132 THE ALIMENTARY SYSTEM. 



layers of involuntary muscle, a thick inner circular layer, and 

 a thinner outer longitudinal layer. Between these two is the 

 nerve-plexus of Auerbach. 



The serous or peritoneal coat is the portion of the peri- 

 toneum reflected over the intestine to form its outer covering. 



The intestine is w r ell supplied with blood and lymphatic 

 vessels, the larger channels of which are in the submucosa and 

 send capillary plexuses into the mucosa. The lacteals con- 

 stitute an important origin of the lymphatic system. 



The intestine is also supplied with two plexuses of nerves ; 

 the plexus of Auerbach is a network of fibres with minute 

 ganglia at their intersections, situated between the two layers 

 of the muscular coat ; the plexus of Meissner, situated in the 

 submucous coat, is connected with and similar to that of 

 Auerbach, but is made up of finer fibres and finer meshes. 



The Large Intestine. 



The large intestine has four coats, mucous, submucous, 

 muscular, and serous, and contains glands of Lieberkiihn and 

 solitary glands. It resembles the iletim in structure, but has 

 no villi or Peyer's patches, and the outer muscular coat is dif- 

 ferently arranged. 



Its mucosa, lined with simple columnar epithelium, is every- 

 where studded with Lieberkiihn's follicles, supported in a 

 delicate subepithelial retiform tissue, which is well supplied 

 with diffuse lymphoid tissue, capillaries, and lymphatics. 



The glands of Lieberkuhn are rather larger than in the 

 small intestine, but are lined with similar cells, among which, 

 however, goblet-cells are much more abundant. 



The muscularis mucosce, vascular and nervous plexuses, sub- 

 mucous and peritoneal coats are much the same as in the small 

 intestine, and solitary glands are abundant. 



The muscular coat has the usual inner circular layer, rather 

 thin in most places. The outer layer of longitudinal, non- 

 striated muscle, however, instead of forming a complete sheet, 

 is limited to three longitudinal bands, which are shorter than 

 the other structures, and thus cause the colon to be puckered 

 or sacculated. 



