91 



ANIMAL PHYSIOLOGY. 



called the ascending colon ; it tlien passes across beneath, the 

 stomach to the left side as the transverse colon, and runs 

 down to the region of the left groin under the name of 

 descending colon ; there it makes a loose bend, termed the 

 sigmoid flexure, and passes into the pelvis, where it is called 

 the rectum, or lower bowel. 



At the entrance of the small intestine into the great, there 



is an arrangement, called 

 the ileo-colic valve, to pre- 

 vent matters which have 

 once passed into the great 

 intestine regurgitating into 

 the ileum. It consists of 

 two redundant folds of the 

 mucous membrane at the 

 opening projecting like an 

 upper and a lower lip into 

 the colon, while from the 

 angles of their junction 

 prominences of mucous 

 membrane, the frsena, pass 

 round so as partially to 

 encircle the great intestine. 

 When the great intestine 

 is distended, the frsena are 

 pulled tight, and the lips 

 of the valve brought into 

 Fig. 51. -ILEO-COLIC VALVE, a, cut firm contact, the distending - 

 end of the ileum ; b, cut end of matters pressing their sur- 

 the colon; c, caput csecum coli; d, faces together. Thus, while 

 vemiifwm appendage; e, lower lip there is no ]b s tacle to the 



passage of matters from 



the ileum into the caecum, regurgitation backwards is 

 effectually prevented, and the more distended the caecum the 

 firmer is the closure of the valve. The efficiency of the valve 

 is independent of muscular action, and can be exhibited 

 perfectly on the dead subject. 



63. As might be expected from the existence of the ileo- 

 colic valve, the contents of the intestine on entering the colon 

 undergo considerable change : here they begin to acquire a 



