TJRETHRAL HALF OF THE REGION. 391 



Veins accompany the different arteries, and have a like course and 

 ramification : the pudic end in the internal iliac. 



NERVES (fig. 129). The nerves to be learned in this part of the peri- 

 neum are, the trunk of the pudic and its inferior hasmorrhoidal and peri- 

 nasal branches ; an offset of the fourth sacral ; and some branches of the 

 small sciatic. 



The pudic nerve comes from the sacral plexus, and accompanies the 

 artery to the genitals. In the anal half of the perinreum it is placed deeper 

 than the artery, and furnishes the two subjoined branches. 



The inferior heemorrhoidal branch (1) crosses the ischio-rectal fossa, 

 and reaches the margin of the anus, where it terminates in offsets to the 

 integument and the sphincter muscle. Other cutaneous offsets of the nerve 

 turn forwards over the fossa, and communicate with one of the superficial 

 perinatal nerves, and with the inferior pudendal (of the small sciatic) on 

 the margin of the thigh. 



The perinceal branch arises about half way along the fossa, and becomes 

 superficial to the bloodvessels. It is larger in size than the continuation 

 of the nerve to the penis, and divides into cutaneous, muscular, and geni- 

 tal offsets. Its two cutaneous - offsets (superficial perinaeal) may be seen 

 on the right side, where they lie for a short distance in the ischio-rectal 

 fossa. 



The heemorrhoidal branch of the fourth sacral nerve ( 3 ) reaches the 

 ischio-rectal fossa by piercing the fibres of the levator ani. Appearing in 

 the posterior part of the fossa, near the coccyx, the nerve ends by supply- 

 ing the external sphincter, and the integuments behind the anus. 



One or two cutaneous branches of the small sciatic nerve ( 4 ) turn round 

 the lower border of the gluteus, in their course to the integuments on its 

 surface. 



ANTERIOR HALF OF THE PERIX^EAL SPACE. 



In the anterior part of the perinaeal space are lodged the crura of the 

 penis, and the tube of the urethra as it courses from the interior of the 

 pelvis to the surface of the body. Placed about midway between the 

 bones, the urethra is supported by the triangular ligament of the perinaeum, 

 and by its union with the penis. 



Muscles are collected around the urethra to aid in the expulsion of the 

 contents of that tube : some of these are superficial to, and some within 

 the triangular ligament. 



The vessels and nerve lie along the outer side, as in the posterior half, 

 and send inwards offsets. 



Dissection (fig. 130). To raise the skin from the anterior part of the 

 perinaeum, a transverse cut is to be made at the back of the scrotum, and 

 is to be continued for a short distance (two inches) on each thigh. A 

 second incision along the middle line will allow the fiaps of skin to be re- 

 flected outwards. After the removal of the skin the subcutaneous fat 

 (superficial fascia) which covers the front of the perinaeal space, is to be 

 blown up by means of a pipe introduced beneath it posteriorly. Each 

 side is to be inflated to demonstrate a partition along the middle line, and 

 a septum between the perinatal space and the thigh which prevents the air 

 passing to the limb. 



The student is next to cut through the superficial fascia on the left side 

 from the scrotum to the ischio-rectal fossa ; and after reflecting it, and 



