208 SURGICAL ANATOMY OF 



reeled obliquely from below upwards and forwards, and 

 afterwards, upwards and backwards. 



A dilated condition of the inferior haBmorrhoidal 

 veins at the lower part of the anus constitutes external 

 piles. 



The superficial fascia, tough and strong, and contain- 

 ing a great deal of fat, has cutaneous vessels and nerves 

 passing through it. The external sphincter muscle is 

 seen attached posteriorly to the tip of the coccyx, and 

 inclosing the margin of the anus, is inserted into the 

 central tendon before mentioned. This circular band of 

 fibres is about one inch in breadth. Between the bowel 

 and the tuberosities of the ischium is the ischio-rectal 

 fossa, which contains a quantity of loose fat and cellular 

 tissue, and lying across it, and passing to the margin of 

 the anus, are the superficial hsemorrhoidal vessels and 

 nerves, which are liable to give a good deal of trouble 

 from hemorrhage, when cut in operations for fistula, &c. 

 On cleaning out the space its shape and boundaries can 

 be defined. In shape it is somewhat triangular, about 

 an inch in width, and about two inches deep ; inferiorly 

 its base is formed by the integuments of the region, and 

 its apex, directed upwards, corresponds to the interval 

 between the lower border of the obturator internus, 

 covered by the obturator fascia, and the outer surface of 

 the levator ani, covered by the anal fascia. Its bounda- 

 ries are, externally, the tuberosity of the ischium and 

 obturator fascia; internally, the sphincter ani, levator 

 ani, covered by anal fascia, and coccygeus ; anteriorly, 

 the triangular ligament ; and posteriorly, the gluteus 

 maximus and great sacro-sciatic ligament. 



Lying in a fold derived from the obturator fascia, on 

 the outer wall of the fossa, the trunks of the internal 



