182 



ANATOMY FOB, NUKSES. 



[CHAP. XV. 



oped, obliquely disposed fibres. The alternate contraction and 

 relaxation of these fibres causes the food to be carried round 

 and round the stomach, and at the same time, subjects it to 

 considerable pressure. 



The mucous membrane is very soft and thick, the thickness 

 being mainly due to the fact that it is densely packed with small 

 tubular glands ; it is covered with columnar epithelium, and in 

 its undistended condition is thrown into folds or rugse. The 

 surface is honeycombed with tiny shallow 

 pits, into which the ducts or mouths of the 

 tubular glands open. The glands are of 

 two kinds, one kind secretes mucus, and the 

 other the special secretion of the stomach, 

 the gastric juice. The stomach is supplied 

 with nerves from the sympathetic system, 

 and also with branches from the pneumo- 

 gastric nerve, which comes from the cerebro- 

 spinal system. 



The small intestine. The small intestine 

 fills the greater part of the front abdominal 

 cavity. It is a convoluted tube about 

 twenty feet (6.0 metres) in length, and 

 gradually diminishes in size from its com- 

 mencement to where it joins the large 

 intestine. The small intestine is divided 

 by anatomists into three portions. The 



FIG. 115. AN INTES- 

 TINAL VILLUS. a, a, a, 

 columnar epithelium ; 



b, b, capillary network; 



c, c, lymphoid tissue first ten or twelve inches (254 to 305 mm.) 



and muscle fibres: d, : ^H^/l 

 lacteal vessel. 1S Cailed 



is called tne duodenum ; the succeeding 

 two-fifths, the jejunum ; and the rest, the 

 ileum. The intestines are invested by a fold of the peritoneum 

 in much the same way as the stomach. In this situation, the 

 fold of the peritoneum is called the mesentery, and between 

 its two layers are numerous blood-vessels, lymphatics, and 

 lymphatic glands. 



The muscular coat of the small intestine has only two layers : 

 an outer, thinner and longitudinal ; and an inner, thicker and 

 circular. 



The mucous coat is highly developed. In the first place it 

 is largely increased by being arranged in permanent folds, the 

 valvulae conniventes (vide Fig. 114), which project transversely 



