THE ISCHIO-KECTAL FOSSA. 



two layers, the more superficial of which is the ordinary subcutaneous fascia, and 

 contains fat, especially in the posterior portion of the space, where it is very 

 abundant and fills the ischio-rectal fossa. The deep layer or fascia of Colles is 

 membranous, and is confined to the anterior part of the space ; it is attached on 

 each side to the rami of the ischium and pubis, and posteriorly to the base of the 

 triangular ligament ; it thus forms a somewhat triangular pouch in the fore part of 

 the perineum, which may modify the course of an extravasation of urine or a 

 collection of pus in this situation. The pouch is, moreover, subdivided posteriorly 

 by a median septum, which extends from the back of the perineum to the scrotum. 

 The hinder part of the perineum is occupied in the centre by the lower end of 

 the rectum, and between this and 

 the ischial tuberosity on each 

 side is a considerable hollow 

 known as the ischio-rectal fossa. 



FIG. 29. DISSECTION OF THE PERINEUM 

 IN THE MALE. (Allen Thomson. ) ^ 



The right side shows a superficial, the 

 left a deeper view. 



a, anus, with a part of the integu- 

 ment surrounding it ; b, left half of the 

 bulb of the corpus spongiosum, exposed 

 by the removal of the bulbo-cavernosus 

 muscle ; c, coccyx ; d, right ischial tube- 

 rosity ; e, e, superficial perineal fascia ; 

 /, fat occupying the right ischio-recta! 

 fossa ; g, gluteus maximus muscle ; 1, 

 on the right transversus perinei muscle, 

 points to the superficial per ineal' artery 

 as it emerges in front (in this case) of 

 the muscle ; 1', on the left side, on the 

 . surface of the triangular ligament, points 

 to the superficial perinea] artery cut 

 short ; 2, on the right ischio-cavernosus 

 muscle, points to the superficial perineal 

 artery and nerves passing forwards ; 2', 

 on the left side, the same vessel and 

 nerves divided ; 3, on the right half of 

 the triangular ligament, points to the 

 transverse perineal artery ; 4, on the left 

 ischial tuberosity, points to the pudic 

 artery deep in the iscbio-rectal fossa ; 

 5. 5', inferior haemorrhoidal branches of 

 the pudic arteries and nerves ; 6, on the 

 left side, placed in a recess from which 

 the inferior layer of the triangular liga- 

 ment has been removed, in order to show 

 the continuation of the pudic artery, its 

 branch to the bulb, and Cowper's gland. 



The ischio-rectaltfossa is a hollow of an irregularly pyramidal shape. Its 

 base is turned downwards, and measures about two inches (5 cm.) from before 

 back, and one inch (2'5 cm.) from side to side. Its outer wall is nearly perpen- 

 dicular, and is formed by the obturator internus muscle covered by its fascia below 

 the level at which the rectovesical fascia is attached to it. The inner wall is 

 oblique in direction and convex towards the fossa ; it is formed by the levator ani 

 muscle, covered by the thin anal fascia, and at the lower part by the external 

 sphincter. Anteriorly, the fossa is limited by the base of the triangular ligament, 

 and posteriorly by the gluteus maximus muscle and the great sacro-sciatic ligament. 

 Its depth is about two inches (5 cm.) from the margin of the tuberosity at the hinder 

 part, where it extends upwards to the ischial spine, the small sacro-sciatic ligament 

 nnd the coccygeus muscle. 



