
 the fourth sacral supplied the coccygeal part of the muscle, whilst a 
 branch from the inferior hsemorrhoidal could be traced to the 
 commissural fibres of the superficial layer as well as to the deep layer. 
 Thus, the female type of external sphincter ani differs from the male 
 type in that the subcutaneous and superficial layers are fused togetlier 
 to form a flat elliptical muscle. The sphincter ani externus profundus 
 remains distinct, as in the male. 
 
 The other varieties which are to be noted of the external sphincter 
 do not claim much attention. It is only necessary to refer to an 
 occasional slip directed to the ascending ramus of the ischium, in 
 addition to the one forming the transversus perinei. Tiedemann names 
 this band of fibres the transversus perinei posticus, and regards it as 
 an independent muscle. On the other hand Theile, who has observed 
 the muscle occasionally, and in both sexes, is of opinion that it is a 
 separated part of the external sphincter ani. 
 
 Comparative Anatomy. — ^It is somewhat remarkable that although 
 so many investigations have been made in comparative myology, 
 the group of perineal muscles has, until quite recently, been almost 
 entirely neglected. 
 
 The observations of Eggeling on marsupials, of Lartschneider on 
 carnivores and primates, of KoUman on tailed apes and anthropoids, 
 of Paulet on carnivores and ungulates, and of HoU on the .muscles of 
 the pelvic outlet, constitute a series of important contributions, how- 
 ever, to the comparative myology of the perineal muscles. 
 
 Paulet, as the result of his observations, came to the conclusion 
 that '' each of the constituent parts of the perineal region in man has 
 its homologue in the perineal region of mammals." The number of 
 animals examined by Paulet was, however, small and this conclusion 
 can only be accepted in a general sense. In lower mammals the 
 arrangement of the perineal muscles is more primitive and less 
 
18 
 
 specially differentiated than in higher types. Some of the perineal 
 muscles do not appear at all in lower mammals. Thus, so far as my 
 dissections show, the transversus perinei does not exist.in marsupials, 
 insectivores, ungulates, and chiroptera, though it is found in carni- 
 vores and primates. 
 
 On the other hand, the external sphincter ani is one of the most 
 constant muscles in mammals, and attains greater development in 
 some of the lower groups than in man. This probably finds explana- 
 tion in the fact that in the latter the levator ani is the more important 
 sphincter of the rectum, whilst in the former the homologous muscles 
 move the tail, and do not form such intimate relationships with the 
 end of the alimentary canal. 
 
 The external sphincter has not the same arrangement in all mam- 
 mals. In monotremes, which are the only representatives possessing 
 a distinct cloaca, we find a sphincter cloacae ; in marsupials a 
 common sphincter surrounds the anal and uro-genital openings. 
 In most other mammals these openings are completely separated from 
 one another, and the anus is then surrounded by its own special 
 sphincter. 
 
 Maesupialia.— In marsupials the common sphincter is differen- 
 tiated into two parts : — a superficial sphincter and a deep sphincter. 
 In the wombat, which possesses a rudimentary tail, the division is 
 especially evident. The muscle is attached to the root of the tail 
 and the bones of the pelvic outlet. I have found a somewhat 
 similar arrangement in Thylacinus and Macropus. The attach- 
 ment to the bones, however, in these animals is not so well marked. 
 Eggeling has examined the muscles of the pelvic outlet in a large 
 number of marsupials including, Phalangista canina, Dasyurus 
 maugei, and Halmaturus Bennetii. He describes the division of 
 the common sphincter into two layers as the usual arrangement, and 
 regards the differentiation as due to the growth into it of the anal 
 glands, which, together with some loose fatty tissue, are found under 
 cover of the superficial layer. 
 
 The division of the sphincter has also been recognised by Professor 
 Young in the Koala (fig. 3). He describes the muscle under the name 
 of sphincter cloacae, and states that " it consists of an external stratum 
 of muscular fibres, which, commencing broad beneath the coccyx, 
 but having no direct attachment to it, passes on each side of the 
 penis, anus, and glands, and surrounds all. Converging, the fibres 
 
C.P 
 
 s,c 
 
 s.c: 
 
 Fig. 3. — Tliu sjiliiiiL-ttT rnusclc in tlie Koala {Phnscolarcto.s cinereuy) 
 sliowing the diffei'entiatiun into twu jiaits. S.C. the 8U|)ei-ticial s].iliineier, anfl 
 S.C, the deep .s^jhincter. Between the two layers are 0.(J., the Cowjjerian 
 f^lands, and tJie bull is of the corpus spongiosum. (From a drawing by 
 Professor Young). 
 
R op 
 
 R - 
 
 Fig. 4. — The arrange- 
 ment of.;the great skin 
 muscle at the ].ielvic outlet 
 in the Hedgehog (Erinaceus 
 euvopitus). H.A., humero- 
 alwloniinalis ; H.C., super- 
 licial sphincter muscle 
 R.l'., retractor penis; P., 
 penis; S.P., section of 
 corpora cavernosa; R.P.P., 
 reti'actor preputialis ; A., 
 
 MA. 
 
 HA 
 
 S.R' 
 
 Fig. 5. — Ventral view 
 of tlie same from the ilglit 
 side. M.A., median ap- 
 <ineui'Osis on the dorsum of 
 tlie penis ; other lettei's as 
 aliove. 
 
 /•^^ 
 
 \' 
 
19 
 
 form a rounded bundle over the dorsum of the penis. Another set of 
 fibres, united with these in the latter situation only, surround the 
 penis and anus, forming a deeper stratum. The Cowperian glands, 
 and the bulbs of the corpus spongiosum, are situated between the 
 two strata, these latter being connected by intermediate muscular 
 fibres which pass between the glands. None of the fibres have any 
 attachment to the pelvis." 
 
 Edentata. — In Dasypus sexcinctus the external sphincter is 
 separated into two divisions : — a superficial and a deep. These appear 
 to correspond to the external and internal sphincters in the cat and 
 other carnivores. In their attachments and relations they resemble 
 the superficial and deep layers of the sphincter ani externus of human 
 anatomy. 
 
 XJngulata. — The sphincter ani in the camel is a powerfully- 
 developed muscle one and a quarter inches deep and consists of 
 a series of muscular rings with fibrous intervals. The whole muscle 
 is attached to the under surface of the root of the tail by a fiat fibrous 
 band, and in consequence of the varying relations of the fibres, 
 it can readily be divided into three layers. 
 
 The most superficial fibres are arranged in a circular manner 
 around the anus. The succeeding ones arise directly from the fibrous 
 aponeurosis and are directed downwards on either side of the rectum. 
 Below the anus some of the fibres decussate in the middle line, but 
 the majority are inserted into the fibrous tissue between the anus and 
 the bulbs of the penis. The deepest fibres are similarly disposed on 
 the side wall of the rectum, but below the anus they are gathered into 
 a thick muscular band, which is continuous with the one of the 
 opposite side. In the illustration (fig. 23) only the- superficial and 
 middle layers are shown. In the dissection, from which the figure is 
 taken, the deep layer was concealed by the other parts of the muscle. 
 
 It is interesting to note that Paulet, from an examination of the 
 external sphincter in three species of deer, describes the muscle as 
 composed of circular fibres arranged for the most part regularly, but 
 in one instance he found a transverse band passing from the 
 external sphincter to be attached to the posterior part of the ischial 
 tuberosity. 
 
 Chiroptera. — Among the chiroptera I have had the oppor- 
 tunity of examining the external sphincter in Pteropus medius, 
 Vesperugo noctula (Schreber), a small'Sized bat with a long tail, and 
 
20 
 
 Oynonycteris segyptiaca (Geoff.); a larger specimen with a very 
 rudimentary tail. In the long-tailed species the sphincter ani was 
 attached to the under surface of the caudal vertebrae, and for a very 
 limited extent to the bony boundary of the pelvic outlet. In Pteropus 
 medius, but markedly so in Oynonycteris, the muscle had a more 
 extensive attachment to the rami of the pubis and ischium. With the 
 reduction of the tail, the attachments of the muscle to the pelvis 
 apparently become of greater importance, and in consequence more 
 extended. The support which the rectum obtained from the caudal 
 vertebrae through the external sphincter in long-tailed bats, is obtained 
 to a large extent from the lower border of the pelvis in the short-tailed 
 species. 
 
 It seems probable that we have here an illustration of an important 
 stage in the phylogeny of the primitive sphincter cloacae. The attach- 
 ment of the muscle to the bones at the exit of the pelvis, is followed 
 later by the differentiation of the erector penis, bulbo-cavernosus, 
 constrictor urethrae, and other muscles of the perineum from it. 
 
 Insectivora. — Dobson, in his admirable monograph on the 
 insectivora, says of Erinaceus europaeus : " In no species of the class 
 mammalia are the skin muscles of such vital importance to the animals 
 possessing them, for it is by their action that the representatives of this 
 genus are enabled to roll themselves into a ball, and thus, protected on 
 on all sides by their spinj' armour, defy the attacks of most predaceous 
 animals." I therefore examined the cutaneous muscles of this animal in 
 the region of the pelvic outlet with special interest, particularly noting 
 their relations to the external openings of the rectal and genito-urinary 
 passages. A strong sphincter muscle surrounds the base of the tail, the 
 anus, and the root of the penis. Although quite separate at the pelvic 
 opening, dorsally, it still retains its connections with a large skin 
 muscle, the humero-abdominalis or platysma ven trails (figs. 4 and 5). 
 
 In the illustrations (figs. 4 and 5) two other muscles are shown : — the retractor 
 preputialis and retractor penis. Both are derived from the humero-abdominalis, 
 according to Dobson. The retractor preputialis is attached behind to the root of 
 the tail and to the ischium near its tuberosity. Passing forwards on either side 
 of the anus, the two muscles form a muscular sheath for the penis which extends 
 as far as the prepuce. The retractores penis consist of a, pair of slender 
 muscles which take origin from the side of the tail. They pass downwards and 
 surround the penis near its root, and, meeting on the dorsum, unite to form n 
 muscular layer which runs as far as the glans penis. The dorsal nerves of the 
 penis run forwards between the two rnuscles, 
 
21 
 
 In addition, a circular band of muscular fibres surrounds the lower 
 end of the rectum. In the hedgehog, therefore, the external sphincter- 
 consists of two parts: — (1) a subcutaneous layer derived from the 
 platysma ventraHs, and (2) a superficial layer derived from the 
 primitive sphincter cloacae. Of these, the former is. much more 
 important. 
 
 Carnivora. — Straus- Durckheim has described in the cat a 
 sphincter externus and a sphincter internus. The former he divides 
 into three parts: — (1) sphincter of the anus, (2) the constrictor of 
 the anal pouches, (3) the levator of the scrotum in the male, or the 
 constrictor of the vulva in the female. 
 
 The "sphincter internus" forms a muscular ring, red in colour, 
 quite distinct from the circular fibres of the intestine. It does 
 not correspond, therefore, to the internal sphincter of human anatomy, 
 but to the sphincter ani externus profundus. The sphincter externus 
 includes the subcutaneous and superficial layers. 
 
 In the female leopard a continuous muscle surrounds the 
 root of the tail, the anus, the anal pouches, and the vulva. It is 
 attached to the sides and under surface of the tail opposite 
 the fifth caudal vertebra; the fibres, however, are not continuous 
 over the root, as Straus-Durckheim describes in the cat. Continuing 
 downwards the muscle divides into two portions which pass on either 
 side of the anus and vulva, to terminate in the superficial fascia over 
 the pubes. Some of the innermost fibres of each portion decussate 
 above the anus, others pass to the interval between the anus and the 
 vulva, and join with fibres from the opposite side, whilst over the pubes 
 the two halves partly unite again before terminating in the superficial 
 fascia. In front of the external sphincter and the anal pouches with 
 their coverings, is a circular band of muscular fibres — the " interna! 
 sphincter " — continuous below the anus ^^'ith the transversus perinei 
 muscle. 
 
 Paulet has examined the external sphincter in the dog, wolf, and 
 tiger. In the first and second of these he finds that tlie disposition 
 of the muscle is very simple and closely resembles the arrangement in 
 man. In the tiger it is much more complicated, and three layers of 
 fibres are distinguishable : — (1) the superficial layer or retractor muscle 
 of the scrotum, (2) the true anal sphincter, and (3) the constrictor of 
 the anal pouch. 
 
22 
 
 (2) Transversus Perinei Superflcialls.^ 
 
 Under this name is included a number of muscular fibres, varying 
 in arrangement, situated transversely in the perineum between the 
 ascending ramus of the ischium and the perineal septum. It is only 
 in comparatively few subjects that the muscle is strongly developed. 
 More frequently, it is represented by one or more feeble muscular 
 slipl, or by a few aponeurotic fibres, whilst in a number of cases it 
 fails entirely. 
 
 Attachments. — The transversus perinei gains attachment to the 
 ascending ramus of the ischium by tendinous fibres, situated either 
 superficial or deep to the ischio-cavernosus. Also, to the base of the 
 triangular ligament, a short distance in front of the line of union with 
 the superficial perineal fascia. Occasionally, a few fibres are attached 
 to the interlobular fibrous septa over the tuber ischii or the anterior 
 part of the ischio-rectal fossa. 
 
 At the perineal septum its connections are worthy of special 
 notice, since the muscle is usually described as terminating in the 
 central point of the perineum, and uniting with the corresponding 
 muscle of the opposite side. Although this arrangement may be 
 observed in some cases, it is by no means uniform, and many show 
 an altogether different disposition. 
 
 I have already pointed out (page 13) in describing the external 
 sphincter, that in some cases the deep layer of that muscle was 
 continuous with the transversus perinei of the opposite side, whilst in 
 others, the continuity was interrupted by the perineal body, with 
 which each muscle appeared to be connected. Occasionally, a few 
 fibres become detached from the transversus perinei between the 
 perineal septum and the ischium, and join with the bulbo-cavernosus 
 or the external sphincter of the same side. 
 
 The muscle assumes a more triangular shape in the female than 
 in the male, and like the external sphincter, shows a greater 
 tendency to flattening, especially at its outer part near the ischial 
 ramus. In both sexes it is often unequally developed on the two sides, 
 and I can support the statement made by Lesshaft, that it is more 
 frequently ill-developed on the right side than on the left. I found 
 that on the right side the muscle was feeble and indefinite in 37 %, 
 
 Transversus Perinei medius of Lesshaft. 
 Transverso-anal of Cruveilhier. 
 
- C.R.C, 
 
 Cav. 
 
 s.v. 
 
 T, RS. 
 
 1. 
 
 I C. 
 
 G M. 
 
 >P 
 
 <w->^ 
 
 Fig 6. — Muscles of the perineum in tlje female. C.R.C, constrictor radicis] 
 clitoridis ; LCav., ischio-cavernosus ; 8.Y., sphincter vagin;^ ; T.P.S., transvcrsus 
 [lerinei superticialis ; O.I., ul.iturator internus ; I.C, cocrycreus ; dS.M., gluteus 
 niaximus ; S.A.iS'., 8. A. 8"., sphincter ani externus siibcutaneus, and supet'ticialis ; 
 E.8.P., sphincter ani externus profundus ; Ii..C, ilio-coccygeus ; P.C., pulio- 
 coC'C3'^''eas ; T.U., triangular ligament; V., vagina; C, clitoris. 
 
23 
 
 whereas on the left side this was noticed only in 27%. It not 
 uncommonly happens in these cases that the muscle on the left side, 
 for example, is strong and triangular in shape. In front of the anus 
 it divides into two strata, a superficial and a deep. The superficial 
 fibres pass to the central point of the perineum, whilst the deeper 
 ones are continuous with the sphincter ani profundus. That on the 
 right side may be so feeble that it fails to reach the middle line, 
 and in that case it is usually directed forwards to join the ischio- 
 cavernosus or the bulbo-cavernosus of the same side. 
 
 It is important to note the number of cases in which absence 
 of the muscle has been recorded. Lesshaft, after examining eighty 
 female subjects, recorded its absence fifty-five times, i.e. 68"75%. 
 It was absent on both sides nineteen times, i.e. 23'75%, and on one 
 side only, thirty-six times, i.e. 45%. Of the latter, absence was 
 noted on the right side twenty-five times, i.e. 31"25%, and on the 
 left side eleven times, i.e. 13'75%. In thirty subjects in which I made 
 special search for the transversus perinei it was absent in fourteen, 
 i.e. 4:6-5%,. Of these it failed on both sides six times, i.e. 20%, and on 
 one side only, eight times, i.e. 26'5%. It should be pointed out, 
 however, that the thirty subjects included eighteen males and fourteen 
 females, and that according to my observations the muscle is less 
 constantly present in the latter, in the proportion of six to eight. 
 This may account for the higher number of failures recorded by 
 Lesshaft. 
 
 Action and Neeve-Supply. — It is usually stated that when 
 the transversi perinei contract, the central point of the perineum is 
 fixed and that this favours the contraction of the bulbo-cavernosus. 
 It thus acts as an accessory muscle in emptying the urethra. 
 
 But, as we have previously seen, the muscle is frequently absent 
 in man, and altogether unrepresented in many of the lower mammals. 
 Its absence, however, does not appear to exercise any adverse 
 influence on the efficiency of either the external sphincter ani, or the 
 bulbo-cavernosus. Indeed, it is difficult to see how its action can be 
 of much importance, and, when present, although it may take an 
 active part in the genito-urinary functions, its intervention is probably 
 not essential. 
 
 The transverse muscle usually derives a branch from the perineal 
 division of the pudic nerve, as this courses along its posterior border. 
 In several of the dissections in which there was undoubted continuity 
 
24 
 
 with the deep layer of the external sphincter, a branch was found 
 passing into the transversus perinei either from the inferior hsemorr- 
 hoidal, or from the nerve to the external sphincter ani. 
 
 A reference to the literature of the transverse muscle of the 
 perineum, reveals an astonishing lack of uniformity in description. 
 Quite different accounts are given by Lesshaft, Tiedemann, Cruveilhier, 
 Bourgery, Theile, and others, although these seem to be based largely, 
 upon a division of the muscle into two or more parts. 
 
 The most elaborate description is given by Lesshaft. He refers to 
 three transverse muscles of the perineum: — (1) transversus perinei 
 superficialis, (2) transversus perinei medius, and (3) transversus 
 perinei profundus. As the last named is situated between the two 
 layers of the triangular ligament, its description is best deferred 
 until we consider the muscles occupying this space. The medius 
 corresponds to the superficialis of other authors, with the exception of 
 Gruber, who adopts the same nomenclature as Lesshaft. The 
 transversus perinei superficialis of Lesshaft and Gruber is therefore an 
 accessory muscle, to which further reference must now be made. 
 
 Lesshaft points out that the transversus perinei superficialis lies in 
 the superficial fascia, and that it is easily removed during dissection. 
 During the examination of 74 female subjects, he found it once on 
 both sides and five times on one side, i.e. 8'1 %, and of the unilateral 
 variety three occurred on the right side and two on the left. It takes 
 origin from the fascia covering the tuber ischii, and passing obliquely 
 to the central point of the perineum, gains insertion into the connective 
 tissue which forms the lower end of the perineal septum, where the 
 fibres from both sides meet and fuse in the case of paired muscles. I 
 noticed the occurrence of an accessory transverse muscle immediately 
 beneath the skin in two subjects in the practical anatomy rooms of 
 the Owens College, during the winter session of 1897-98, and in each 
 case I regarded the accessory muscle as an additional rudiment of the 
 panniculus carnosus. Embleton has recorded, as an anomaly in the 
 perineum, two transverse muscles on each side, and Gruber three 
 cases of transversus perinei superficialis arising outside the perineum 
 from the fascia over the gluteus maximus. 
 
 Tiedemann, in his plates of the arteries of the human body, shows 
 
25 
 
 t^vo transverse muscles on each side, which he calls the transversi 
 perinei posticus, and anticus. They appear to correspond to the 
 superficialis and medius of Lesshaft. 
 
 Henle, on the other hand, describes one superficial transverse 
 muscle (medius of Lesshaft), and includes the subcutaneous fibres 
 (sui)erficialis of Lesshaft) in his list of varieties. This adoption 
 seems much preferable. At least, it avoids the introduction of 
 additional terms which may lead to confusion in nomenclature. 
 
 A brief reference is necessary to an x)ccasional muscle in the 
 perineum, which was first described by Cuvier as the ischio- 
 bulbosus. Lesshaft, Holl, and Jarjavay refer to it as an accessory 
 head of the bulbo-cavernosus, whilst Paulet regards it as a few 
 separated fibres of the transversus perinei superficialis. It will be 
 referred to at greater length in the description of the bulbo-cavernosus. 
 
 Morphology. — From a consideration of the foregoing state- 
 ments, it seems reasonable to suppose that the transversus perinei 
 muscle in man is not an independent muscle, but a derivative from 
 some other muscle in its immediate neighbourhood. It is usually 
 regarded as a segmented portion of the primitive sphincter cloacae, 
 which, according to Gegenbaur, becomes differentiated into a posterior 
 or anal division, and an anterior or uro-genital division when 
 the cloacal stage is passed. It is from the uro-genital division that 
 the bulbo-cavernosus, the ischio-cavernosus, and the transversus perinei 
 are believed to arise, and as far as I have been able to ascertain, with 
 the exception of Holl, no objection seems to have been raised against 
 this view. 
 
 In 1897, Holl suggested that the transversus perinei was derived 
 from the" levator ani. He described it as arising from the innermost 
 fibres of the pubo-rectalis, i.e., from those fibres of the leva.tor 
 ani which arise from the pubis and surround the rectum. After 
 arising from the back of the pubis, the fibres become detached 
 from the pubo-rectalis and crossing at the central point of the 
 perineum, gain attachment to the ascending ramus of the ischium of 
 the opposite side. He points out that the decussation of the fibres at 
 the central point may be interrupted by the intervention of tendinous 
 tissue, so that the primitive arrangement is lost. 
 
 A consideration of the arrangement of the muscles corresponding 
 to the levator ani in some of the lower animals in which the 
 transversus perinei is present, will not however allow us to accept, 
 
26 
 
 at least without some qualification, the view advanced by Holl. 
 In carnivora, for example, two muscles, the ilio-coccygeus and pubo- 
 coccygeus correspond to the levator ani of primates, but instead of 
 being intimately associated with the rectum, they belong to a group 
 of muscles whose function is to move the tail. No fibres encircle the 
 rectum to form a muscular sling as in man, and none pass to the central 
 point of the perineum. It is only when the tail atrophies and the 
 upright posture, either partial or complete, is assumed that we find 
 fibres passing to the central point of the perineum from the re- 
 formed tail muscles (levator ani), and consequently it is only then 
 that the central decussation, to which Holl refers, could occur. 
 Further, a trans versus perinei is a conspicuous object in the pelvic 
 outlet in a leopard or a cat. It is difficult to see how such a 
 transverse muscle could originate from one which passes from the 
 side wall of the pelvis to the tail, and whose action is almost 
 wholly exerted in moving that structure. I might mention that, 
 on one occasion, I found a few fibres passing from the levator ani 
 to the ascending ramus of the ischium on the same side in man, 
 but they did not pass through the central point of the perineum. 
 A trans versus perinei was present in the same subject on both sides. 
 
 I have already pointed out in the description of the external 
 sphincter ani that the irregular fibres, which are included under the 
 name of transversus perinei of human anatomy, represent simply 
 an extension of the external sphincter ani profundus to the ascending 
 ramus of the ischium, and as such, must be regarded as derived 
 from the transversalis stratum of the primitive ventral muscle. 
 
 The attachment to the bony pelvis tends to increase the efficiency 
 of the external sphincter. The lower end oi the rectum is fixed 
 and sustained against downward pressure, whilst contraction of the 
 fibres elevates the rectum towards the pelvic cavity, and in this way 
 it supplements the action of the pubo-coccygeus. The looped 
 arrangement of the fibres also contributes to the greater efficiency 
 of the sphincteric action of the muscle. 
 
 Such a view receives support from a consideration of its nerve- 
 supply. It is always supplied by the internal pudic nerve, either 
 through the perineal or the inferior haemorrhoidal branch, and it is 
 interesting to note, that when the nerve-supply was directed through 
 the haemorrhoidal, the continuity of the two muscles was most 
 perfectly retained. 
 
27 
 
 Finally, Holl regards all inconstant muscular fibres which arise 
 from the corpus cavernosum, the ischio-cavernosus, or the triangular 
 ligament, as vestiges of the most superficial layer of the bulbo- 
 cavernosus, i.e., a part of the anterior division of the primitive 
 sphincter cloacae which takes origin from the frame of the pelvis or 
 its neighbourhood. 
 
 Comparative Anatomy.— The transverse muscle of the perineum 
 is perhaps more frequently absent than present, and even in those 
 mammals in which it has been observed, its occurrence is not constant. 
 The muscle is found most frequently in carnivores and primates. 
 
 In the monotremes, marsupials, edentates, ungulates, chiroptera, 
 and insectivores which I have had the opportunity of dissecting, it 
 was not present. Dobson, however, found it in one of the last-named 
 group, viz., in centetes. 
 
 In carnivores I have found the muscle present in the leopard, 
 and other investigators have either described or observed in different 
 carnivores what must be regarded as the transverse muscle of the 
 perineum. Thus, Straus-Durckheim describes in the cat a muscle 
 which he names the " p6rin6en," and which in his opinion 
 corresponds to the transversus perinei of human anatomy. Professor 
 Windle, who very kindly examined for me six specimens from his 
 unique collection of carnivores found a well marked transversus 
 perinei in Ursus americanus and in Cynictis. Still, it is by no 
 means a constant muscle even in carnivores, since Professor Windle 
 failed to find it in the jackal, the kinkajou, the ichneumon, or the 
 fossa, and it is also absent in the dog. Paulet failed to find it also in 
 the tiger, wolf, and dog, and states that no muscle identical with that 
 which we describe in man under the name of superficial transverse, 
 i.e., a muscle directed from the ischial tuberosity to the median line 
 where it terminates immediately in front of the anus, exists in 
 carnivores. There is, however, according to Paulet a transverse 
 muscle in the animals named, to which there is no corresponding 
 muscle in ruminants and solipeds, the study of which is very impor- 
 tant from the point of view of estabUshing the homologies' between 
 the- perineum of man and monodelphian mammals. Cuvier has 
 described the same muscle in the bear, raccoon, and in the greater 
 apes. Because of its relations to the urethra, Paulet names it the 
 transverso-urethral muscle. This is probably ^e same muscle which 
 Houston describes as the compressor velfse dorsalis penis, and 
 
28 
 
 Vlacovitch as the ischio-pubicus. That the transversus perinei is 
 present, however, in some carnivores is beyond doubt, and more 
 frequently so indeed, than in any other group of mammals except 
 primates. 
 
 In the appended list I have given the names of those animals in 
 which the transversus perinei has been observed and also those in 
 which its absence has been noted. Very few observations have been 
 published on the transverse muscle in lower mammals so that the Hst 
 is necessarily short and incomplete. At the same time it shows in 
 which groups of mammals the muscle is usually absent, and in which 
 groups it is usually, though by no means invariably, present. 
 
