494 



THE ALIMENTARY CANAL ; SECKETING GLANDS [CH. XXXI. 



small intestine, known as the duodenum, an additional set of glands, 

 called the glands of Brunner, are found. They are imbedded in the 

 submucous coat, and the duct of each gland passes upwards to open 

 on the surface of the mucous membrane. Each gland is a branched 

 and convoluted tube lined with columnar epithelium. Fig. 342 shows 

 these two kinds of glands, and also the villi of the surface. 



Figs. 343 and 344 are more highly 

 magnified views of the villi, which 

 increase the surface of the small intes- 

 tine mainly for the purpose of absorp- 

 tion. A villus is a small projection 

 made of loose lymphoid tissue, covered 

 with columnar cells; it contains in 

 its interior a plexus of blood-capillaries 

 under the basement membrane, and one 

 or more commencing lymphatic vessels 

 or lacteals situated centrally. 



FIG. 342. Vertical section of duode- 

 num, showing a, villi ; ft, crypts 

 of Lieberkuhn, and c, Brunner's 

 glands in the submucosa s, with 

 ducts, d ; muscularis mucosae, m ; 

 and circular muscular coat, /. 

 (Schofield.) 



FIG. 343. Vertical section of a villus of 

 the small intestine of a cat. a, 

 Striated border of the epithelium ; b, 

 columnar epithelium ; c, goblet cells ; 

 d, central lymph-vessel; e, smooth 

 muscular fibres ; /, adenoid stroma of 

 the villus in which lymph corpuscles 

 lie. (Klein.) 



(4) Glands of the large intestine. Here there are no villi, but 

 the crypts of Lieberkuhn are present and are larger than in the 

 small intestine. Many of the cells lining these tubes are seen 

 breaking down to form goblet cells, and the mucus so furnished is 

 the main substance of importance secreted in this part of the 

 alimentary canal. 



All of the foregoing glands are situated in the wall of the 

 alimentary canal. Those situated at a distance from it, and which 



