PENIS AND URETHRA' 1035 



a compressor of the dorsal vein. The rest of the fil^res pass around the Vjulb to 

 become lost in the connective tissue on the dorsal aspect of the latter, between it 

 and the corpora cavernosa; the two muscles thus practically encircle the bullj, and 

 act as an annular sphincter u]>on the contained portion of the urethra. It is often 

 joined by til)res from the sphincter ani and deej) transversus perina-i. 



The superficial transversus perinaei is the most variable of all the perinatal 

 muscles. It usually arises from the inner surface of the tuberosity and ramus of 

 the ischium, l)lendinji; with the ori<!;in of the ischio-cavernosus, and passes inwards 

 and forwards to its insertion into the tendinous centre of the perineum, interlacing 

 with the posterior fibres of origin of the bulbo-cavernosus. Some of its fibres may 

 blend with those of the sphincter ani and levator ani. 



These three pairs of muscles possess each a thin fascial sheath, and lie in the 

 superficial perinaeal interspace between the fascia of Colics and the superficial 

 triangular ligament. They are supplied by branches of the deep division of the 

 sujjerticial perineal nerves and vessels. 



The action of the penile muscles is not very ol)vious. The compressores venae 

 dorsalis when present may aid in erection by impeding tlie retvn-n of venous blood 

 from the organ, but there is no reason to believe that any disadvantage attaches to 

 their absence. The bulbo-cavernosus, with its fellow, is. however, of value as a 

 compressor of the bulbous portion of the urethra, and thus assists in the ejaculation 

 of the semen, continuing the action of the ejaculatory fibres of the prostate and of 

 the deep transversus perinaei; and it may also be of service in expelling the last 

 drops of the urine. The compression of the vessels of the bulb favours the 

 engorgement of the rest of the corpus spongiosum. 



The ischio-cavernosus in the absence of its dorsal fasciculus can scarcely justify 

 its older name of erector penis, but it appears to have the power of impressing 

 voluntary movements upon the turgid organ. The superficial transversus perinaei 

 is accessory to the bulbo-cavernosus, fixing the raphe from which its fibres arise, and 

 it adds slightly to the strength of the muscular floor of the jDclvis. 



Vessels and Nerves of the Penis. 



Artery. — The envelopes of the penis are sujiplied by the external pudic, the 

 superficial perinaeal, and the dorsal artery; the first from the femoral, the others 

 from the internal pudic. The corpora cavernosa are supplied by the cavernous 

 branch of the pudic; the corpus spongiosum by the special artery of the bulb 

 (internal pudic) and the dorsal artery. 



Veins. — The veins of the coverings of the penis end in one or two superficial 

 dorsal veins which run in the connective tissue layer between the dartos and fascial 

 sheath, and end in the long saphenous and femoral veins. The deep veins of the 

 corpora cavernosa and corpus spongiosum terminate partly in the plexus of 

 Santorini (chiefly through the deep dorsal vein), and partly in the internal pudic. 

 They communicate freely with each other and with the superficial veins. 



Lymphatics. — The lym])hatics run with the veins, those of the coverings being 

 collected by superficial dorsal trunks which pass to the inguinal glands. The deep 

 lymphatics from the corpora cavernosa and corpus spongiosmii for the most ])art 

 join a dorsal cord which runs with the deep dorsal vein to end in the inguinal 

 glands; a few probably reach the pelvic and lumbar glands. 



Nerves. — The integumentary structures are supplied by the genital 1)ranch of the 

 genito-crural and the superficial perina'al branches of the pudic. The erectile bodies 

 receive filaments from the dorsal nerve of the penis, the suj^erficial perina?al, and 

 the hypogastric plexus. 



THE URETHRA 



The urethra is the mucous canal extending from the bladder to the extremity 

 of the glans penis. In its course it j)ierces the ]>rostate from l)ase to ajiex. the deep 

 and superficial triangular ligaments with the intervening comjiressor urethric, and 

 the whole length of the corpus spongiosum. It may hence be divided into three 

 segments: — (1) Prostatic; (2) membranous (the ])ortion lying in the space between 

 the two transverse ligaments); and (3) spongy (fig. 630). 



The prostatic portion runs almost vertically downwards from the internal 



