740 ORGANS OF DIGESTION. 



peritoneal coat is thrown into a number of small pouches filled with fat, called 

 appendices epiploicse. They are chiefly appended to the transverse colon. 



The muscular coat consists of an external longitudinal and an internal circular 

 layer of muscular fibres. 



The longitudinal fibres are found as a uniform layer over the whole surface of 

 the large intestine. In the caecum and colon, they are especially collected into 

 three flat longitudinal bands, each being about half an inch in width. These 

 bands commence at the attachment of the appendix vermiformis to the csecum ; 

 one, the posterior, is placed along the attached border of the intestine ; the ante- 

 rior band, the largest, becomes inferior along the arch of the colon, where it 

 corresponds to the attachment of the great omentum, but is in front in the 

 ascending and descending colon and sigmoid flexure ; the third, or lateral band, 

 is found on the inner side of the ascending and descending colon, and on the 

 under border of the transverse colon. These bands are nearly one-half shorter 

 than the other parts of the intestine, and serve to produce the sacculi which 

 are characteristic of the caecum and colon; accordingly, when they are dis- 

 sected off, the tube can be lengthened, and its sacculated character becomes lost. 

 In the sigmoid flexure, the longitudinal fibres become more scattered, but upon 

 its lower part, and round the rectum, they spread out, and form a thick uniform 

 layer. 



The circular fibres form a thin layer over the caecum and colon, being espe- 

 cially accumulated in the intervals between the sacculi ; in the rectum, they 

 form a thick layer, especially at its lower end, where they become numerous, 

 and form the Internal Sphincter. 



The cellular coat connects the muscular and mucous layers closely together. 

 The mucous membrane, in the caecum and colon, is pale, and of a grayish or 

 pale yellow color. It is quite smooth, destitute of villi, and raised into nume- 

 rous crescentic folds, which correspond to the intervals between the sacculi. In 

 the rectum, it is thicker, or of a darker color, more vascular, and connected 

 loosely to the muscular coat as in the oesophagus. When the lower part of the 

 rectum is contracted, its mucous membrane is thrown into a number of folds, 

 some of which near the anus, are longitudinal in direction, and are effaced by 

 the distension of the gut. Besides these, there are certain permanent folds of a 

 semilunar shape, described by Mr. Houston. 1 They are usually three in num- 

 ber ; sometimes a fourth is found, and, occasionally, only two are present. One 

 is situated near the commencement of the rectum, on the right side ; another 

 extends inwards from the left side of the tube, opposite the middle of the sa- 

 crum ; the largest and most constant one projects backwards 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 intestine they overlap each other, as Mr. 

 Houston remarks, so effectually as to require considerable manoeuvring to con- 

 duct 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 towards 

 the anus, where its presence always excites a sensation demanding its discharge." 

 The mucous membrane of the large intestine presents for examination, epithe- 

 lium, simple follicles, and solitary glands. 

 The epithelium is of the columnar kind. 



The simple follicles are minute tubular prolongations of the mucous mem- 

 brane, 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 intestine; and they open by minute rounded orifices upon the surface, 

 giving it a cribriform appearance. 



The solitary glands in the large intestine are most abundant in the caecum 



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1 Dub. Hosp. Reports, vol. v. p. 163. 



