THE SMALL INTESTINE 119 



and to its different parts have been given appropriate 

 regional names. The part next to the stomach, and con- 

 tinuing for some twenty feet from the pyloric orifice, is 

 all included under the name small intestine. It varies in ' 

 diameter from two inches at the stomach end to less than 

 an inch where it enters the large intestine. By large 

 intestine we include the five odd feet of tube extending 

 from the point where the small intestine is considered to 

 end to the anus. This portion of the tract has a diam- 

 eter of from two and a half to one and a half inches. The 

 relative position, size, and general arrangement of the two 

 intestines are shown in Fig. 39. 



The small intestine. — (See Ex. XXXII.) The entire 

 part of the alimentary canal included under the name of 

 small intestine is held in place by a fold of the peritoneum 

 called the mesentery. This mesentery is about four inches 

 in length at its back edge where it is fastened to the spinal 

 column, and widens to twenty feet at its outer edge. The 

 intestine is hung in this fold like an arm iij. a sling, and 

 the outer edge of the mesentery and the intestine are very 

 much coiled and folded to confine this long tube to the 

 space adapted for it. The different regions of the small 

 intestine are indicated by three names. The twelve inches 

 nearest the stomach receive the name of duodenum, the 

 succeeding two fifths is caUed the jejunum, and the re- 

 mainder is called the ileum. These names are mainly 

 useful in permitting us to designate special parts of the 

 tube. 



Like the stomach the small intestine has four coats (see 

 Ex. XLT.) or layers, an external serous layer (peritoneum), 

 next inside a muscular layer, inside of this a submucous 

 coat, and a lining of mucous membrane. (See Fig. 40.) 



