1 84 THE NERVOUS SYSTEM 



The Perineal Nerve contains both motor and sensory 

 fibres. The former supply the levator ani and the muscles of 

 the urogenital triangle of the perineum, i.e. the sphincter 

 (compressor) urethrse, the ischio- and the bulbo-cavernosus 

 (the erector penis and the ejaculator urinae) and the transverse 

 perineal muscles. The sensory fibres supply the skin of the 

 perineum anterior to the anus, including the skin of the 

 scrotum. In addition, they supply the bulb of the penis and 

 the corpora cavernosa. 



The Dorsal Nerve of the Penis supplies the whole of the 

 skin covering the penis, including the deep surface of the 

 prepuce and the surface of the glans. 



Referred pain may be experienced in the perineum, scrotum 

 and penis, in pathological conditions of the viscera which are 

 innervated by the sacral segments of the spinal medulla. 

 It is especially common in vesical calculi, but it also occurs in 

 inflammatory or irritative conditions of the lower part of the 

 rectum, the anal canal, the prostate and the seminal vesicles. 



The Perforating Cutaneous Nerve (S. 2 and 3) pierces the 

 sacro-tuberous (great sacro-sciatic) ligament and the lower 

 border of the glutaeus maximus, and supplies the skin of the 

 buttock in the neighbourhood of the coccyx. 



The Perineal Branch of the Fourth Sacral helps to supply 

 the external sphincter. 



In addition to the named branches, the pudendal plexus 

 gives off branches of supply to the levator ani and the 

 coccygeus. These two muscles form the floor of the pelvis 

 and shut it off from the ischio-rectal fossae. The levatores 

 ani arise from the pelvic wall and project downwards and 

 inwards to meet one another. They are attached to a median 

 raphe, which extends from the tip of the coccyx to the 

 posterior aspect of the anal canal, and they constitute a 

 muscular bed on which the terminal part of the rectum lies as 

 it runs horizontally forwards (p. 283). The anterior fibres, which 

 arise from the pelvic surface of the pubis, pass downwards and 

 backwards ; some of them blend with the muscular wall of 



