204 STRUCTURE OF THE VERTEBRATES 



the posterior three-fifths. The small intestine enters the colon 

 at the ileo-colic valve. 



The colon is nearly five feet in length, the ileo-colic valve 

 which constricts the entrance of the ileum being about three 

 inches from its blind end. The vermiform appendix aver- 

 ages a few inches in length. Its lumen, which opens into the end 

 of the caecum, varies widely. At times the point of division be- 

 tween appendix and caecum is hardly determinable. The juncture 

 of the ileum and colon, and the position of the appendix, is nor- 

 mally in the lower right side. From this point the colon passes 

 anteriorly as the ascending colon ; bends and lies across the body 

 as the transverse colon; and on the left side near the spleen it 

 bends posteriorly at the splenic flexure, and passes posteriorly 

 as the descending colon. In the posterior part of the body cavity 

 the colon makes a curved turn, the sigmoid flexure, and then 

 enters the rectum. The latter is slightly less than six inches in 

 length. 



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