204 



HISTOLOGY. 



called mill. Since the villi are from 0.2 to i.o mm. in height they may be 

 seen macroscopically under favorable conditions. In Fig. 228, A, which 

 represents an enlarged surface view of the hardened mucosa, the orifices 

 of the intestinal glands and the projecting intestinal villi are clearly indi- 

 cated. The villi of the duodenum are low (0.2-0.5 mm.) and leaf-like as 

 seen in the reconstruction Fig. 228, B. 



FIG. 228. 



A, Surface view of the hardened mucosa of the small intestine (after Koelliker). B, Side view of a wax 

 .reconstruction of the epithelium in the human duodenum (Huber). i. g., Intestinal gland; v., villus. 



There is no sharper line of separation between the stomach and duode- 

 num than the sphincter muscle of the pylorus. Intestinal glands have been 

 recorded in the stomach, and pyloric glands are said to extend into the 

 duodenum. Moreover the leaf-like duodenal villi resemble the villous 

 folds of the pylorus. 



Intestinal glands. .. 

 Epithelium. Villi. 



Tunica propria. 



Muscularis mucosae. 

 Submucosa. 



Stratum of circular 



muscle. 

 Stratum of longi-_ 



tudinal muscle. 

 Connective tissue. 



Duodenal gland in the 



tunica propria. 

 Plica 



circularis. Duodenal glands in 

 Fat. the submucosa. 



FIG. 229. LONGITUDINAL SECTION OF THE HUMAN DUODENUM. X 16. 



The duodenum differs from the remainder of the small intestine by 

 containing duodenal glands [glands of Brunner]. These are branched tu- 

 bulo-alveolar structures which extend into the submucosa (Fig. 229). 

 To a small extent they branch among the intestinal glands inside the muscu- 

 laris mucosae, as seen in Fig. 230. Their ducts may either enter the bases 