 Monolremata. — St. George Mi vart, who has dissected the perineal 
 region of Echidna hystrix very completely, does not mention the 
 transverse muscle. It was absent in a specimen which I dissected. 
 Marsupialia. — Neither Cunningham, EggeUng, nor Young, 
 describe the muscle iti any specimen of marsupial. It was absent 
 in Phascolomys Wombat, Macropus major, and Thylacinus cyno- 
 cephalus according to my own dissections. 
 
 Edentata. — The muscle was absent in Dasypus sexcinctus. 
 Ungulata. — Said to be present in Equus. Paulet thinks 
 that if the perineum were more frequently dissected in this animal 
 its absence would be often noted, as in the two specimens which he 
 examined it was not present. Absent in Cervus according to 
 Paulet, and in Camelus droraedarius, Equus, and Ovis according to 
 my own dissections. 
 
 Chiroptera. — The muscle was absent in Pteropus medius, 
 Vesperugo noctula, and Cynonycteris aegyptiaca (Geoff.). 
 
 Insectivora. — Present in Centetes according to Dobson. Absent 
 in Erinaceus europseus. 
 
 Camivora. — Present in Felis catus (Straus-Durckheim), Ursus 
 americanus and Cynictis Levaillantii (Windle), and in Felis 
 leopardus. Absent in Cercoleptes caudivolvulus, Cryptoprocta 
 ferox, Herpestes griseus, and Canis mesomelas (Windle). Absent 
 also in Canis familiaris and Phoca vitulina. 
 
 Primates. — Present in Simla satyrus, though feebly developed. 
 Absent in Papio, according to Paulet, and also in Macacus rhesus. 
 
29 
 (3) Bulbo-cavernosus (Male). 
 
 The bulbo-cavernosus in the male is composed of two lateral parts. 
 These, which are usually but not invariably symmetrical, are united 
 medially by a sagittal tendinous raph6. The raphe indicates the 
 line of union of the originally separate halves of the muscle, and 
 from it fibres arise on each side. Each half consists of layers of 
 muscular fibres superimposed upon each other surrounding the bulb 
 of the penis, the hinder part of the corpus spongiosum, and in many 
 cases, by a narrow band of the most anterior fibres, the body of the 
 penis also. 
 
 In its most differentiated form four distinct layers of fibres may 
 be distinguished, but either from non-development of one or more, 
 or as the result of fusion, the number is very frequently less. The 
 arrangement may be unsymmetrical, so that four layers .may be 
 present on one side and only two or three on the other. 
 
 Kobelt's description of the muscle in 1844, seems to have been 
 very generally followed by subsequent writers. It is especially note- 
 worthy on account of a reference to a layer of fibres enveloping the 
 free rounded end of the bulb of the penis which had not previously 
 been recognised in man, and also because we find in it the first notice 
 of the division of the bulbo-cavernosus into a layer enveloping the 
 bulb and hinder part of the corpus spongiosum (compressor bulbi 
 proprius), and a layer passing round the root of the penis on to the 
 dorsum of that structure (constrictor radicis penis). 
 
 Cuvier found also in ruminants a band of fibres passing from the 
 tuberosity of the ischium to the bulb of the penis, which he named 
 the ischio-bulbosus. This has since been recognised in man by Lesshaft 
 and Holl, the former of whom has identified it as an accessory head 
 of the bulbo-cavernosus; it constitutes one of the four layers of 
 muscle. 
 
 The four layers of the bulbo-cavernosus are named as follows : — 
 
 (1) Ischio-bulbosus. 
 
 (2) Constrictor radicis penis. 
 
 (3) Compressor bulbi proprius. 
 
 (4) Compressor hemisphaeriiim bulbi. 
 
 The most constant of the four divisions, according to my dissec- 
 tions, is the constrictor radicis penis, and the same statement may be 
 made concerning the corresponding fibres in the female. In the latter 
 
30 
 
 the bulbo-cavernosus is often very feebly developed, and the part of 
 the muscle which persists when others fail is a slender bundle of 
 muscular fibres which passes towards the suspensory ligament of the 
 clitoris to terminate in the subcutaneous tissue of the mons Veneris. 
 This bundle, to which the name of constrictor radicis clitoridis has 
 been given, is the homologue of the constrictor radicis penis. Both the 
 ischio-bulbosus and the compressor hemisphseritim bulbi are subject 
 to considerable variation. They are frequently absent, and even when 
 present are often represented only by a few scattered fibres. The 
 conipressor hemispheeri^im bulbi rarely fails to be symmetrical, whereas 
 the ischio-bulbosus is more commonly unilateral. 
 
 The compressor bulbi proprius is usually present, but its degree of 
 development is largely dependent upon the ischio-bulbosus. It attains 
 its maximum size when the ischio-bulbosus is absent, whereas if both 
 the compressor bulbi proprius and the ischio-bulbosus occur on the 
 same side, the former is correspondingly reduced and part of it maj^ 
 fail entirely. It would seem as if the ischio-bulbosus were present at 
 the expense of the compressor bulbi proprius. 
 
 (1) The Ischio-bulbosus. — This muscle arises either from the 
 inner surface of the ischial tuberosity or from the ascending ramus 
 of the ischium. It is directed obliquely inwards and forwards to the 
 bulb of the penis, upon which its fibres spread out into a thin layer 
 which covers the compressor bulbi proprius. The fibres terminate 
 anteriorly either in the median raphe or by joining with those of 
 the subjacent layers. In a few subjects in which the muscle showed 
 exceptional development I have been able to trace the fibres some 
 distance beyond the bulb, where they terminated on the outer surface 
 of the corpus cavernosum. 
 
 The existence of the ischio-bulbosus does not appear to influence 
 to any appreciable extent the size of the constrictor radicis penis. 
 On the other hand, as we have already seen, the development of 
 the ischio-bulbosus and the compressor bulbi proprius is inversely 
 proportional. 
 
 The ischio-bulbosus may be mistaken for the transversus perinei, 
 especially in those cases in which the fibres do not extend far 
 enough forwards to obtain attachment to the corpus cavernosum. Its 
 attachments and relations to the bulb, however, are usually sufficient 
 to enable us to form a right conclusion. The attachment of the 
 transverse muscle is, in a large proportion of cases, superficial to the 
 
C.R.R 
 
 T.U, 
 
 C 8.P, 
 
 T.U. 
 
 TP.S-. 
 
 
 Fig. 7. — Muscles forming tlie j)erineal triangle in the male. C.S., corpus 
 spongiosum; C.R.P., constrictor radicis penis; I.Cav., ischio-cavernosus ; I.B., 
 ischio-bulbosus ; C.B.P., compressor bulbi proprius ; T.P.S., transversus jjerinei 
 superficialis ; T.U., triangular ligament; I., ischi\im ; I.B'., insertion of ischio- 
 bulltosus ; C'.C, corpus ca\^ernosuni. 
 
31 
 
 isehio-eavernosus, whereas the origin of the ischio-bulbosus is usually 
 deeper than it. 
 
 Theile describes a bundle of muscular fibres which apparently 
 corresponds to the ischio-bulbosus. According to his observations it is 
 very frequently present, but he expresses a very doubtful opinion as 
 regards its meaning. It may be a part of the bulbo- cavernosus, the 
 ischio-cavernosus, or it may represent an independent muscle. He 
 favours the latter view to such an extent that he suggests that the name 
 "retractor urethrae?" be applied to it. I think there are two points 
 which strongly support the view advanced by Lesshaft, that the 
 ischio-bulbosus is a part of the bulbo^cavernosus. The first is the 
 insertion of the anterior fibres into the corpus cavernosum. It is 
 extremely unlikely that fibres of the transverus perinei should take the 
 usual insertion of certain fibres of the bulbo-cavernosus. Again, 
 there is the accompanying diminution of the compressor bulbi proprius 
 when the ischio-bulbosus is present. This circumstance is very 
 suggestive of a cleavage of the compressor bulbi into two layers, of 
 which the superficial — the ischio-bulbosus — has obtained attachment 
 to the adjacent bone. 
 
 (2) Constrictor eadicis penis. — Although the second and 
 third divisions are for the most part in the same plane, fibres of the 
 constrictor radicis may occasionally be observed extending backwards 
 to the central point of the perineum superficial to the compressor 
 bulbi. For this reason the constrictor radicis is described as a 
 separate layer. 
 
 The fibres are commonly united at the median raphfe with those of 
 the compressor bulbi, but towards their insertion they are quite 
 distinct. In the few cases in which the muscle can be traced on to 
 the dorsum of the penis, and to the subcutaneous tissue in front 
 of the pubis, the muscle may have a separate course for four or 
 even six inches. 
 
 It takes origin from the side of the median tendinous raph6 for the 
 anterior third or fourth of its extent. The fibres are directed forwards, 
 upwards, and outwards ; they diverge from those of the opposite side 
 at an acute angle, and in some cases partially and in others wholly 
 encircle the root of the penis by a narrow band of muscular fibres 
 about half an inch broad. 
 
 The insertion takes place in one of two ways. The fibres either 
 end tendinously on the lateral surface of the corpus cavernosum 
 
32 
 
 immediately anterior to the insertion of the ischio-cavernosus, or 
 they pass on to the dorsum of the penis, and gradually losing their 
 muscular character terminate in a flattened fibrous expansion 
 covering the dorsal vessels and nerves, which may finally be traced 
 to the subcutaneous tissue in front of the body of the pubis. The 
 significance of these latter fibres will be considered after the description 
 of the corresponding muscle in the female. 
 
 Kobelt's description conveys the impression that the last described 
 mode of insertion is the usual one. My own observations, on the con- 
 trary, have shown that it only occurred in about 15 per cent, of the 
 subjects which I examined, and these included both the foetus and 
 adult. 
 
 Theile refers to the fibres which go to the front of the pubis in a 
 paragraph on anomalies of the bulbo-cavernosus. The existence of 
 these fibres is, he states, not very rare though the frequenc}' is not 
 stated. He applies to them the name of levator penis or pubo- 
 cavernosus, though Henle, along with J. Miiller and Kobelt, have 
 assigned this term to the fourth part of the ischio-cavernosus. 
 
 (3) CoMPEEssoK BULBi PEOPBius. — This division is situated 
 immediately behind the preceding and arises from the central point 
 of the perineum where fibres are continued into it from the external 
 sphincter ani and the transversus perinei superficialis, and from the 
 side of the median tendinous raph6 for the posterior two thirds or 
 three fourths of its extent. The fibres are directed upwards and 
 slightly forwards, covering the inferior and lateral surfaces of the bulb 
 and adjacent part of the corpus spongiosum. The hindmost fibres 
 gain insertion into the inferior surface of the triangular ligament. 
 The succeeding ones, and these comprise the anterior and larger part 
 of the layer, encircle the corpus spongiosum, and on its dorsal surface 
 meet witli the fibres from the opposite side to form a fibrous 
 aponeurosis. The aponeurosis is situated between the corpus 
 spongiosum and the united crura of the penis, and is firmly attached 
 to the three parts of this body. But whereas the corpus spongiosum 
 may be dissected from the aponeurosis without much difficulty, 
 the union of the latter with the two crura, especially in the middle 
 line is much more intimate. The parts are so fused together that 
 a separation can only be made artificially. It is evident, therefore 
 that the compressor bulbi proprius covers those parts only of the 
 bulb of the penis which are not in direct contact with the triangular 
 
c.s" 
 
 m.f:a 
 
 C.RP 
 
 IB. 
 
 C.B.P 
 
 C.H.B. 
 
 ^^$'' 
 
 
 Fig. 8. — Bulho-cavefnosiis in tlie male. The two halves have been 
 leflected from the median raphe and tlie bidlj turned downM'ards after division 
 of the corpus sjiongiosum. C.S., coi'pus sponj^dosum ; C.R.T'., constrictor radicis 
 penis; I.E., ischio-lmlljosus ; C.B.P., comjiressor Ijullji [jrojnius ; C'.H.B., com- 
 pressor hemispluerium Ijulbi; C.S. and CIS"., corpus spongiosum; U., urethra; 
 JI.F.A., median aponeuro.sis ; C.C., corpus caveinosum. 
 
33 
 
 ligament. On the other hand, it surrounds the adjacent part of 
 the corpus spongiosum entirely. 
 
 (4) Compressor hemisph^eiu.m bulbi.' — This forms the 
 deepest layer of the bulbo-cavernosus. It is a ring-shaped 
 muscle consisting of two symmetrical halves investing the free 
 rounded end of the bulb of the penis. It lies immediately subjacent 
 to the compressor bulbi proprius, and a. distinct layer of connective 
 tissue intervenes between them. 
 
 The fibres take origin from a median tendinous raphe situated on 
 the posterior curvature of the bulb. The superior fibres, namelj-, 
 those immediately beneath the triangular ligament, are directed 
 almost horizontally forwards, the middle, arising from the raph6 
 lower down, ascend obliquely over the lateral aspect of the bulb, 
 whilst the inferior are directed outward and then almost vertically 
 upwards. All the fibres converge to a flat, narrow, and usualh' 
 indistinct median tendon situated on the dorsal surface of the bulb of 
 the penis, immediately in front of the point at which the membranous 
 urethra sinks into the substance of the bulb. As Kobelt pointed out, 
 the muscle surrounds the hemispheres of the bulb in the form of 
 a closely fitting cap. 
 
 The compressor hemisphseriCim bulbi is frequently absent. In 
 many cases it forms a very thin muscular layer, difficult to recognise 
 from the surrounding structures. 
 
 In those animals in which the bulb of the penis is bifurcated at its 
 free posterior extremity, each division is covered by its own compressor. 
 
 ' The muscle is best exposed by making a sagittal incision parallel with the 
 median raph^, and turning the two halves of the constrictor radicis and the 
 compressor bulbi outwards. Great care is necessary at the posterior end of the 
 bulb, and if the parts are blood stained which is not infrequent, the difficulties are 
 much increased. In favourable subjects, especially in those preserved with carbolic 
 acid, a distinct layer of fine connective tissue forms an important guide in the 
 dissection. When the reflection has been completed, a transverse incision should 
 be made through the corpus spongiosum an inch or so in front of the bulb, 
 and the parts behind the section dissected from the dorsal aponeurosis and 
 turned backwards. In this way a good view is obtained of the compressor 
 hemisphaariilm bulbi. A very useful plan in examining this muscle, and one which 
 I have frequently adopted, is to remove the bulb and its muscular envelope from 
 the triangular ligament, by cutting through the urethra behind, and the corpus 
 spongiosum in front. If the dissection be continued in weak spirit, the compressor 
 is much more easy to recognise. 
 
34 
 
 As examples, Kobelt mentions the rat and certain marsupials, and I 
 have noticed a similar arrangement in the camel. In them, apparently, 
 the independence of this muscular layer is more obvious than in man. 
 
 Action and Nekve-Supply. — The name given by the earliest 
 anatomists of accelerator urinse et seminis sufficiently indicates 
 its functions, and but little need be added to previous descriptions. 
 One point, however, deserves special mention, viz., the action of the 
 compressor hemisphairilim bulbi. Whilst there can be little doubt 
 that its chief action is exerted on the lateral surface of the bulb, it is 
 important to note that the urethra may be compressed at the point 
 where it is sinking into the substance of the bulb, by the dorsal tendon 
 which unites the two halves of the muscle. 
 
 Several branches from the perineal division of the pudic nerve 
 enter the bulbo-cavernosus and supply its various parts. Of these, the 
 nerve to the constrictor radicis penis may be .traced in many cases 
 ))etween the bundles of the compressor bulbi proprius, and is remark- 
 able on account of its length. Again, the branch to the compressor 
 hemisphaeriiim bulbi runs for a short distance, before entering its 
 muscle, in the layer of tissue immediately under the compressor 
 bulbi proprius. 
 
 The descriptions of the bulbo-cavernosus by other writers may 
 now be referred to. Kobelt in his memoir Die Wollust-Organe des 
 Mensehen describes two layers, superficial and deep. The former he 
 sub-divides into the compressor bulbi proprius and the constrictor 
 radicis penis. The deep layer he names the compressor hemisphaerium 
 bulbi. 
 
 Henle on the other hand describes three layers superimposed upon 
 each other. The most superficial appears to correspond to the 
 constrictor radicis penis, the middle layer to the compressor bulbi 
 proprius, whilst the third layer is identical with Kobelt's compressor 
 hemisphaeriiim bulbi. Henle describes the third layer as immovably 
 attached to the bulb of the penis. He also remarks that the whole 
 muscle may be reduced to a single layer by failure of the deepest set 
 of fibres and fusion of the superficial and middle layers. 
 
 Theile, like Henle, describes three divisions to the bulbo-cavernosus 
 and names them simply posterior, middle, and anterior. They do 
 not, however, correspond to the three layers of Henle. The posterior 
 division includes those fibres attachecj to the triangular ligament, the 
 
35 
 
 middle division, those fibres which pass to the median aponeurosis on 
 the dorsal aspect of the corpus spongiosum, Avhilst the anterior division 
 corresponds to the constrictor radicis penis. Theile does not mention 
 the deepest fibres which envelop the bulb. 
 
 Luschka, after describing superficial and deep layers like Kobelt, 
 refers to the band of fibres which Lesshaft regards as the accessory 
 head of the bulbo-cavernosus. He considers that the latter is derived 
 from the transversus perinei superficialis, and adds that from its 
 position between the ascending ramus of the ischium and the bulb of 
 the penis, the error that has been made of regarding the muscle as 
 an integral part of the bulbo-cavernosus is excusable. 
 
 Lastly, Holl gives a full account of the bulbo-cavernosus under 
 the four divisions adopted in this thesis, and the three original 
 drawings which accompany the description form a special feature 
 of his important monograph on Die Muskeln und Fascien dcs 
 Beckenausganges. , 
 
 Comparative anatomy.^ — The arrangement of the bulbo-cavernosus 
 in those mammals in which the bulb of the corpus spongiosum is 
 divided is of special interest. Professor Young in his account of the 
 generative organs of the male koala points out that in this, as in all 
 other described marsuj)ials, the bulb is bifurcated. Paulet found a 
 bifurcated bulb in the tiger, ox, and horse, and I have observed a 
 partially bifurcated bulb in the camel. In all these animals the 
 investing bulbo-cavernosus is correspondingly divided more or less 
 completely and a muscular capsule is provided for each division of 
 the bulb. 
 
 Developmental history shows that the bulb of the penis consists 
 primarily of two halves each invested by its own muscle, and that, in 
 most male mammals, the structures unite at the middle line to form a 
 median bulb covered by a median muscle. On the other hand, no 
 union occurs in the female and thus the primary condition is retained 
 throughout life. 
 
 The bifurcated bulb and separate bulbo-cavernosi in the animals 
 mentioned above, are thus easily explained. The two halves of the 
 bulb have remained permanently separate, and in conformity with 
 this arrangement the two halves of the bulbo-cavernosus have 
 remained distinct from one another to forrn a covering for each 
 bulb. 
 
36 
 
 The bulbo-cavernosus in the camel' presents one important point 
 of difference from the arrangement usually ' fourici in ' arfimals with 
 bifurcated bulbs. Immediately in front of the bulbs (fig. 23), the 
 two halves unite at the middle line by means of a fibrous raphe. The 
 union, however, involves the muscles only for a limited distance, so 
 that in front of and behind the raphfe there is no difficulty in recognising 
 two distinct and separate structures. The disposition of the bulbo- 
 cavernosus in the camel thus illustrates- an intermediate stage in. the 
 history of the muscle. Although the two halves are completely 
 separated in marsupials and certain ungulates, and completely united 
 in some of the highest mammals as in man, the two halves in the 
 camel, though separate along the greater part of their .length, exhibit 
 a tendency to unite and form a median raph6. 
 
 The extent and development of the bulbo-cavernosus varies 
 considerably in different animals. In some it forms a, simple 
 muscular capsule for each of the bulbs of the penis, as described by 
 Professor Young in the koala. In others it is much more strongly 
 developed and may — as observed by Gurl in the horse — even extend 
 as far forwards as the glans penis. 
 
 An interesting account has been given by Professor Milne Edwards 
 of the bulbo-cavernosus in the squirrel and ichneumon. In' both, 
 the muscle is rudimentary. But whereas in the former the muscle is 
 confined to the bulb of the penis, in ichneumon the muscle has 
 become so much reduced that it acts solely on the glands of Cowper. 
 
 ' When the ventral surface of the corpus spongiosum is dissected in the camel, 
 it appears as if the two halves of the bulbo-cavernosus were united along the 
 middle line as far as the anterior limit of the muscle. This is not so however. 
 A layer of loose connective tissue unites the adjoining edges of the muscles, and 
 as soon as this is touched with the knife they fall apart as represented in the 
 illustration. 
 
C.P. 
 
 B.C.; 
 
 Fig. 9. — Root of the penis in the Ivoala (Phascolavetos ciiiereuy). 
 G.P., t,'laiis penis; (i., gracilis; S., sominieinl)ranosns ; S'., semitendinosiis ; 
 I.e., iscliio-eavernosiis covering the crus penis wliicli is quite free from liony 
 attaclnnent ; 0.14., CVni'iierian glands ; B.C.S., the two sei)arate liulbs of the 
 corpjns sp(jngiosinn, each covei'C*! hy a muscular capsule — the Imlbo-cavernosus ; 
 B., bice])s ; (x.M., gluteus ma.\imus ; C.P., ci us. penis ; R.P., reti'actor peni,^. 
 (From a drawing by Professor Voung.) 
 
37 
 (4) Bulbo-cavernosus (Eemale). 
 
 The bulbo-cavernosus in the female is a composite structure like 
 the corresponding muscle in the male. It extends from the perineal 
 septum behind. to the clitoris and symphysis pubis in front, and is 
 situated on the outer aspect of the bulbs of the vestibule and Bartholin's 
 glands. Below and internal to the bulb a few fibres are in relation to 
 the lower end of the vagina and urethra. 
 
 The whole group of fibres is usually referred to as the sphincter 
 vagina;, though it should be pointed out that the muscle bearing this 
 name is not the only one which can influence the size of the vaginal 
 canal. Indeed, so many conflicting statements have been made con- 
 cerning its attachments, functions, and even its very existence, that it 
 seems desirable that the muscle should be described under the name 
 of bulbo-cavernosus, and that one should endeavour to trace the 
 homology between the difierent sets of fibres in the two sexes. 
 
 Attachments. — The bulbo-cavernosus arises at its lower and 
 posterior end from the central point of the perineum, where it also 
 receives fibres from the external sphincter ani and the transversus 
 perinei. The muscle is then directed forwards and outwards on each 
 side, round the posterior commissure, and after proceeding for a short 
 distance it is occasionally joined by a narrow bundle of fibres which 
 take origin from the fibrous septa in the ischio-rectal fossa. Thus 
 constituted, it forms a muscular band about three-quarters of an inch 
 wide encircling the vaginal orifice and covering the bulbs of the 
 vestibule and Bartholin's glands. 
 
 Anteriorly the muscular fibres terminate in three ways. The 
 external set are attached to the inner margin of the pubic and some- 
 times the ischial ramus, blending with the adjacent triangular 
 ligament and the tunica fibrosa of the corpus cavernosum of the 
 clitoris. The middle set form a distinct bundle which crosses the 
 crus of the clitoris superficially to terminate in the neighbourhood of 
 the suspensory lig9,ment of that organ, in the substance of the mons 
 Veneris. Finally the internal set pass into the preputium clitoridis, 
 the anterior vaginal wall, and the tissue between it and the lower 
 end of the urethra. 
 
 The attachments of the sphincter vaginse were shown by 
 Professor Young in 1890 in a demonstration on this muscle given at 
 a meeting of the North of England Obstetrical and Gynaecological 
 
38 
 
 Society, a brief account of which may be found in the Medical 
 Chronicle for July, 1890. 
 
 Subsequently, further dissections were made both by Professor 
 Young and Mr. J. W. Smith, and I have gladly availed myself of the 
 unpublished notes and sketches of these additional observations 
 which have been kindly placed at my disposal. 
 
 The demonstration of the sphincter muscle was given by Professor 
 Young to prove that the sphincter vaginae was something more than 
 the " dissecting-room curiosity " described by Professor Lawson Tait, 
 who, whilst admitting that a few bundles of fibres may exist 
 occasionally, considered even then they were not functional. 
 
 In each of the dissections shown by Professor Young the muscle 
 was strongly developed and formed a sheet of well-defined muscular 
 fibres on each side of the vaginal orifice, covering the bulbs and 
 measuring about an inch broad on each side. Posteriorly, a few 
 of the fibres were attached to the central point of the perineum, but 
 the bulk of them arose external to this by an extended origin from the 
 ischio-perineal ligament of Savage. The fibres terminated in front on 
 the margin of the pubic ramus, in the suspensory ligament of the 
 clitoris, and in the preputium clitoridis. Finally Professor Young, 
 from an examination of a further series of subjects in the dissecting- 
 room, has been able to satisfy himself of the almost constant occurrence 
 of the muscle. ^ 
 
 Having examined a number of subjects with the special object of 
 observing the frequency with which fibres terminate in the mons 
 Veneris, I am able to support this last statement. The bulbo- 
 cavernosus was nearly always present in some degree, though I was 
 somewhat surprised to find how very frequently the mug^cles of the 
 two sides showed unequal development. Whereas that on the right 
 side may be an inch wide, the left muscle may be so small that it 
 does not exceed a fourth or a sixth of an inch across its widest part. 
 
 As the existence of the muscle has been doubted, it may not be 
 inopportune if I append here the measurements of four examples 
 taken from subjects in the dissecting-room : — 
 
 (1) Breadth of muscle over the bulb ... f in. 
 
 Breadth of muscle in front of the posterior 
 
 commissure fin. 
 
 Breadth of antero-posterior diameter 
 
 of perineal decussation -Jin. 
 
C.R.C. 
 
 V.B 
 
 S.L.C, 
 
 T.U 
 
 TP5 
 
 I89S, 
 
 Fig. 10. — Bulljo-caA'einosus and superficial transverne muscles in the female. 
 S.L.C, suspensory ligament of the clitoiis ; S.V.P. , s])hinct.er va.g~in;e su[ierficialis ; 
 C.R.C, constiictor radicis clitoridis; C'.B.P. , compressoi' lailbi [ii'oprius ; ^^. , A'agina ; 
 T.P.S., transvensus perinei superficialis ; T.U., triangular' lip;anient : V.B., \'aginal 
 hull> : C, clitoi'is ; CR.C, prol(aigation of the constiactor raclicis elitoiidis into 
 the sulicutaneous tissue of the mons Veneris. 
 
39 
 
 Breadth of external sphincter ani at its 
 
 widest part fin. 
 
 Girth of anal and vaginal sphincters on 
 the same side — 
 
 Sphincter ani fin. 
 
 Sphincter vaginse ^in. 
 
