SPECIAL HISTOLOGY. 



OF THE DIGESTIVE ORGANS. 



I.— OF THE INTESTINAL CANAL. 



§ 128. 



The intestinal canal is composed fundamentally of the so- 

 called membranes of the intestine. The innermost of these, 

 the mucous membrane, membrana mucosa, corresponds in its 

 structure with the skin, and like it possesses, (1) a non-vascular 

 investment composed of cells — the epithelium; (2) the mucous 

 membrane, more strictly speaking, composed of connective and 

 elastic tissues; containing vessels, nerves, smooth muscular 

 fibres, and different forms of minute glands, and often present- 

 ing peculiar processes {papillae, villi); and (3) an external 

 layer of loose connective tissue, the submucous cellular tissue. 

 The second intestinal tunic, the muscular membrane, tunica 

 muscularis, is provided, for a certain distance at the commence- 

 ment and at the termination of the intestine, with striated 

 fibres, but in the remainder of its extent the muscles are every- 

 where of the smooth kind, and form in general two distinct 

 layers ; an external, with longitudinal, and an internal, with 

 transverse fibres ; more rarely there are three separate layers. 

 The third membrane, the serous, tunica serosa, exists only 

 upon those portions of the intestine which occupy the cavi- 

 ties of the abdomen and pelvis ; it is a delicate, transparent 

 membrane, poor in nerves and vessels, and provided with an 

 epithelium ; it invests the intestinal canal, and connects it with 

 the walls of the abdominal cavity and with the other viscera. 



jr n. i 



