452 THE HUMAN BODY 



of the glands, an incomplete layer of larger oval cells (p, Fig. 129). 

 The glands frequently branch at their deeper ends. 



The Pylorus. If the stomach be opened it is seen that the 

 mucous membrane projects in a fold around the pyloric orifice and 

 narrows it. This is due to a thick ring of the circular muscular 

 layer there developed, and forming around the orifice a sphincter 

 muscle, which, by its contraction, keeps the passage to the small 

 intestine closed except when portions of food are to be passed on 

 from the stomach to succeeding divisions of the alimentary canal. 



The Small Intestine (Fig. 136), commencing at the pylorus, 

 ends, after many windings, in the large intestine. It is about six 

 meters (twenty feet) long, and about five centimeters (two inches) 

 wide at its gastric end, narrowing to about two-thirds of that 

 width at its lower portion. Externally there are no lines of sub- 

 division on the small intestine, 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, and the rest the ileum, I. 



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 noth- 

 ing answering to the great omentum; this double fold slinging the 

 intestine is named the mesentery. The muscular coat is composed 

 of plain muscular tissue arranged in two strata, an outer longitu- 

 dinal, and an inner transverse or circular. The submucous coat is 

 like that of the stomach; consisting of loose areolar tissue, binding 

 together the mucous 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 be- 

 fore entering the mucous membrane. 



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

 extremely vascular. It does not present temporary or effaceable 

 folds like those of the stomach, but is, throughout a great portion 

 of its length, raised up into permanent transverse folds in the form 

 of crescentic ridges, each of which runs transversely for a greater 

 or less way round the tube (Fig. 130). 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 