 (2) Breadth of muscle over the bulb ... -Jin. 
 Length of muscle from central point of 
 
 perineum to termination of fibres 
 
 in the mons Veneris 3f ins. 
 
 (3) Breadth of muscle over the bulb ... ^^ in. 
 Length of muscle from central point of 
 
 perineum to termination of fibres 
 
 in the mons Veneris... ... ... 2Jiiis. 
 
 (4) Breadth of muscle over the bulb ... fin. 
 Length of muscle from central point of 
 
 perineum to termination of fibres 
 
 in the mons Veneris 3J ins. 
 
 The most striking features of these measurements are the increase 
 in bulk of the vaginal sphincter over the anal sphincter in the first 
 dissection, and the length of the vaginal sphincter in the last three 
 dissections ; the length recorded may perhaps suggest unusual 
 development, though in some subjects dissected since these 
 measurements were taken, a length of four inches has been noted. 
 
 Proceeding now to compare the bulbo-cavernosi in the two sexes, 
 it may be stated that although the two muscles do not apparently 
 resemble each other, it is not difficult to establish the homology 
 between them. The only division w'hich, so far as I know, has not 
 been recognised in the female is that corresponding to the compressor 
 hemisphserium bulbi of Kobelt in the male. On the other hand, 
 each of the three remaining parts of the male bulbo-cavernosus is 
 represented in the female. Thus, the most superficial layer — the 
 ischio-bulbosus — may be present as a layer of muscle arising from the 
 ascending ramus of the ischium and terminating in the muscle which 
 covers the bulb, though according to my results this layer is not 
 present so frequently as in the male. 
 
 The compressor bulbi proprius and the constrictor radicis clitoridis 
 constitute the group of fibres enveloping the bulbs of the vestibule 
 and the glands of Bartholin. As they correspond to the main parts of 
 
40 
 
 the bulbo-cavernosus in the male, it seems preferable that the same 
 nomenclature should be employed in the two sexes. 
 
 Finally, there are the inconstant fibres situated below and internal 
 to the bulb of the vestibule and in relation to the lower end of the 
 vagina and urethra. It is probable that they do not belong to the 
 bulbo-cavernosus, but represent a prolongation of the external 
 sphincter ani round the orifice of the vagina. To these fibres the 
 name of sphincter vagina superficialis may appropriately be applied. 
 Obviously, the muscle so generally referred to as the sphincter 
 vagina, consists of different groups of fibres ; these can usually be 
 separated without much difficulty into — 
 
 (1) The ischio-bulbosus. 
 
 (2) Constrictor radicis clitoridis. 
 
 (3) Compressor bulbi proprius. 
 
 (4) Sphincter vaginae superficialis. 
 
 (1). The ischio-bulbosus is very similar to the corresponding 
 nmscle in the male, and little need be added to the description 
 previously given. Jarjavay describes the muscle in his Traite 
 d'anatomie chinirgicale and mentions the fibres terminating on the 
 bulb of the vagina. According to my dissections the insertion usually 
 intermingles with the fibres of the constrictor radicis clitoridis. 
 
 (2). CoNSTEicTOR RADICIS CLITORIDIS. — Under this name is 
 included those fibres which, arising from the central point of tho 
 perineum, pass forwards to terminate in the subcutaneous tissue 
 of the mons Veneris, and if any evidence were necessary to complete 
 the homology of the bulbo-cavernosi muscles in the two sexes, these 
 remarkable strands of muscular fibres would supply it. As 
 previously mentioned, this bundle appears to be the most constant part 
 of the bulbo-cavernosus, for on numerous occasions when the latter 
 has been feebly developed, I have found that the constrictor radicis 
 clitoridis has persisted and the other portions have failed entirely. 
 
 Kobelt has recognised in several subjects bundles of muscular fibres 
 two inches long passing into the mons Veneris, though curiously enough, 
 Lesshaft has not seen any muscle extending so far forwards in the 
 female, but lie has observed the arrangement on one occasion 
 in the male. HoU figures and describes fibres in front of the pubes in 
 the male, whilst Theile includes under the anomalies of the bulbo- 
 cavernosus in the female a fleshy band of fibres which takes origin 
 from the suspensory ligament of the clitoris near the superior bolder 
 
41 
 
 of the symphysis pubis and gains insertion into the bulbo-cavernosus. 
 
 My results show, however, that when the external sphincter ani 
 and the bulbo-cavernosus muscles are strongly developed, it is usual 
 to find muscular fibres extending forwards from the constrictor 
 radicis clitoridis into the mons Veneris, though, like those forming the 
 other muscles of the perineum, they vary in size and extent within 
 fairly wide limits. For example, the fibres may terminate on the 
 fibrous investment of the clitoris, in the suspensory ligament of the 
 clitoris, or in the subcutaneous tissue of the mons Veneris bej^ond this, 
 but undoubtedly they can be recognised in nearly all cases. On the 
 other hand, it must be admitted that the number of subjects in 
 which, according to Kobelt, the fibres in the mons Veneris attain a 
 length of two inches is relatively small. 
 
 I specially examined twelve female subjects with the object of 
 estimating the frequency with which the constrictor radicis cUtoridis 
 showed such exceptional development. In two, i.e., 16'6 °/o the fibres 
 reached as far forwards as the upper margin of the pubis. In both 
 cases the full length of the constrictor radicis amounted to four 
 inches, and of this, the anterior prolongation beyond the clitoris 
 contributed between 1^ and If inches. 
 
 (3). Compressor bulbi proprius. — The fibres'of this division 
 are situated immediately external to those of the constrictor radicis 
 clitoridis. They take origin from the central point of the perineum, 
 and after forming a covering for the bulb of the vestibule, obtain 
 insertion into the margin of the pubic arch, the tunica fibrosa 
 of the corpus cavernosum, and the triangular ligament. HoU and 
 other observers have described fibres from one side uniting with 
 those of the opposite side to form a flat fibrous plate in the angle 
 between the corpora cavernosa of the clitoris. 
 
 On this point my experience is simikr to that of Lesshaft who 
 states that he has been unable to recognise this formation. The 
 latter observer gives the insertion of the lower fibres of the bulbo- 
 cavernosus (compressor bulbi proprius) pa"rtly into the corpus 
 cavernosum clitoridis and partly into the fascia of the clitoris above 
 the dorsal vessels and nerves. The attachment of the fibres to the 
 margin of the pubic arch, which Lesshaft does not specially mention, 
 has an important bearing upon the action of the muscle. 
 
 (4). Sphincter vaqinje superficialis. — It is especially significant 
 that in some animals the sphincter vaginae superficialis is represented, 
 
42 
 
 while the bulbo-cavernosus fails entirely. For example, in the cat, 
 Straus- Durckheim describes a releveur de la vulve corresponding to the 
 constricteur de la vulve in woman, and then states that he has been 
 unable to find the analogue of the bulbo-cavernosus of the male. 
 
 In the female orang-utan a superficial sphincter vaginae is 
 present along with the bulbo-cavernosus, and the two are much more 
 distinct than in the human subject. In the latter the fibres of the 
 two muscles have intermingled to such a degree that there is no 
 longer any clear separation of the constituent fibres though they 
 are still easily recognisable. 
 
 According to Lesshaft, Luschka first pointed out the existence of 
 the sphincter vaginse or constrictor vestihuli in woman, and named 
 it the constrictor cunni profundus, whereas the bulbo-cavernosus he 
 named the constrictor cunni superficialis. These terms, however, do 
 not denote the relative positions of the bulbo-cavernosus and 
 sphincter vaginse superficialis, described here. 
 
 The fibres of the superficial sphincter vaginse are usually pale 
 and sometimes insignificant and therefore not always easy to 
 distinguish. Lesshaft has shown that the muscle is best developed 
 in nullipara. 
 
 As briefly mentioned the superficial sphincter vaginse surrounds 
 the lower end of the vagina, and according to HoU, its level corresponds 
 with that of the hymen or carunculse myrtiformes. Its connections 
 posteriorly with the external sphincter ani are very intimate. Indeed 
 Bourgery shows in his illustrations the two muscles forming a figure of 
 eight and speaks of an intercrossing of fibres of the constrictor 
 vaginse with those of the sphincter ani at a point corresponding to 
 the middle of the perineum. Anteriorly the fibres terminate on the 
 vaginal wall in the neighbourhood of the urethra, and in the prepuce 
 of the cUtoris. 
 
 Action and Nerve-Supply. — So many various statements have 
 been made concerning the action of the group of fibres surrounding 
 the lower part of the vagina, that one may well hesitate before 
 attempting to put forward any further views on this point. At the 
 same time, in the light of certain new observations which have been 
 made on neighbouring muscles, more particularly on the fibres of the 
 levator ani arising from the back of the body of the pubis, a somewhat 
 different conception, from that which is usually held of the manner in 
 which the lumen of the vagina is narrowed, may be advanced. 
 
43 
 
 The narrowing of the lower end of the vaginal canal by the 
 so called sphincter vaginae cannot be compared to the closure of 
 the lips by the orbicularis oris, or even to the closure of the anus 
 by the external sphincter, inasmuch, as it is not the result of the 
 contraction of a single sphincter muscle, but it is a more complicated 
 arrangement dependent upon the co-operation of different muscles. 
 
 It will be remembered that a great many of the fibres of the 
 bulbo-cavernosus are inserted into the descending ramus of the pubis 
 and the ascending ramus of the ischium. If the central point of the 
 perineum be movable these fibres act from their anterior attachments, 
 and whilst drawing the walls of the vagina together, pull the orifice 
 upwards and forwards towards the apex of the pubic angle. 
 
 Diagram to show the sphinoter-like arrangement of muscles around the 
 lower end of the vagina. The superficial muscle is the sphincter vaginae 
 (bulbo-cavernosus) ; the deeper muscle is the pubo-coccygeus. 
 
 But the vagina is also in relation in front with the two pubo- 
 coccygeal portions of the levator ani, and these pass backwards from 
 the pubes on either side of the canal in such a way that the latter is 
 received into the angle formed by the two diverging muscles. It is 
 evident, therefore, that there is a sphincter-like arrangement of 
 muscular fibres surrounding the lower end of the vagina, and that in 
 shape it resembles a rhomb, the two posterior walls being formed by 
 the bulbo-cavernosi and the two anterior walls by the pubo-coccygei. 
 
 It is by the combined action of these muscles that the narrowing 
 of the lower end of the vagina is brought about. The pubo-coccygei, 
 
44 
 
 acting from a fixed point at the back of the pubes, compress the vagina 
 from side to side, and it is obvious that the result can be best assured 
 the more the vagina is brought into the angle formed by the two 
 muscles. This is precisely the action of those fibres of the bulbo- 
 cavernosus which are attached to the margin of the subpubic arch. 
 
 The pathological condition known as vaginismus is probably due 
 to the contraction of the pubo-coccygei and bulbo-cavernosi acting in 
 the way described above. Dr. Matthews Duncan stated in 1878, that the 
 muscles affected were the sphincter vaginae and the levator ani, though 
 he did not suggest how they were associated. In a clinical lecture on 
 this subject he said "the spasm of vaginismus is, so far as it affects the 
 voluntary muscles, a tonic spasm. The voluntary muscles that it 
 affects are the constrictor vaginae and the anterior part if not the whole 
 of the levator ani. One result of the spasm of these muscles is com- 
 plete closure of the vagina as a passage." 
 
 In the report^ of the demonstration given by Professor Young 
 I find the following remarks which illustrate in a striking manner 
 the diversity of opinion which surrounds this important question. 
 He thought "that gynaecologists would consider the anatomy of 
 this muscle (the so-called sphincter vaginae) of special interest in 
 relation to the causation of vaginismus, a condition due, in the 
 opinion of Dr. Marion Sims, to the spasmodic contraction of the 
 sphincter." Lawson Tait, however, denies the existence of such 
 contraction, and states, as a result of "a systematic enquiry amongst 
 the teachers of anatomy in this country and abroad," that "grave 
 doubts" are thrown "on the existence of the muscle," and that it is 
 "certain that the few bundles of muscular fibre which have been 
 occasionally seen in such a position, that they could not act as 
 constrictors of the vagina, never could by any possibility give rise 
 to the symptoms referred to them." 
 
 Professor J. Symington regards the action of the bulbo-cavernosus 
 as purely that of compressing the bulbs of the vestibule. According 
 to him, the muscle does not exert any appreciable influence on the 
 lumen of the vagina. He is supported in this opinion by Lesshaft, 
 who attributes to the bulbo-cavernosus the power of compressing the 
 bulb and pushing it inwards, but not of narrowing the vagina. 
 
 Whilst this may be correct as regards the action of the bulbo- 
 cavernosus alone, I feel satisfied that when associated with the pubo- 
 
 • Log. cit. 
 
45 
 
 coccygei, an important sphincter action is exerted,' and I would 
 therefore summarise the actions of the bulbo-cavernosus as follows : — 
 It raises the vagina upwards and forwards towards the symphysis 
 pubis, and into the angle formed by the two diverging pubo-coccygei ; 
 and by acting in concert with the latter muscles the narrowing of 
 the inferior part of the vagina is brought about. Its subordinate 
 functions include the compression of the vaginal bulbs and the 
 glands of Bartholin. 
 
 The sphincter vaginae superficialis is frequently' so feeble and 
 ill-developed that its action cannot be of much importance. At the 
 same time, when the muscle is functional it will narrow the vulvo- 
 vaginal orifice. 
 
 As the bulbo-cavernosus and sphincter vaginae superficialis are 
 derived from the primitive sphincter cloacae, they draw their nerve- 
 supply from the internal pudic. 
 
 The descriptions by Lesshaft, Holl, Sappey and others of the bulbo- 
 cavernosus do not differ essentially from that given above, inasmuch 
 as the differences are mainly referable to the nomenclature. Lesshaft 
 describes a bulbo-cavernosus and a sphincter vaginas, though he does 
 not divide the former into its two constituent elements. Holl, on the 
 other hand, represents these two divisions in his illustrations, but not 
 the sphincter vagina;, though the latter is described in the text. 
 Sappey and others employ the term constricteur de la vulve to denote all 
 the muscular bundles encircling the lower end of the vagina and the 
 vaginal bulbs, whilst Kobelt and Luschka refer to the same fibres 
 as the constrictor cunni. Luschka regards the latter as an independent 
 muscle strengthened by fibres from the external sphincter ani and the 
 superficial transverse. 
 
 Henle recognises at the insertion of the bulbo-cavernosus three flat 
 bands, of which, one spreads tendinously into the corpus cavernosum 
 clitoridis, another to the dorsal surface of the bulb, whilst a third is 
 lost in the mucous menjbrane of the vestibule between the clitoris 
 and the opening of the urethra. 
 
 Finally, Kobelt divides the bulbo-cavernosus into two flat portions, 
 a posterior and an anterior, both of which form flattened tendons with 
 those of the opposite side. The posterior corresponds to the com- 
 pressor bulbi proprius, and the anterior to the constrictor radicis 
 clitoridis. 
 
46 
 
 Morphology. — The homological study of the bulbo-cavernosua 
 will be much facilitated if reference be first made to its developmental 
 history. 
 
 Duiing the course of the development of the genito-urinary orgai'is 
 a cloacal aperture exists till about the fifth week, and a sphincter 
 muscle is arranged around it — the sphincter cloacae. Very quickly — 
 i.e., during the fifth or sixth week— a separation of the cloaca takes 
 place into two parts, a dorsal or anal, and a ventral or uro-genital, and 
 coincident with this change the sphincter cloacse becomes divided into 
 dorsal and ventral divisions, the former surrounding the anal aperture 
 and constituting a part of the external sphincter ani, the ventral 
 surrounding the uro-genital sinus. With the formation of the root 
 of the penis or clitoris the fibres of the ventral division become disposed 
 around it. 
 
 The uro-genital sinus appears alike in both sexes up to the third 
 or fourth month, and the presence of this median sinus has an 
 important bearing upon the formation of the root of the penis or 
 clitoris and the muscles associated with it. As the embryonic 
 tissue which precedes the corpus spongiosum extends backwards from 
 the genital tubercle, it becomes divided into two parts situated one on 
 either side of the median uro-genital sinus, and their enlarged 
 terminations, constituting the vascular bulbs, participate in the same 
 arrangement. Muscular fibres are arranged around each bulb from 
 the corresponding half of the ventral division of the primitive 
 sphincter cloacse. 
 
 This primary condition is retained in the female throughout life, 
 and the muscular investment of the bulb becomes the bulbo-cavernosus. 
 In the male, however, the condition is profoundly modified by the 
 union of the lips of the median fissure and consequent closure of the 
 uro-genital sinus. The urethra is enclosed in the corpus spongiosum, 
 the two vascular bulbs come together and form the median bulb of 
 the penis, whilst the two muscular envelopes unite to form the bulbo- 
 cavernosus, the median raphd permanently indicating the previous 
 bilateral condition. 
 
 There can, therefore, be no doubt about the origin of the bulbo- 
 cavernosus from the ventral division of the sphincter cloacse or the 
 homology between the muscles in the two sexes. Concerning the 
 significance of the remarkable strands of fibres which terminate in 
 the skin, and subcutaneous tissue in front of the pubes, I will refer, in 
 
47 
 
 the first place, to the observations of Holl on the sphincter cloacse of 
 the rabbit, and his deductions from them. 
 
 In the rabbit, a muscle surrounds the anal opening in the 
 male and female like a sphincter cloacae. It is arranged in the form 
 of a band-shaped muscle, which Holl regards as a derivative from 
 the M. cutaneus maximus, and which arises in the middle line from 
 the dorsal surface of the tail, near its root. It passes forwards at the 
 side of the rectum, and in the female at the side of the vagina also, to 
 be inserted into the fibrous covering of the corpus cavernosum penis 
 or clitoridis, close to the terminal tendons of the ischio-cavernosus and 
 pubo-cavernosus. Other fibres pass into the skin of the prepuce of 
 penis or clitoris (M. preputialis) . The two muscles thus form a clamp 
 which embraces the tail, rectum, and uro-genital canal. 
 
 Holl believes that the part of the sphincter cloacse, which in the 
 rabbit does not approach the corpus cavernosum, but passes into the 
 skin of the prepuce, is represented in man by the variable fibres of 
 the constrictor radicis penis on the dorsum of the root of the penis. 
 The disposition of the muscles at the pelvic outlet in certain other 
 animals is, however, somewhat opposed to this view. For instance, a 
 somewhat similar arrangement of the cutaneous muscle at the pelvic 
 outlet is found in the hedgehog. Fibres also pass on to the dorsum of 
 the penis, and a slip is detached to form the M. preputialis. But it is 
 clear, in this animal at least, that all these muscular fibres are parts of 
 the great skin muscle, and that the muscles which, presumably, 
 have arisen from the primitive sphincter cloacse, viz., the accelerator 
 urinse, and the erector penis, occupy a deeper plane. Holl says the 
 bulbo-cavernosus is absent in the rabbit, but in the hedgehog it is 
 exceedingly well-developed. According to Dobson's account we find 
 that " the circular muscular fibres of this muscle surround the urethra 
 between the bladder and the insertion of the suspensory ligaments 
 of the penis, forming a muscular sheath, under cover of which the 
 ducts of Cowper's glands, the vesiculse seminales, and the vasa 
 deferentia go to their termination in the urethra." 
 
 It is at once apparent that, in the hedgehog, the fibres, which are 
 derived from the great skin muscle, and which form the M. preputialis 
 are quite distinct from the bulbo-cavernosus. Rudiments of the great 
 skin muscle in the region of the pelvic outlet are seen in man as the 
 subcutaneous layer of the external sphincter and other irregular strands, 
 but none of these exhibit any connection with the bulbo-cavernosus. 
 
48 
 
 If we examine for a moment the arrangement of the primitive 
 ventral muscle as described by Humphry, we obtain a clue to the 
 real nature of these interesting fibres. 
 
 In writing of the muscles in vertebrate animals, he says: 
 " In the hinder part of the tail the ventral muscle much resembles 
 the dorsal muscle of the same part; but, anteriorly, the symmetry 
 between the muscles above and below the lateral line is destroyed by 
 the expansion of the ventral muscle over the visceral cavity, by the 
 formation of the limb girdles in its substance, and by its relations to 
 the limbs Travelling forwards, it first comes into relation with the 
 openings of the alimentary, urinary, and genital organs, and detaches 
 muscles to them. It then encounters the pelvis and hind limb, which 
 more or less, interrupt and make demands upon it. Next it is 
 expanded, and the direction of its fibres is modified, by the visceral 
 cavity. Then the shoulder-girdle and fore-limb, the branchial and 
 hyodean apparatus, the larynx and pharynx, ths lower jaw and the 
 face necessitate modifications to meet the several requirements, which 
 vary in different animals and which lead to almost infinite diversities 
 in the disposition of the several parts of the muscle." 
 
 From this account it is clear that when the two halves of the 
 pelvic girdle were formed and approached each other at the symphysis 
 pubis, the course of the ventral muscle was interrupted. The portion 
 behind, afterwards differentiated into the sphincter cloacae, became 
 separated from that in front which was to give rise to the various 
 muscular layers in the wall of the visceral cavity. When the bulbo- 
 cavernosus (formed from the sphincter cloacae) extends into the tissue in 
 front of the pubes, the prolongation may be regarded as representing 
 the connecting fibres of a muscle now interrupted, but which at 
 one time extended continuously along the ventral aspect of the body. 
 
 Kobelt asks " whether the muscular bundle which passes from the 
 anterior portion of the bulbo-cavernosus to the mons Veneris to be 
 inserted into the skin, is perhaps intended for the more sensitive 
 (empfindlicheren) stretching of the mons Veneris?" But the 
 comparatively small number of cases in which the fibres are present 
 would tend to negative the question of functional activity. 
 
 CoMPABATiVE aiJatomy. — Kobelt has described the constrictor 
 cuhrii in the mare, sow, and bitch, and has shown that in each of these 
 anirnals the muscle coiisisted of two separate parts, a posterior and an 
 anterior. In the mare, for example, the posterior part formed a capsule 
 
49 
 
 surrounding the bulb, whilst the anterior part .was a long narrow 
 muscle, like the omo-hyoid, which passed to its insertion on the 
 dorsum of the clitoris. The fibres of both divisions were continuous, 
 in many cases, with the sphincter ani externus, and they closely 
 resembled the two parts of the bulbo-cavernosus of human anatomy, 
 viz., the compressor bulbi proprius and the constrictor radicis cUtoridis. 
 
 On the other hand, the arrangement of the vaginal sphincter in 
 the cat, leopard, and orang-utan suggests that two different 
 groups of muscular fibres take part in its formation. One corre- 
 sponding to the male bulbo-cavernosus, the other to a prolongation of 
 fibres of the external sphincter ani around the orifice of the vulva, 
 and either one or both may be present. As previously mentioned, 
 Straus-Durckheim describes the releveur de la vulvc in the cat as a 
 subcutaneous muscle whose fibres are continuous above with the 
 external sphincter ani, and the constrictor of the anal pouches. He 
 has not, however, found the bulbo-cavernosus. 
 
 In the leopard and orang both the bulbo-cavernosus and the 
 subcutaneous sphincter were represented. In the former, the muscle 
 surrounding the termination of the vagina was about an inch deep, 
 and received fibres from the external sphincter ani, though there could 
 be no doubt that these were reinforcements only. The main part of 
 the muscle represented the bulbo-cavernosus, and below the orifice of 
 the vagina the muscular fibres terminated by decussating with fibres 
 from the opposite side in the superficial fascia over the pubes. 
 
 In the orang the sphincter ani externus and the superficial vaginal 
 sphincter formed a figure of eight. An additional layer of muscular 
 fibres situated more deeply on the lateral wall of the vagina and 
 covering the bulb, represented the bulbo-cavernosus. 
 
 It is interesting to note the special features of the bulbo- 
 cavernosus in the female Indian elephant. According to Professor 
 Paterson and Dr. Dun, the muscle formed a complete investment for 
 the uro-genital canal. As the latter attained a length of three feet in 
 the specimen examined by them, the muscle was correspondingly 
 elongated, and one obtains a striking illustration of the modifications 
 which the muscle may undergo. From the attachments, the authors 
 regard the action of the muscle to be that of aiding in the retraction 
 of the uro-genital canal, and by its anterior fibres, that of producing 
 eversion of the edges of the vulva. 
 
50 
 (5) IscMo-cavernosus (Male). 
 
 The ischio-cavernosus muscle embraces the crus penis and extends 
 along the margin of the pubic arch from the ischial tuberosity 
 behind, to the lateral aspect of the penis in front. It is usually 
 about four inches long, but if, as sometimes is the case, the fibres are 
 prolonged backwards on to the great sacro-sciatic ligament, or 
 forwards on to the dorsum of the penis, the length may be increased 
 to five or six inches. The ischio-cavernosus is flattened somewhat 
 at its origin from the ischial tuberosity, but where the muscle 
 invests the corpus cavernosum its sectional appearance is crescentic. 
 The lower part of the ischio-cavernosus is chiefly muscular, its 
 upper part markedly tendinous, and the general arrangement of the 
 muscular fibres is such that they form remarkably slender bundles, 
 many of them nearly two inches long. This feature may be strikingly 
 demonstrated by removing the root of the penis and its muscular 
 coverings and dissecting the parts under water, and the accompanying 
 illustrations of the ischio-cavernosus in the two sexes represent the 
 muscles after being dissected in this way. 
 
 Attachments. — The ischio-cavernosus has an extensive origin 
 from the inner surface of the ischial tuberosity and in many cases 
 from the great sacro-sciatic ligament. Also, from the conjoined rami 
 of the ischium and pubis on each side of the attachment of the crus 
 penis. It is inserted chiefly by means of a tendinous expansion, 
 which is spread over the free surface of the crus, into the under and 
 outer sides of that body at its front part. Although the ischio- 
 cavernosus presents no external evidence of division, the various fibres 
 as they are directed forwards fall readily into groups, and as these 
 present different attachments and relations, it will be convenient to 
 describe the muscle in four parts which may be named as follows : — 
 
 (1) Ischio-cavernosus internus. 
 
 (2) Ischio-cavernosus medius. 
 
 (3) Ischio-cavernosus externus. 
 
 (4) The occasional pubo-cavernosus. 
 
 (1) IscHio-cAVEENOSDS INTERNUS.— The fibres of this division arise 
 from the tendinous fascia covering the inner surface of the ischial 
 tuberosity and usually from the great sacro-sciatic ligament and its 
 falciform prolongation. Also, internal to the root of the corpus 
 
51 
 
 cavernosum directly from the ascending ramus of the ischium. The 
 fibres are directed upwards and forwards on the inner side of the crus 
 penis ; they quickly become tendinous and a few being detached are 
 inserted into the lower surface of the triangular ligament. The 
 remainder are directed towards the angle formed by the corpora 
 cavernosa, and a great portion of these end in the tunica fibrosa of 
 the crus penis at its fore part. A few fibres may reach the middle 
 line, but according to my dissections this arrangement is by no means 
 constant. 
 
