DISSECTION OF THE PERINiEUM IN THE MALE. 283 



condition of the subject, but is greater in the young than in the old 

 animal. In this fat the perineal nerves are to be followed. 



Perineal Cutaneous Nerves. — 1. Hemorrhoidal Branch of 5th 

 Sacral Nerve. This nerve will be found emerging at the hinder edge 

 of the coccygeal origin of the semimembranosus, and curving down- 

 wards and inwards at the root of the tail. It supplies the skin there, 

 and gives some twigs downwards to the skin of the anus. 



2. Hcemorrhoidal Nerve. The trunk of the hemorrhoidal nerve, 

 which cannot be reached at present (page 355), divides between the 

 sacro-sciatic ligament and the retractor ani. Its branches are as 

 follows: 1. A branch appears at the inner side of the coccygeal origin 

 of the semimembranosus, and is distributed at the side of the anus. 

 2. External to the preceding a branch perforates the semimembranosus ; 

 and, descending over the tuber ischii, it is distributed at the side of 

 the penis. 3. About an inch or two below the anus a branch appears 

 near the middle line, and descends over the urethra. 



3. Pudic Nerve. Ascending on the side of the anus, beneath the 

 branches of the hsemorrhoidal nerve, are some twigs from the pudic 

 nerve. They terminate in the skin and the sphincter ani. 



Perineal Fascia. The lower part of the perinseum is covered by 

 two layers of fascia, viz., a superficial and a deep. The superficial 

 layer is attached laterally to the fascia covering the muscles on the 

 inside of the thigh, towards the anus it loses its aponeurotic character 

 and becomes cellular, and inferiorly it blends with the dartos. The 

 deep layer is reflected upwards at each side of the penis, while above 

 and below it loses its distinctness and becomes cellular. 



Directions. — These layers of fascia should be removed, and the parts 

 should be cleaned after the manner of Plate 37. Beneath the deep layer 

 a branch of the pudic nerve will be found descending on the accelerator 

 urime muscle. The transversus perineei, if present (it was absent in the 

 subject from which the Plate was taken), will be found concealing the 

 internal pudic artery, and may be removed on one side. 



The Internal Pudic Artery. This vessel is a branch of the internal 

 iliac artery (Plates 46 and 47). It descends obliquely along the side 

 of the pelvis, on the inner side of the sacro-sciatic ligament or within 

 its texture. At the small sacro-sciatic foramen it passes backwards 

 and inwards to turn round the ischial arch. It penetrates the urethral 

 bulb, immediately resolving itself into a number of branches that 

 supply the erectile tissue of that body. Its position should be par- 

 ticularly noted with reference to the operation of lithotomy, in which, 

 by making a mesial incision, the urethra may be opened without 

 danger of wounding the artery. 



In this part of its course the vessel gives off small branches to the 

 anus and to the erector penis muscle. 



