420 SuRGfCAL ArrLiED ANATOMY. [Chap. xvm. 



long enema tube, and their position should be therefore 

 borne in mind. 



The vessels, and especially the veins, at the lower 

 part of the rectum, are apt to become varicose and 

 dilated, and form piles. The tendency to piles can 

 in part be explained by the dependent position of the 

 rectum, by the pressure effects of hardened faeces 

 upon the returning veins, and by the fact that part 

 of the venous blood returns through the systemic 

 system (internal iliac vein) and part through the 

 portal system (inferior mesenteric vein). This con- 

 nection with the portal trunk causes the rectum to 

 participate in the many forms of congestion in- 

 cident to that vein. The veins of the rectum, also, 

 can be affected by violent expiratory efforts. For 

 the last four inches, moreover, of the bowel, the ar- 

 rangement of the vessels is peculiar, and is such as to 

 favour varicosity. The arteries, "having penetrated 

 the muscular coats at different heights, assume a longi- 

 tudinal direction, passing in parallel lines towards the 

 edge of the bowel. In their progress downwards they 

 communicate with one another at intervals, and they 

 are very freely connected near the orifice, where all 

 the arteries join by transverse branches of consider- 

 able size " (Quain). The veins form a plexus with a 

 precisely similar arrangement. 



A LUIS. The skin about the anus is thrown into 

 numerous folds, and it is in these that the ulcer 

 or fissure of the anus forms. The extreme painful- 

 ness of these ulcers is due to the exposure of a nerve- 

 fibre at their base, and to the constant contraction of 

 the sphincter muscle that they excite. Relief is given 

 by incising the base of the ulcer, so as to divide 

 some part of the sphincter ; or by violently dilating 

 the anus, so as to tear up the base of the ulcer and 

 paralyse for a while the action of the disturbing 

 muscle. A fine white line around the anus, at the 