 Holl, on the other hand, describes tendinous fibres passing to the 
 angle of union of the two corpora cavernosa and there meeting and 
 uniting with corresponding fibres from the opposite side. He suggests 
 that the name of ligamentum intercrurale be given to the median 
 tendon thus formed, and ischio-cmernosus accessoriiis to the inner 
 division of the ischio-cavernosus, of which the tendinous fibres are a 
 continuation. 
 
 Bourgery, in his illustrations, represents each ischio-cavernosus in 
 the female as two distinct and separate bellies. One is internal and 
 named the ischio-cavernosus, the other is external and named the 
 ischio-clitoridicus. The ischio-cavernosus internus corresponds to 
 the ischio-cavernosus in the female, as described by Bourgery. 
 
 Although both Holl and Bourgery describe and figure the inner 
 fibres of the ischio-cavernosus as a distinct muscle, I have not, up to 
 the present time, met with any specimen which showed a clear 
 separation of this group of fibres. Indeed, it was only by careful 
 examination that the various fibres could be made out, so that it 
 can hardly be considered that the arrangement, described by these 
 authors is the normal one. 
 
 (2) Ischio-cavernosus medius. — The middle group of fibres, like 
 the preceding, arises chiefly from the tendinous structure covering the 
 inner surface of the ischial tuberosity and partly direct from the 
 ischial ramus. The fibres are arranged in two layers, a superficial and 
 deep. The former soon becomes tendinous and gains insertion into 
 the fibrous investment of the corpus cavernosum at a point imme- 
 diately behind the insertion of the constrictor radicis penis. It forms 
 the narrow tendon on the surface of the ischio-cavernosus which is 
 observed after removing its fascial sheath. The deep layer is chiefly 
 muscular and forms an immediate investment for the crus penis. 
 
52 
 
 (3) IscHio-CAVEENOSUS EXTEENDS. — The fibres of 'the external 
 division arise chiefly from the interval between the two lips of the 
 conjoined rami of the pubis and ischium. Their development is 
 subject to considerable variation. Whilst in some subjects they can 
 scarcely be recognised, in others strong bundles of muscle are found in 
 this situation. Directed forwards on the outer side of the crus penis 
 the muscular fibres terminate in short tendons which pass into the 
 fibrous covering of the corpus cavernosum a little anterior to the 
 insertion of the middle group of fibres. In a few instances the fibres 
 may pass round the body of the penis and terminate in a fibrous 
 membrane on the dorsum of that structure. HoU points out that 
 these fibres are always directed on either side of the dorsal vessels 
 and nerves towards the glans penis. 
 
 According to Houston, and Henle, however, the part of the muscle 
 which passes on to the dorsum of the penis is separated from the 
 outer part of the ischio-cavernosus by an interval. The former 
 observer has named it the compressor vense dorsalis penis and 
 Henle, the pubo-cavemosus or levator penis. 
 
 (4) PuBO-CAVERNOSUS. — The prolongation of fibres from the 
 ischio-cavernosus on to the dorsum of the penis, which forms the 
 pubo-cavernosus, rarely occurs in man. It is however well marked in 
 some lower mammals. The prolongation has been specially sought for 
 in the human subject by J. Miiller who, out of twenty subjects 
 found it on two occasions, and by Kobelt and Henle, each of whom, 
 in a large number of dissections, found it once only. In these cases the 
 bundle of fibres constituting the pubo-cavernosus was quite distinct 
 from the ischio-cavernosus ; it arose from the descending ramus of the 
 pubis and passed on to the dorsum of the penis where the fibres were 
 soon lost in the subcutaneous tissues. According to Henle, the fibres 
 may meet with those of the opposite side to form a median tendinous 
 expansion which covers the dorsal vein of the penis, and it is 
 generally believed that these fibres correspond to the special muscle 
 which Houston has described in the dog and other animals under 
 the name of compressor vense dorsalis penis. 
 
 There is every reason to believe, however, that these fibres do not 
 correspond to the compressor vense dorsalis penis of the dog, wolf, 
 bear, etc., but that they are morphologically the same as the levator 
 penis of many of the lower animals, and further, that the compressor 
 vense dorsalis penis is represented in man by a vestigial muscle 
 
53 
 
 situated between the two layers of the triangular ligament to which 
 Vlacovitch' has given the name of ischio-pubicus. 
 
 Houston says of the compressores venx dorsalis that " they are less 
 distinct in man than in most of the mammalia. They arise from 
 the rami of the pubis, above the origin of the erectores penis and 
 crura, and ascending in a direction forwards are inserted above the 
 vena dorsalis by joining with each other in the mesian line. They 
 form a thin stratum of muscular and tendinous fibres, about one inch 
 long and three-quarters of an inch broad, and may perhaps be looked 
 upon as portions of the erectores penis, which, instead of being 
 inserted into the sides and lower part of the corpora cavernosa, 
 mount over those bodies, to exert their compressing influence on the 
 vena dorsalis. They enclose between them and the penis, the vein, 
 arteries, and nerves of this region. Their anterior fibres are dis- 
 tinguished from those of the erectores by the fibrous attachment of 
 the crura to the pubis ; their posterior margins are kept distinct from 
 the front part of the levatores ani, known under the name of Wilson's 
 muscles, by the pudic artery which divides them in its course towards 
 the dorsum of the penis." 
 
 From Houston's description it is clear that the compressor venae 
 dorsalis, at least as regards its origin, is intra-pelvic. The situation of 
 the muscle corresponds precisely to that of the rudimentary ischio- 
 pubicus ; both are situated above the ischio-cavernosus. In the dog 
 also, the compressor venae dorsaUs bears a similar relation to the 
 ischio-cavernosus. A further point of resemblance between the two 
 muscles is established by the fact, that both the compressor vena3 
 dorsalis of the lower animals and the ischio-pubicus in man send 
 fibres across the dorsal vein of the penis. 
 
 On the other hand the pubo-cavernosus is situated at the upper 
 and anterior part of the ischio-cavernosus and its fibres are directed 
 immediately on to the dorsum of the penis. This arrangement 
 corresponds with what is found constantly in certain animals, namely, 
 a muscle arising from the pubis and terminating on the dorsum of the 
 penis — the levator penis. The latter muscle has been described by 
 Owen, Cunningham, and Young in marsupials, and by Cuvier in the 
 baboon, hare, marmot, and elephant. 
 
 ' I have not, up to the present, been able to obtain Dr. Vlacovitch's paper in the 
 "Atti ddV iii-ftiluto veneto di scienze." But Prof. HoU refers to Vlacovitch as the 
 first observer to name this muscle ischio-pubicus. 
 
64 
 
 The fibres of the levator penis maj' or may not join across the 
 dorsal vessels, but they are invariably directed towards the glans 
 penis. Young describes in the koala a muscular arch with the 
 convexity forwards, formed by the two muscles. In the camel the 
 fibres are directed towards the glans on either side of the dorsal 
 vessels, and the two muscles remain quite distinct. 
 
 The fibres on the dorsum of the penis which are directed towards 
 the glans, and which Henle has termed the pubo-cavernosus, are 
 therefore to be regarded as the representative of a specially developed 
 levator penis in some of the lower mammals. The differentiation 
 of the muscle from the anterior end of the sphincter cloacae has 
 probably been associated with the development of the corpora 
 cavernosa. As these bodies have increased in length, a few of the 
 peripheral fibres of the sphincter cloacse, which primarily invested the 
 roots of the corpora cavernosa, have been carried along on to the 
 dorsum of the penis. 
 
 Henle, Kobelt, Theile, and Sappey, have each written special 
 accounts of the ischio-cavernosus. 
 
 Henle divides the ischio-cavernosus into four parts: — (1) lower, 
 (2) middle, (3) lateral, and (4) pubo-cavernosus. The lower part 
 corresponds to the ischio-cavernosus internus described above, though 
 Henle gives as an additional insertion, fibres passing into the 
 connective tissue mass which fills in the interspace between the roots 
 of the. corpora cavernosa penis. The middle division practically 
 includes the same group of fibres as the ischio-cavernosus medius. 
 Its fibres, however, arise from the descending ramus of the pubis, and, 
 according to Henle's description, the superficial tendon joins with 
 that of the lower division previous to its insertion. The lateral 
 portion includes those fibres which arise from the conjoined rami and 
 pass to be inserted into the tunica fibrosa of the corpus cavernosum. 
 Henle does not describe any fibres from this division passing on to 
 the dorsum of the penis. If dorsal fibres are present he refers to 
 them separately as the pubo-cavernosus and regards them as an 
 entirely independent muscle. 
 
 Kobelt adopted a somewhat simpler plan of description. He 
 divided the muscle into two parts, a lower muscular and an upper 
 tendinous. He further pointed out that the muscular bundles had a 
 three-fold origin without being separated into three heads. The 
 main portion arose from the inner surface of the tuber ischii, a 
 
C.P 
 
 G S.L 
 
 Fig. 11. — ( 'fiii'M iif penis and isr-liin-r';u'ern(isi ninseles aftei' removal 
 and dissection in weak spirit. O.F., iseliio-ca\"efnosiis externns ; M.F., ischio- 
 cavernosus medius ; I.F., ischio-eavernosiis internns ; (i.S.L., sreat saci'o-sciatic 
 ligament; C.P., I'vns penis; L.I., li,ij;anientum interenn-ilc (HolU ; CO., corpus 
 cavernosum penis. 
 
55 
 
 second division from the inner lip of the pubic arch, and a third from 
 the outer lip of the pubic arch. All the various bundles passed to be 
 inserted into the angles and borders of a triangular shaped aponeurosis 
 which covered the bulb ' of the corpus cavernosum. This arrangement 
 of a fibrous aponeurosis over an enlargement of the corpus cavernosum 
 showed that "the ischio-cavernosus was not a band-shaped muscle 
 but hoUowed or funnel-shaped." 
 
 Theile has noted the ischio-cavernosus divided into two parts in 
 man, and of these one was anterior, the other posterior. The latter 
 arose from the inner aspect of the tuber ischii and was inserted almost 
 entirely into the root of the corpus cavernosum, and no fibres were 
 traced from this division on to the root of the penis. The anterior 
 part arose from the inferior aspect of the corpus cavernosum below 
 the pubic arch, and its fibres were directed upwards and forwards to 
 be inserted on the dorsum of the penis, into the corpus cavernosum 
 of the same side. Theile refers to the statement made by other 
 observers, that a tendinous aponeurosis is formed above the dorsal 
 vessels by the union of the fibres from the two sides, and says "that 
 he has never seen this arrangement and that he cannot believe it to 
 be normal." Thus, Theile's results are also opposed to the view that 
 the fibres which pass on to the dorsum of the penis from the ischio- 
 cavernosus represent the compressor venae dorsalis penis of lower 
 mammals. 
 
 Lastly, Sappey describes the ischio-cavernosus as consisting of two 
 fascicles, an internal and external. The former of these arises from 
 the ischial tuberosity, and the latter from the ischio-pubic rami. The 
 fleshy fibres cover the external surface of the subjacent root, and are 
 inserted into the lateral part of the corpus cavernosum below the sus- 
 pensory ligament of the penis. 
 
 Development and Comparative Anatomy. — Although the general 
 plan of construction of the penis is the same in different groups of 
 mammals, the disposition of the roots of the corpora cavernosa and 
 the muscles associated with them varies considerably. 
 
 Apart from differences in size and shape, we find that in certain 
 animals the crura of the corpora cavernosa are quite free in the 
 perineum, and it is almost possible to trace the various stages from this 
 
 ' Kobelt uses the term bulb to indicate not only the posterior enlargement of 
 the corpus spongiosum but also a. similar enlargement at the posterior end of the 
 corpus cavernosum. 
 
56 
 
 primitive arrangement to the more highly developed condition in which 
 the corpora cavernosa are attached to the bones of the pelvic outlet. 
 
 In certain marsupials, for example, the posterior extremities of 
 the corpora cavernosa, and the ischio-cavernosi which invest them, 
 are quite free. This has been noted by Cunningham in Phalangista, 
 and by Young in the Koala. 
 
 In other marsupials an arrangement is found by means of 
 which the mobility of the crus penis is diminished, though the crus 
 still remains free from bony attachment. This is brought about by 
 the fibres of the ischio-cavernosus being attached to the ramus of the 
 ischium by one extremity, and investing the crus ponis by the other. 
 Such an arrangement has been described by Eggeling in Didelphis 
 virginianus and Phalangista canina. 
 
 Whether the attachment of the ischio-cavernosi to the bones of 
 the pelvis is the cause of the subsequent attachment of the corpora 
 cavernosa is uncertain, but it is obvious that the contraction of the 
 muscular fibres would tend to bring the free end of the corpus 
 cavernosum towards the ischium, and eventually to retain it in that 
 position. At any rate, we find that in a large number of animals the 
 corpus cavernosum and the ischio-cavernosus are attached to the 
 bones at the pelvic outlet, and the relation of the muscle to the corpus 
 cavernosum is such as to enable us to divide these animals into two 
 groups. In the first group, which, as shown by Kobelt's dissections, 
 includes the bull, horse, dog, rabbit, hedgehog, boar, cat, and rat, the 
 ischio-cavernosus surrounds the crus on all sides, so that the latter 
 lies along the pubic arch enveloped in a muscular covering. In the 
 second group, which includes the camel, man, and most of the higher 
 mammals, the muscular fibres situated between the crus and the bone 
 have disappeared, so that the ischio-cavernosus now covers only the 
 free surface of the crus penis. 
 
 A reference to the work of Retterer on the development of the 
 root of the penis in man, shows that the centre of the genital 
 eminence is occupied by a mass of dense cellular tissue which 
 is vascular from the beginning. As this central mass extends 
 backwards, it becomes separated into a dorsal part — the corpora 
 cavernosa and a ventral part — ^the corpus spongiosum. The posterior 
 extremities of the corpora cavernosa remain free for some time, and 
 receive a muscular investment from the uro-genital division of the 
 primitive sphincter cloacae. Eventually, they get attached to the 
 
57 
 
 pubic and ischial rami, but it is clear that the stage in which the 
 crura of the penis are free, although only temporary in man, is a 
 permanent one in some marsupials. 
 
 Apart from developmental considerations it is interesting to note 
 the special arrangement of the ischio-cavernosus in cetaceans and in 
 the camel. Although the pelvis in cetaceans is rudimentary, Cuvier 
 describes the roots of the corpora cavernosa as being largely developed, 
 and as being attached to the styliform bones which represent the 
 pelvis. After joining the two styliform bones together by means of 
 muscular fibres, the ischio-cavernosi are directed forwards on to the 
 roots of the two corpora cavernosa. 
 
 In the camel the ischio-cavernosus is large and strong. It has an 
 extensive origin from the great sacro-sciatic ligament, from the ischial 
 tuberosity, and from the conjoined rami of the pubis and ischium. It 
 is significant that a large number of fibres arise from the sacro-sciatic 
 ligament, since, as we have previously noticed, this origin is frequently 
 observed in the human subject. The majority of the fibres of the 
 muscle are attached to the under surface of the corpus cavernosum 
 penis in union with the bulbo-cavernosus. Anteriorly, the fibres 
 which arise from the pubis, though not separated from the remainder 
 of the ischio-cavernosus pass on to the dorsum of the penis, forming 
 the pubo-cavernosus or levator penis. The fibres can be traced on 
 either side of the dorsal vessels towards the glans penis, and in the 
 specimen which I dissected the fibres continued forwards in this way 
 for about two inches. The two pubo-cavernosi were not united across 
 the dorsal vessels of the penis, and, therefore, one could not regard 
 them as compressores vense dorsalis (fig. 23). 
 
58 
 
 (6) Ischio-cavernosus (Female). 
 
 It is generally asserted that the erectur clitoridis corresponds 
 almost completely to the erector penis. Indeed, the oiily point of 
 difference usually raised in comparing the two muscles is that of size, 
 though most authors are agreed that the ischio-cavernosus is smaller in 
 the female than in the male. Kobelt, however, holds a different view 
 and states that the ischio-cavernosus in the female is not orily relatively 
 but absolutely larger than the corresponding muscle in the male. My 
 observations show that the muscle is distinctly smaller in the female. 
 
 But a further difference is apparent if the roots of the penis 
 and clitoris with the ischio-cavernosi muscles are carefuUy removed 
 and pinned out under water. It is then seen that the crus 
 clitoridis, besides being smaller than the crus penis, is covered by a 
 flat tendon which invests the whole free surface of that body and 
 which receives almost all the muscular fibres of the ischio-cavernosus. 
 In some cases a few fibres pass along its outer edge towards the dorsum 
 of the clitoris, but in none of my dissections did I find any fibres 
 extending further forwards than those shown in the accompanying 
 illustration (fig. 12). Henle, on the other hand describes fibres 
 passing on to the dorsum of the clitoris and forming a median 
 aponeurosis with those of the opposite side. Neither Lesshaft nor 
 HoU have observed this arrangement, and HoU regards. Henle's 
 description as incorrect. Lesshaft does admit, however, that he has 
 observed fibres fusing with the albuginea clitoridis. 
 
 In the female, therefore, the upper part of the ischio-cavernosus is 
 more markedly tendinous and the volume of the muscle is smaller 
 corresponding to the smaller size of the corpus cavernosum clitoridis. 
 Below and behind, the resemblance between the muscles in the two 
 sexes is more apparent, and the fibres can be traced backwards as far 
 as the great sacro-sciatic ligament; the muscular fibres are also 
 arranged in similar groups. 
 
 The flat tendon investing the root of the corpus cavernosum is 
 triangular in shape with the apex below and the base above. It 
 receives at the apex and two sides the various fibres of the ischio- 
 cavernosus, whereas the base fuses with the fibrous investment of the 
 corpus cavernosum clitoridis. For example, the ischio-cavernosus 
 externus terminates chiefly on the outer border, the ischio-cavernosus 
 medius is inserted into the apex and also to the lower parts of the inner 
 and outer borders, whilst the ischio-cavernosus internus terminates on 
 
G.S.L. 
 
 Fig. 12. — Clitoris and isdiio-civernosi muscles aftci- removal and disseetion 
 in weak spiiit. C'.C., eiiis elitoridis ; O.F., il.F., I.F., iscliio-eavernnsus extermis, 
 niedius, and inteiTuis ; (J.S.L., great sacro-seiatie ligament; T.l'., ti-iangular 
 a|)onenro.sis at insertion of muscle; B.C., lindy of clitoris: (i.C, glans 
 clitoi'idi.s. 
 
59 
 
 the inner border of the tendon. A few fibres of the latter division 
 pass upwards towards the angle of union of the corpora cavernosa 
 clitoridis, and, according to HoU, there is a similar formation of a 
 ligamentum intercrurale as in the male. Henle describes muscular 
 fasciculi passing from the inner edge of the muscle to the tissue under 
 the body of the clitoris, but my observations agree with those of HoU 
 and Lesshaft who have failed to recognise this distribution. 
 
 In Bourgery's description of the ischio-cavernosus in the female 
 we find, as previously mentioned on page 51, that the muscle is 
 divided into inner and outer divisions, the ischio-cavernosus and 
 ischio-clitoridicus respectively. He describes the ischio-clitoridicus as 
 follows : — " Parallel to the ischio-cavernusus, it takes origin from the 
 ischium in front of this latter, on the external surface of which it lies 
 and with which it is connected. Its muscular fibres are very long, and 
 following the direction of the corpus cavernosum, terminate on a 
 narrow flat tendon which is inserted above the free extremity of the 
 clitoris." 
 
 The double nature of the ischio-cavernosus in the female as 
 described by Bourgery, raises the important question of homology 
 between the muscles in the two sexes. Are the two divisions together 
 the representative of the ischio-cavernosus in the male, or is the inner 
 division alone — i.e., the ischio-cavernosus — the corresponding muscle, 
 and the ischio-clitoridicus an accessory muscle? To this question 
 Kobelt replies that he regards the ischio-clitoridicus as an aberrated 
 portion of the constrictor vestibuli, and in this opinion he is supported 
 by Luschka. In that case the inner division of the ischio-cavernosus 
 in the female is homologous to the ischio-cavernosus in the male. 
 
 Very Uttle has been recorded of the erector clitoridis in lower 
 animals. Straus-Durckheim, and Paterson and Dun, have described 
 the muscle in the cat and Indian elephant respectively, and I have 
 observed it in the leopard and orang-utan. In aU these aninials the 
 general arrangement of the erector clitoridis closely resembled that in 
 the human subject, except that in the leopard and orang-utan the 
 muscle was almost entirely free from tendinous fibres. In the elephant, 
 on the other hand, it is somewhat surprising to find it feebly developed. 
 In the specimen dissected by Professor Paterson and Dr. Dun " the 
 only trace of the muscle was in the form of a thin layer of muscular 
 fibres surrounding each crus clitoridis on its way to form the clitoris." 
 
60 
 
 B. Muscles between the two layers of the 
 Triangular Ligament. 
 
 [Constrictor iirethrse, transversus perinei profundus, and ischio- 
 pubicus.] 
 
 (1) Constrictor urethras (male). 
 
 The muscle situated between the two layers of the triangular 
 ligament and known as the constrictor urethrae consists of a series of 
 fibres which present different relations and perform different functions. 
 Whilst many fibres extend transversely or obliquely across the pubic 
 arch, others, which reach as far as the prostate, surround the 
 membranous urethra in a circular manner. Lastly, a few fibres are 
 arranged in the form of a muscular covering or investment for 
 Cowper's glands. 
 
 In lower mammals the corresponding muscular fibres are arranged 
 in a much simpler manner, and it will perhaps be advantageous if 
 a short reference be first made to them. 
 
 In the camel, for example, the constrictor or sphincter urethrae 
 forms a muscular sheath surrounding the urethra from the 
 neck of the bladder to the bulbs of the penis. In the elephant 
 Watson describes a continuous layer of muscle, one quarter of an inch 
 in thickness, arranged transversely around the membranous urethra, 
 and a similar arrangement has been observed in other animals. 
 No fibres of the sphincter urethras are attached to the bones of the 
 pelvis. 
 
 In the camel, Cowper's glands also attain a large size. They are 
 situated in the perineum between the ischio-cavernosus and the bulbs 
 of the penis, and under cover of the ischio-cavernosus (fig. 23). 
 The glands are ovoid bodies nearly two inches long and each is 
 completely invested by a special muscle — the compressor glandulse 
 Cowperi — the fibres of which are prolonged backwards as far as the 
 great sacro-sciatic ligament where they are connected with the origin 
 of the ischio-cavernosus, whilst in front the fibres extend as far 
 forwards as the duct which leaves the anterior part of the gland. 
 
61 
 
 The sphincter urethrse and the compressor of Cowper's glands in 
 the camel, therefore, are separate and distinct muscles. 
 
 In the human subject these muscles are greatly modified. 
 Some of the fibres of the sphincter urethraj are attached to the 
 bones of the pubic arch and they form a muscular support for the 
 urethra as it passes under the symphysis pubis. It is with these 
 fibres, in some form, that Wilson's name has become associated. 
 
 In 1809 this observer published an account of two muscles which 
 took origin from the back of the bodies of the pubes and passed round 
 the urethra to form a muscular sling, by means of which the canal 
 could be raised towards the symphysis pubis. These longitudinal 
 fibres have not been recognised by succeeding observers. Indeed, 
 Paulet suggests that the expression " Wilson's muscle " should not be 
 used. He states that when adopted in human anatomy it 
 perpetuates an error of observation, and that it is even more incorrect 
 when used in comparative anatomy, since it is then applied to a 
 sphincter muscle of the urethra, of which Wilson did not appear 
 to have known the existence. 
 
 In man, Cowper's glands are very much diminished in size and. 
 importance and lie behind the membranous portion of the urethra. 
 Their muscular investments are proportionately reduced and the 
 compressor is represented by a small bundle of muscular fibres closely, 
 associated with the sphincter of the urethras. 
 
 The compressor urethrae of man, therefore, includes two muscles : — 
 
 (a) Sphincter urethrse membranacese. 
 
 (b) Compressor glandulse Cowperi. 
 
 (a) Sphincter urethrse membrance/e. — In this muscle two 
 distinct groups of fibres can be recognised. One group extends 
 transversely or obliquely across the pubic arch, a few fibres in 
 front of, but the majority behind the membranous urethra. The 
 other group is arranged circularly around the membranous urethra 
 and extends a variable distance towards the prostate. In fact, Holl 
 describes fibres of this muscle lying on the lateral aspect of the 
 prostate and forming a sphincter muscle of the prostatic urethra. 
 
 The transverse fibres arise from the desceriding ramus of the pubis, 
 from the two layers of the triangular ligament between which they 
 are situated, and from the back of the transverse ligament of the 
 perineum. They converge round the urethra towards the middle line 
 where they meet with the fibres from the opposite side and form a 
 
62 
 
 median tendinous raph6, though in some cases the fibres on the two 
 sides are uninterruptedly continuous. Comparatively few fibres pass 
 in front of the urethra. 
 
 The true sphincter fibres are arranged around the membranous 
 urethra in the form of a muscular sheath. According to HoU, they 
 are disposed in a series of layers, in some of which the fibres run 
 circularly, in others longitudinally. In new-born children this 
 arrangement is very characteristic as shown by Cadiat by means of 
 microscopical sections of the perineum. He found that the urethra 
 from the neck of the bladder up to the bulb is surrounded by a 
 cylinder of muscular fibres of which some are striated, others smooth ; 
 at many points the elements are intermingled. 
 
 (b) Compressor glandulae Cowperi. — The fibres constituting 
 this muscle arise from the transverse ligament of the perineum at the 
 upper edge of the triangular ligament, and in some cases from the 
 descending ramus of the pubis. Passing downwards and inwards 
 they come into relation with the under surface of Cowper's glands 
 and form a muscular investment for those bodies. The fibres 
 terminate in the middle line, either by joining with those of the 
 opposite side or by joining with the transversus perinei profundus. 
 In some subjects the muscle is difficult to recognise, whilst in others 
 it forms a weU-defined muscular bundle, the lateral fibres of which 
 may extend outwards as far as the bones of the pubic arch. 
 
 In many ungulates and carnivores the compressor of Cowper's 
 gland is strongly developed. The arrangement in the camel has 
 already been referred to. In the elephant, as shown by Watson, 
 the muscle does not completely envelop the gland, but forms an 
 elliptical belly which embraces and conceals its perineal aspect. 
 Paulet, on the other hand, has pointed out that in the horse the 
 muscle consists of two layers, a superior and an inferior, which join 
 at their lateral margins so that every part of the gland is covered 
 by muscle. 
 
.^^ 
 
 Fig. 13.— Murtoles lietwcen the two layevH of the triangular ligament (male). 
 D.V.P., dorsal vein of j^eni.s ; T.L.P., transverse li,u;ament of pehns — ruilimentary 
 iseliio-puhieus ; il.U., mem!)ra.noas methra. ; I.Cav., isuhio-cavernosus ; T.IM*., 
 transver.sus perinei [)rof andus ; C.M.U., tilires of the constrictor in-ethrie ; A.(\, 
 acetabulum ; T.F., thyroid foramen ; H.P., horizontal ramus of pubis ; C.C., corjms 
 eavei'nosum. 
 
