MUSCLES OF THE PERINEUM. 261 



bladder. At the place where it is reflected inwards to the side of the 

 bladder, it forms the lateral true vesical ligament. At the side of the 

 bladder and prostate, the recto-vesical fascia gives a prolongation forwards 

 on the veins (prostatic) which cover the prostate, and is firmly adherent to 

 the capsule of that organ, except at its ba*e, where an angular furrow, 

 occupied by large veins, exists between the prostate and bladder, into this 

 furrow the incision for lithotomy ought not to extend, on account of the 

 danger from wounding the veins and from the infiltration of urine. A 

 portion of the recto-vesical fascia invests the vesiculse seminales, and is 

 extended across between the bladder and the rectum ; continuing into 

 the membrane of the opposite side, it supports the bladder, and separates 

 that organ from the intestine. On the rectum the fascia is also reflected 

 upwards and downwards, gradually degenerating into a thin membrane over 

 the surface of the bowel, as it likewise does on the bladder. 



c. The obturator fascia is a membrane stretched over the lower part of 

 the surface of the obturator internus muscle within the pelvis. It is 

 connected superiorly with the white band before referred to, which consists 

 indeed of its superior fibres, and it is attached in the rest of its circumference 

 to the rami of the pubis and ischium, the ischial tuberosity, and the greater 

 and lesser sacro-sciatic ligaments. It lies between the obturator internus 

 muscle and the ischio-rectal fossa, and presents in its substance towards 

 the muscle a canal, which contains the internal pudic artery and nerve in 

 their course to the perinseum. 



The obturator fascia is sometimes included in the description of the pelvic fascia, 

 while the recto-vesical is considered as an offset from it. It will be found, however, 

 on dissection, that the recto-vesical fascia is always most directly continuous with the 

 pelvic fascia, and that the obturator fascia is only loosely connected with it. Indeed, 

 the fibres of the levator ani muscle in most cases pass upwards to some extent beyond 

 the white line, and thus separate the obturator from the pelvic fascia. 



The ischio-rectal fossa is a pyramidal space occupied by subcutaneous fat. 

 It is bounded externally by the obturator fascia, posteriorly by the gluteus 

 maximus muscle and great sacro-sciatic ligament, and internally by the 

 recto-vesical fascia ; anteriorly, its base is limited by the margin of the 

 perinseal and the subpubic fasciae. 



In the female, the pelvic fascia is connected with the vagina in the same 

 manner as with the other pelvic organs. 



MUSCLES OF THE PERINEUM. 



The muscles of the perinseum differ somewhat in the two sexes, and must 

 therefore be separately described in each. In both sexes they may be 

 divided into two groups, according as they are more immediately connected 

 with the lower orifice of the alimentary canal or with the genito-urinary 

 outlet. In both groups superficial and deep muscles are to be distin- 

 guished. 



A. IN THE MALE. 



a. ANAL GROUP. The internal or circular sphincter is a thick ring of 

 uustriped muscle connected with the lowest circular fibres of the rectum, 

 which will fall more naturally to be considered along with the anatomy of 

 that organ. 



