ISCHIO-CA VERNOS US 



451 



perineum. To a greater or less extent, depending on the development of the two muscles, the 

 compressor covers the more posterior part of the constrictor. 



3. The compressor hemisphcerium bulbi arises from a tendon common to the muscles of the 

 two sides on the dorsum of the bulbous part of the urethra near the membranous part. The 

 fibre-bundles embrace the hemisphere of the bulb and are inserted into the median raphe. This 

 muscle is covered by the preceding. It not only compresses the bulb, but also is a sphincter 

 of the urethra. 



4. The ischio-bulbosus is placed by HoU in this group. It arises from the pelvic surface of 

 the tuberosity and of the inferior ramus of the ischium and when well developed is inserted into 

 the median raphe, superficial to the compressor bulbi proprius or the constrictor radicis pro- 

 prius. Frequently, however, it does not extend over the bulb but is inserted into the inferior 

 surface of the corpus cavernosum. It is more frequently absent than present. (See fig. 404.) 



Nerve-supply. — The perineal division of the pudic nerve sends several branches to the bulbo- 

 cavernosus. 



Action. — It compresses the bulb and at the same time the bulbous portion of the urethra. 

 The turgescence of the penis is thus increased and urine or semen is expelled from this portion 

 of the urethra. 



Relations. — It lies beneath the skin and subcutaneous tissue. 



Variations. — The muscle is variable in structure as is indicated by the different descriptions 

 given by different authors. The compressor vence dorsalis described by Houston is composed of 



Fig. 405. — Diagrammatic Representation of the Perineal Structures in the Female. 



Ischio-pubic arch 



Crus clitoridis with 

 ischio-cavernosus 



Bulbo-cavernosus 

 covering bulbus 

 vestibuli 



Inferior layer of uro- 

 genital trigone 



Glans clitoridis with 

 prepuce 



Pars intermedia 

 Mucous membrane of 

 vestibule 



Urethral orifice 



Bulbus vestibuli 



Greater vestibular 

 gland 



External sphincter ani 



a few fasciculi which arise from the sheath of the corpus spongiosum, and from the median 

 raphe and are united to those of the opposite side by a tendon which passes over the dorsal vein. 



The bulbo-cavernosus {sphincter vagince) (fig. 392, 405) in the female arises (1) from fibrous 

 tissue dorsal to the clitoris, (2) from the tunica fibrosa of the corpus cavernosum and from the 

 superficial layer of the urogenital trigone in the angle between the crura of the chtoris. The 

 fibre-bundles form a band of tissue about two centimetres wide at the side of the vagina and are 

 inserted into the posterior part of the superficial (inferior) layer of the trigonum and into the 

 central tendon of the perineum where some of the fibre-bundles interdigitate with those of other 

 muscles attached here. The fibre-bundles arising from the back of the chtoris correspond with 

 those of the constrictor radicis penis in the male. The other fibre-bundles correspond with those 

 of the compressor bulbi proprius in the male. 



Nerve-supply. — From the perineal division of the pudic. 



Action. — To compress the vagina. 



Relations. — It covers the bulb of the vestibule and the great vestibular gland (Bartholin's). 

 It is covered by skin and superficial fascia. 



The ischio-cavernosus (figs. 398, 405) (erector penis or clitoridis) arises from the pelvic 

 surface of the tuberosity and inferior ramus of the ischium, back and on each side of the attach- 

 ment of the crus. The fibre-bundles form a thin sheet which is spread over the crus into the 

 medial and inferior surfaces of which it is inserted near the symphysis pubis. It is better devel- 

 oped in the male than in the female. 



Nerve-supply. — By branches of the perineal nerve. 



Action. — By constricting the crus to maintain turgescence of the penis or chtoris. 



Relations. — Superficially it is covered by skin and subcutaneous tissue. Laterally it lies 

 next the ischio-pubic ramus. Medially it bounds a space lying between the crus and the bulb 

 and filled with fat. 