63 
 
 (2) Constrictor urethrse (Female). 
 
 The constrictor urethras in the female is usually more difficult 
 to demonstrate than the corresponding muscle in the male. This 
 is largely due to the number of smooth muscular fibres which 
 enter into its substance, and to the prominent venous plexus which 
 lies on the anterior wall of the vagina and urethra. 
 
 Apart from sections of the pelvis in which the extent and 
 relations of the muscle can be particularly well studied, I have 
 found that the constrictor urethras may be readily exposed by 
 dissecting from the pelvic cavity and removing the fascia which 
 lies on its upper surface. Lesshaft, on the other hand, recommends 
 that a sagittal section be made through the symphysis pubis, 
 urethra, and vagina, and that, after separating the mucous 
 membrane of the urethra, the dissection be continued from within 
 outwards. He has found that by adopting this method the 
 constrictor urethree can be demonstrated with certainty. 
 
 In those subjects in which the muscle is strongly developed it 
 can be shown to consist of two distinct groups of fibres like the 
 sphincter of the membranous urethra. One group surrounds the 
 urethra in the form of a muscular sheath, the other extends 
 transversely or obliquely across the pubic arch, and this part of the 
 muscle is almost completely divided into lateral halves by the vagina. 
 
 The fibres constituting the muscular sheath for the urethra are 
 to be regarded as the true sphincter urethras. They arise from 
 the walls of the veins which take part in the plexus previously 
 mentioned, and from the tough fibrous tissue lying on the urethra 
 between the back of the syinphysis pubis and the neck of the 
 bladder. Surrounding the urethra either circularly or obliquely, 
 most of the fibres terminate in the tissue between the urethra and 
 the anterior vaginal wall. It should be pointed out, however, that 
 whilst this is the general arrangement of the true sphincter fibres 
 of the constrictor Urethree, a bundle of fibres may frequently be 
 observed directed sagittaUy on either side of the urethra, which 
 obtains attachment to the lowest part of the back of the symphysis 
 .pubis. 
 
 The transverse fibres of the constrictor urethras are situated 
 between the two layers of the triangular Ugament. They take 
 origin from the descending ramus of the pubis, from the transverse 
 ligament of the perineum, and from the walls of the neighbouring 
 
64 
 
 veins. Their insertion varies at the upper and lower parts of the 
 layer. The superior fibres are directed inwards, and in front of the 
 urethra join with the corresponding fibres from the opposite side. 
 The succeeding fibres pass to the tissue between the urethra and the 
 anterior vaginal wall where they meet and join with fibres from 
 the transversus perinei profundus. The lowest fibres are directed 
 obliquely inwards and downwards and blend with the vaginal wall. 
 It is to the anterior set of fibres that Lesshaft has given the name 
 of " transversus urethrse." He describes the muscle separately from 
 the constrictor urethras, though there can be little doubt that it 
 constitutes a part of that muscle. The fibres of the transversus 
 urethras, according to Lesshaft, pass in front of the urethra where 
 the muscles of the two sides meet and fuse and afterwards pass 
 into the walls of the surrounding veins. A few, however, appear 
 to pass out of the pelvic cavity under the subpubic ligament, and 
 these terminate in the fascia covering the clitoris. Lesshaft further 
 points out that the transversus urethra is feebly developed and 
 often absent in the female. Out of seventy subjects it was found 
 well developed in twelve, i.e., 17%. 
 
 (3) Transversus perinei profundus. 
 
 The deep transverse muscle is situated at the lower and posterior 
 edge of the compressor urethrse, and in a plane above and in front 
 of the transversus perinei superficialis. The fibres arise from the 
 neighbourhood of the point of union of the pubic and ischial rami, 
 and passing inwards to the middle line are inserted into a median 
 raph6, situated between the muscles of the two sides. The median 
 raph6 closely adjoins the one formed by the union of the two halves 
 of the transverse fibres of the constrictor urethrse. 
 
 It is usually considered that these transverse fibres belong to the 
 constrictor urethrse; different views have been advanced, however, 
 by Cadiat and by Paulet. 
 
 According to Cadiat's observations on new-born children, there 
 exists in the perineum, between the sphincter ani and the sphincter 
 urethrse, a transverse bundle of muscular fibres. These fibres are 
 
65 
 
 attached on the one hand to the median raph6, and on the other 
 hand to some cellular tissue belonging to the pelvic cavity, or 
 to the subcutaneous structures, according to the level at which 
 they occur. One group of fibres forms the trans versus perinei 
 profundus; aiiother the superficial transverse muscle; whilst the 
 most inferior fibres belong to the bulbo-cavernosus. Further, Cadiat 
 suggests that the functions of the muscular bundle may be, perhaps, 
 to isolate the effect of the contractions of the two sphincters (urethral 
 and anal) between which it is situated. 
 
 Paulet beUeves that the deep transverse muscle in man is 
 homologous to the transverso-urethral muscle of carnivores. The 
 identity of this latter muscle with the compressor vense dorsalis 
 penis of Houston and the ischio-pubicus of Vlacovitch will, however, 
 be shown in discussing the homology of the ischio-pubicus. 
 
 In the female the arrangement of the transversus perinei profundus 
 is somewhat similar to that in the male, though, owing to the 
 presence of the vagina, the mode of insertion is slightly altered. As 
 the muscle approaches the middle line it spreads out, and a few 
 of the most anterior fibres pass to the anterior wall of the vagina 
 and lie behind the urethra. These fibres have been named by 
 Fiihrer the " transversus vagina." The remaining fibres pass 
 behind the vagina to the central point of the perineum. On 
 account of the course which the fibres of the transversus perinei 
 profundus take round the vaginal wall, Fiihrer refers to the whole 
 muscle as the " levator vaginae." In the female the muscle is more 
 frequently absent than in the male. 
 
 (4) Ischio-pubicus. 
 
 This rudimentary muscle arises from the conjoined rami of the 
 pubis and ischium ventral to the attachment of the constrictor 
 urethr£E. Passing forwards it terminates in a fiat tendon which is 
 directed across the pubic arch and which unites with the tendon from 
 the opposite side under the dorsal vein of the penis. 
 
 Although the main part of the muscle is frequently absent, or 
 replaced by fibrous tissue, the united tendons of the two muscles 
 can nearly always be recognised. They form in many cases a 
 
66 
 
 well-defined fibrous band situated near the upper margin of the 
 triangular ligament, of which, under the name of transverse hgament 
 of the perineum, it is usually regarded as a thickening. 
 
 There can be little doubt that this muscle is the representative 
 in man of the compressor venae dorsalis penis described by Houston, 
 and the transverso-urethral muscle described by Paulet. Both of 
 these observers have apparently described the same muscle in the 
 dog, wolf, cat, bear, and other carnivores, but each has given a 
 different name to it. Although a muscle undoubtedly exists 
 in many carnivores which compresses the dorsal vein of the penis, 
 opinions have hitherto been at variance in determining the 
 homologous muscle in man. Paulet believed that the transverso- 
 urethral muscle in carnivores — a muscle whose function he admitted 
 was to compress the dorsal vein of the penis — was represented in 
 man by the deep transverse muscle of the perineum, whilst Houston 
 considers that the compressor is represented by a portion of the erector 
 penis, but which apparently corresponds in position to the ischio- 
 pubicus. I have pointed out (p. 54) that the muscular fibres in 
 man, which other writers have . regarded as corresponding to the 
 compressor vense dorsalis penis, are probably the homologue of the 
 levator penis of lower mammals. 
 
 On the other hand, the rudimentary ischio-pubicus in man 
 corresponds almost precisely in its- position and attachments to the 
 more active muscle in carnivores and other mammals. This will 
 be more apparent if we examine the compressor venae dorsalis 
 penis in one of the carnivores, for example, a dog. 
 
 In the dog the erector penis is an oval-shaped muscle attached to 
 the ischium immediately behind the symphysis pubis. Dorsal to this 
 muscle and within the pelvic cavity there arises also from the ischium 
 the compressor venae dorsalis penis of Houston. Inclining forwards 
 and inwards it ends in a glistening tendon directed across the dorsal vein 
 of the penis, at which point it is joined by the tendon from the 
 opposite side. Some of the fibres of the tendon pass in front of the 
 vein and others behind it so that the tendon appears to be perforated 
 by a transverse slit through which the vein is directed. The muscle 
 in a dog eighteen inches high, measured nearly an inch long and 
 about one third of an inch wide. 
 
 It is clear that there is a close resemblance between the muscle 
 just described and the ischio-pubicus. The latter is situated dorsal, to 
 
67 
 
 the erector penis, and the tendons of the two muscles join in the 
 middle line, in this case however (i.e., in man), beneath the dorsal 
 vein of the penis. 
 
 What has become of the fibres which passed above or in front of 
 the dorsal vein ? According to Holl, the tendon of the ischio-pubicus 
 divides near the symphysis pubis into two parts, one of which goes to 
 the under edge of the symphysis and forms with that of the opposite 
 side " the inferior arcuate ligament of the pubic bones." The 
 remaining part of the tendon passes across the angulus pubicus and 
 fuses with the tendon from the opposite side. By this arrangement a 
 space is left for the passage of the dorsal vein of the penis. 
 
 I have not noticed any difference in the arrangement of the muscle 
 in the two sexes, beyond the fact that it is more difficult to recognise 
 in the female than in the male. 
 
PART II. 
 
 Muscles derived from the Primitive Flexors and 
 Abductors of the caudal division of the 
 vertebral column. 
 
 [ (1) Levator aiii.= Flexor Ilio-coccygeus and Flexor Pubo- 
 eocoygeus. 
 
 (2) Coccygeus or l8cliio-coccygeus.=Abductor caudse. 
 
 The muscles of both sides form the — 
 
 Diaphragma pelvis (Meyer) ; or 
 
 Diaphragma pelvis rectale seu proprium (Holl). J 
 
 (1) Levator ani. 
 
 In 1555 Andreas Vesalius wrote an account of this muscle under 
 the name of " Musculus sedem attoUens," and although the latter has 
 been superseded by the more definite name of levator ani, the 
 description as given by him has been adopted with little or no 
 essential alteration until a few years ago. 
 
 A short reference to the history of the levator ani is found in 
 Professor Sappey's text-book of anatomy, published in 1869. He says 
 that " the levator ani is one of those muscles which has been studied 
 the most, and at the same time, one about which we know the least. 
 The doctrine of continuity of fibres between two or more muscles of 
 independent action has been applied to it at various scientific epochs, 
 and this ancient error, renewed without ceasing, has singularly 
 contributed to complicate its study." 
 
 A glance at the literature of the levator ani shows what a great 
 amount has been written on the anatomj' and functions of this 
 
69 
 
 muscle. Being such an important factor in the female pelvic floor, 
 one finds that the muscle has received very careful consideration by 
 gynaecologists, and many of the descriptions which are in use at the 
 present day are largely based on the results obtained by their 
 investigations. 
 
 At the same time it is admitted that there is no muscle of similar 
 size in the body whose form and functions are -more difficult to 
 understand than those of the levator ani. In the first place, the 
 nomenclature of its various parts is confusing. No uniform method 
 of description has hitherto been adopted, though some anatomists 
 have recommended the discontinuance of the name levator ani 
 entirely and the substitution of those names which denote the 
 corresponding muscles in lower animals. If this recommendation be 
 adopted, many of the difficulties previously encountered will be 
 removed and the constitution of the muscle more easily understood. 
 
 It is curious to see how the descriptions of the various parts of 
 the levator ani vary, more particularly as regards strength, 
 importance, and function. By recognising the primary condition of 
 the muscle and the subsequent changes which have afiected it, one 
 can, however, understand more clearly why certain parts are liable to 
 thinning, and may be, to complete failure, whilst other parts are 
 markedly increased in size. 
 
 Therefore, as a preliminary to the study of the human levator 
 ani, it will obviously be advantageous to consider the corresponding 
 muscles in lower mammals. 
 
 In marsupials there is no levator ani as in man ; but a group of 
 separate muscles, which collectively represent it, arises from the 
 inner aspect of the side wall of the pelvis and passes to be inserted 
 into the caudal vertebrae. In those marsupials which possess a 
 strongly developed tail it is evident that the muscles pass through 
 the outlet of the pelvis to reach the various points of insertion, 
 whereas, in those in which the tail is rudimentary, the muscles are 
 confined to the pelvic cavity. The group comprises three muscles, 
 viz., the sacro-coccygeus, ilio-coccygeus, and pubo-coccygeus, and 
 although the origin of each of the constituent parts is different, 
 and takes place either from the body of the pubis, horizontal ramus 
 of pubis, the ilio-pectineal line, or sacrum, each part is inserted into 
 the caudal vertebrae. 
 
 The pubo-coccygeus arises either from the back of the body of the 
 
70 
 
 pubis or its horizontal ramus, and the ilio-coccygeus from the 
 ilio-pectineal line or from the side wall of the pelvic cavity 
 immediately below it. Their attachments and nerve-supply show 
 that they correspond to the human levator ani, whilst the sacro- 
 coccygeus is occasionally represented in man by the curvator 
 coccygis. From a consideration of their attachments it is obvious 
 that any action which these muscles exert on the rectum is limited to 
 lateral compression, and is quite secondary to that of moving the tail. 
 
 As I have previously pointed out,' the ilio-coccj^geus and 
 pubo-coccygeus are similarly arranged in the majority of mammals. 
 Even in man in whom, in consequence of the retrogression of the 
 caudal vertebrae and the assumption of the erect posture, the greatest 
 modifications are evident, the primitive arrangement of two muscles 
 passing from the side wall of the pelvis to the rudimentary coccyx is 
 retained to a remarkable extent. In man, however, they are modified 
 to effect a more efficient closure of the pelvic outlet and to support 
 the superimposed viscera. 
 
 That the reduction of the tail has a very marked influence on the 
 flexores caudiB is shown by the observations of KoUman on tailed 
 apes and anthropoids. The levator ani in tailed apes arises from the 
 back of the symphysis pubis and from the internal arcuate line as far 
 as the sacro-iliac synchondrosis. It can readily be divided into three 
 parts — (1) a ventral portion arising from the back of the symphysis; 
 (2) a lateral portion arising from the upper angle of the symphysis 
 as far as the canalis obturatorius ; and (3) a dorsal portion arising 
 from the internal arcuate line, extending from the canalis obturatorius 
 as far as the sacro-iliac synchondrosis.^ 
 
 The three divisions are inserted as follows : — The ventral portion 
 passes to the wall of the rectum in which it decussates with the 
 recto-coccygeus. The lateral and dorsal portions leave the pelvis and 
 are inserted into the first caudal vertebra and into the remains of the 
 haemal arches on the under surface of the succeeding four vertebra?. 
 
 'In a, paper "On the Levator ani or ischio-anal muscle of ungulates, with 
 special reference to its morphology,'' read before the Anatomical Society of 
 Great Britain and Ireland in November, 1898. 
 
 ^ The three parts of the levator ani in tailed apes do not correspond to the three 
 muscles described in marsupials. The dorsal portion is the ilio-coccygeus, and the 
 lateral and ventral portions together equal the pubo-coccygeus. 
 
s.c 
 
 IL.C 
 
 P C.l 
 
 
 Fig. 14. —Flexor muscles of the tail in a monkey (Macacus rhesus). 
 Left .side from within. P.P., psoas parvus; P.M., [jsoas magnus : O.N., obturator 
 nerve; P. C, pulio-coceygeus ; O.I., obturator internus ; Il.C, ilio-coccygous ; 
 S.C, sacro-coccy:;eus ; S.N., sacral nerves; I. A., external iliac arter)'. (In this 
 s])cciijten tlie " le\'ator ani " consisted of only two parts. — the pul)o-cocc3^geu.s 
 an- 1 iiio-cuccygeus. ) 
 
71 
 
 In anthropoids the caudal vertebrae are much reduced, and in 
 consequence there are some remarkable differences in the disposition of 
 the levator ani. 
 
 The dorsal portion of the muscle is wholly converted into fibrous 
 tissue so that only the lateral and ventral parts exist. There is also a 
 great change in the thickness of the muscle. Whereas in tailed apes 
 the levator ani attains a thickness of more than 5 m.m., in anthropoids 
 it is thin and almost transparent. The lateral portion at its insertion 
 into the sides and tip of the coccyx forms an aponeurosis with the 
 corresponding division of the opposite side. The fibres of the ventral 
 division pass partly behind the rectum, joining with the opposite 
 muscle to form a muscular sling, and partly into the wall of the 
 rectum. 
 
 The levator ani in anthropoids closely resembles that in man, 
 though there are several well-marked points of difference. Apart from 
 the complete reduction of the ilio-coccygeus to fibrous tissue which 
 does not occur constantly in the human subject, though I have noticed 
 it on several occasions, in anthropoids there is no arcus tendineus, i.e., 
 "white line." The bundles of the levator ani arise from the back of the 
 pubis, this attachment having been inherited, according to KoUman, 
 from tailed forms, and also from the internal arcuate line by a thin 
 aponeurosis, 1'5 cm. in length. A similar arrangement is described by 
 Luschka of the levator ani in the human subject. He says that the 
 lateral part of this muscle arises from the internal arcuate line, and 
 that the attachment of the muscle to the "white line" is very weak and 
 only by means of fine connective tissue. 
 
 The levator ani in the human subject arises along an uninterrupted 
 line from the back of the body of the pubis, from the pelvic fascia on 
 the side wall of the pelvis and from the spine of the ischium. Its 
 fibres are inserted into the coccyx and the ano-coccygeal raphfe, whilst 
 a few pass to the central point of the perineum. It is clear, therefore, 
 that most of the fibres at their insertion are post-anal. 
 
 It is not always easy, but usually possible, to find the interval 
 between the part arising from the pubis and the part arising from the 
 pelvic fascia, since in most cases the adjoining edges of the two muscles 
 overlap one another. . It was this interval which led Lartschneider to 
 describe two parts of the levator ani, a portio pubica and a portio iliaca, 
 and Savage to speak of pubo-coccygeus and obturato-coccygeus. It 
 seems preferable, however, to refer to the two muscles as pubo- 
 
72 
 
 coccygeus and ilio-coccygeus, inasmuch as these are the names given 
 to the two homologous muscles in lower mammals. It may be urged 
 against this nomenclature that although the pubo-coccygeus arises 
 from the pubis, the ilio-coccygeus does not arise from the ilium. But, 
 as I shall show when describing the ilio-coccygeus, the origin of the 
 latter has been transferred from the iUo-pectineal Hne to the lateral 
 wall of the pelvic cavity, so that it now arises from the pelvic fascia 
 along the " white line." The change from one to the other was clearly 
 shown in a young kangaroo which I recently dissected. The ilio- 
 coccygeus consisted of several parts which arose at various levels 
 from the lateral pelvic wall. The highest division was attached to the 
 ilio-pectineal line, and then in succession below this, two parts were 
 attached to the periosteum covering the ischium. If we take into 
 account the history of the ilio-coccygeus, there is ample evidence to 
 support the retention of the name for the lateral part of the levator ani 
 of human anatomy. 
 
 Further, the pubo-coccygeus consists of two parts, one which passes 
 to the coccyx and a second which passes round the rectum to form a 
 sling with the fibres of the opposite side. Holl has named these latter 
 fibres the pubo-rectalis. Similarly with the ilio-coccygeus, two parts 
 can very frequently be recognised, one corresponding to the lateral 
 part of the levator ani, the other situated in front of the coccygeus 
 and named by His, the ilio-sacralis. The following muscles may thus 
 be recognised : — 
 
 (^w, T,. ("(a) Ilio-coccygeus. 
 
 (1) Iho-coccygeus { [bj mo-sacrSs. 
 (2) Pubo-coccygeus... { W Pubo-coccygeus. 
 ^ ^^ 1(d) Pubo-rectalis. 
 
 Levator ani 
 
 (a) — nio-coccygeus. 
 
 In certain mammals the iUo-coccygeus consists of two parts which 
 Holl refers to as the dorsal and ventral divisions of the muscle. In 
 man both may be represented, though in most cases only the ventral 
 division persists. If the dorsal division is present, it is found in front 
 of the coccygeus, and forms an accessory muscle — the ilio-sacralis. 
 
 In the human subject the ilio-coccygeus is liable to considerable 
 variations. It may fail entirely or be replaced by fibrous tissue as in 
 anthropoids, and only in. a comparatively small number of subjects 
 
M S.fl. 
 
 L.S. 
 
 l.C._ 
 
 ■ c.v 
 
 
 IlC 
 
 MS' / SAP, 
 
 ■ i ~— -, > - -^ 7" P f ' C . 
 
 Il.C." 
 
 T E. E ; ■ I G H A M . 
 
 (&9 3 . 
 Fig. 15. — Su'jittal sfcti.iii iif tlie pelvis to sIkiw tin; jielvic ili:i]>lir.i;^nii .-111.1 
 external .--|iliiiirter .-iiii. S. , sacmni ; il.S.A., niiilille .sacial artery; L.,S., 
 liijinnentuin sacro-cocej'geum .aiitiains ; I. (J., (■ijccj'oeus ; ( ' .\ ., eoecyi^eal vtrtelirii' ; 
 Ii. .(_"., ilio-eoeevg-eus ; T.P.P.C, teii'linoiis a]iii]ieiirosis nf | lulio-oiuTy.yens ; Ii, .('"., 
 i'a[jlii' foniieil liy iliu-eoeeypei ; S.T-!., yiihiiieter recti; S.A.S'., S.A.H"., tsjihiiieter 
 aiii externus .sulieutaneus ami sujierlrei.alis : S.A.l*., s|>liini;t.er ; iii extcrmis 
 lirofunilns: K., rertiim ; A'., va-^ina ; U., urethra; I'.t'., jmijo-eoeeyo'eus ; O.F., 
 obturator canal ; S.i'., ^ynijiliy.-is pubis. 
 
73 
 
 is the muscle strongly developed. It is usually thin and trans- 
 parent, and the muscular bundles are separated so frequently by 
 broad membranous intervals, that, taken in conduction with the in- 
 sertion of the muscle into the rudimentary caudal vertebrae, the ilio- 
 coccygeus must be regarded as a degenerating muscle whose primary 
 function has been lost. In virtue of its position, however, it con- 
 tributes to the formation of the pelvic floor. 
 
 Much has been written on the size and thickness of the ilio- 
 coccygeus in the male and female, and in comparing them reference 
 is usually made to the peculiarities in the female consequent on 
 greater functional activity. But any differences, and these are 
 generally in the direction of thickness and size of the membranous 
 intervals, simply indicate the degree to which degeneration has 
 extended. Obviously, these variations are to be found as frequently 
 in the female as in the male. 
 
 Attachments. — The ilio-coccygeus arises from the pelvic fascia 
 and from the inner aspect of the spine of the ischium. Its attach- 
 ment to the pelvic fascia is along a curved line whose concavity is 
 directed upwards. The line has a varying relation to the side wall 
 of the pelvis; in some cases it is situated almost as high as the 
 obturator canal, and in other cases considerably below it. Posteriorly 
 the origin of the ilio-coccygeus extends as far as the margin of the 
 great sacro-sciatic notch, whilst anteriorly its limit is not always easy 
 to determine. It reaches almost as far as the commencement of the 
 obturator canal, and for those cases in which there is no clear 
 separation between the ilio-coccygeus and pubo-coccygeus HoU gives 
 the following directions : — " Draw a line through the anterior edge of 
 the tuber ischii and the point of junction of the iUac bone with the 
 pubis. The point where this line crosses the crescentic line on the 
 side wall of the pelvic cavity indicates the anterior limit of the ilio- 
 coccygeus." 
 
 The line of origin of the ilio-coccygeus just described does 
 not completely coincide with the "white line" of the pelvic fascia. 
 Posteriorly they may coincide, but in front the "white line" 
 occupies a lower level, and is situated on the fibres of the ilio- 
 coccygeus as a thickening of the recto-vesical fascia. 
 
 At the Anatomical Congress in Basle ' in 1895, the origin of the 
 
 1 Die Anatomisohe Nomenclatur (Nomina Anatomica). Edited by Professor 
 W. His, Liepzig, 1895. 
 
74 
 
 levator ani was specially considered. The crura of the tendinous arch 
 on the fascia obturatoria, from which arise the lateral fibres of the 
 levator ani, were described as reaching as high as the brim of the 
 pelvis, and the concavity of the arch as high as the obturator canal. 
 The arch was referred to as the arcus tendineus musculi levatoris ani 
 and special attention was drawn to the fact that it did not correspond 
 to the arcus tendineus of the pelvic fascia, i.e., " white line." It was 
 stated that the latter crossed the tendinous arch of the levator 
 ani and came to lie on the muscle itself, from which it could readily 
 be separated. 
 
 Muscular fibres may take origin from the arcus tendineus of the 
 pelvic fascia, but these are exceptional. 
 
 Luschka gives the origin of the levator ani from the fascia obtur- 
 atoria along a line of crescentic shape whose lowest point is situated 
 5"5 cm. below the ilio-pectineal line. His observations support the 
 conclusion that there is no absolute connection between the line of 
 origin and the arcus tendineus of the pelvic fascia. Luschka regards 
 the arcus tendineus either as an elongated thickening ur as a 
 duplicature of the pelvic fascia which projects as a ledge into the 
 pelvic cavity and lies on the upper surface of the muscle. 
 
 From the origin the fibres of the ilio-coccygeus are directed down- 
 wards, backwards, and inwards to the coccygeal vertebra;. They are 
 inserted from behind forwards into the lateral margin of the last two 
 pieces of the coccyx, into the tip of the coccyx and into a median 
 raph^ which runs from the tip of the coccyx to the posterior margin 
 of the anus. Holl regards the median raph6 as the degenerated 
 continuation of the caudal end of the vertebral column. 
 
 At their insertion the fibres of the ilio-coccygeus are not all in the 
 same plane but form a series of layers superimposed upon each other. 
 The upper layer consists of fibres from the posterior end of the muscle, 
 the middle layer is composed of fibres from the ilio-coccygei of both 
 sides which decussate without forming a fibrous raph6, whilst the 
 most inferior layer forms a strongly developed fibrous plate or raph6 
 into which the majority of the fibres are inserted. 
 
 The extent oi the ilio-coccygeus is largely infiuenced by the 
 behaviour of the lower sacral and coccygeal vertebrae. The upper 
 edge of the muscle is reduced by fusion of the proximal caudal vertebrae 
 with the sacrum : the lower edge of the muscle is reduced by loss of 
 the terminal coccygeal vertebrae. In a small number of cases the ilio- 
 
\ PC' 
 
 u. 
 
