450 



THE MUSCULATURE 



The Iransversus vaginas arises from the ischio-pubic rami and is inserted into the lateral wall of 

 the vagina. Some of the fibre-bundles pass above and some below the vagina. This muscle 

 corresponds with the transversus urethrse of the male but is, apparently, seldom fully developed. 

 The ni. constrictor vaginae, on the other hand, seems to be more constant. It is composed of 

 fibre-bundles which embrace the lateral wall of the vagina and are inserted above into the peri- 

 urethral framework, below into the raphe between the two deep transverse perineal muscles. 

 Some of the fibre-bundles are attached to the vaginal wall. Some interdigitate with the sphinc- 

 ter urethrae, others with the deep transverse perineal muscle and with the transversus vaginaj. 



Nerve-supply. — By a branch from the perineal nerve. 



Action. — To compress or close the urethra and in the male to compress the prostate and 

 Cowper's glands, in the female to compress the vagina and Bartholin's glands. 



Relations. — On the pelvic side it is separated from the levator ani by the deep layer of the 

 urogenital trigone, and on the perineal side it is separated from the superficial muscles by the 

 superficial layer of the trigone. Toward the anus it is closely associated with the deep trans- 

 verse perineal muscle. Venous plexuses are well developed near the sphincter urethra) in both 

 sexes, but especially in the female. 



Fig. 404. — Bulbo-cavernosus in the Male. 

 The two halves have been reflected from the median raphe, and the bulb turned downward after 

 division of the corpus spongiosum. (The ischio-bulbosus is not present on the right side.) 



Corpus cavemosum penis 



Cut surface of corpus cavemosum 

 urethrae 



Median aponeurosis 



Urethra 



Cut surface of corpus 

 cavemosum urethrae 



Corpus cavemosum urethrae 

 (corpus spongiosum) 



Constrictor radicis penis 



Ischio-bulbosus 



Compressor bulbi proprius 



Compressor hemisphserium 

 bulbi 



Variations. — It has already been pointed out that there is considerable variation in the 

 muscles composing urogenital sphincter. Occasionally a rudimentary ischio-pubicus is found 

 arising from the ischio-pubic ramus and terminating in a tendon which unites with that of the 

 oppo.site side beneath the dorsal vein of the penis (clitoris). The tendon may be present as 

 the transverse ligament of the pelvis when the muscle itself is absent. It represents the com- 

 pressor of the dorsal vein found in lower mammals. , 



C. External Genital Muscles 



TIk; bulbo-cavernosus (figs. 394, 404) in tlie male ensheaths the bulb. The fibre-bundles 

 arise from the den.se tissue covering the corpus cavemosum at the root of the penis and from the 

 subpubic connective tissue dorsal to the bulbar part of the urethra and are inserted into its median 

 raphe on the ventral side of the bulb and into the central tendon of the perineum. Several 

 parts may be mon; or less clearly distinguished. 



1. The constrictor radicis penis arises usually from the lateral surface of the corpus caver- 

 nosum penis at the base of the penis, but may arise from the under surface or from the dorsal 

 surface, or even from the suspensory ligament of the penis. The fibre-bundles pass obliquely 

 backward and medialward and are inserted into the median raphe on the perineal surface of the 

 bulb. 



2. The compressor hulhi proprius arises (1) from a strong fil)rous aponeurosis situated 

 between the corpus spongiosum and the united crura of the penis and firndy adherent to the 

 former, and (2) from tlie superficial layer of the trigone. The fibre-bundles ensheath the bulb 

 and are inserted into the posterior part of the median raphe and into the central tendon of the 



