THE MALE GENITAL ORGANS. 863 



transverse fibres thrown over the membranous portion of the urethra, and 

 united at their extremities, which are attached by means of aponeurotic 

 fasciculi, to the lateral walls of the pelvis. Behind, the superior fibres 

 cover Cowper's glands, and, like the inferior, are mixed with the accelerator 

 urinae. 



b. Accelerator Urince. Composed of transverse fibres encircling the 

 urethra 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 ; they do not join ; so that the circle formed by this 

 muscle is necessarily incomplete. 



c. Ischio-urethral muscle (compressor urethrce). This is a thin fleshy 

 band, pair, situated below and at the side of the membranous portion of the 

 urethra. Attached by some aponeurotic fibres to the ischial arch, this 

 muscle passes forward on Cowper's gland, whose lower face it covers. At 

 the periphery of that organ, it is confounded with the portion of Wilson's 

 muscle that envelops its upper surface. 



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

 scarcely distinguishable from the ischio-anal muscle (levator 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 

 perineum, where its fibres, confounded with those of its homologue on the 

 opposite side, appear to be inserted in the accelerator urinse at its origin. 



e. Action of the urethral muscles. 1. Wilsons' muscle, 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 vesiculaa 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 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 ischio-urethral 

 muscle pulls back the membranous portion of the urethra, with Cowper's 

 glands, and, like Wilson's muscle, acts as a compressor to these. 4. The 

 transversus perinei 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 dorsal 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 nervous filaments are from the internal piidic and great 

 sympathetic. 



5. APONEUROSES OF THE PERINEUM. In the perineal 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 perineum, 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 aponeurosis, formed of white inelastic fibrous tissue, adheres to 



