THE PELVIS 369 



of sciatica. The lower third of the rectum rests on the pelvic 

 floor (p. 356) and is surrounded by the rectal layer of the visceral 

 pelvic fascia. 



The hypogastric (internal iliac) vessels,, and lymph glands 

 and the ureters are related to the sides of the rectum, but the 

 latter are only in contact with its wall when the gut is con- 

 siderably distended. 



Structure of the Rectum. The submucous coat consists of very loose 

 areolar tissue, and, as a result, the mucous coat may become prolapsed through 

 the anus, following violent straining. 



The circular muscular coat forms a complete covering for the gut but 

 the longitudinal coat is arranged in two broad bands, which lie one on its 

 anterior and the other on its posterior surface. The shortness of these bands, 

 relative to the length of the mucous and circular muscular coats, accounts for 

 the production of the lateral flexures of the rectum. 



The Anal Canal, which is about one and a half inches long, 

 passes downwards and backwards from the rectal ampulla to the 

 anus. Except during defaecation, its walls are kept in apposition 

 by the action of the levatores ani and sphincter muscles. The 

 sides of the anal canal are in relation to the elastic pads of fat 

 which occupy the ischio-rectal fossae (p. 373). Anteriorly, the 

 anal canal is related to the urogenital diaphragm, the 

 membranous part of the urethra and the bulb of the penis 

 (Fig. 115). The surgeon takes advantage of this relation when 

 he is negotiating a bougie through a difficult stricture of the 

 urethra. By inserting the forefinger of his left hand into the 

 rectal ampulla, he can control the point of the instrument and 

 can recognise at once if it is making a " false passage." Further, 

 in supra-pubic prostatectomy, the enucleating finger of the 

 right hand within the bladder will be greatly assisted if the 

 surgeon passes his left forefinger into the ampulla of the rectum. 



The recto-urethralis muscle extends from the anterior surface 

 of the upper end of the anal canal to the superior fascia of the 

 urogenital diaphragm. When it has been cut transversely, 

 the finger can be inserted into a loose cellular interval which 

 lies between the rectum and the prostate, and these two viscera 

 can then be easily separated. Section of the recto-urethralis 

 is an important step in the operations of prostatectomy and 

 excision of the rectum by the perineal route (p. 379). 



The muscular coat of the anal canal is very strongly 

 developed. The circular fibres of the rectum are continued 

 downwards to form the internal sphincter, which clothes the 

 upper two-thirds of the canal. The levatores ani lie external 



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