 Ttj',<lh■,^!lnl 
 
 Fig. 16. — Pulio-eocfygeuy, ilio-coccytj;eu.s, and coccygeus lml^^(.'les in the 
 female, from lielow and lieliiiid. I. (J., coccygeus ; Ii,.C., ilio-coccygeiis ; 
 
 P.C., pubo-coccygeus ; P.C"., pi'c-anal lifji'ert of the pu!)0-coi;cygea.s ; U., nrethra ; 
 v., vagina; A., anus; P.C"., pubo-reutaUs ; M.R., ano-coceygeal raphe. 
 
IL.C' 
 
 IlC," 
 
 M S fl. 
 
 
 Fig. 17. — Flexor iiiiisoles of tlir tail in a y<)Uii<4' KMn,u'ai-oo, .seuti from tlic 
 front and .slightly from tin- li.-ft siiK.-. aftn- wide r:;fparatioii of the symphysi.s. 
 O.N., ohtm'ator nerve; I. A., external iliae artery: P.r., psoa.s ])arvus ; M.S. A., 
 middle wacral artery; li..C, ilio-eoeeyu-eus ariwin.;' fiom ilio-jiet.'tineal line (u])per 
 divi.sion); S.CI., .Ha<'ro-eoeeyg'en.s internum; IlX"., ilio-coee3'treus (middle division); 
 Il.C"., ilio-eoeeyLnfuw (lower diA'ision) ; vS.('.E., saei'o-coecytreii.s externus ; !.<..'., 
 coceyj^eu.s ; ]*.(_'., puho-ooeeytreus. 
 
75 
 
 coccygeus is entirely absent, so that on removing the peritoneum a gap 
 is observed in the pelvic floor which may lead, according to Holl, to 
 " hernia perineaUs." On the other hand though the ilio-coccygeus be 
 absent there may be no gap. In these cases the pubo-coccygeus has 
 extended its attachment along the pelvic wall and the opening is 
 thus completely closed. It is significant that in ungulates the ilio- 
 coccygeus is always absent. 
 
 Little difference is observed between the ilio-coccygeus in the male 
 and female, and it is difficult to say in which sex degeneration of the 
 muscle is carried to the furthest point. According to my dissections the 
 muscle is usually thinner and more membranous in the female, though 
 probably this is due to stretching of the muscle during parturition. 
 Luschka, from a consideration of the size of the pelvis in the two 
 sexes, points out that the levator ani as a whole is smaller, especially 
 in its vertical measurement in woman than in man, just as the height 
 of the pelvis is less in the former. With these exceptions, the ilio- 
 coccygeus in the female corresponds in situation, form, and attach- 
 ments to the homologous structure in the male, and in both it is 
 distinctly a degenerated muscle. 
 
 Morphology. — The insertion of the ilio-coccygeus into the reduced 
 caudal vertebras and its homology with the ilio-coccygeus of lower 
 mammals points to the muscle as a derivative from the primitive 
 ventral caudal muscle. Primarily, the muscle passes from the ilium 
 to the caudal vertebrae — ^a condition retained in most mammals. But 
 the reduction of the caudal vertebrae has been accompanied by a 
 corresponding reduction in the muscles which act on them, so that the 
 ilio-coccygeus in man is just as much a degenerated muscle as the 
 coccygeus or abductor caudae. Since the muscle has no direct con- 
 nection with the rectum, obviously it should be regarded as quite 
 distinct, and should be separately described from the pubo-coccygeus ; 
 further modifications in the latter, although it is just as much a caudal 
 muscle as the ilio-coccygeus, have resulted in the formation of a strong 
 muscle whose functions are of the utmost importance. In fact, 
 Henle includes in the levator ani the pubo-coccygeus only and 
 describes the ilio-coccygeus as a separate muscle under the name of 
 ischio-coccygeus. This is a good plan, but the use of the latter term, 
 which hitherto has been employed to denote the coccygeus, may lead 
 to confusion. 
 
 The action of the ilio-coccygeus must necessarily be feeble and is 
 
76 
 
 practically limited to drawing forwards the coccyx and the fibrous 
 raphfe between it and the anus. When ankylosis occurs of the various 
 pieces of the coccyx, and of the coccyx with the sacrum, the action of 
 the muscle is still further restricted. 
 
 In some of my dissections of the ilio-coccygeus, I have noticed a 
 tendency for the posterior or upper edge of the muscle to extend 
 upwards towards the ilio-pectineal line, and in one specimen at least it 
 approached within a fourth of an inch of it. As previously mentioned, 
 the ilio-coccygeus in many lower mammals arises from the ilio- 
 pectineal line and the occasions in which fibres of the muscle in 
 the human subject deviate from what is now considered the normal 
 attachment and reach a higher level, may be regarded as illustrations 
 of a reversion to a more primitive condition. 
 
 It is clear, therefore, that one stage in the phylogeny of the 
 ilio-coccygeus is the descent of its origin on the lateral wall of the 
 pelvic cavity from the ilio-pectineal line, to the ischium as found in 
 the rabbit, or the fascia obturatoria as in man. That the descent 
 actually occurs is placed beyond doubt by what I found' in a young 
 kangaroo. 
 
 In this interesting specimen which measured about twelve inches 
 long, excluding the tail, the ilio-coccygeus, as mentioned on page 72, 
 consisted of three parts (fig. 17). I shall refer to these simply as the 
 upper, middle, and lower divisions. 
 
 The upper division, dorsal in position, arose from the ilio-pectineal 
 line just above the strongly marked ilio-pectineal tubercle and quite 
 close to the sacrum. 
 
 The middle and lower divisions, ventral in position, were attached 
 to the side wall of the pelvis; the former of these was situated 
 immediately below the obturator foramen, the latter a short distance 
 further down. The lower division could only be satisfactorily studied 
 by removing the middle layer, and it was then seen to have a 
 remarkable tendinous origin i to J in. in length, which appeared to 
 come from a "white line." On close examination, however, it was 
 clear that this was simply the attachment of the tendon to the 
 periosteum covering the bone. The Une of attachment coincided with 
 one drawn horizontally backwards from the lower margin of the 
 symphysis pubis to the posterior border of the ischium. 
 
 Lower down the three divisions fused together and formed a 
 rounded muscular bundle which passed on to the under surface of the 
 
Il.C- 
 
 S, C 
 
 .— \,1. 
 
 P. P, 
 
 Il.C 
 
 P. C 
 
 ../>^^ 
 
 Fig. 18. — l^lexur muscles uf tl.e t^il in Ei.-liidiia liyslrix. .M.ll., iii;i!svi|n;il 
 lione ; IM*., ]tsoiis })arviis ; Ii,.C'., ilio-uoocyyeii.s ; ]'.(..'., ] ml )o-eoceytj;eus ; 
 .S.C, sacro-cocryj^eu.s ; It;.(''., lilires of ilio-0(iocy;:ieiis ai'isiii'j^ from saoi'iini. 
 
77 
 
 tail quite cloae to the median line. It finally terminated in three 
 slender tendons which were inserted into the prominent tubercles on 
 the under surface of the bodies of the 7th, 8th, and 9th caudal 
 vertebrae. Although the ilio-coccygeus arises in the neighbourhood of 
 the ilio-pectineal line in Echidna, Felis leopardus, Phoca vituUna, 
 Dasypus sexcinctus and many others, and from the side wall of the 
 pelvis at a lower level in Erinaceus europaeus, Lepus cuniculus, Cavia 
 cobaya, Thylacinus cynocephalus, and in man, the young kangaroo 
 is the first example that I have seen, and as far as I have been able to 
 ascertain, the first that has been recorded, in which the ilio-coccygeus 
 exhibited both attachments in the same animal. Such a disposition 
 illustrates in a marked degree the transference of a part of the ilio- 
 coccygeus from the ilio-pectineal line to a lower level on the pelvic wall. 
 Further, this part has, in its turn, divided so that the lower division 
 has continued the descent. In this way the origin of the ilio- 
 coccygeus in the kangaroo has become tripartite and thus the varying 
 height of the ilio-coccygeus in man, and its occasional proximity 
 to the ilio-pectineal line becomes intelligible. 
 
 In Echidna the ilio-coccygeus arises from the ilium and from 
 the sacral vertebrae (fig. 18). 
 
(b) Ilio-sacralis. 
 
 The ilio-sacral muscle is an accessory slip of the ilio-coccygeus 
 situated at the dorsal edge of that muscle and in front of the coccygeus. 
 It represents the dorsal fibres of the ilio-coccygeus in some of the 
 lower animals. 
 
 In the hedgehog a sheet of muscular fibres extends from the inner 
 aspect of the side wall of the pelvis to the caudal vertebrae, and 
 although there is no clear separation of the constituent elements three 
 muscles are recognisable (fig. 19). 
 
 The muscle which arises from the horizontal ramus of the pubis 
 is the pubo-coccygeus.' Both the remaining parts represent the ilio- 
 coccygeus and, as the illustration shows, they arise from the ilium 
 behind the obturator nerve. Of the two divisions one is dorsal, the 
 other ventral in position, so that it is convenient to refer to the dorsal 
 and ventral fibres of the ilio-coccygeus. All the three muscles are 
 inserted into the transverse processes of the caudal vertebrae. 
 
 One of the best examples of both dorsal and ventral divisions of 
 the ilio-coccygeus occurring in the human subject was found in a 
 negro dissected in the practical anatomy rooms of the Owens College 
 during the summer of 1898 and is well shown in fig. 20, in which the 
 pelvic diaphragm is seen from above after removal of the rectum and 
 separation of the pubic bones. The pubo- and ilio-coccygei, which in 
 this case were fused together, formed a ventral muscular sheet which 
 arose from the side wall of the pelvic cavity. At the dorsal edge of this 
 
 * It is significant that the pubo-coooygeus in the hedgehog arises from the 
 horizontal ramus, and not from the body of the pubis. This modification may, 
 perhaps, be due to the traction exerted by the tail. The tail of the hedgehog is in 
 a condition of hyper-extension, sometimes so pronounced that the tail lies flat 
 on the back of the animal. The hyper-extension is probably due to 
 the insertion into the tail of the great skin muscle, the development of which forms 
 so prominent a feature of this type of insectivores. As a result of the shifting of 
 the origin of the pubo-coccygeus from the body on to the horizontal ramus of the 
 pubis, the adjacent fibres of the ilio-coccygeus are partly concealed beneath it. 
 
 At a meeting of the Anatomical Society in November, 1898, Mr. F. G. Parsons 
 suggested that the attachment of the pubo-coccygeus to the horizontal ramus of 
 the pubis might be due to the frequency with which the body of the pubis fails in 
 insectivores. Mr. Parsons instanced examples of the group, in which the body of 
 the pubis was normally absent, and he thought that the change of origin of the 
 pubo-coccygeus in the hedgehog, from a point which was more or less unstable 
 to one which was subject to little or no change, might be explained on these 
 grounds. 
 

 Il.C 
 
 Il.C. 
 
 Fig. 19. — Flexni' iiuiseleH iif the tail in the Hedgehog (Erinaceus eiU'O- 
 jKeus). I., ilium; P.P., pso i.s iiarvivs ; O.N., olitiirator nerve; P.C, ijuljo- 
 coeeygeiis ; 8. P., .^ympliysis [iiiliis; Ir,.C"., ventral til n-es of the ilio-coccygeus ; 
 Il.C, florsal hbres of ilio-coccygeus; I.C., ischio-coccygeus ; fS., sacrum. 
 
79 
 
 sheet were two muscles, one, posterior in position, the coccygeus, the 
 other lying on the anterior surface of the coccygeus representing the 
 dorsal fibres of the ilio-coccygeus or ilio-sacralis. The latter some- 
 what triangular in shape was separated from the adjacent edge of 
 the ilio-coccygeus (ventral fibres) by a rather wide interval. Before 
 dissection and preservation in alcohol the interval was relatively 
 small, and filled up by a fibrous membrane which extended between 
 the two muscles. A good plan in studying the two parts of the 
 ilio-coccygeus and the membrane between them, is to remove the 
 coccygeus from behind and display the structures on its deep surface. 
 
 These attenuated muscular strands are the representatives of the 
 dorsal fibres of the ilio-coccygeus in the hedgehog and other mammals. 
 Each arose from the fascia obturatoria at a somewhat higher level 
 than the ventral fibres of the muscle. This is especially noticeable on 
 the right side where the origin of the ilio-sacralis. extended upwards 
 almost as far as the ilio-pectineal line close to the sacro-iliac 
 synchondrosis. The fibres were inserted into the lower end. of the 
 sacrum and the first piece of the coccyx. 
 
 Professor His' has recognised this muscle, and refers to it as 
 follows : — " Exceptionally there is present also a small independent 
 muscle which goes from the ilio-pectineal line of the ilium to the lateral 
 border of the sacrum, and which covers from the inner side the 
 coccygeus. I give a sketch of such an accessory M. ilio-sacralis, 
 which I have recently come across in the dissecting-room." 
 
 It was customary before the introduction of the nerve-test as a 
 guide to homology to rely solely upon the attachment and position of 
 a muscle. And although the nerve of supply furnishes valuable 
 corroborative evidence in the case of the ilio -sacral muscle, its attach- 
 ments alone, especially to the ilio-pectineal line, afford striking 
 testimony of its true nature. 'Ihe flexor group of tail muscles have 
 been formed as differentiations of one single powerful tail muscle — 
 the sacro-coccygeus, and the common origin is shown by the branches 
 which each receives from the fourth sacral nerve. The ilio-sacral 
 muscle when present participates in the same nerve-supply. 
 
 . ' Loc. cit. 
 
80 
 
 (c) Pubo-coccygeus. 
 
 The pubo-coccygeus invariably arises from some part of the pubis. 
 In the wombat, and in echidna the origin takes place from the back of 
 the body of the pubis, in the leopard, kangaroo, and thylacine from 
 the back of the symphysis pubis, and in the armadillo and hedgehog 
 from the back of the horizontal ramus of the pubis. The origin 
 usually extends outwards as far as the ilio-pectineal eminence, but 
 this varies in different animals, and it is considerably influenced by 
 the development of the os pubis. For instance, in the seal in which 
 the pubic bone is greatly elongated, the width of the pubo-coccygeus 
 at its origin exceeds four inches, whereas in the wombat and in 
 echidna the width of the muscle at the same point is relatively small. 
 
 In most mammals the fibres of the pubo-coccygeus are directed 
 backwards and upwards towards the caudal vertebrae into which they 
 are inserted. During their course the fibres simply lie on the lateral 
 aspect of the rectum and consequently exert little or no influence 
 upon it. But in a few marsupials, seals, and primates, fibres are 
 detached from the inner edge of the muscle and pass round the 
 rectum in the form of a sling. Apart from the support which such 
 an arrangement provides for the bowel it is probable that these fibres, 
 in primates at least, act as a sphincter of the rectum. 
 
 In the human subject the origin and insertion of the pubo-coccygeus 
 conform to what is constant in lower mammals; it arises from the 
 pubis and is inserted into the rudimentary caudal vertebrae. On the 
 other hand, the muscle has been profoundly modified in such a way 
 that as its influence over the caudal vertabrae has diminished its 
 influence over the rectum has increased, and a large number of fibres 
 losing their connection with the coccyx pass round the rectum to 
 form a sling — a change, the commencement of which is seen in certain 
 marsupials and carnivores. It is to these detached fibres which form 
 a loop around the rectum that HoU has given the name of pubo- 
 rectalis or sphincter recti. 
 
 A.TTACHMEXTS. — The pubo-coccygeus arises in man from the back 
 of the body of the pubis along an oblique line which extends from the 
 lowest limit of the symphysis upwards and outwards towards the 
 obturator canal. Also, from the obturator fascia for a limited extent 
 along a line continued forwards from the origin of the ilio-coccygeus. 
 The limits of the two muscles at this point are often difficult to define 
 but HoU points out an easy method for distinguishing one from the 
 
81 
 
 other. He prolongs the origin of the muscles upwards to the ilio- 
 pectineal line and notes the point of junction of the pubis with the 
 ilium. The fibres in front of this point belong to the pubo-coccygeus, 
 the fibres behind to the ilio-coccygeus. According to Luschka, the 
 levator ani arises from the horizontal ramus of the pubis, commencing 
 1-5 cm. from the middle line of the symphysis and 3-5 cm. below its 
 upper edge. 
 
 The obturator nerve bears an important relation not only to the 
 pubo-coccygeus but also to the ilio-coccygeus. In Phoca vitulina, 
 Erinaceus europseus, and Dasypus sexcinctus the nerve is covered for 
 a short distance before it enters the obturator canal by the origin of 
 the pubo-coccygeus (fig. 19). In those mammals, however, in which, 
 consequent on the reduction of the caudal vertebrae, the origin of the 
 pubo-coccygeus occupies a lower level on the back of the pubis, the 
 obturator nerve passes to the obturator foramen uncovered by muscle, 
 as in man and anthropoid apes. The ilio-coccygeus is situated either 
 under cover of the obturator nerve, as in Erinaceus europseus, or 
 below it, as in man. I have found this arrangement of the pubo-and 
 ilio-coccygei of much assistance in distinguishing the muscles on the 
 side wall of the pelvis. 
 
 The fibres of the pubo-coccygeus form a flat band about an inch 
 wide, thick at its mesial border, thin where it overlaps the ilio- 
 coccygeus. It is directed backwards almost horizontally along the 
 side of the anal canal towards the coccyx and sacrum to which it 
 obtains attachment. To the arrangement of the fibres behind the 
 rectum further reference is necessary. 
 
 Between the termination of the vertebral column and the anus 
 the two pubo-coccygei come together and form a thick fibro-muscular 
 layer lying on the raphfe formed by the ilio-coccygei (figs. 15 and 20, 
 T.p.p.c, iL.c). It will greatly facilitate the description if the fibres 
 which come from the pubis are referred to as the pubic fibres, and 
 those from the obturator fascia as the obturator fibres. 
 
 Nearly aU the pubic fibres pass backwards to the vertebral column. 
 They are joined behind the rectum by the corresponding fibres from 
 the opposite side and becoming tendinous, form a thick aponeurosis 
 or plate. This is continued upwards in front of the coccyx for some 
 distance and finally divides into two lateral portions which have been 
 named the ligamenta sacro-coccygea anteriora (figs. 15 and 20, l. s.). 
 These are situated one on either side of the middle sacral artery and 
 
82 
 
 are finally inserted into the last one or two pieces of the sacrum and 
 the first piece of the coccyx. 
 
 A few of the pubic fibres, however, pass inwards to the central 
 point of the perineum, descend in close contact with the walls of the 
 rectum, and finally terminate in the external sphincter ani and skm 
 of the anus (pre-anal fibres of the levator ani). HoU describes fibres 
 passing backwards at the lower edge of the tendinous plate and 
 remaining muscular so that the internal layers (pubic fibres) of 
 both sides are united behind the rectum and in front of the coccyx 
 by means of a plate which is partly tendinous and partly muscular. 
 Only the tendinous fibres are inserted into the sacral and coccygeal 
 vertebrae. 
 
 The obturator fibres (fig. 15) form the outer border of the muscle 
 and becoming tendinous join with the ligamentum sacro-coccygeum 
 anterius. A few decussate in the middle line and lie on the upper 
 aspect of the thick tendinous aponeurosis which constitutes the chief 
 insertion of the pubo-coccygeus (fig. 20). 
 
 The insertion of the pubo-coccygeus into the end of the vertebral 
 column is not admitted by all observers. In many descriptions only 
 the hindmost fibres of the levator ani (ilio-coccygeus) are described as 
 terminating on the coccyx. Indeed, Dr. Dickinson of New York 
 has come to the conclusion that no fibres are inserted into the coccyx, 
 and that the name of pubo-coccygeus is no longer tenable. On this 
 point, however, his conclusions are opposed to those of most modern 
 observers. 
 
 The description of the pubo-coccygeus, which I have just given, 
 differs from most previous ones in the absence of any reference to fibres 
 terminating in the walls of the rectum. It is generally considered that 
 some fibres of the levator ani terminate in the rectal walls, but although 
 a very close relationship undoubtedly exists between the two 
 structures, I have not been able to satisfy myself that fibres end in 
 this way. On the contrary, from a series of dissections which I made 
 with the special object of noting the relations between the rectum and 
 the pubo-coccygeus, I can afiirm that no such fibres were present. 
 
 On this point my results confirm the conclusions which HoU had 
 arrived at, viz., that no fibres from the levator ani descend in the 
 walls of the rectum. He finds, however, " that those fibres which form 
 the innermost and lowest part of the pubic origin descend anterior to 
 the rectum and, becoming tendinous, form with those of the opposite 
 
iside an aponeurosis which adjoins the anterior wall of the lowest 
 division Of the rectum, and finally divides into fine fibres which 
 terminate in the skin of the perineum." 
 
 On the other hand, many observers describe fibres from the levator 
 ani as terminating in the walls of the rectum. liUsehka refers to 
 bundles of fibres which issue from the deep layers of the muscle and 
 course downwards between the longitudinal fibres of the rectum as far 
 as the connective tissue which surrounds the anus. He affirms that 
 this arrangement is beyond doubt and ought not to be questioned. 
 Luschka names these fibres "the longitudinal portion of the 
 levator ani." 
 
 Pre-anal fibres of levator ani.J- — It is admitted by nearly all 
 observers that the most anterior fibres of the levator ani pass to the 
 central point of the perineum (fig. 20). They constitute a small 
 bundle which passes backwards and downwards on the side of the 
 prostate, and in some cases on the side of the urethra immediately it 
 emerges from the prostate. Few muscles have had so many names 
 applied to them (see below). 
 
 The foregoing statements regarding the pubo-and ilio-coccygei and 
 their attachments are based entirely upon dissections." Professor 
 Symington from a study of vertical mesial sections of the pelvis, 
 supplemented by transverse sections to ascertain lateral relations 
 has, however, arrived at practically similar conclusions. He found 
 that the pubo-coccygeus and obturator-coccygeus (ilio-coccygeus) 
 
 jPars Prostatioa levatoria ani (Luschka). 
 
 Pars Urethralis levatoris ani (Luschka). 
 
 Compressor Prosbatse (Albinus). 
 
 Adductor Prostatse (Santorini). 
 
 Levator Urethra (Krause). 
 
 Abductor Prostatse. 
 
 Fibres pre-rectales (Testut). 
 
 Levator prostatse. 
 * Many of the dissections were carried out in the following manner. A pelvis was 
 taken in which the perineum had previously been dissected and after removing the 
 external sphincter ani, the examination was continued from above. By separating 
 the rectum from surrounding structures one arrived at the point at which the 
 rectum passed through the pelvic floor to the exterior. The parts were then 
 carefully separated and the rectum pulled upwards through the iioor leaving the 
 pubo-coccygeus intact. In this way one obtained an excellent view of the whole 
 of the levator ani, and the position of the muscular canal through which the 
 rectum is transmitted (fig. 20). 
 
84 
 
 differ not only in the arrangement of their fibres but ako 
 in function. According to his observations "the pubo-coccygeus 
 arises from the posterior surface of the pubis and the posterior layer 
 of the triangular ligament. Its fibres pass backwards on the side of 
 the lower part of the vagina and on the side of the anal canal 
 to the last two pieces of the coccyx. A few of its innermost fibres 
 turn inwards in the perineal body in front of the internal sphincter 
 of the anus. Behind the anus and in front of the coccyx there is a 
 partial blending of fibres of opposite sides in the middle line. The 
 obturator- coccygeus consists of those fibres of the levator ani that arise 
 from the pelvic fascia between the pubis and the ischial spine. Its 
 fibres run backwards and inwards to the coccyx. These fibres have no 
 direct action upon any of the pelvic viscera. They constitute a thin 
 layer of fibres which in addition to raising the coccyx can elevate the 
 pelvic floor a little after it has been depressed." 
 
85 
 
 (d) Pubo-rectalis or SpMncter recti. 
 
 This name is applied by HoU to those fibres of the pubo-coccygeus 
 which, in man, form a muscular sling round the lower part of the 
 rectum. As the corresponding fibres in some of the lower mammals 
 exhibit a simpler arrangement, a reference may first be made to 
 them in the thylacine and seal. 
 
 In thylacine the pubo-coccygeus arises from the back of the body 
 of the pubis and is inserted into the chevron bones under the third 
 and fourth caudal vertebrae. A few of the lowest and most mesial 
 fibres are detached and jiass round the rectum where they join with 
 the deeper layers of the sphincter cloacae. A similar arrangement 
 occurs in the kangaroo and according to Eggeling in Phalangista 
 canina. 
 
 In Phoca vitulina and also in Arctocephalus, according to Miller, 
 fibres of the pubo-coccygeus pass round the rectum and vagina under 
 the sphincter and join the deeper fibres of this muscle as in the 
 marsupials. 
 
 These fibres from the pubo-coccygeus are to be regarded as the 
 commencement of an arrangement which in man reaches its highest 
 degree of development. 
 
 In many carnivores and marsupials the symphysis is long and 
 includes part of both pubis and ischium. The origin of the pubo- 
 coccygeus in the kangaroo and thylacine, for example, extends along 
 the back of the symphysis for nearly its whole length ; it is, in fact, not 
 a pubo-coccygeus but an ischio-pubo-coccygeus. In other marsupials, 
 as in the wombat, the lower and mesial fibres have disappeared so that 
 the muscle is reduced to a pubo-coccygeus corresponding to the pubo- 
 coccygeus in man. According to Eggeling, the reduction is connected 
 with changes in the length and mobilitj' of the tail. In thylacine and 
 in Phalangista the fibres of the pubo-coccygeus which correspond to 
 the pubo-rectaHs in man take origin from the hindmost part of the 
 pubo-ischial symphysis. 
 
 It is an interesting fact that the fibres of the pubo-rectalis 
 in man frequently arise from the descending ramus of the pubis, and 
 according to Theile, they may extend downwards as far as the 
 falciform prolongation of the great sacro-sciatic ligament. There is, in 
 these cases, a marked resemblance between the attachments of the 
 pubo-recLalis in man and those of the corresponding fibres in certain 
 marsupialsr^ 
 
86 
 
 Attachments. — The fibres of the pubo-rectalis generally arise 
 from the back of the lowest part of the symphysis pubis under cover 
 of the pubo-coccygeus, from the upper layer of the triangular ligament, 
 and from the pubis immediately below the symphysis. From this 
 origin the fibres pass round the lower part of the rectum and meeting 
 with the fibres from the opposite side form a strong loop or. girdle 
 which slings the rectum up to-the symphysis pubis (fig. 15. P.E.). 
 
 Holl refers to the pubo-rectalis as the best developed muscle in the 
 pelvic diaphragm. According to his description its fibres fuse partly 
 directly and partly by decussation with, those of the opposite side 
 under the tip of the coccyx and thus form' a thick loop surrounding 
 the perineal flexure of the rectum. 
 
