94 PHYSIOLOGY. 



sac, about two and one-half inches in length and breadth. Toward 

 its bottom it curves inwardly and backward and is abruptly reduced 

 to a wormlike prolongation the vermiform appendix. The small 

 intestine opens into the caecum, the orifice being guarded by the ileo- 

 caBcal valve. The second and largest part of the large intestine is 

 the colon, and it extends from the caecum to the rectum. It consists 

 of four parts: the ascending, transverse, and descending colon, with 

 the sigmoid flexure. Its diameter is greatest at its commencement, 

 being about two and one-half inches; but it gradually lessens to an 

 inch. The sigmoid flexure is shaped like the letter S. It is the nar- 

 rowest part of the colon. The rectum extends from the sigmoid flex- 

 ure to the anus. It is about seven inches in length. When distended 

 the rectum is club-shaped, being narrow above and expanded just 

 before it contracts to the anus. The anus is completely surrounded 

 by a sphincter muscle. ' 



Structure of the Large Intestine. 



The caecum and colon, like the small intestine, have four coats : 

 the (1) serous, (2) muscular, (3) submucous, and (4) mucous. The 

 mucous membrane contains two kinds of glands: the glands of Lie- 

 berkiihn and the solitary glands. The glands of Lieberkuhn are 

 closely set together and give a peculiar sievelike appearance to the 

 surface of the mucous membrane. 



Experiments upon the ca?cum of the cadaver prove that the 

 action of the ileo-caecal valve is not dependent upon muscular con- 

 traction, for fluid forced through the large intestine rarely passes 

 into the ileum. When the ca3cum is filled the dilatation of the same 

 presses upon the folds of the valve so as to press them tightly 

 together and thus prevent any reflux into the small intestine. 



MOVEMENTS OF THE INTESTINES. 



As was the case with the oesophagus, the intestines are com- 

 posed of two muscular coats : an outer longitudinal one and an inner 

 circular one. Movements in them are caused by alternate contrac- 

 tions and relaxations of adjoining portions of the tube. To the 

 characteristic movements of the intestines two names have heen 

 given to describe two separate forms : (1) peristaltic and (2) pendular. 



Peristalsis. By this term is implied the alternate contractions 

 and dilatations of adjoining segments to produce a wavelike motion 

 which proceeds from its point of origin anywhere along the intestinal 

 tract away from the stomach. "Antiperistalsis" is the term used to 



