1678 



HUMAN ANATOMY. 



the descending faeces, while at other times, by its antero-posterior fibres, it may 

 compress the sides of the gut. To the action of the levator is probably due the 

 control of the faeces which sometimes persists after division of the sphincter, unless, 

 indeed, the upper part of the latter has escaped. 



The Ischio-Rectal Fossa. — This space is a deep, roughly pyramidal hollow, 

 filled chiefly with fat, on either side of the rectum. The base is at the skin between 

 the tuberosity of the ischium and the anus, bounded in front by the line of reflection 

 of the deep perineal fascia and behind by the great sacro-sciatic ligament and the 

 edge of the gluteus maximus. The base measures some 5 cm. (2 in.) from before 

 backward and half as much crosswise. The fossa is bounded externally by the tuber- 

 osity of the ischium and above the latter by the obturator fascia, internally by the 

 external sphincter and the under surface of the levator ani. The space narrows 

 above to a line at the splitting of the pelvic fascia ; hence it can only vaguely be 

 called pyramidal. The depth of the fossa is about 5 cm. (2 in.). 



Venous plexus 

 Pelvic fascia 



Fig. 1426. 



Anterior wall of bladder 



Superior pubic ramus 



Diaphragmatic 

 fascia 



Obturator fascia 



Levator ani 



Gluteus maximus 

 Ischio-rectal fossa 



Obturator inlernus 



>a^ Obturator 

 >.' - ' membrane 



Obturator externus 



Tuberosity of 

 ischium 



Rectum 



External sphincter 



Internal sphincter 



Oblique transverse section through pelvis in plane shown in small outline figure. 



The diaphragmatic fascia, the inward continuation of the pelvic fascia which 

 covers the upper surface of the levator ani, reaches the side of the rectum as a bed 

 of areolar tissue beneath the peritoneum, and is more or less closely attached to the 

 gut, sometimes by muscular bands, as already stated. The systematic description 

 of this fascia 13 given elsewhere (page 559). 



The rectal fascia is a dense layer of areolar tissue surrounding the rectum 

 below the reflection of the peritoneum, being continuous below with the preceding 

 fascia. It is particularly dense behind the rectum, which it separates from the 

 sacrum and coccyx. 



The anal fascia is a web-like areolar sheet covering the under side of the 

 levator ani. 



A superficial fascia between the skin and the base of the ischio-rectal fossa 

 can be artificially dissected, but is of little importance. 



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