100 



ANIMAL PHYSIOLOGY. 



best brought into view by laying the opened intestine in 

 water, so as to make them float. They are as much as half 

 a line long in the duodenum, and extremely crowded, but 

 gradually get shorter and fewer in the lower parts of the 



small intestine, until, 

 near the termination of 

 the ileum, they degene- 

 rate into scattered wart- 

 like eminences. The villi, 

 are confined entirely to 

 the small intestine, and 

 are a means of increas- 

 ing the extent of mucous 

 membrane for the pur- 

 pose of absorption ; each 

 villus being dipped like 

 a finger in the chyme, 

 and sucking up the di- 

 Fig. 55. VALVUX.E CONNIVENTES, gested parts of it by 

 exhibited in a portion of jejunum every portion of its sur- 

 cut open. Two-thirds natural size. f ace< The absorbent 

 surface of the small intestine is further increased by 

 crescentic folds of the mucous membrane passing more than 

 half round it, and dipping into the interior. They are 

 called valvulce conniventes, and, like the villi, are most 

 numerous and well developed in the duodenum and 

 jejunum. 



The thickness of the mucous membrane of the small intes- 

 tine is occupied, like that of the stomach, with closely set 

 tubules, only they are much smaller than those of the 

 stomach, contain no other than columnar epithelium, and 

 are quite simple ; these are called the follicles or crypts of 

 Lieberkuhn. The duodenum has likewise three other secre- 

 tions poured into it, namely, the bile, the pancreatic juice, 

 and the secretion of a number of minute glands of a lobu- 

 lated description, scattered beneath its mucous membrane, 

 and called Brunner's glands. 



69. The pancreas is a large lobulated gland, about eight 

 inches long and one inch and a half broad, not unlike the 

 salivary glands in appearance, and sometimes called by 