 Further, he divides the muscle into upper and lower layers, both 
 supplied by the same nerve and separated at their origin by a 
 prolongation of the fascia obturatoria which is generally very feeble. 
 A comJ)lete separation of both layers is not so obvious anteriorly, as an, 
 interchange of fibres takes place between the two layers. Th« upper 
 la^yer surrounds the lower one on nearly all sides in such a way that the 
 latter lies in a muscular groove or furrow formed by the upper layer. 
 The muscles of the two sides are united behind the rectum by a median 
 faph6, which is attached either to the tip of the coccyx or fuses with 
 the strong aponeurosis formed- by the pubo-eoccygei. As previously- 
 mentioned (p. 26) Holl describes fibres passing from the pubo-rectalis 
 to form the transversus perinei. He refers also to others, which, 
 join with the sphincter ani externus of the same side or of the opposite 
 side, and he traces fibres into the antero- lateral wall of the rectum, 
 which soon became tendinous and, together with the longitudinal 
 bundles of the rectum, terminate either in the skin of- the anus 
 or the central point of the perineum. 
 
 It is clear, therefore, that the origin of the pubo-coccygeus in man- 
 and lower mammals, allowing for variations in development, is 
 practically identical, and that the only essential difference at the 
 insertion is due to a bundle of fibres losing its connections with the 
 coccyx and forming a sling-like muscle round the rectum, and the 
 beginning of this change can be observed in some of the lower animals. 
 After all, then, there is no very great difference in the attachments 
 of the pubo and ilio-coccygei of lower mammals and the levator ani of 
 man. The great difference lies in the change of function of one, at 
 least, of the two constituent elements of the levator ani— ^the pubo- 
 
T.P.P-C. 
 
 V^'^ 
 
 Fig. 20. — The pelvic diapla-agm in a. neffro, seen fi-ora above, after 
 removal of tlie rectum and separation of tlie puliic bones. Il.S., ilio- 
 
 saeralis ; I.C, coccyseus ; Il.C, fibres of ilio-coccygeus arising' from spine 
 of ischium; Il.C, ilio-coccygeus ; P.C, pulio-coccy,tjeus ; P.A.F., pru-anal 
 fibres of puljo-cocej'geus ; P.R., pa.ssac^e for rectum; fS.P.. sympliysis ]iuliis; 
 T.P.P.C, aponeuro.^is of pu):io-coccygeus ; S.C, sacro-cocc^'geus — cin\"ator 
 coccygis ; L.S., ligamentum saci'o-coccygeum anterius. 
 
. ^ -7 
 
 Fig. 21. — Musi/lejs i[t tlie pelvic outlet in the Leoitivd (Felis k-ojmnbis), 
 ri<,rlit side fiom lieliiml. Ih.C, Ilio-fooeygeu.s ; P.O., Piil«)-coccyo;eiis ; C.R., 
 Ciiuilo-rectal ; E.S.A., s|i]iiiicter ani externiis ; A. P.. anal ]«iurli; P>., re.-tuiii ; 
 v., ^'ap■ina ; C.A., caTidd-aiial and eaudo -^■aoi^aI muscles. 
 
87 
 
 coccygeus — and the differentiation of the pubo-rectalis. As the caudal 
 muscles lost their primary function, consequent on the reduction of the 
 tail, a change in position of the long axis of the body, from horizontal 
 to vertical, necessitated several further modifications at the pelvic 
 outlet. Of these, perhaps the most important were the changes 
 directed to the support of the superimposed viscera. It was necessary, 
 for example, that additional support should be given to the rectum, 
 and this has been obtained l\v the increase in size and importance 
 of the pubo- coccygeus, and the formation of practically a new 
 muscle, the pubo-rectalis. 
 
 We have already referred to the commencement of the formation of 
 the pubo-rectalis in some of the lower animals, and it is a remarkable 
 occurrence that in nearly all of these the axis of the body is not strictly 
 horizontal, but tends to become vertical ; in other words, the rectum 
 in these animals is in such a position that it requires, though perhaps 
 only to a slight degree, some additional support, and this is obtained 
 from one of the muscles contiguous to it. 
 
 The first modification of the flexor tail muscles of lower mammals 
 in forming the levator ani of primates may, therefore, be observed in 
 certain marsupials and aquatic carnivores. But in them nearly the 
 whole of the pubo-coccygeus is attached to the caudal vertebrae and 
 only a few fibres are detached to support the rectum. In the kangaroo 
 and seal the long axis of the body, though obviously different from 
 most quadrupeds, has not become so upright that the rectum requires 
 much additional support. 
 
 In tailed apes fibres pass round the rectum from the pubo-coccy- 
 geus as in the kangaroo and seal, and in addition fibres pass, according 
 to Kollman, directly into the walls of the rectum. In anthropoids we 
 find a muscular sling strongly developed for the first time. It is clear 
 that the fibres which pass into the walls of the rectum act as a retractor 
 recti when the long axis of the body is horizontal, and that the 
 muscular sling acts as a levator of the pelvic fioor when the axis is 
 more or less vertical. In man the retractor action of the muscle has 
 been lost, and consequently no fibres terminate in the rectal walls. On 
 the contrary, the arrangement of a rauscular sUng— the pubo-rectalis — 
 attains its highest development in man. By its action the rectum can 
 be raised upwards and forwards towards the symphysis pubis. At the 
 same time it exerts an important sphincter action on the bowel, and 
 assists the anal sphincters in guarding the rectal opening. 
 
88 
 
 One of the most recent contributions to our knowledge of the 
 anatomy of the levator ani comes from Professor Browning of 
 Brooklyn. He has made dissections of the muscle in the human 
 subject and in lower animals, and in his opinion the description given 
 by Savage is much more correct than that of Luschka. Browning 
 describes the levator ani in the female as follows : — 
 
 " The levator ani may very properly be divided into three portions. 
 This division has reference both to the origin and to the insertion of its 
 fibres. The so-called pubo-coccygeus of Savage arises from the intra- 
 pelvic surface of the body of the pubis and the posterior or superior 
 layer of the triangular Ugament. This latter fascia blends with the 
 obturator fascia along the descending pubic ramus, thus rendering the 
 origin of this portion of the muscle more extensive than usually 
 described. It will be seen also to be on a plane superficial to and 
 intersecting that of the portion of the muscle posterior to it. The 
 fibres arising as above described soon gather to form a band distinctly 
 separable from the rest of the muscle, and about one- half inch in 
 width and one-eighth thick. It takes a course nearly horizontally 
 backward to the anus. At its insertion it is bilaminar. The super- 
 ficial fibres are continued into the external sphincter ani muscle. Of 
 the deep fibres a few turn forwards and are lost in the perineal body. 
 I have been unable to trace them to the median line. By far the 
 greater number take a backward course. Posterior to the rectum they 
 come in close contact with their fellows from the opposite side, but 
 are not continuous with them without the intervention of tendon. 
 Some terminate in the recto- coccygeal raph6, but may reach the 
 coccyx. I have been unable to verify the statement of some authors 
 that fibres from the pubic band terminate in the rectal wall or even in 
 a fascia closely connected therewith. The pubic band as it sweeps by 
 the vagina is separated therefrom by an interval of one-quarter inch, 
 but a few stray fibres from its lowermost margin cross it and terminate 
 in the vaginal wall." 
 
 " The fibres of the levator ani which arise from the ischial spine, 
 form a distinct bundle separable also from those of fascial origin. It 
 takes a transverse course and is for the most part inserted into the 
 fourth coccygeal segment. A few superficial fibres, however, turn 
 forward and are inserted into the recto-coccygeal raph6. This bundle 
 might very properly have been denominated the ischio-coccygeus 
 muscle though it was to the coccygeus that Savage gave that name." 
 
89 
 
 "The intermediate portion of the levator ani is thin and mem- 
 branous. It consists of a number of fascicles which arise from a 
 fascia, weakly attached to the " white line." Their direction is down- 
 ward, backward, and inward toward the rectum and the recto-coccy- 
 geal raphS. I have not been able to trace any of these fibres to the 
 rectal walls; but find when they reach the side of the rectum and 
 approach the raph6, all turn sharply backward and run nearly parallel 
 to the middle line. Some reach the coccyx ; others became aponeurotic 
 before doing so." 
 
 In Echidna, Felis leopardus, and man the ilio-and pubo-coccygei 
 are more or less completely fused to form a muscular sheet which arises 
 from the side wall of the pelvic cavity, though the various elements 
 can easily be recognised by referring to the origin from the pelvic wall. 
 
 In Macropus, Phascolomys Wombat and Thylacinus cynocephalus 
 among marsupials, and in Dasypus sexcinctus the two elements are 
 quite distinct, whilst in Phoca vitulina they are in a somewhat inter- 
 mediate condition, being quite separate at their origin and uniting 
 midway between the side wall of the pelvis and the insertion into the 
 caudal vertebrae. The arrangement in Felis leopardus is interesting 
 (fig. 21). The two muscles form a muscular layer situated at the side of 
 the rectum and passing backwards to be inserted into the caudal 
 vertebrae. There is no clear division into two parts, but the layer varies 
 in thickness. The upper and anterior border is thick and rounded, the 
 lower part is thin and transparent. If the two parts thus distin- 
 guished are traced to their attachments at the innominate bone, one 
 finds that the thick upper border is attached to the ilium and repre- 
 sents the ilio-coccygeus, whilst the remainder is attached to the back 
 of the symphysis pubis and represents the pubo-coccygeus. It is 
 difiicult to explain the varying conditions of the two muscles in 
 different animals, but they are probably associated with changes in 
 length, mobility, and functions of the tail. 
 
 Dr. J. Lartschneider has introduced a description of the levator ani 
 differing from all preceding ones. He suggests that it would be 
 advisable, for the complete understanding of this muscle, to give the 
 following account in place of the one so far adopted. 
 
 " The levator ani subdivides into two portions — a portio pubica 
 and a portio iliaca." 
 
 The portio pubica arises as a thin muscular layer on both sides of 
 the symphysis pubis extending outwards as far as the entrance into 
 
90 
 
 the obturator canal. The fibres are directed backwards at the sides 
 of the rectum and converge behind it where the mesial fibres cross 
 and form a loop. The fibres which, on both sides, arise more laterally 
 from the pubes are directed towards the coccyx and are inserted by 
 means of a common tendinous aponeurosis into the second, third, and 
 fourth coccygeal vertebrae. Between the coccyx and the tendinous 
 aponeurosis, there exists a space exactly in the middle line which is 
 filled partly with fatty tissue and which serves as a passage for the 
 nerves, venous plexuses, and the end of the middle sacral artery. 
 
 The portio iliaca arises in the continuation of the line of origin of 
 the pubic portion as far as the ischial spine, to a greater extent from 
 the obturator fascia, and to a smaller extent behind this, from the 
 mesial surface of the ischium. The most posterior fibres are inserted 
 into the lateral border of the last coccygeal vertebra, whilst the fibres 
 in front of these are attached to the raph6 which extends from the tip 
 of the coccyx to the anus. By this raph6 the portio iliaca of one side 
 is joined with that of the opposite side to form a muscular plate 
 stretched obliquely behind the portio pubica. 
 
 According to Lartschneider these two parts of the levator ani are 
 morphologically and phylogenetically different. He regards the 
 portio pubica (along with the sphincter ani externus, bulbo- 
 cavernosus, and ischio-cavernosus) as a derivative from the great skin 
 muscle — M. cutaneus maximus, and the portio pubica is described in 
 edentates, marsupials, carnivores, prosimiee and primates to illustrate 
 successive stages in its histor}'. 
 
 On the other hand he regards the portio iliaca as a lateral 
 extension on to the pelvic wall from the flexor group of tail muscles 
 situated on the ventral aspect of the caudal part of the vertebral 
 column. 
 
 Lartschneider's description of the levator ani, and his views on the 
 morphology of its two parts have not been adopted )iy succeeding 
 writers, and this for various reasons. 
 
 Lartschneider applies the terms portio pubica and portio iliaca, 
 not only to the human levator ani, but also to the corresponding 
 muscles in other mammals. The portio iliaca, however, as pointed 
 out by Holl, does not correspond to the ilio-coccygeus of lower 
 mammals, since the ilio-coccygeus in man represents the ventral 
 fibres only, and to complete the homology between the two muscles 
 we must include the ilio-sacral muscle as the representative of the 
 
91 
 
 dorsal fibres. The term portio iliaca, therefore, does not indicate 
 the same structures in man and lower mammals. 
 
 Again, the human pubo-coccygeus includes the pubo-reetalis — a 
 muscle confined to man and a few other mammals. The portio 
 pubica of the levator ani is, therefore, not precisely the same muscle 
 as the pubo-coccygeus of mammals generally. 
 
 With the exception of Lartschneider, most observers are agreed 
 that the pubo- and ilio-coccygei have the same origin from a median 
 flexor of the tail situated on the under surface of the sacral and 
 caudal vertebrae. 
 
 The view advanced by Lartschneider, that the portio pubica 
 of the levator ani, i.e., the pubo-coccygeus, is developed from the 
 great skin muscle of certain mammals, depends very largely upon 
 what he observed in the rabbit. From the illustrations which 
 Lartschneider has given, it appears as if the superficial sphincter 
 muscle of the pelvic outlet in the rabbit had been taken as the 
 pubo-coccygeus, and Holl, apparently regarding the illustration in the 
 same way, states that the conclusions which Lartschneider has arrived 
 at are incorrect. 
 
 Action op the Levator Ani. — Whilst the whole of the levator 
 ani takes part in the formation of the pelvic diaphragm and thus 
 contributes to the support of the abdominal viscera, the constituent 
 elements of which it is composed, have widely different functions. 
 
 From a consideration of the attachments and strength of the ilio- 
 and pubo-coccygei, it is clear that the ilio-coccygeus, at least, acts 
 almost exclusively as a supporting agent. The muscle flexes the 
 coccygeal vertebrae on one another, and the coccyx as a whole on the 
 sacrum during the early period of life, but it has no direct action upon 
 the rectum or any other of the pelvic viscera. 
 
 On the other hand, the pubo-coccygeus attains the highest 
 functional importance, particularly in the female. Not only does 
 it act on the rectum and support the viscera in both sexes, but in 
 the female it also iafluences the lumen of the vagina, and has an 
 important bearing on the mechanism of parturition. It will be found 
 convenient to consider each of its actions separately : — 
 
 (1) Action on the rectum. 
 
 (2) Action on the vagina. 
 
 (3) Action during parturition. 
 
 (4) As a support to the viscera. 
 
92 
 
 (1) Action on the Rectum. — The view advanced by Andreas 
 Vesalius, in 1555, that the " Musculus sedem attollens " raised the 
 floor of the pelvis, was generally accepted by succeeding anatomists 
 until 1850. About this time, however, Cruveilhier referred to the 
 levator ani as a constrictor of the rectum like the external sphincter 
 ani, and this suggestion has received the support of Henle, Lesshaft, 
 Symington, Budge, and others. These observers are agreed that the 
 levator ani is not a true levator, but a sphincter of the lower part 
 of the rectum. 
 
 It is probable, however, that the pubo-coccygeus is both a levator 
 of the pelvic floor and a sphincter of the rectum, though the 
 sphincteric action is the more important of the two. 
 
 Fig. 20 shows the two levatores ani forming a muscular diaphragm 
 through which the rectum is transmitted, and by which it may be 
 compressed on all sides.' It is clear that the muscular fibres form 
 almost a complete circle round the rectum, and that the part which 
 is deficient is in front, where the pre-anal fibres terminate in the 
 fibrous tissue constituting the central point of the perineum. Such 
 an arrangement must lead to narrowing of the rectum when the 
 muscle is thrown into action. 
 
 Further the pubo-rectalis forms a muscular loop which embraces 
 the rectum and slings it up towards the pubes, and these fibres are 
 capable of raising not only the rectum, but the pelvic floor as a 
 whole. 
 
 Briefly, therefore, the action of the pubo-coccygei on the rectum 
 is to constrict the lower part of the bowel ; at the same time it can 
 elevate the anus upwards and forwards towards the symphysis pubis, 
 and this is precisely what happens during the act of defsecation. 
 
 Professor GoSe, of New York, compares the action of the levator 
 ani during defsecation to the action of the same muscle in the 
 mechanism of labour and finds that they are "analogous." During 
 parturition the levator ani contracts, and sweeping the perineum 
 over the face of the child raises it to its normal position. In the 
 same way during defsecation, "while the intra-abdominal pressure 
 maintains the position of the contents of the rectum, the levator ani 
 
 ' Dr. Taylor, in 1896, in a series of special dissections which he made of the 
 levator ani showed "how the two levatores ani muscles form, as it were, a 
 muscular button-hole through which the rectum passes, and by which it is 
 laterally compressed." 
 
93 
 
 lifts the perineum over it and the fsecal matter is extruded." It 
 should be noted, however, that in the former case the movable 
 point of insertion of the levatores ani is behind the protuding mass, 
 whereas in the latter it is in front of it. 
 
 (2) Action on the Vagina. — It has been pointed out in 
 describing the action of the sphincter vaginse that the closure of the 
 vaginal canal is the result of the contraction of two associated muscles — 
 the pubo-eoccygei and sphincter vaginae. 
 
 The pubo-coccygei pass backwards from the pubes on either side of 
 the vagina, and in consequence, are capable of exerting an important 
 lateral compression upon it. A more pronounced action is Observed 
 when the pubo-coccygei are associated in action with the sphincter 
 vaginae. The former compress the canal from side to side, the latter 
 from front to back by raising the vagina up towards the symphysis 
 pubis, and in this way the closure of the passage is brought about. 
 
 The pubo-coccygeus is more strongly developed in the female than 
 in the male, and this is probably due to increased functional activity. 
 In the female the functions which the muscle has to perform are more 
 varied, and the weight which it has to support greater than in the male. 
 
 In some female subjects the pubo-coccygeus is greatly hyper- 
 trophied and forms a prominent muscular ring encircling the rectum 
 and vagina, the thickening being more marked near its origin from 
 the pubis and where it lies in contact with the lateral vaginal wall. 
 The level where the muscle lies in relation with the vagina corresponds 
 to a point, a quarter to half an inch above the level of the hymen. 
 
 Experiments have been made by Budin and Dickinson to 
 show, by means of impressions on wax, the influence of the pubo- 
 coccygei on the lateral walls of the vagina. The method of procedure 
 was to insert into the relaxed vagina of a patient in the dorsal 
 decubitus, a cylinder of softened modelling wax and then to ask the 
 patient to firmly contract. In this way an impression of the contract- 
 ing pubo-coccygei on the wax was obtained. 
 
 The anatomical results of these experiments were — 
 
 (a) That the distance from the hymen to the inner edge of 
 
 the pubo-coccygeus averages somewhat less than half-an-inch. 
 (6) That the double band is always sharply defined, 
 (c) That the larger the cylinder, and consequently the more 
 
 the pubo-coccygei are stretched, the closer together the strong 
 
 edges are found. 
 
94 
 
 (3) Action- during Parturition. — During normal parturition 
 the action of the pubo-coccygei is chiefly exerted in pulling the 
 perineum upwards after it has been depressed by the advancing head 
 of the child. But cases constantly occur in which the muscle 
 appears to obstruct the act of labour rather than to assist it; the 
 obstruction may be but slight and easily overcome, or it may 
 be more pronounced. Its extent depends upon the amount of 
 contraction and consequent shortening of the pubo-coccygei. 
 
 (4) As A SUPPORT TO Viscera — The pubo-coccygei are perhaps 
 the most important muscles in the pelvic floor, since upon them 
 depends the restoration of the floor to its normal position after it 
 has been depressed by defaecation, parturition, etc. The two muscles 
 form a well-marked curve with the concavity upwards and the 
 convexity downwards, and attached at each end to the bones of 
 the pelvic outlet. The anterior end is attached to the pubes, the 
 posterior end to the coccyx, whilst between these two points, the 
 central parts are free from bony attachments. When the pelvic 
 floor is depressed its concavity is increased; it is raised when the 
 pubo-coccygei contract from the two fixed points, and the concavity 
 is diminished. This arrangement of the pubo-coccygei is admirably 
 adapted for the support of superimposed structures. 
 
 Comparative Anatomy. — I have mentioned that the general 
 arrangement of the ilio- and pubo-coccygei is the same in most 
 mammals, but in the description of the levator ani, and as 
 opportunity has arisen, I have referred to some important modifi- 
 cations of these muscles. 
 
 Deviations from the general arrangement are most striking in 
 imgulates and chiroptera than in any other group. I have already 
 drawn attention to these in ungulates in a communication read 
 before the Anatomical Society ' of Great Britain and Ireland, in 
 November, 1898. 
 
 The object of the communication was to show that the so-called 
 levator ani of ungulates was an entirely different structure from the 
 muscle bearing the same name in man and anthropoid apes. I 
 pointed out that the levator ani did not exist in ungulates and that 
 the muscle so designated should be called, as indeed it is by 
 veterinarians, the ischio-anal muscle. 
 
 '■ Loo. cit. 
 
Iscf. 
 
 E.S.A. 
 
 i<^. 
 
 -f.t'^;;? 
 
 Fig. 22.— Iscliio-Jinal and (.■iiccj-oeiis nniKcli-s in tlir ('amfl (Caiiiehis iln)nic- 
 
 darius I. Isrir., isidiiiini ; I.C 
 veitelir;r; I.A'„ and I. A"., 
 E.S.A., cxternid .sithinctcr an 
 
 , I'drryo-fiis passinjr to In- inserted into the I'ani'.al 
 ii.'liio-anal nniseloM of tlie two sides; P,., leetuni ; 
 ; S.P.. syinjOiysis pnliis; T.P., thyroid toi'anien. 
 
_. P.C. 
 
 u. 
 
 _I.C. 
 
 TJ. 
 B.P. 
 
 3.A.E 
 
 C.G. 
 
 LA 
 
 S.A.E'. 
 
 . F.A. 
 
 Fig. 23. — Perineal muscles of the Camel (Camelus dromedaiiiiM). l'.(.'., )mlio- 
 CiiverriDsiis or levator penis ; U., layer of muscular fibres under uretlmi ; I.C, iscliio- 
 cavcrnosus ; T.I., tuber ischii ; B.P., bull] of penis; i^.A.E., s[)liincter ani 
 extei'nus ; C.<J., C'ow]jer's ^land ; I. A., iscliio-anal muscle: S.A.E'., circular 
 fibi'es of sphincter ani externus ; F.A., fibrous ajioneiufusis by wliich tlic sphincter 
 ani extei'nus is attached to the t:iil. 
 
95 
 
 From dissections of the camel, cow, bull, mare, and stallion, I have 
 satisfied myself, so far at least as these animals are concerned, that 
 neither the ilio-coccygeus nor the pubo coccygeus are present, and 
 inasmuch as the levator ani is admittedly only a specially modified 
 form of these muscles it is obvious that there is no morphological 
 equivalent of the levator ani in the ungulates referred to. 
 
 In the camel, which may be taken as a type, there are two muscles 
 which arise in close apposition from the internal surface of the 
 ischium, but they are morphologically distinct from both the ilio- and 
 pubo-coccygei. One arising close to the spine and passing to be 
 insertied into the caudal vertebrae is dorsal in position, the other 
 arising close to the thyroid foramen is ventral ; the ventral muscle 
 passes along the lateral aspect of the rectum to terminate in short 
 tendinous fibres in its walls near the anus. At the insertion the 
 fibres intermingle with the deeper layers of the external sphincter ani 
 and none are attached to the caudal vertebrae. 
 
 There can be no doubt that the dorsal muscle is the ischio- coccygeus 
 or abductor caudse, but the significance of the ventral muscle, which 
 from its attachments is well named ischio-anal, seems to have been 
 misunderstood. By most observers it is regarded as corresponding to 
 the levator ani, and if this is so the question naturally arises — To 
 which of the flexor tail muscles does it correspond, the ilio-coccygeus 
 or pubo-coccygeus, or does it represent both ? 
 
 Apparently observers do not agree on this point. Holl, who 
 has found a similar disposition of the two corresponding muscles 
 in the horse and roebuck, is of opinion that the dorsal muscle is 
 the ilio-coccygeus and the ventral muscle the pubo-coccygeus. He 
 thinks this view is not unhkely because in the rabbit and guinea-pig 
 the origin of the ilio-coccygeus is transferred to the mesial surface of 
 the ischium in the region of the spine. It may be pointed out, 
 however, that the descent of the attachments of the flexores caudse on 
 the lateral pelvic wall does not appear to influence their insertion into 
 the caudal vertebrae. In the rabbit, guinea-pig, and even in man, 
 although the transference of the pelvic attachment has undoubtedly 
 taken place the connection of the muscles with the vertebral column 
 is still retained. 
 
 Lartschneider after examining the horse and stag came to the 
 conclusion that the dorsal muscle was the ischio-coccygeus and that 
 the ventral muscle was the homologue of the pubo-coccygeus of the 
 
96 
 
 rabbit and edentates. But Holl has shown that what Lartschneider 
 regarded as the pubo-coccygeus in the rabbit was a part of the 
 sphincter cloacse. Lartschneider commenced with this observation in 
 tracing the phylogenetic history of the pubo-cuccygeus and he believed 
 that the pubo-coccygeus of edentates, and indeed of mammals 
 generally, was derived, like the sphincter cloacse, from the great skin 
 muscle (M. cutaneus maximus). HoU has shown that this view is 
 untenable and that the pubo-coccygeus of the rabbit and edentates is, 
 like the similar structure in other mammals, an extension of the tail 
 musculature. 
 
 Lastly, Paulet writing on the comparative anatomy of the perineum 
 states that the ischio-anal muscle in the stag is homologous with the 
 levator ani of man but that it differs from it in form. He regards 
 the muscle as corresponding only to a limited part of the levator 
 ani, viz., to that which remains if the fibres from the pubis and 
 obturator fascia be removed. It is noteworthy that Paulet whilst 
 holding this view was struck with the close resemblance of the ischio- 
 anal muscle in the stag and in the cow and horse. 
 
 Thus, whilst Holl, Lartschneider, and Paulet disagree as to the 
 precise homologies of the ilio- and pubo-coccygei, and differ particu- 
 larly as regards the extent to which they are represented in the 
 "levator ani" of the ungulates which ~ they examined, they are 
 apparently in accord in stating that the levator ani represents one or 
 other of the two muscles, wholly or in part. A careful consideration 
 of (1) the attachments and (2) nerve-supply has convinced me that 
 this view is probably incorrect. 
 
 There is no resemblance between the attachments of the pubo- 
 coccygeus of other mammals and the ischio-anal muscle of ungulates. 
 No fibres of the latter arise from the pubis and none pass to the 
 caudal vertebrae. I have examined specimens of monotremesj 
 marsupials, carnivores, rodents, insectivores, and primates, and in all 
 the pubo-coccygeus never failed to exhibit in some degree its 
 primitive attachments. Invariably the muscle took origin either 
 from the back of the symphysis, from the body of the pubis, or from 
 the horizontal ramus of the pubis. Similarly with regard to its 
 insertion, fibres could always be traced either to the bodies or trans- 
 verse processes of the proximal caudal vertebrje. Nevertheless, 
 Lartschneider, whilst admitting that no fibres are attached -to the 
 vertebral column, believes that the ischio-anal muscle represents th& 
 
97 
 
 pubo-coccygeus of edentates, marsupials, carnivores, and primates, and 
 that its peculiarities depend on the size of the body and the mode of 
 nutrition of the animal. 
 
