THE SMALL INTESTINE 141 



The muscular coat comprises two layers (like the esophagus), 

 an inner layer of circular fibers, an outer one of longitudinal 

 fibers. 



The intestine is divided into the following parts: 



Duodenum f Cecum 



( Ascending 



Small intestine Jejunum Large intestine { Colon Transverse 



( Descending 



Ileum I Rectum 



The Small Intestine 



The small intestine is about twenty feet in length, and about 

 two inches wide in its upper (widest) part. It extends from the 

 stomach to the colon, beginning with the pyloric sphincter in the 

 right hypochondrium and ending with the ileo-colic sphincter in 

 the right iliac region. 



The mucous coat of the small intestine forms circular folds 

 (old name, valvulae conniventes) which are permanent, that is, 

 they never disappear however widely the bowel may be distended. 

 They serve to increase the area of mucous membrane for purposes 

 of digestion and absorption (Fig. 108). This layer contains the 

 intestinal glands. 



The entire mucous coat is covered with tiny projections hair- 

 like in. size (from 1/2 to i mm. long) called villi, which give it a 

 velvety appearance (Fig. 107). 



The villi are absorbing structures or absorbents. (They may 

 be demonstrated in a good light by laying a piece of intestinal wall 

 in a shallow tray of clear water; the water will float their free 

 extremities.) 



In the midst of each villus is a minute lymph capillary, surrounded by a 

 fine network of blood-vessels and lymph spaces, the whole covered by a layer 

 of the special epithelium of the intestine. Lymph vessels of villi are called 

 lacteals because during digestion they contain a milky-looking fluid. 



The muscular coat is in two layers circular within, longitudinal 

 without pretty evenly distributed. 



The serous coat covers all except a portion of the first division 

 (see duodenum). 



The duodenum is the first division of the small intestine 



