286 STUDIES IN ADVANCED PHYSIOLOGY. 



the submucous coat are nodules of lymphatic tissue which 

 are called the patches of Peyer. These patches may be but 

 tiny nodules invisible to the unaided eye, or may attain the 

 size of lumps distinctly visible and easily felt. Such larger 

 patches may materially distend the submucous coat and 

 may even reach up into the mucous coat displacing the villi 

 in the manner indicated in Figure 115. That such lymphatic 

 glands are scattered so generally through the wall of the 

 small intestine, and even occur in numbers in the mesent- 

 ery, suggests that the leucocytes which arise in these glands 

 may in some direct way be concerned with the phenomena 

 of absorption. 



6. THE LARGE INTESTINE. 



The small intestine leads into the large intestine. At 

 the point of the junction there is a valve called the ilio- 

 colic valve, so arranged that food may easily pass into the 

 large intestine but cannot pass in the reverse direction. 

 The opening of the small intestine into the large is, how- 

 ever, not a terminal one, the ilio-colic valve being situated 

 on the side of the large intestine. That portion which is 

 back of this valve is spoken of as the blind sac or the 

 cczcum. Attached to the caecum there is a small hollow 

 continuation known as the vermiform appendix. While 

 both the caecum and vermiform appendix in man are quite 

 small and probably have no function at all as far as we 

 know, these structures are very large in the herbivorous 

 animals, and in them serve to hold the food in order to sub- 

 ject it more thoroughly to the digestive action of the juices 

 and the absorptive action of the intestine. 



The large intestine differs materially from the small not 

 only in its larger size, but also in its structure. The mus- 

 cular coats are not so well developed, the circular coat in 

 places being entirely absent. This arrangement of the cir- 

 cular coat gives the wall of the large intestine its pouched 

 appearance. On the mucous coat there are no villi at all. 

 The crypts of L,ieberkuhn of the small intestine are here 

 replaced by quite similar tubular glands which, however, 



