64 THE PERINEUM OF THE MALE. 



The pudic vessels and the dorsal and perineal divisions of the pudic nerve run 

 forwards along the outer wall of the fossa, being embedded in the obturator fascia 

 about an inch and a half (3'5 cm.) above the lower margin of the ischial tuberosity ; the 

 inferior hsemorrhoidal branches of these trunks run obliquely inwards and forwards 

 from the hinder part of the fossa towards the anus ; and anteriorly the superficial 

 perineal vessels and the perineal nerve leave the shelter of the hip-bone and also 

 enter the fat of the fossa. 



The ischio-rectal fossa is often the seat of abscesses which burrow freely in the 

 loose fat of the part, and frequently result in the formation of a fistula in ano, 

 involving a communication with the bowel, sometimes above, but more frequently 

 below, the external sphincter. 



The lower dilated part of the rectum, which occupies the space between the two 

 ischio-rectal fossae, is supported by the levatores ani and the external sphincter 

 muscles, as well as by the recto-vesical fascia. Its lateral wall is exposed for 

 a distance of about three inches (7'5 cm.), its posterior wall for little more than an 

 inch (3 cm.). 



On removing the fasciae of the fore part of the perineum the bulbo-cavernosus 

 muscle is exposed covering the corpus spongiosum, the ischio-cavernosus covering the 

 cms penis on each side, and the transversus perinei directed inwards over the base 

 of the triangular ligament to meet the first-named muscle, as well as the external 

 sphincter and its fellow of the opposite side, in the central point of the perineum. 

 Between the bulbo-cavernosus, ischio-cavernosus, and transversus muscles is a small 

 triangular space, in which a portion of the triangular ligament is exposed, and over 

 the surface of the muscles (sometimes in part beneath or through the transversus) 

 the superficial perineal vessels and nerves run forwards to the scrotum, while the 

 small transverse perineal artery is directed inwards close to the transverse muscle 

 towards the central point of the perineum. 



The triangular ligament or deep perineal fascia, which occupies the subpubic 

 arch, has a depth of an inch and a half in the middle line, but extends somewhat 

 farther backwards on each side, at its attachment to the ischial ramus. It consists 

 of two layers, the upper of which is continuous with the recto-vesical fascia. The 

 membranous part of the urethra descends, first through the superior, and then 

 through the inferior layer, about an inch from the pubic symphysis, and it is 

 surrounded by the fibres of the constrictor urethras muscle, which occupies the 

 greater part of the space between the two layers. Near the urethra, also embedded 

 in the muscular fibres, is Cowper's gland. The pudic vessels and the dorsal nerve 

 of the penis enter the base of the triangular ligament and run forwards close to the 

 bone, in small canals formed in the origin of the constrictor muscle, and the artery 

 gives off here its considerable branch to the bulb, which is directed inwards about 

 half an inch (1 cm.) from the base of the triangular ligament, and an inch and a 

 half (3'5 cm.) in front of the anus. 



Resting on the upper surface of the triangular ligament is the apex of the 

 prostate, and this body is surrounded by its sheath, which is continuous on each 

 side with the upper layer of the ligament ; beneath the sheath is the large prostatic 

 plexus of veins, derived mainly from the breaking up of the dorsal vein of the penis, 

 which passes into the pelvis between the pubic symphysis and the triangular liga- 

 ment. In the recess between the lateral part of the upper surface of the triangular 

 ligament and the sheath of the prostate, the anterior part of the levator ani muscle 

 is lodged. 



Above the prostate, and at a depth generally of from two and a half to three 

 inches (6 7 cm.) from the surface, is the bladder, the base of which projects back- 

 wards into the concavity formed by the rectum and overlaps the second part of 



