190 MICROSCOPIC ANATOMY OF THE ORGANS. 



drical, finely granular, and much like those of the pyloric 

 glands. During secretion they are smaller and less clear than 

 when no food is being digested. The blind ends of the 

 gland tubules are dilated often like those of alveolar glands. 

 Around the tubules there is to be seen a structureless basement 

 membrane. 



The muscularis consists of an inner circular and an outer 

 longitudinal layer of smooth muscle fibres. In the large intes- 

 tine the outer layer is very thin in general, but is thickened in 

 three strong flat bands, which are called the tcenice coli. In 

 certain places the circular layer is thickened also, especially at 

 the opening of the rectum, where it forms a strong circular 

 band, the musculus sphincter ani interims. 



The different regions of the intestine are distinguished easily 

 from one another microscopically. The duodenum is character- 

 ized by the presence of Brunner's glands and leaf-like villi ; 

 the jejunum and ileum, by the absence of these and the presence 

 of columnar villi. The ileum can usually be distinguished 

 from the jejunum by the greater abundance of lymphoid 

 tissue. The large intestine is characterized by the complete 

 absence of villi, the abundance of goblet-cells, and the dispo- 

 sition of the external muscle coat. 



Blood-vessels, Lymph-vessels, and Nerves of the Stomach and 



Intestine. 



The arrangement and relation of the blood-vessels' in the 

 stomach and large intestine are so similar that they may be 

 described together. In the small intestine the presence of villi 

 causes a considerable difference. 



The arteries enter the intestinal wall from the outside and pass 

 through the outer layers to the submucosa. On the way small 

 branches are given off to the peritoneum and the muscularis, 

 to form capillary networks in these regions. In the submucosa 

 the arteries break up to form a network of large vessels parallel 

 to the surface. From these arteries branches pierce the muscu- 

 laris mucosse and form a second finer network in the tunica 

 propria, which gives off branches to make up a capillary plexus 