 It should be mentioned here that in the cow and bull some of the 
 fibres of the ischio-anal muscle do not pass into the walls of the rectum 
 but unite with the fascia of the tail. Lartschneider has noted a similar 
 arrangement in the stag and horse. I shall refer to the significance of 
 these fibres subsequently. 
 
 Again, with reference to the possible correspondence of the 
 ischio-anal muscle to the iUo-coccygeus. The latter muscle is always 
 attached to the caudal vertebrae. Its origin, it must be admitted, is 
 not always from the iHum. The origin may descend on the side 
 wall of the pelvis and the muscle may then arise from the ischium as 
 in the rabbit and guinea-pig according to HoU, or from the fascia 
 obturatoria'as in man. 
 
 From the attachments therefore, we may reasonably conclude that 
 the ischio-anal muscle of ungulates corresponds neither to the 
 pubo-coccygeus nor to the ilio-coccygeus of other mammals. Moreover, 
 its direct connection with the rectum suggests that it should be 
 included with the external sphincter ani in the group of extrinsic 
 rectal muscles. 
 
 The considerations of nerve-supply lend additional support to this 
 conclusion. The importance of including the nerve-supply of a 
 muscle in the consideration of morphological questions is recognised 
 by all observers. Quite recently. Dr. MaU, in a paper on the 
 " Development of the Ventral Abdominal walls in man," says on this 
 subject, that "the studies in comparative anatomy by Gegenbaur, 
 Huxley and Kollmari have proved almost beyond doubt that nerve and 
 muscle are associated with each other in the earliest stages of develop- 
 ment, and that comparison of muscles can be made satisfactorily only 
 when their nerve-supply is included." According to his views " the 
 history of a muscle is indicated by its nerve, and in studying the 
 development of a muscle, our main guide is its nerve." On the other 
 hand. Professor Cunningham has shown that nerve-supply " is not an 
 absolutely infallible guide." 
 
 As already mentioned, the ilio-and pubo-coccygei are simply 
 differentiated parts of a single powerful tail muscle — which we may 
 now refer to as the sacro-coccygeus— situated on the ventral 
 aspect of the sacral and caudal vertebrae, and it is particukrly 
 
98 
 
 interesting and significant to note than in monotremes and some 
 marsupials, the three muscles are not distinct from one another. 
 Whilst, however, there is no clear separation of the three constituent 
 elements, they are easily recognisable and the whole group appears as 
 a flat muscular sheet passing from the side wall of the pelvis to the 
 tail. This continuous sheet receives a continuous nerve-supply. The 
 sacro-coccygeus is innervated by twigs from the sacral plexus and the 
 laterally extended differentiations of ilio-coccygeus and pubo-coccygeus 
 respectively carry with them their nerve-supply from the same source. 
 This holds good also in those animals in which the individual 
 muscles of the group are more or less completely separated from each 
 other. I have indeed found no exception in the animals I have had 
 the opportunity of dissecting, but I note that Leche describes the 
 ilio-coccygeus in chrysochloris as being supplied by a branch of the 
 obturator nerve. 
 
 The levator ani in man receives its nerve-supply partly direct from 
 the fourth sacral and the branches from this source enter the muscle 
 on its pelvic surface. In addition, branches from the internal pudic 
 are also distributed to it and these pierce its external surface. This 
 variation from the primitive type may perhaps be looked upon as an 
 example of transference of nerve fibres from a familiar to an 
 unfamiliar route. The transference becomes intelligible if we 
 remember that the internal pudic supplies the group of muscles 
 derived from the primitive sphincter cloacae, and that as a result of 
 the formation of a pelvic floor two muscular layers have been brought 
 into close apposition, viz., one consisting of modified caudal muscles — 
 levator ani, the other the superficial perineal muscles. We have here 
 an excellent illustration of what has been described as "the struggle 
 for supremacy between two contiguous nerves supplying contiguous 
 groups of muscles."^ 
 
 In ungulates the ischio-anal muscle is apparently always supplied 
 by branches from the internal pudic nerve. Apart from my own 
 observations which support this statement, I find that Chauveau 
 describes the ischio-anal muscle in solipeds as supplied by the 
 hsemorroidal nerve, and Professor Paterson and Dr. Dunn have 
 recently described the levator ani in the Indian elephant receiving 
 its innervation from the same source. In all the ungulates I 
 examined I failed to find any nerves passing direct from the 
 
 ' Vide Cunningham.- 
 
99 
 
 sacral plexus to the ischio-anal muscle, and this attracted my 
 attention the more since in other mammals in which the ilio-and 
 pubo-coccygei were present, rierve fibres from the sacral plexus direct 
 were invariably found. On the other hand a number of branches 
 proceeded from the internal pudic nerve and these supplied not only 
 the ischio-anal muscle but also the external sphincter ani. 
 
 The nerve associated with the primitive sphincter cloaciE is the 
 internal pudic, and all the muscles which are differential ed from it 
 derive their nerve-supply from the same source. And although, as 
 illustrated by the innervation of the levator ani, there is a tendency 
 for the nerve to overstep its original limits and extend its territory, 
 these invasions must be regarded as secondary and they need not 
 obscure the primitive arrangement. 
 
 The conclusion arrived at from a consideration of the muscular 
 attachments, viz., that the ischio-anal muscle corresponds neither to 
 the iUo-coccygeus nor the pubo-coccygeus of other mammals, is thus 
 supported by the further consideration of the nerve-supply of these 
 muscles, and the fact that the ischio-anal muscle receives its nerve 
 supply solely from the internal pudic affords additional evidence that 
 this muscle should be associated with the anal sphincter and the other 
 superficial muscles of the pelvic outlet. 
 
 I therefore venture to suggest that the ischio-anal muscle is not a 
 tail muscle like the iUo-coccygeus and pubo-coccygeus, and that it 
 cannot be regarded as homologous to them or to the modified levator 
 ani. Its connections and nerve-supply show that it is probably derived 
 from the primitive sphincter cloacae like the bulbo and ischio-cavernosi. 
 It has not, however, like these muscles, become attached to the 
 circumference of the pelvic outlet but has passed within its margin to 
 the neighbourhood of the spine of the ischium, possibly, and at any 
 rate the more easily, in consequence of the absence of the iUo-and 
 pubo-coccygei muscles. 
 
 The connections between it and the other superficial perineal 
 muscles are very intimate and at once suggest a common origin. In 
 the camel this is especially evident. The external sphincter ani 
 muscle encircles the posterior part of the rectum and passes 
 below into the bulbo-cavernosus. At the lateral margin of the 
 continuous muscular mass two muscles are found on each side. Of 
 these, one situated at the root of the penis is the ischio-cavernosus, 
 the other situated at the side of the rectum is the ischio-anal muscle. 
 
100 
 
 and this extends upwards into the pelvic cavity to be attached to the 
 side wall near the spine of the ischium. 
 
 The insertion of the fibres of the ischio-anal muscle into the fascia 
 of the tail in the cow, stag, and horse, finds an explanation if this 
 view of the origin of the muscle be accepted. We know that the 
 sphincter cloacae is primarily attached to the under surface of the tail, 
 and this caudal attachment is retained in ungulates not only by the 
 external sphincter ani, but also by the ischio-anal muscle. 
 
 The development of the ischio-anal muscle and the peculiar course 
 of its fibres may possibly be explained by the behaviour of the 
 rectum during defaecation. The muscle is specially developed in those 
 animals in which protusion of the rectal mucous membrane occurs 
 during the expulsion of the faeces, and the function of the muscle is 
 clearly to pull the anus forwards and retract the protruded mucous 
 membrane after the rectal contents have been expelled. Hence the 
 name retractor ani, which has, and not inappropriately, been applied 
 to it. 
 
 Professor Sir William Turner in describing the retractores ani in 
 the dolphin remarks that "from the presence of this pair of muscles 
 it is probable that the dolphin like the horse protrudes the anal 
 mucous membrane in the act of defsecation and the functions of these 
 muscles is to retract it on the completion of the act." The attach- 
 ments of the retractor ani in the dolphin closely resemble those of the 
 ischio-anal or retractor ani in ungulates. In the former the muscle 
 arises from the pelvic bone and ends in the muscular mass of the 
 sphincter. Lartschneider regards the muscle in question in ungulates 
 as a true levator ani, i.e., a sling muscle of the rectum, but with this 
 I cannot agree. 
 
 Since then the ilio-arid pubo-coccygei muscles are apparently not 
 represented at all in ungulates, one may in conclusion ask — ^what has 
 determined their absence? To this question I am not at present 
 prepared to give any definite answer. It may be due to the skeletal 
 peculiarities, to the size of the body, or to the mode of nutrition. 
 We know that in the herbivora the capacity of the intestinal canal 
 assumes considerable proportions and that this is largely dependent on 
 the nature of the aliment. Their food contains a small proportion 
 of nutritive elements enclosed in an abundant matrix, so that they 
 are compelled to ingest large quantities at short intervals. As the 
 gastric and intestinal parts of the alimentary canal have been so 
 
101 
 
 profoundly modified to meet these special demands, there seems no 
 reason why the modifications should not have been extended to the 
 rectum and the muscles in relation with it, though it is by no means 
 evident why suppression of certain of the caudal muscles should have 
 resulted. 
 
102 
 
 (2) Coccygeus or Ischio-coccygetts. 
 
 The coccygeus is a small flat muscle, triangular in shape, which 
 extends between the spine of the ischium and the vertebral column. 
 When the ilio-sacralis is absent the coccygeus appears to be a con- 
 tinuation backwards of the levator ani, but in reality it is in a plane 
 behind it, and the continuation backwards of the levator ani — the 
 ilio-sacralis — passes in front of the coccygeus. It is one of the most 
 constant muscles in lower mammals ; and even in man, in whom it is 
 clearly a degenerated muscle, it can almost invariably be recognised. 
 In tailed mammals the coccygei are strongly developed. They 
 receive the name of "abductores caudse," and Ihey move the tail 
 alternately from side to side. When the tail becomes reduced, the 
 abductors undergo corresponding retrogressive changes, so that in 
 man, for example, the muscles are largely replaced by fibrous tissue. 
 In man the coccygeus muscle arises from the spine of the ischium, 
 from the adjoining fascia obturatoria, from the margin of the great 
 sacro-sciatic notch, and from the deep surface of the lesser sacro-sciatic 
 ligament. It is inserted by its base into the lateral margin and, 
 slightly into the anterior surface of the lower two sacral and upper 
 two coccygeal vertebrae. 
 
 As the tail becomes rudimentary, the coccygeus tends to lose its 
 muscular character and to become transformed into fibrous tissue. It 
 is noteworthy, however, that in man the muscle is subject to consider- 
 able variation. In some cases the coccygeus is strong and fleshy; 
 in others the retrograde changes have taken place to such a degree 
 that the fleshy fibres have disappeared altogether, and a thin fibrous 
 layer on the deep surface of the small sacro-sciatic ligament represents 
 the muscle. Between the two extremes, cases occur in which 
 tendinous fibres are present in the coccygeus to a greater or less 
 degree. The part of the muscle which is most subject to degenerative 
 changes is, according to Holl, the part which is inserted into the 
 sacral vertebrae. In man, the coccygeus no longer performs its 
 primary function, but it assists in closing the exit of the pelvis. The 
 variations of the muscle are thus easily understood. 
 
 I append an account of the coccygeus muscle in a few of the lower 
 mammals. In some the tail was long, in others, rudimentary. 
 
 Marsupials. — I have found the coccygeus present in all the 
 marsupials which I dissected, viz., kangaroo, thylacine and wombat. 
 
A-3.M 
 
 Fig. 24. — Muscles of the ijelvic cavity in the Womluit (PhaM-oloiiiys), 
 fioiii tlie front aftei' wifle separation of tlie syni[)hysis. P.l* , psoas paiA-iis ; 
 O.N. , oljturator neT'\'e ; 1*., pyi'ifonnis : It.. C, iIio-coccy<.^ens (se[jarate(l strand 
 of fibres;; !S.C., sacro-coccygeus ; P.O., pnbo-coecygens ; R.C, recto-coccygeii.s ; 
 C.R., caudo-rectalis ; I.C, eoeeyyeus ; Ir..C., ilio-coceygeus ; A.S.M., arteria 
 tiacra media. 
 
103 
 
 In the kangaroo and thylacine the tail is strongly developed and 
 the coccygeus shows the same arrangement as in other tailed 
 animals. In the wombat, however, the tail is rudimentary and 
 Eggeling says that he has not been able to demonstrate the coccy- 
 geus in the specimens of this animal which he has dissected. On 
 the other hand I have found the muscle weU marked. In fig. 24, 
 which represents the flexor muscles of the tail in the wombat, 
 a muscle is shown arising from the spine of the ischium and 
 passing to be inserted into the caudal vertebrae which must be 
 regarded as corresponding to the coccygeus in other animals. He 
 further points out that in Phascolarctos cinereus the diminution of 
 the length of the tail is accompanied by a diminution in the size 
 of the coccygeus so that the muscle is represented by only a few 
 bundles of weak fibres. 
 
 Dasypus sexcinctus. — In the armadillo the origin of the 
 coccygeus is somewhat different. The muscle arises from the 
 ischial tuberosity and from the ascending ramus of the ischium 
 almost as far as the symphysis pubis. It is inserted into the 
 transverse processes of the first and second caudal vertebrae. 
 According to Murie, fibres are inserted into the carapace, but in the 
 specimen which I dissected I failed to recognise these. Fibres 
 are inserted, however, into the bony investment of the tail. 
 
 Camelus dromedarius. — The coccygeus is situated immediately 
 above and behind the ischio-anal muscle. It arises from the 
 roughened posterior border of the ischium, corresponding in 
 position to the spine, which receives the name of supra-cotyloid 
 crest. It passes upwards and inwards in contact with the wall 
 of the pelvis to the tail, where it is inserted into the transverse 
 process of the third caudal vertebra. In addition, fibres pass 
 forwards to fuse with the strong fascia covering the sacro- 
 coccygeus, and backwards to join the thick aponeurosis investing 
 the tail. As previously pointed out, the corresponding muscle 
 both in the horse and roebuck has been regarded by HoU as the 
 ilio-coccygeus. Lartschneider on the other hand after examining 
 the horse and stag, believes that it represents the coccygeus of 
 other animals. It is interesting to find that the coccygeus 
 is apparently a constant muscle in ungulates since, as shown 
 above, the flexores ilio- and pubo-coccygei are unrepresented. 
 
 Felis leopardus. — The coccygeus is strongly developed. It 
 
 M 
 
104 
 
 arises from the spine of the ischium, partly by fleshy and partly 
 by tendinous fibres. From its origin the muscle spreads out in a 
 triangular shape and passing towards the tail is inserted into 
 the transverse processes of the first five caudal vertebrae. The 
 muscle is remarkably fleshy and has few tendinous fibres in its 
 substance. It overlaps the ilio-caudal muscle. 
 
 Erinaceus europmus. — In the hedgehog the interval between 
 the spine of the ischium and the adjacent caudal vertebrae is very 
 small and the fibres of the coccygeus are correspondingly short 
 (fig. 19). The muscle arises from the spine of the ischium and from 
 the posterior border of the bone above and below it. The short 
 tendinous fibres are inserted into the transverse processes of the 
 first, second, and third caudal vertebrae. At its insertion the 
 muscle is intimately fused with the ilio- and pubo-coccygei. 
 
Bibliography. 
 
 Albisus, B. Historia musculorum hominis. Leid. 1734. 
 
 BouROERY, J. M. Anatomie de I'homme. Vol. II. Myologie. 1834. 
 
 BoYEB, A. Traits d'anatomie. Paris, 1803. 
 
 Bronn. Klassen und Ordnungen des Thier-Reichs. Siiugethiere. Fortgesetzt 
 
 von Leche. Leipzig und Heidelberg. 1884. 
 Brownini;, W. W. A contribution to the knowledge of the Anatomy of the 
 
 levator ani muscle. The Medical Neim, New York. June, 1897. 
 BuDis, P. Obstetrique et Gyneoologie. Paris, 1885. (Dickinson). 
 BuDGB. Ueber die Funktion des M. Levator ani mit Riicksicht auf die Pathogenese. 
 
 Berlin, 1875. 
 Cadiat, M. Etude sur les muscles du p^rin^e en particulier sur les muscles 
 
 dits de Wilson et du Guthrie. Journal de I' Anatomie et de la 
 
 Phyniologie. Paris, 1877. 
 Callexder, S. W. Notes on some points in the anatomy ot the perineum. 
 
 Journal of Anatomy and Physiology. 1869. 
 Chauveau. The comparative anatomy of the domesticated animals, translated 
 
 by Fleming. 1873. 
 Cruveilhier, J, Traite d'Anatomie descriptive. 3rd edition. Paris, 1852. 
 Cunningham, D. J On some points in the Anatomy of the Thylacine (Thylacinus 
 
 oynocephalus), Cuscus (Phalangista maculata), and Phascogale (Phasco- 
 
 gale calura), with an account of the Comparative Anatomy of the 
 
 Intrinsic Muscles and Nerves of the Mamnaalian Pes. Challenger 
 
 Reports. Vol. V. 
 CuviBE, G. Lemons d'anatomie compares. 
 Dickinson, R. L. Studies of the levator ani muscle. The American Journal of 
 
 Obstetrics. Vol. XXH. 1889. 
 DOBSON, G. E. A Monograph of the Insectivora. Part. I. 1882. 
 DORAN, A. A dissection of the muscles of the female pelvis and perineum. 
 
 Obstetrical Transactions. Vol. XXVIII. 1886. 
 Duncan, J. M. Medical Times and Gazette. Vol. II. 1878. 
 Edwards, H. M. Le9ons sur la physiolgie et I'anatomie comparfe de I'homme 
 
 et des animaux. Paris, 1870. 
 Eggelinc. H. Die Dammmusculatur der Beuteltiere. Heidelberg, 1895. 
 Embleton, D. Anomalies of arrangement. Journal of Anatomy and Physiology. 
 
 Vol. VI. 1872. 
 FiCK. R. Vergleichend anatomische Studien an einem erwachsenen Orang-Utan, 
 
 Archiv. fiir Anatomie und Physiologie, anatom. Abtheilung, 1895. 
 Flower and Lydbkkbk. Mammals living and extinct. London, 1891. 
 FiJHREE, A. Handbuch der chirurgischen Anatomie, 2 Abt. Berlin, 1857. 
 Gegenbaur, C. Lehrbuch der Anatomie des Menschen. 2 Vols. Leipzig, 1895. 
 GoFEE, J. R. The Anatomy and Functions of the pelvic floor in woman and 
 
 the operations for its repair. The Medical News, New York. 
 
 May 28, 1898. 
 
106 
 
 Grueer, W. Anatoraische Notizen. Virchow's Archives, 1876. 
 
 Guthrie, G. J. On the anatomy and diseases of the urinary and sexual organs. 
 
 3rd edition, 1843. 
 GuRL. Die Anatomie des Pferdes. pi. 12, fig. '2. (Milne Edwards). 
 Hart, D. Berry. — 
 
 (a) The nature and aim of investigations on the structural anatomy of the 
 
 female pelvic floor. Edinhnrcjh Medirid Joumai. Vol. XXXIV. 
 1888-9. 
 
 (b) Atlas of Female Pelvic Anatomy. Edinburgh, 1884. 
 
 fcj Contributions to the Topographical Anatomy of the female pelvis. 
 Edinburgh, 1885. 
 Henle, J. Handbuch der systematischen Anatomie des Menschen, 1873. 
 His, W. Die Anatomische Nomenklatur (Nomina Anatomica). Leipzig, 1895. 
 Hoi.L, M Die Muskeln und Fascien des Beckenausganges. Von Bardeleben. 
 
 Hanbuch der Anatomie, vii Band, 4. Lieferung, Jena, 1897. 
 Houston, J. An account of two newly discovered muscles for compressing the 
 dorsal vein of the penis in man and other animals. Dtihlin HonpitcU 
 Reports. Vol. V. 1830. 
 Hujiphry, S. M. Sir. Muscles in Vertebrate Animals. Joumai of Anatomy and 
 
 Physiology. Vol. VI. 1872. 
 Jarjavay. Traits d'anatomie chirurgicale. 2 Vols. Paris, 1852. 
 KoEELT, G. L. Die miinnlichen und weiblichen WoUust-organe des menschen 
 
 und einiger Ssiugethiere, Freiburg, 1884. 
 KoLLMANN, J. Der Coccygeus und der Levator ani bei den geschwanzten Affen 
 und den Anthropoiden. Anatomischer Anzeiger. ix Band. May, 1894, 
 Lartsohneider, J. — 
 
 (a) Zur vergleichenden Anatomie des Diaphragma pelvis. Wien, 1895. 
 (bj Die Steissbeinmuskeln des Menschen und ihre Beziehungen zum M. 
 levator ani und zur Beckenfascie. Wien, 1895. 
 Leche, W. Zur Anatomie der Beckenregion bei insectivora. Stockholm, 1883. 
 Lesshapt, p. ijber die Muskeln und Fascien der Dammgegend biem Weibe. 
 
 Morphologisches Jahrbuch. 1884. Band 9. 
 LusCHKA, H. Die Anatomie des Meschen. Tubingen, 1864. 
 Macalistbb, A. — 
 
 (aj A Text-Book of Human Anatomy. London, 1889. 
 
 (bJ Observations on Muscular anomalies in Human Anatomy. 
 
 CcJ A monograph of the anatomy of Chlamydophorus truncatus with notes 
 
 on the structure of other specimens of Edentata. 
 (dj Report on the Anatomy of insect Edentates. Transactioiis of the 
 
 RoyaX Irish Academy. Dublin, 1875. Vol. XXV. 
 (e) On the myology of Bradypus Tridactylus with remarks on the general 
 muscular anatomy of the Edentates. Magazine of Natural 
 History. 1869. 
 Mall, F. P. Development of the ventral abdominal walls in man. Joumai of 
 Morphology. June, 1898. 
 
107 
 
 Meyek, G. H. Lehrbuch der Anatomie des Menschen. Leipzig, 1861. 
 
 Miller, W. C. Myology of the Pinnipedia. Appendix to the Report on the 
 
 Seals. Cludleiiger Reports. 1873-76. 
 MiVART, St. Geoege. ■ On some points in the anatomy of Echidna Hystrix. 
 
 Traiisactiotis of the Linnean Society, of London. Vol. XXV. 1866. 
 MiJLLER, J. Encyklopadisches Wox-terbach der midizinischen Wissenschaften, 
 
 sub voce : Erector penis ; Ueber die organischen Nerven der erektilen 
 
 mannlishen Geschlechts-organe, Kgl. Akad. d Wisaensch aus dem J. 
 
 1835. Berlin, 1837. (HoU). 
 MuRiB, J. On the habits, structure and relations of the three-banded Armadillo. 
 
 Trans. Linnean Society. London, 1875. 
 Owen. Comparative Anatomy and Physiology of vertebrates. Vol. III. Mammals. 
 
 London, 1850. 
 Paterson, a. M., and Dunn, R. C. The genito-urinary organs of the female 
 
 Indian Elephant. Journal of Anatomy and Physiology. Vol. XXXII. 
 
 April, 1898. 
 Paulet, Dr. Recherohes sur I'anatomie compar^e du P^rin^e. Journal de 
 
 I'anatomie el de la physiologic. Vol. XIII. 1877. 
 QuAiN. Elements of Anatomy, Edited by E. A Schafer and G. D. Thane. 10th 
 
 edition. 3 Vols. London, 1893. 
 Retterer, E. Sur I'origine de revolution de la r(5gion Ano-G^nitale des Mammi- 
 
 feres. Journal de, I'anaiomie et de la physiologic. Vol. XXVI. 1890. 
 RuoB, G. Die Hautmuskulatur der Monotremen und ihre Beziehungen zu dem 
 
 Mursupial und Mamma-apparate. Jena, 1895. 
 
 Santorini, J. D. — 
 
 (a) Septemdeoim tabulae, edit. Girardi, 1715. 
 
 (b) Observations anat. 1739. 
 
 Sappey, p. C. Traits d' Anatomie Descriptive. 2nd edition. 
 
 Savage, H. The surgery, surgical Pathology and Surgical Anatomy of the female 
 
 pelvic organs. 5tli edition. 1882. 
 Stbaus-Durckheim. — Anatomie descriptive et comparative du chat. 1845. 
 Symington, J. — 
 
 (a) A contribution to the normal anatomy of the female pelvic floor, 
 
 lidinlnirgh Medical Journal. Vol. XXIV. 1888-9. 
 
 (b) The rectum and anus. Journal of Anatomy and Physiology. Vol. XXIII. 
 
 1889. 
 Tait, L. Diseases of women and abdominal surgery. Vol. I. 1889. 
 
 Taylor, E. H. The operative treatment of cancer of the rectum. Aniuds of 
 
 Surgery. April, 1897. 
 Testitt, L. Traits d'anatomie humaine. 2. edition. Paris, 1893. 
 Theile, F. G. Encyclopedie Anatomique. Tome III. Myologie et Ang^iologie. 
 
 Trans, from the German by A. Jourdan. 1843. 
 Tiedemann. Plates of the Arteries of the human body engraved by Mitchell. 1831. 
 
108 
 
 Turner, W. Sir. Notes on some of the viscera of Risso's Dolphin (Grampus 
 
 Griseus). Journal of Anatoiny and Physiology. Vol. XXVI. 1892. 
 Velpbau, a. — 
 
 (a) Traits complet d'anatomie chlrurgicale du Corps Humain. Paris, 1837 
 (h) Anatomy of Regions. Translated from the French by H. Hancock. 
 London, 1838. 
 Vesalics, a. De Corporis Human! Fabrica. 1555. 
 Vlacovitch. Atti dell'instituto veneto di soienze. 1865. Serie 3. Vol. X. 
 
 (Holl). 
 Waldeyer, W. Das Beoken. Bonn, 1899. 
 Watson, M. Contributions to the anatomy of the Indian Elephant. Part II. 
 
 Urinary and Generative organs. Journal of Anatomy and Physiology. 
 
 Vol. VII. 1873. 
 Wilson, J. A description of two muscles surrounding the membranous part of 
 
 the urethra. Transactions of the Medico-chirurgical Society, London. 
 
 Vol. I. 1809. 
 WiNSLOw, J. B. An anatomical exposition of the structure of the human body. 
 
 Translation. London, 1749. Vol. II. 
 Young, A. H. — 
 
 (a) Note on the Sphincter vaginae muscle. Report of the North of England 
 
 Obstetrical and Gynaecological Society. Medical Chronicle, 1890. 
 
 (b) On the male Generative organs of the' Koala. Jouriud of Aiiatomy 
 
 and Physiology. Vol. XIII. 1879.