THE LARGE INTESTINE. 



929 



near the commencement of the rectum, on the right side ; another extends inward 

 from the left side of the tube, opposite the middle of the sacrum ; the largest and 

 most constant one projects backward from the fore part of the rectum, opposite the 

 base of the bladder. When a fourth is present, it is situated about an inch above 

 the anus on the back of the rectum. These folds are about half an inch in width, 

 and contain some of the circular fibres of the gut. In the empty state of the intes- 

 tine they overlap each other, as Houston remarks, so effectually as to require con- 

 siderable maneuvering to conduct a bougie or the finger along the canal of the 

 intestine. Their use seems to be " to support the weight of fecal matter, and 

 prevent its urging toward the anus, where its presence always excites a sensation 

 demanding its discharge." 



As in the small intestine, the mucous membrane consists of a muscular layer, 

 the muscularis rnucosae ; of a quantity of retiform tissue in which the vessels 

 ramify ; of a basement-membrane and epithelium, which is of the columnar variety, 

 and exactly resembles the epithelium found in the small intestine. The mucous 

 membrane of this portion of the bowel presents for examination simple follicles and 

 solitary glands. 



The simple follicles are minute tubular prolongations of the mucous membrane 

 arranged perpendicularly, side by side, over its entire surface ; they are longer, 

 more numerous, and placed in much closer apposition than those of the small intes- 

 tine ; and they open by minute rounded orifices upon the surface, giving it a cribri- 

 form appearance. 



The solitary glands (Fig. 510) in the large intestine are most abundant in the 

 ccecum and vermiform appendix, but are irregularly scattered also over the rest of 

 the intestine. They are similar to those of the small intestine. 



Surface of mucous membrane, 

 u'ith. openings of Lieberkilhn't 

 follicles. 



Lieberkiihn's folliclet. 



Muscularis mucosa (two layers). 

 Submucous connective tissue. 



Fotilnry (/land 



FIG. 510. Minute structure of large intestine. 



Vessels and Nerves. The arteries supplying the large intestine give off large 

 branches, which ramify between the muscular coats supplying them, and, after 

 dividing into small vessels in the submucous tissue, pass to the mucous membrane 

 The rectum is supplied mainly by the superior hemorrhoidal branch of the inferior 

 mesenteric, but also at its lower end by the middle hemorrhoidal from the internal 

 iliac, and the inferior hemorrhoidal from the pudic artery. The superior hemor- 

 rhoidal, the continuation of the superior mesenteric, divides into two branches, which 

 run down either side of the rectum to within about five inches of the qnus ; they 

 here split up into about six branches, which pierce the muscular coat and descend 

 between it and the mucous membrane in a longitudinal direction, parallel with 

 each other as far as the Internal sphincter, where they anastomose with the other 

 hemorrhoidal arteries and form a series of loops around the anus. The veins of 



59 



