6i4 A MANUAL OF ANATOMY 



wall about i^ inches above the lower part of the tuber ischii, 

 and they are contained in Alcock's canal. The inferior hemor- 

 rhoidal vessels and nerve cross the fossa transversely from the 

 outer wall to the anal canal. The superficial perineal vessels and 

 nerves on their way forwards lie for a short distance in the front 

 part. At the back part of the fossa, winding round the lower border 

 of the gluteus maximus, the gluteal cutaneous branches of the 

 small sciatic nerve and sciatic artery, as well as the perforating 

 cutaneous branch of the sacral plexus, are met with. 



The fossa is filled with loose fat, which also extends into the 

 anterior and posterior diverticula. 



This fat is badly supplied with bloodvessels, and its vitality is therefore 

 low. As a consequence, an ischio-rectal abscess is of not infrequent occur- 

 rence. When an abscess forms, the pus has a tendency to discharge itself 

 in two directions, namely, through the skin forming the floor of the fossa, 

 and through the wall of the anal canal about half an inch above the anus. 

 When this happens a complete fistula in ano is the result. 



The severe pain which accompanies an ischio-rectal abscess is due to 

 pressure upon the following nerves : (i) the inferior hemorrhoidal ; (2) the two 

 superficial perineal nerves ; and (3) the gluteal cutaneous branches of the small 

 sciatic. 



Uro-Genital Division. 



Superficial Fascia. — ^The superficial fascia resembles that over the 

 lower part of the anterior wall of the abdomen in being divisible 

 into two layers, which are called the subcutaneous layer and the 

 deep layer or fascia of Colles. 



The subcutaneous layer is fatty and granular. When followed 

 backwards on either side it forms the floor of the ischio-rectal 

 fossa. At the middle line it is continuous with the corresponding 

 layer of the opposite side. Externally it passes freely over the 

 ischio-pubic ramus, and is continuous with the superficial fascia of 

 the inner side of the thigh. Anteriorly it passes into the scrotum, 

 where it joins the deep layer or fascia of Colles. The resultant 

 fascia, now free from adipose tissue, contains involuntary muscular 

 tissue, and forms the tunica dartos. The subcutaneous layer 

 represents the fascia of Camper of the lower part of the anterior 

 abdominal wall. 



The deep layer constitutes the fascia of Colles. It is mem- 

 branous and strong. Externally, it is attached to the anterior 

 everted lip of the inner border of the ischio-pubic ramus, as far 

 back as the tuber ischii, immediately outside the attachment of 

 the crus penis. Internally, the fascia of one side is continuous with 

 that of the other along the middle line. Posteriorly, the fascia 

 turns round the posterior border of each superficial transverse 

 perineal muscle, and joins the base of the triangular ligament. 

 Anteriorly, it passes into the scrotum, where it joins the sub- 

 cutaneous layer, the two forming the tunica dartos. 



The fascia of Colles represents the fascia of Scarpa of the anterior 

 abdominal wall. It encloses a space over the anterior division of 

 the perineum, called the perineal pouch. This pouch is partially 



