62 U.S. NATIONAL MUSEUM BULLETIN 2 73 



membranacea deep to the bulbus penis and corpus spongiosum penis. 



M. sphincter urethrae (fig. 21) : It is represented by a rather weak 

 group of muscular fibers which from the midhne, deep to the bulbus, 

 pass transversely toward msertion on the ramus inferior of the pubis 

 and the ramus and body of the ischium. Some of its fibers encircle 

 the urethra and the muscle is reinforced in front and laterally of the 

 urogenital canal by m. ischiourethralis. It blends posteriorly with 

 the well developed superficial perineal fascia. 



M. retractor recti et urethrae (fig. 22) : A long but not so wide 

 band which from the proximoventral part of the tail passes forward 

 around the large rectum and the prostate. It arises from hemal arch I 

 by tendinous fibers which shortly become fleshy. The muscle runs 

 ventrally deep to the pubo- and iliocaudalis, crosses on the lateral 

 aspect of the rectum and prostate between the medial edge of the 

 pubocaudalis and the lateral and anterior puboprostatic ligaments. 

 It ends by fibrous strands on the lateral part of the rectum and prostate 

 up to the anterior border of this gland. 



M. caudoanalis : This is a paired muscle which from the tip of the 

 first hemal arch runs ventrocaudally at each side of the midline to 

 join the circular fibers of the sphincter ani externus (fig. 22). 



M. candor ectalis: An unpaired muscular band which from the 

 second hemal arch ascends ventrally into the ischiorectal fossa to 

 join the longitudinal fibers of the rectum (fig. 22). It occupies the 

 space left inbetween the two retractors of the rectum and lu-ethra. 



M. sphincter ani externus (figs. 21, 22) : The circular fibers of this 

 l^rominent and unpaired muscle form a thick ring around the anal 

 canal. They occupy most of the anal triangle but are separated from 

 the tail by a space filled with fatty clumps. The muscle as a whole 

 and, therefore, the anal canal also have a rather forward position in 

 relation to the caudal appendage. The origin of its fascicles is difficult 

 to identify. They appear to come from an area between the rectum 

 and the urogenital canal where connective tissue is abundant. Some 

 of the anal fibers seem to extend to the rear end of m. sphincter 

 urethrae and m. bulbocavernosus. 



PERINEAL MUSCULATURE — FEMALE 



M. sphincter cloacae: This is a muscular sheet formed by fibers 

 surrounding the anal and urogenital openings. The fleshy fascicles are 

 supplemented by membranous ones. Some of them encircle only the 

 rectum and correspond to the sphincter ani externus. 



M. ischiocavernosus : Less developed than in the male, its fibers 

 end on the fibrotendinous assemblage in the ventral end of the cloacal 

 sphincter above the crura. 



