THE MALE PELVIS 1385 



hsemorrhoidal veins traverse the fossa obliquely from the lateral wall downward and medially. 

 They are usually somewhat dilated near the anal orifice, and when morbidly enlarged constitute 

 the condition known as haemorrhoids ("piles"). The inner opening of an anal fistula caused 

 by the bursting of an ischio-rectal abscess into the gut is usually within 2 cm. of the anal margin, 

 between the internal and external sphincters. 



The central point of the perineum is in the adult nearly an inch (2.5 cm.) in 

 front of the anus, or midway between the centre of the anus and root of the scro- 

 tum. Here the following structures meet, viz., the levatores ani, the two trans- 

 verse perineal muscles, the bulbo-cavernosus, and the sphincter ani. 



The comparative weakness of the attachment of the sphincter ani in front, i. e., not into a 

 bony point, is important in the division of it, as in operation for fistula. The sphincter should 

 never be cut through anteriorly, especially in women, where its attachment here, blending with 

 the sphincter vaginae, is a very weak one. This point also corresponds to the centre of the 

 lower margin or base of the uro-genital diaphi-agm (triangular ligament). Its development 

 varies much in different bodies. A little in front of this point is the bulb, with the corpus 

 spongiosum passing forward from it. This would also be the level of the artery of the bulb, 

 so that in lithotomy the incision should always begin below this point. A knife introduced 

 at the central point, and carried backward and very shghtly upward, should enter the mem- 

 branous urethi-a just in front of the prostate, e. g., in median lithotomy and Cock's external 

 urethrotomy. If pushed more deeply, it would enter the neck of the bladder. 



In median lithotomy, an incision 3.7 cm. (1| in.) long is made through the central tendinous 

 point and raphe, so as to hit the membranous urethra. The following structures are divided: — 

 Skin and fasciae; some of the most anterior fibres of the external sphincter ani; raphe and 

 central tendinous point; minute branches of transverse perineal vessels and nerves; base of 

 uro-genital diaphragm in centre; membranous urethra and constrictor urethrse. 



The attachments and arrangements of the superficial fascia (fig. 1115) must be 

 traced and remembered. If the two layers of which it con.sists, the superficial 

 alone extends over both urethral and rectal triangles alike, and is continuous with 

 the similar structures in adjacent regions, the only difference being that, if traced 

 foward into the scrotum and penis, it loses its fat, and contains dartos fibres. 

 The deeper layer, found only over the urethral triangle, is called the fascia of Colles 

 (fig. 1115). Attached at the sides to the rami of the pubes, behind to the base of 

 the uro-genital trigone or diaphragm, and open in front, it forms the superficial 

 wall of a somewhat triangular pouch, limited behind by the uro-genital trigone, 

 and containing the superficial vessels, nerves, and muscles, the bulb, adjacent 

 part of the urethra, and crura of the penis. Ownng to this space being closed behind 

 and open in front, and to its containing the above structures, fluids extravasated 

 within this space will obviously tend to make their way forward into the scrotum, 

 penis, and lower part of the abdominal wall. 



The uro-genital triangle is subdivided into two planes by the inferior fascia of 

 the uro-genital diaphragm and fascia of Colles. The structures in the superficial 

 plane, between the uro-genital diaphragm and the fascia of Colles, have been 

 given above. Those in the deeper, i. e., between the two layers of fascia of the 

 diaphragm, are — (1) The membranous urethra; (2) deep transverse perineal 

 muscle and sphincter of the membranous urethra; (3) the bulbo-urethral (Cow- 

 per's) glands; (4) and (5) part of the pudic artery and nerve, and branches. 



The scrotum. — The skin of the scrotum is thin and delicate so that when 

 distended, as by a hydrocele in the tunica vaginalis, it is remarkably translucent. 

 Attached to its deep aspect is a layer of involuntary muscle, the dartos. When 

 the dartos is contracted, as under the influence of cold, the scrotal skin becomes 

 rugose. 



To this tendency to wTinkling, with consequent irritation from retained dirt, and the 

 presence of many sweat glands the frequency of epitheUoma in this part is due. The dartos is 

 apt to cause inversion of the skin in wounds of the scrotum, but this difficulty in suturing may 

 be counteracted by the application of a hot sponge, which relaxes the muscle. 



The superficial fascia of the scrotum is continuous with the fascia of Colles and the super- 

 ficial fascia of the penis. Hence extravasation of urine under the fascia of Colles's balloons the 

 scrotum and penis. The laxity of the areolar tissue under the dartos accounts for the great 

 swelling that occurs in oedema of this part. 



The lymphatics of the scrotum, important by reason of the extension of 

 scrotal cancer, drain into the superficial inguinal nodes. Those from the anterior 

 aspect nearest the median raph6 run to the supero-lateral glands of this group, 

 within a few cm. of the anterior superior spine.* 



* Morley: Lancet, 1911 (ii), p. 1545. 



