1166 



DIGESTIVE SYSTEM 



circulares are absent from the first part of the duodenum, but become well-marked in the descend- 

 ing portion (fig. 922). They are largest and best developed in the lower duodenum and upper 

 half of the jejunum, below which they gradually become smaller (fig. 924) and disappear at the 

 lower end of the ileum. 



The digestive and absorptive surface of the small intestine is further greatly increased by 

 multitudes of small processes, the villi (figs. 925, 927), which give the mucosa a velvety appear- 

 ance. They are largest (.5 to .7 mm. in height) and most numerous in the duodenum and 

 jejunum, where they are typically leaf-shaped, and gradually become smaller, scattered and 

 conical in the ileum. The villi are much reduced in distention of the intestine, and may even 

 be temporarih' obhterated. Between the bases of the vilh there open short, simple tubular 

 glands — the crj^pts of Lieberkuehn [gl. intestinales], whose fundus cells (of Paneth) probably 

 secrete digestive enzymes. In the duodenum there are found, in addition, the larger tubulo- 



FiG. 925. — .4, Surface View^of the Hardened Mucosa of the Small Intestine. (After 

 Kolliker.) B, Side View of a Wax Reconstruction of the Epithelium in the Human 

 Duodenum. (Huber.) i.g., Intestinal gland, v., Villus. 



racemose glands of Brunner [gl. duodenales], which occupy the submucosa, and are especially 

 numerous in the upper portion of the duodenum. They are purely mucous in character ac- 

 cording to Bensley, although Oppel describes granular cells, similar to Paneth cells, which may 

 secrete digestive enzymes. 



Scattered over the whole of the mucous membrane of the small intestine are numerous 

 small lymph-nodules, the larger of which extend into the submucosa; these are the so-called 

 solitary glands [noduli lymphatici solitarii]. Aggregations of lymph-nodules, known as Peyer's 

 patches [noduli lymphatici aggregati], situated in the mucosa and submucosa, are found in 

 the ileum especially toward the lower end (fig. 926). They are oval, from 1.2 to 7.5 cm. in 

 length and about 1 to 2.5 cm. in breadth, and are placed in the long axis of the bowel along a 

 line most remote from the mesentery. They are variable in number, the average being about 

 20 to 30. 



Fig. 926. — Surface View of the Mucosa of the Ileum, Showing Aggregated Lymph 

 Nodes (Peyer's Patch). (From Toldt's Atlas.) 



Aggregated lymph nodes 

 (Peyer's patch) 



Solitary lymph nodes 



The submucosa is in general a loo.sc areolar layer containing vascular and sympathetic 

 plexu-ses (figs. 927, 928). The muscularis is composed of smooth muscle arranged in the two 

 typical layers, — a thiimer, outer longitudinal and a thicker, inner circular, — both of which 

 become thinner toward the lower end of the ileum. The serosa is typical in structure, the 

 squamous epitlifliul covering being ab.sent in the retroperitoneal areas of the duodenum. 



Blood-supply of the small intestine. — The .small intestine receives its blood from the superior 

 mesenteric artery and a branch comhig indirectly from the hepatic, the superior pancreatico- 

 duodenal. The superior mesenteric artery runs between the layers of the mesentery and gives 

 off six or seven relatively large brandies and a variable number of smaller branches. The 

 first two or three of tlie larger branches divide into an ascending and a descending branch, 

 which join above and below with the corresponding Ijranches of the continguous arteries, form- 

 ing thus a single row of arches. From about the bc^ginning of the second quarter of the small 



