320 THE HUMAN BODY. 



cause feelings of oppression in the chest, or palpitation of 

 the heart. 



The Small Intestine (Fig. 103*)f, commencing at the 

 pylorus, ends, after many windings, in the large. It is 

 about six meters (twenty feet) long, and about five centi- 

 meters (two inches) wide at its gastric end, narrowing to 

 about two thirds of that width at its lower portion. Exter- 

 nally there are no lines of subdivision on the small intes- 

 tine, but anatomists arbitrarily describe it as consisting of 

 three parts; the first twelve inches being the duodenum, D, 

 the succeeding two fifths of the remainder the jejunum, J 9 

 ind the rest the ileum, L 



Like the stomach, the small intestine possesses four coats; 

 a serous, a muscular, a submucous, and a mucous. The 

 serous coat is formed by a duplicature of the peritoneum,, 

 but presents nothing answering to the great omentum; this 

 double fold, slinging the intestine as the small omentum 

 slings the stomach, is called the mesentery. The muscular 

 coat is composed of plain muscular tissue arranged in two 

 strata, an outer longitudinal, and an inner transverse or 

 circular. The submucous coat is like that of the stomach; 

 consisting of loose areolar tissue, binding together the mu- 

 cous and muscular coats, and forming a bed in which the 

 blood and lymphatic vessels (which reach the intestine in 

 the fold of the mesentery) break up into minute branches- 

 before entering the mucous membrane. 



The Mucous Coat of the Small Intestine. This is pink, 

 soft, and extremely vascular. It doec not present tempo- 

 rary or effaceable folds like those of the stomach, but is, 

 throughout a great portion of its length, raised up into per- 

 manent transverse folds in the form of crescentic ridges, 

 each of which runs transversely for a greater or less way 

 round the tube (Fig. 98). These folds are the valvulce- 

 conniventes. They are first found about two inches from 

 the pylorus, and are most thickly set and largest in the 

 upper half of the jejunum, in the lower half of which they 

 become gradually less conspicuous; and they finally disappear 

 altogether about the middle of the ileum. The folds 

 serve greatly to increase the surface of the mucous mem- 

 brane both for absorption and secretion, and they also de- 



tP.328. 



