'BULBO-CA VERNOS US 



443 



which in part interdigitate across the median line, and in part are inserted into a 

 median raphe. 



The musculature of the urogenital diaphragm is enclosed between two well 

 marked fascial layers (fig. 400, 403), the deep (superior) and superficial (inferior) 

 laj'^ers of the urogenital trigone (triangular ligament). The anterior margins of 

 the two fascial layers are fused to form the transverse ligament of the pelvis 

 which extends between the inferior pubic rami, beneath the dorsal nerves and 

 veins of the penis (clitoris). At the anal margin of the musculature these two 

 laj^ers are also fused with one another. The deep layer of the urogenital trigone 

 forms the floor of the anterior recess of the ischio-rectal fossa (fig. 400). 



Superficial to the urogenital trigone lie the external genitalia (figs. 392, 394). 

 Voluntary muscle is here found in connection with the crura of the penis (clitoris) 

 and the bulb of the penis (vestibule). Although the musculature in the two sexes 

 is fundamentally similar, nevertheless, owing to the differences in the structure of 

 the genitalia in the two sexes, it is convenient to take up first the external genital 

 musculature in the male and then that in the female. 



Fig. 398. — Muscles between the Two Layers of the Urogenital Trigone (Male.) 



Corpus cavernosum 



7 



Dorsal vein of 

 penis 



Transverse liga- 

 ment of pelvis 



Urethra, sur- 

 rounded by 

 sphincter 



Ischio- 



cavernosus 



Transversus urethrae 



Transversus perinei profundus 



In the male the crus penis, the posterior part of the corpus cavernosum, is 

 relatively large. It lies in the groove between the ischio-pubic ramus and the 

 urogenital trigone (fig. 398), to the former of which it is firmly united. It is 

 enwrapped on its free medial surface by the ischio-cavernosus muscle (erector 

 penis) (figs. 398, 402). The fibre-bundles of this muscle arise from the ischial 

 tuberosity and from the ischio-pubic ramus on each side of the attachment of the 

 crus. It is inserted into the medial and ventral surfaces of the crus near the 

 attachment of the suspensory ligament. Some of the fibre-bundles may fre- 

 quently be traced to the dorsal surface of the root of the penis (levator penis 

 muscle). 



The corpus spongiosum [corpus cavernosum urethrse] terminates posteriori}^ 

 in the bulb which lies on the urogenital trigone between the two crura (figs. 394, 

 402). It is united to the superficial layer of the trigone (fig. 402). It is envel- 

 oped by the bulbo-cavernosus muscle, composed of right and left halves united by 

 a median raphe on the superficial surface of the bulb (fig. 394). Each half con- 

 sists of several superimposed layers of fibre-bundles described below. The 

 component fibre-bundles arise from the superficial layer of the urogenital trigone, 

 from fibrous tissue on the dorsum of the bulb in the angle between the two crura, 

 from the lateral surface of the corpus cavernosum penis in front of the ischio- 

 cavernosus and from the dorsal surface of the penis. It is inserted into a tendi- 

 nous structure situated in front of the anus, the central tendon of the perineum, 



