972 GENERATIVE APPARATUS. 



from the ischial arch to the free extremity of the penis, this will also be studied 

 as a single organ, separated into two lateral portions by a median raphe passing 

 along the whole posterior face of the urethra. The fibres pass from this raphe 

 to the right and left, enter the furrow of the corpora cavernosa, and reach the 

 upper surface of the urethra, where they advance towards each other, but do not 

 join in the middle line ; so that the circle formed by this muscle is necessarily 

 incomplete. 



c. Compressor muscle of Gowper''s glands. — This muscle is composed of two 

 layers of fibres — a superior and an inferior — confounded on the periphery of 

 Cowper's glands. The superior layer is continuous, it may be said, with the 

 upper part of the urethral sphincter. The inferior layer is attached, posteriorly, 

 by some aponeurotic fibres to the ischial arch. 



d. Transversus peritKsi. — This is a very thin ribbon-like fasciculus, often 

 scarcely distinguishable from the ischio-anal muscle (^retractor ani). It extends 

 transversely from the ischial tuberosity — to which it is attached through the 

 medium of the sacro-sciatic ligament — to the mesial line of the perinaeum, where 

 its fibres — confounded with those of its homologue on the opposite side — appear 

 to be inserted in the accelerator uringe muscle at its origin. 



e. Action of the urethrcd muscles. — 1. The uretlircd sphincter, when it contracts, 

 compresses between its two layers the membranous portion of the urethra. It is 

 a veritable sphincter, and opposes the escape of the urine ; when the semen is 

 thrown from the vesiculae seminales into the urethra, it also prevents that fluid 

 entering the bladder, by permitting the accelerator to empty, from before to 

 behind, the initial dilatation of that canal. 2. The accelerator urince is correctly 

 named, from the part it plays in ejecting the semen from the urethra — it being 

 the chief agent in this act. 3. The compressor of Cowper^s glands pulls back the 

 membranous portion of the urethra, along with Cowper's glands, and acts as a 

 compressor to these. 4. The transversus perinoei dilates the bulbous portion of 

 the urethra, by drawing it out laterally. 



4. Vessels and Nerves. — The urethra is supplied with blood by the bulbo- 

 urethral arteries and the two pairs of arteries — the dorsals of the penis. Voluminous 

 veins — frequently varicose, and satellites of the arteries — carry it away. The 

 lymphatics form a very rich plexus beneath the mucous membrane ; their trunks 

 pass to the inguinal, and some to the sublumbar, glands. The «erye-filaments 

 are from the internal pudic and great sympathetic. 



5. Aponeuroses of the Perineum. — In the perinaeal region, the urethra 

 is covered by two superposed fibrous layers. 



The superficial aponeurosis is fibro-elastic, and appears to arise from the inner 

 surface of the thighs, where it is mixed with the dartos ; it covers the peringeum, 

 and its fibres, becoming disassociated, disappear on the sides of the sphincter ani. 

 This membrane is in relation, externally, with the skin, and, internally, with the 

 deep aponeurosis. On the middle of its external face, it receives the insertion of 

 a muscular fasciculus, which is detached from the sphincter. 



The deep or perinatal aponeurosis, formed of white inelastic fibrous tissue, 

 adheres to the preceding by its outer face, and to the accelerator urince and 

 ischio-cavernous muscles by its inner face. Above, it is lost around the termina- 

 tion of the rectum ; below, it expands between the thighs. To the right aud 

 left, it insinuates itself between the erector penis and semimembranosus muscles, 

 to be attached to the ischiatic tuberosity ; it is prolonged in the pelvic cavity 

 between the bladder and rectum, where it limits two independent spaces : 1. A 



