MUSCLES OF THE PERINEUM. 



843 



The Erector Penis covers the unattached part of the crus penis. It is an 

 elongated muscle, broader in the middle than at either extremity, and situated 

 on either side of the lateral boundary of the perineum. It arises by tendinous 

 and fleshy fibres from the inner surface of the tuberosity of the ischium, behind 



Fig. 457. The Superficial Muscles and Vessels of the Perineum. 



Grf Saero- Sciatic Ligt- 



Superficial Perinal Arttry 

 Superficial Perincal Xervt 

 Internttl PuAic Nerve 

 Internal Pudic Artery 



the crus penis, from the surface of the crus, and from the adjacent portion of 

 the ramus of the pubes. From these points, fleshy fibres succeed, which end 

 in an aponeurosis which is inserted into the side and under surface of the crus 

 penis. This muscle compresses the crus penis, and thus serves to maintain the 

 organ erect. 



The Transversus Perinsei is a narrow muscular slip, which passes more or less 

 transversely across the back part of the perineal space. It arises by a small 

 tendon from the inner and fore side of the tuberosity of the ischium, and, pass- 

 ing obliquely forwards and inwards, is inserted into the central tendinous point 

 of the perineum, joining in this situation with the muscle of the opposite side, 

 the Sphincter Ani behind, and the Accelerator Urinas in front. 



Between the muscles just examined, a triangular space exists, bounded in- 

 ternally by the Accelerator Urinas, externally by the Erector Penis, and behind 

 by the Transversus PerinsBi. The floor of this space is formed by the triangular 

 ligament of the urethra (deep perineal fascia), and, running from behind for- 

 wards in it, are the superficial perineal vessels and nerves, the transverse 

 perineal artery coursing along the posterior boundary of the space, on the 

 Transversus Perinsei muscle. 



In the lateral operation of lithotomy, the knife is carried obliquely across 

 the back part of this space, downwards and outwards, into the ischio-rectal fossa, 

 dividing the Transversus Perinaei muscle and artery, the posterior fibres of the 

 Accelerator Urinse, the superficial perineal vessels and nerve, and more poste- 

 riorly the external hsemorrhoidal vessels. 



The superficial and transverse perineal arteries have been already described ; 

 also the superficial perineal and inferior pudendal nerves. 



