108 THE OSTEOLOGY AND MYOLOGY 



Muscles of the Perin^eum. 



Although these muscles, properly speaking, belong rather to special organs than to the 

 general frame-work of the body, and consequently, like the pharyngeal, laryno-eal, and 

 some others, scarcely fall within the scope of the present memoir, I give them brief notice, 

 on account of their intrinsic interest. The muscles of the organs of generation, as mio-ht 

 be expected, offer some unusual conditions, as compared with those of ordinary mammals, 

 though they are not peculiar to the animal in its own order. 



Sphincter ani. — The external sphincter, which surrounds and includes the uro-genital 

 as well as the anal orifice proper, is rather small and thin, and ver}^ intimately adherent to 

 the integument around the common opening. It is circular in general outline, but after 

 embracing the anus extends forward, with a tliscial attachment towards the symphysis, over 

 the dorsum of the penis, when the latter lies occluded by retraction. It is presumed to aid 

 or continue the erection of the organ, Avhen the latter is protruded, by compressing the 

 dorsal veins. 



Sphincter cloacce. — Within or above the preceding lies the proper sphincter of the rec- 

 tum, which appears to represent the " internal sphincter " of anthropotomy, and to be 

 formed mainly or wholly by an aggregation of the circular fibres of the rectum ; it has no 

 direct action upon the genital apparatus. 



Levator ani. — The muscular floor of the pelvis is well developed. It forms a rather thin, 

 subcircular plane, corresponding, in a general way, to the contour of the pelvic outlet ; 

 and embraces the genitalia as well as the rectum. Posteriorly, where the muscle is thickest, 

 the margin is free, or at least without direct fascial attachment to the caudal vertebrae ; and 

 the fibres run uninterruptedly from one side to the other. These circular fibres curve for- 

 ward on either side, and converge over the penis ; the anterior and lateral margins of the 

 muscle have extensive, though diffuse, fascial attachment to the ischia and pubes — to the 

 latter more particularly. Large masses of fat usually rest upon the levator, forming pro- 

 tuberances on either side of the rectum. 



Levator recti. {Eecto-coccygeus). — This little muscle appears to compensate for want 

 of decided attachment of the levator ani to the coccygeal vertebrte behind : it may really 

 belong to that muscle, but my dissections showed it as distinct. It is a delicate fasciculus, 

 of considerable length, that arises from the chevron bone of the second or third coccygeal 

 vertebra, or both, and proceeds forward and downward above the plane of the levator 

 ani, to the rectum itself, upon which it spreads. It makes direct traction upon the gut, 

 and must exert considerable force when the tail is fixed, notwithstanding its delicate 

 proportions. 



Levator penis. — This peculiar muscle, the most exceptional of the set acting upon the 

 organ, as it appears to be characteristic of those marsupials that have a forked glans, and 

 is not found throughout the order, occurs in a highly developed and curious condition. It 

 is the most superficial and lateral of the penal muscles, and is immediately exposed upon 

 removal of the levator ani, above the plane of which it lies, upon the crura, and afterwards, 

 in its tendinous portion, upon the dorsum, of the penis. The muscular part consists of 

 opposite halves, each of which takes extreme origin from the ramus of the ischium, and is 

 also attached to the surfiice of a crus, as it passes over the latter, and forms a spindle- 

 shaped belly, that mounts the dorsum of the penis, just behind the border of the symphysis 



