SURGICAL ANATOMY. 337 



EXTERNAL SPHINCTER ANI muscle arises from the apex of 

 the coccyx and the superficial fascia, and is inserted into the 

 perineal centre, blending with the levator am, accelerator urinae, 

 and transversus perinei. It closes the anus. Nerve, fourth 

 sacral. 



INTERNAL SPHINCTER ANI is an aggregation of circular 

 fibres of the intestine, forming a muscular ring one inch in 

 breadth, surrounding the lower portion of the rectum. 



SPHINCTER TERTIUS is a ring of fibres described by Hertyl 

 and others, arising from the sacrum and surrounding the rectum 

 about four inches above the anus. 



FIG. 171. 



Female perineum: A, anus; B, bulbo-vaginal; C, coccyx; G, glu- 

 teus maximus; P, perineal body; U, urethra; V, vagina; G, vulvo- 

 vaginal gland; 1, clitoris; 2, its suspensory ligament; 3, crura clito- 

 ridis; 4, erector clitoridis; 5, bulbo-cavernosus; 7, transversus periuaei; 

 8, sphincter ani; 9 and 10, levator ani; 11, coccygeus; 12, obturator 

 externus. 



ANAL ELEVATOR (levator ani) arises in front from body 

 and ramus of pub is and symphysis, posteriorly from spine of 

 ischium, and on cither side from angle of arcus tendinse (white 

 line). It is inserted by posterior fibres into coccyx, and ante- 

 rior fibres into the muscle of opposite side in a median m />/((' 

 extending from coccyx to anus; middle liluvs into rectum, join- 

 ing with sphincter; anterior to prostate, blending with external 

 sphincter and transverse fascia. In the female it is inserted into 

 the vagina instead of the prostate. 



