222 MUSCLES OF THE PERINEUM. 



down the bladder from its attachment to the os pubis, and removed a 

 plexus of veins and the posterior layer of the deep permeal fascia. 



The SPHINCTER ANI is a thin and elliptical plane of muscle closely ad- 

 herent to the integument, and surrounding the opening of the anus. It 

 arises posteriorly in the superficial fascia around the coccyx, and by a 

 fibrous raphe from the apex of that bone ; and is inserted anteriorly into 

 the tendinous centre of the perineum, and into the raphe of the integument, 

 nearly as far forwards as the commencement of the scrotum. 



Relations. By its superficial surface with the integument. By its deep 

 surface with the internal sphincter, the levator ani, the cellular tissue and 

 fat in the ischio-rectal fossa, and in front with the superficial perineal 

 fascia. 



The SPHINCTER ANI INTERNUS is a muscular ring embracing the ex- 

 tremity of the intestine, and formed by an aggregation of the circular 

 fibres of the rectum. 



Part of the levator ani may be seen during the dissection of the anal 

 portion of the perineum, by removing the fat which surrounds the termi- 

 nation of the rectum in the ischio-rectal fossa. But to study the entire 

 muscle, a lateral section of the pelvis must be made by sawing through 

 the pubes a little to one side of the symphysis, separating the bones 

 behind at the sacro-iliac symphysis, and turning down the bladder and 

 rectum. The pelvic fascia is then to be carefully raised, beginning at the 

 base of the bladder and proceeding upwards, until the whole extent of 

 the muscle is exposed. 



The LEVATOR ANI is a thin plane of muscular fibres, situated on each 

 side of the pelvis. The muscle arises from the inner surface of the os 

 pubis, from the spine of the ischium, and between those points from the 

 angle of division between the obturator and the pelvic fascia. Its fibres 

 descend, to be inserted, into the extremity of the coccyx, into a fibrous 

 raphe in front of that bone, into the lower part of the rectum, base of the 

 bladder, and prostate gland. 



In the female, this muscle is inserted into the coccyx and fibrous raphe, 

 lower part of the rectum and vagina. 



Relations. By its external or perineal surface, with a thin layer of 

 fascia, by which, and by the obturator fascia, it is separated from the ob- 

 turator internus muscle ; with the fat in the ischio-rectal fossa, the deep 

 perineal fascia, the levator ani, and posteriorly with the gluteus maximus. 

 By its internal or pelvic surface, with the pelvic fascia, which separates it 

 from the viscera of the pelvis and peritoneum. 



The COCCYGEUS MUSCLE is a tendino-muscular layer of triangular form. 

 It arises from the spine of the ischium, and is inserted into the side of the 

 coccyx and lower part of the sacrum. 



Relations. By its internal or pelvic surface, with the rectum ; by its 

 external surface, with the lesser and greater sacro-ischiatic ligaments. 



The muscles of the perineum in the female are the same as in the male, 

 and have received analogous names. They are smaller in size, and are 

 modified to suit the different form of the organs ; they are 



Constricto- vaginae, Sphincter ani, 



Erector clitoridis, Levator ani, 



Transversus perinei, Coccygeus. 

 Compressor urethrae, 



