348 ABDOMEN 



lateral side of the tuber ischiadicum. Having secured these vessels and 

 nerves, clean the distal margin of the glutaeus maximus, and then proceed 

 to dissect the ischio-rectal fossa. If the subject is obese, a considerable 

 quantity of fat may be removed at once without endangering the inferior 

 hasmorrhoidal vessels and nerve. Take the surface of the glutseus maximus 

 and the margin of the external sphincter as guides, and transfix the fat 

 with the knife in this plane. The adipose tissue superficial to this plane 

 may be removed en masse with safety. The hamorrlioidal vessels and 

 nerve may be found by dissecting cautiously in the fat and carrying the 

 knife in an oblique direction, from behind forwards and from the lateral to 

 the medial wall of the space. The perineal branch from the fourth sacral 

 nerve appears by the side of the coccyx. 



Roof of the Space. When the contents of the space are 

 secured, continue to remove the fat from the fossa until its 

 walls are fully displayed. On passing the finger upwards, its 

 passage into the pelvis is prevented by the junction of the 

 anal fascia with the parietal or obturator layer of the pelvic 

 fascia (Fig. 130, p. 346). Further, if the anal fascia be 

 removed, its entrance into the pelvis is still resisted by the 

 levator ani muscle and also by the visceral layer of pelvic 

 fascia, which at this level passes medially on the superior 

 surface of the levator ani. 



Internal Pudendal Vessels (O.T. Internal Pudic) and 

 Piidendal Nerve (O.T. Pudic). The dissector should now 

 pass his finger upwards and downwards, over the surface 

 of the parietal or obturator layer of the pelvic fascia which 

 covers the obturator internus muscle and forms the lateral 

 wall of the ischio-rectal fossa. About an inch and a half 

 above the inferior border of the ischial tuberosity he will 

 feel, very distinctly, the pudendal vessels and nerve as they 

 pass forwards to gain the urethral triangle. In this position 

 they are enclosed in a tube or sheath formed by the parietal 

 pelvic fascia. This fascial tunnel is called Alcock's canal. 

 The student must for the present be satisfied with palpating 

 these structures. To expose them would necessitate the 

 division of the parietal part of the pelvic fascia, and this 

 should be kept entire until the pelvic fascia can be studied 

 as a whole. 



Arteriae Hsemorrhoidales Inferiores. The inferior haemor- 

 rhoidal arteries, usually two or three in number, are branches 

 of the internal pudendal. They pierce the medial wall of 

 Alcock's canal, and pass medially through the fat of the 

 ischio-rectal fossa to supply the anal canal and the muscles 

 in connection with it, as well as the skin around the anus. 



