394 DISSECTION OF THE PERINEUM. 



The anterior branch ( 3 ) passes under the transverse muscle, and accom- 

 panies the other to the scrotum. Muscular offsets are furnished by it to 

 the levator ani and the other superficial muscles. 



The superficial perimval branches communicate with one another, and 

 the posterior is joined by the inferior pudendal nerve. At the scrotum 

 they are distributed by long slender filaments, which reach as far as the 

 under surface of the penis. In the female these nerves supply the labia 

 pudendi. 



Other muscular branches of the pudic will be afterwards examined (p. 

 399). 



The inferior pudendal nerve ( 4 ) is a branch of the small sciatic. It 

 pierces the fascia lata about one inch in front of the ischial tuberosity, and 

 enters beneath the superficial fascia of the perinaeum, to end in the outer 

 and fore parts of the scrotum. Communications take place between this 

 nerve, the inferior hsRmorrhoidal, and the posterior of the two superficial 

 perinneal branches. In the female the inferior pudendal nerve is distri- 

 buted to the labium. 



Dissection. For the display of the muscles, the fatty layer, as well as 

 the vessels and nerves of the left side, must be taken away from the ante- 

 rior half of the perinaeal space. Afterwards a thin subjacent aponeurotic 

 layer is to be removed from the muscles. Along the middle line lies the 

 ejaculator urinae ; and in cleaning it the student is to follow two fasciculi 

 of fibres from it on the same side one in front, the other behind. On the 

 outer part of the space is the erector penis. And behind, passing obliquely 

 between the other two, is the transverse muscle. 



The student should seek, on the right side, the branches of the two 

 superficial perinseal nerves to the underlying muscles ; and beneath the 

 transversalis, an offset of the perinoeal branch which supplies the deep 

 muscles and the urethra. 



MUSCLES (fig. 130). Superficial to the triangular ligament in the ante- 

 rior half of the perinseal space, are three muscles, viz., the erector penis, 

 the ejaculator urinae, and the transversalis perinasi. Other muscles of the 

 urethra are contained between the layers of the triangular ligament, and 

 will be subsequently seen. 



Central point of the per inceum. Between the urethra and the rectum is 

 a white fibrous spot, to which this term has been applied. It occupies the 

 middle line, half an inch in front of the anus. In it the muscles acting on 

 the rectum and the urethra are united ; and it serves as a common point 

 of support to the space. 



The ERECTOR PENIS (fig. 130, B ) is the most external of the three mus- 

 cles, and is narrower at each end than in the middle. It covers the crus 

 penis; and its fibres arise from the ischial tuberosity farther back than the 

 attachment of the penis, and from the bone on each side of the crus. Su- 

 periorly the muscle is inserted into the inner and outer surfaces of the crus 

 penis. It rests on the root of the penis and the bone. 



Action. The muscle compresses the crus penis against the subjacent 

 bone, and retards the escape of the blood from that organ by the veins : in 

 that way it will contribute to the continuance of distension. 



The EJACULATOR URINAE muscle (fig. 130, A ) lies on the urethra. The 

 muscles of opposite sides unite by a median tendon along the middle line 

 and in the central point of the perinreum (origin). The fibres are directed 

 outwards, curving around the convexity of the urethra, and give rise to a 

 thin muscle, which has the following insertion: The most posterior fibres 



