146 



THIRTEENTH LECTURE. 



digest albumen must be left for discussion in another lec- 

 ture. 



Let us pass to the small intestine. 



Its serous covering and the smooth muscles, forming a double 

 layer, we here omit. The mucous membrane, on the con- 

 trary, requires an accurate description, for its structure is 

 more complicated than in the stomach. 



In the first place, we meet with innumerable large crescen- 

 tic folds (increasing downwards in height), the valvulae con- 

 niventes Iverkringii. The surface of the small intestine, be- 

 sides, projects in millions of complicated papillae, the intes- 

 tinal villi. In the mucous membrane we meet, furthermore, 

 with an infinite number of small glandular tubes, the Lieber- 

 kuhnian glands; and in the duodenum, with small racemose 

 organs, the Brunonian glands. Finally, the small intestine 

 contains solitary and aggregate (Peyerian) lymph follicles. 



The tissue of the mucous membrane of the small intestine 

 also shows a muscularis mucosae, but it is thinner than in the 



stomach, and then a reticu- 

 lar connective substance 

 containing numerous lym- 

 phoid cells (Fig. 47, a). 

 The villi (Fig. 137) — we 

 have already mentioned 

 them in a previous lecture 

 — also consist of a similar 

 tissuu. Even the surface 

 is distinctly fenestrated, 

 although with narrower 

 meshes. In the axis we 

 find the chyle vessel (Fig. 

 95, d), single or multiple, 

 in the latter case sometimes connected in an arched and 

 bridge-like manner, covered by thin slips of smooth muscle 

 {c) derived from the muscularis mucosae, and finally circum- 

 voluted by a looped net-work of capillaries (b . We are 

 already familiar with this from what has preceded. 



U~o 



Fig. 137. — Lieberkiihnian glands (a) of the cat, 

 with the intestinal villi [b) situated over them. 



