906 A MANUAL OF ANATOMY 



show the fibres of the obturator internus muscle. In dissecting the inner wall 

 of the fossa the anal or ischio-rectal fascia is to be studied, and thereafter 

 removed to show the levator ani muscle descending upon the side of the rectum 

 and anal canal. Posterior to the levator ani is the coccygeus, and emerging 

 between the two will be found the hemorrhoidal or perineal branch of the 

 fourth sacral nerve. Under cover of the lower border of the gluteus maximus 

 there should be shown the inferior border of the great sacro-sciatic ligament. 

 The anterior limit of the fossa is not to be disturbed in the meantime, but the 

 dissector should make himself aware that it is partially limited by the reflection 

 of Colles's fascia round the superficial transverse perineal muscle to join the 

 base of the triangular ligament. 



The ischio-rectal fossa having now been displayed, the following points 

 in connection with it are to be noted : its measurements, including its depth ; 

 its boundaries, and, in connection with the outer boundary, the position of 

 the internal pudic vessels, and in connection with the inner boundary, the 

 rectum and anal canal ; the loose fat which fills the fossa ; the inferior hemor- 

 rhoidal vessels and nerve crossing the fossa from side to side ; and the super- 

 ficial perineal artery and two superficial perineal nerves in the anterior part 

 of the fossa, passing in a forward direction. It is further to be observed 

 that there are two prolongations or diverticula connected with the fossa, 

 anterior and posterior. The anterior diverticulum is to be found at the front 

 part of the fossa above the junction of Colles's fascia with the base of the 

 triangular ligament. It is of large size, and reaches almost as far forwards as 

 the symphysis pubis, but it will be better understood in the deep dissection 

 of the anterior part of the perineum. The posterior diverticulum will be 

 found between the great sacro-sciatic ligament and the lower border of the 

 gluteus maximus, its direction being outwards and inwards. 



The dissector is now to turn his attention to the anterior or uro-genital 

 division of the perineum. The arrangement of the superficial fascia is to 

 receive careful attention. It can easily be shown to be divisible into a sub- 

 cutaneous fatty layer, having no special name, and a deep membranous layer, 

 known as the fascia of Colles. The subcutaneous fatty layer is traceable 

 backwards over and into the ischio-rectal fossa, outwards to the inner 

 aspect of the thigh, and forwards into the scrotum, where it will be again 

 noticed. The fascia of Colles has an important bearing upon the course taken 

 by urine when extra vasated into the anterior part of the perineum. The 

 disposition of this fascia is best studied by inserting the end of a blow-pipe 

 underneath it at its back part, on one side of the middle line. Air having 

 been blown in, the fascia will be seen to be attached externally to each ischio- 

 pubic ramus ; posteriorly it turns round the posterior border of each super- 

 ficial transverse perineal muscle to join the base of the triangular ligament ; 

 internally (towards the median line) it is continuous with the corresponding 

 fascia of the opposite side ; and anteriorly it passes into the scrotum, where 

 it joins the subcutaneous fatty layer, and forms the tunica dartos. Inflation 

 with air reveals the fact that beneath the fascia there is a space known as the 

 perineal pouch, which is divided posteriorly into two compartments by an 

 incomplete septum. This is demonstrated by the air at first passing forwards 

 on its own side, then crossing the median line, and travelling backwards on 

 the opposite side. Further, the air passes forwards into the scrotal wall 

 beneath the dartos tunic. The attachments of the fascia of Colles clearly 

 explain in what direction extravasated urine can only pass, and from what 

 courses it is debarred. 



Beneath Colles's fascia the following structures are to be dissected on each 

 side, namely, the superficial perineal vessels and the three long scrotal nerves. 

 The two superficial perineal nerves will be found entering the perineal pouch 

 at its back part, and the long pudendal nerve of Soemmering will be found 

 appearing through the fascia lata of the thigh about an inch in front of the 

 tuber ischii, after which it passes inwards and forwards, entering the perineal 

 pouch from the outer side. All these structures are to be dissected forwards 

 to the scrotum. The following structures are next to be dissected : the bulbo- 

 cavernosus, covering the bulb in the middle line ; the ischio-cavemosus, 



