FEMALE PERINEUM 195 



vagina. Its anterior fibres blend with the posterior fibres of 

 the sphincter of the urethra. The sphincter consists of an 

 internal layer of fibres arranged circularly round the urethra, 

 and an external layer which springs from the pubic arch, 

 anterior to the origin of the deep transverse muscle, and from 

 the inferior fascia of the urogenital diaphragm. As the fibres 

 of this layer approach the median plane some pass in front 

 of the vagina and urethra, and others are attached to the 

 posterior wall of the vagina. Both the above muscles are sup- 

 plied by twigs from the perineal branch of the pudendal nerve. 



Arteria Pudenda Interna et Nervus Pudendus. The 

 internal pudendal artery and the pudendal nerve have a dis- 

 position similar to' the corresponding artery and nerve in the 

 male (see p. 176), but they are smaller and the names 

 of some of their branches are different, in association with 

 the different names of the parts to which they are distri- 

 buted ; thus the posterior labial branches of the perineal 

 division of the pudendal nerve of the female correspond to 

 the posterior scrotal nerves of the male, and the dorsal nerve 

 of the clitoris corresponds to the dorsal nerve of the penis. 

 Similarly the posterior labial branches of the perineal artery 

 of the female correspond to the posterior scrotal arteries of 

 the male ; the artery to the bulb of the vestibule of the 

 female corresponds to the artery to the bulb of the urethra 

 in the male, and the dorsal and deep arteries of the clitoris 

 are homologous with the dorsal and deep arteries of the penis. 



Nervus Perinei. As in the male, the pudendal nerve, as 

 it lies in the posterior part of the canal in the obturator 

 fascia on the lateral wall of the ischio-rectal fossa, gives off 

 its inferior haemorrhoidal branch, and then divides into two 

 branches, the perineal nerve and the dorsal nerve of the 

 clitoris. 



The perineal nerve runs forwards in the canal below the 

 internal pudendal artery, and, near the anterior part of the 

 ischio-rectal fossa, it divides into a superficial and a deep 

 division, both of which pierce the medial wall of the canal 

 and enter the anterior part of the fossa. The superficial 

 division is cutaneous ; it divides into the posterior labial 

 nerves which pierce the base of Colics' fascia and run 

 forwards in the superficial pouch of the urogenital triangle 

 to supply the skin of the labia of the corresponding side. 

 The deep branch is mainly muscular. It supplies twigs to 



ii 13a 



