DIGESTIVE SYSTEM. 



layer throughout; of a middle circular layer on the body and 

 pyloric end, where it forms the sphincter; and of an internal 

 circular layer on the fundus. The submucous is loose connect- 

 ive tissue. The mucous is thickest at the pylorus. [1058] 



Structure of Intestines. All have four coats, as follows, 

 from without inward: Peritoneal, varying in extent. The 

 muscular coat consists of an inner circular layer, forming the 

 pyloric and ilio-csecal valves; and an outer longitudinal layer 

 covering the small intestine completely but gathered in three 

 bands (tsenise coli) on the large intestine. The submucous is 

 loose areolar tissue. The mucous consists, from within out- 

 ward, of an epithelial layer, a basement membrane, a retiform 

 layer, and a muscular layer (Muscularis mucosae). [1061] 



The valvulcc conniventes are permanent transverse and rather 

 crescentic folds which rarely form a complete circle, and are 

 composed of two layers of mucosa with submucosa. They 

 occur only in the small intestine, beginning in the duodenum 

 an inch or two below the pylorus, becoming prominent in its 

 lower half and the upper half of the jejunum, and then dis- 

 appearing at the middle of the ileum. The vitti are minute 

 projections on the mucosa. [1062] 



The solitary glands are minute lymphatic nodules found 

 everywhere in the mucosa. Peyer's patches are aggregations of 

 solitary glands which form slightly elevated areas, half an 

 inch long, or less. There are thirty or forty, found only in the 

 small intestine, chiefly in the lower part of the ileum and al- 

 ways along the free border. [1063] 



Small Intestine. This is cylindrical, an inch or more in 

 Jiameter, and over twenty feet long. It is divided into the 

 duodenum, the upper eleven inches, which is fixed and has 

 no mesentery; the jejunum, the upper two-fifths of the re- 

 mainder, about eight feet long, lying above and to the left; 

 and the ileum, the lower three-fifths, about twelve feet long, 

 lying below and to the right. [1064] 



Duodenum. From the pylorus this curves round the head 



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