ORGANS AND PROCESSES OF DIGESTION 159 



It is a nearly straight tube, from six to eight inches in 

 length, and connects with the external surface of the body. 

 The general structure of the large intestine is similar to 

 that of the small intestine, and, like the small intestine, it 

 is held in place by the peritoneum. It 

 differs from the small intestine, how- 

 ever, in its lining of mucous membrane 

 and in the arrangement of the muscular 

 coat. The mucous membrane presents 

 a smooth appearance and has no villi, 

 while the longitudinal layer of the mus- 

 cular coat is limited to three narrow 

 , , , . FIG. 74. Section 



bands that extend along the greater of large intestinej 



length of the tube (Fig. 74). These showing the coats, i. 

 bands are shorter than the coats, and Serous coat. 2. Cir- 



draw the large intestine into a number cula ' ^yer of muscle ' 



f u 11 u v. u- u -4. j-i 3 ' Submucous coat - 



of shallow pouches, by which it is readily 4 Mucous membrane . 



distinguished from the small intestine 5. Muscular bands ex- 



(Fig- 71 Y . tending lengthwise 



' Work of the Large Intestine. - The over the intestine " 

 large intestine serves as a receptacle for the materials from 

 the small intestine. The digestive fluids from the small 

 intestine continue their action here, and the dissolved 

 materials also continue to be absorbed. In these respects 

 the work of the large intestine is similar to that of the 

 small intestine. It does, however, a work peculiar to itself 

 in that it collects and retains undigested food particles, 

 together with other wastes, and ejects them periodically 

 from the canal. 



Work of the Alimentary Muscles. The mechanical 

 part of digestion is performed by the muscles that encircle 

 the food canal. Their uses, which have already been 

 mentioned in connection with the different organs of 



