198 



DIGESTION 



in the fundus of stomach. Their function must be different, however, 

 for no pepsin is formed in the duodenum; enterokinase, for example, 

 is, however. These are largest in the upper part of the duodenum, 

 but are not found below the first portion of the jejunum (simple follicles). 

 The crypts of Lieberkuhn are simple glands in the mucosa between the 

 bases of the villi. Scattered among these are the goblet-cells, producing 

 mucus; what else they secrete is still unknown. The valvulse con- 

 niventes are prominent acute ridges running part way around the interior 

 of the gut-wall. Their use is apparently to many times increase the 

 secretive and absorptive surface of the intestine and also to retard the 

 downward passage of the chyle. Some of these are nearly a centimeter 

 in height. The villi are minute finger-like projections into the lumen 



FIG. 96 





Goblet-cells from the gut of geotriton, to show the different functional conditions of this sort 

 of epithelium. In the first, a secretory act has just ended and a second is beginning. In the 

 second and third and fourth cells various stages of activity are shown, both in the cytoplasm 

 and in the nucleus. (Galeotti.) 



of the small intestine. They are largest and most numerous in the 

 duodenum and jejunum. Krause estimates their number at about 

 4,000,000, and they are from 0.5 to 3.0 mm. in length. From 

 without inward a villus is composed of striped columnar epithelium, 

 with goblet-cells scattered here and there through it. Beneath this 

 is the membrane, then comes the reticular adenoid tissue, containing 

 lymph-corpuscles, bloodvessels, and nerves in abundance. There are 

 also numerous smooth muscle fibers, especially about the large lymphatic 

 vessel in the middle of the villus. The lymph-nodules of the gut-wall 

 are most numerous in the lower half of the ileum, where there are no 

 valvulse conniventes, especially in the ileum. These combine in masses 

 to form Peyer's patches, which are from 1 to 10 cm. long. 



The nerve-supply of the small intestine comes from the spinal cord 



