THE EECTUM. 379 



but both layers become darker and redder towards the termination of 

 the bowel. 



The tmicous momlrane of the rectum is thicker, redder, and more 

 vascular than that of the colon ; and it moves more freely upon the mus- 

 cular coat ; — in this respect resembling the lining membrane of the 

 oesophagus. It preseuts numerous folds of diflFerent sizes, and running 

 in various directions, nearly all of which are effaced by the distension of 

 the bowel. Xcar the anus these folds are principally longitudinal, and 

 seem to depend on the contraction of the sphincter muscles outside the 

 loosely connected mucous membrane. The larger of these folds were 

 named by Morgagni the columns of the rectum {columiuc rorii). These 

 columns contain longitudinal muscular fibres (apparently part of tlie 

 muscularis mucosae), which terminate both superiorly and inferiorly in 

 elastic tissue (Trcitz). Higher up in the intestine, the chief folds are 

 transverse or oblique. Three prominent folds, larger than the rest, 

 l^eing half an inch or more in depth, and having an oblique direction 

 in the interior of the rectum, have been pointed out specially by 

 Houston. One of these projects backwards from the upper and fore 

 part of the rectum, opposite the prostate gland ; another is placed higher 

 up, at the side of the bowel ; and the third still higher. From the 

 position and projection of these folds, they may more or less impede 

 the introduction of instruments (Dublin Hospital Eeports, vol. v.). 



Vessels and Nerves of the Recttim. — Tlie artcricx of the rectum spring 

 from three sources, viz., the superior hemorrhoidal branches from, the inferior 

 mesenteric ; the middle hajmorrhoidal branches from tlie internal iliac directly 

 or indirectly ; and, lastly, the external or inferior haimorrhoidal branch from the 

 pudic artery. The aiTangement of the vessels is not the same tlu-oughout the 

 rectum. Over the greater part the arteries penetrate the muscular coat at short 

 intervals, supplying its layers as they pass through, and, at once dividing into 

 small branches in the submucosa, fonn a network by their inter-communication. 

 Towards the lower end, for foiu' or five inches, the arrangement is different. Here 

 the vessels, having penetrated the muscular coat at different heights, assume 

 a longitudinal dii-ection. passing in pai-allel lines towards the end 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 considerable size. (Quain, Diseases of the Rectum.) 



The veins are very numerous, and fonn a complex interlacement resembling 

 that of the ax-teries just described, and named the lia'inorvho'uJal 2>lcxus. After 

 following a longitudinal coiu'se upwards similar to that of the arteries which 

 tliey accompany, they end partly in the internal iliac vein by branches which 

 accompany the middle ha3morrlioidal artery, and partly in the inferior mesenteric 

 vein. Hence, the blood from the rectum is returned in jjart into the vena cava, 

 and in part into the portal system. 



The lijmplKitica enter some glands placed in the hollow of the sacram, or those 

 of the lumbar series. 



The nerves are very numerous, and are derived from both the cerebro-spinal 

 and the sjanpathetic systems. Tlie fonner consist of branches derived from the 

 sacral plexus ; and the latter, of offsets from the inferior mesenteric and hypo- 

 gastric plexuses. 



THE ANUS AND ITS MUSCLEH. 



The anus, or lower opening of the alimentary canal, is a dilataljle 

 orifice, surrounded internally by the mucous membrane, and externally 

 by the skin, which tw^o structures here become continuous with and 

 pass into each other. The skin around the borders of the anus, which 



