DISSECTION OF THE PERINEUM IN THE MALE. 283 



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. Hcemorrkoidal Branch of 5fh Sacra/ 

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

 coccygeal origin of the semimembranosus, and curving downwards 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. Hoemorrhoidal 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. Ex- 

 ternal 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 sziperficial 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 

 urinse muscle. The transversus perinsei, 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 particularly 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. 



