332 



ABDOMEN 



The Ileo-Caecal Orifice is an antero-posterior slit, bounded 

 by two protruding lips, a superior and an inferior, which are 

 formed by the partial invagination of the lower end of the 

 ileum into the caecum. The two lips are the two segments 

 of the valve of the colon (O.T. ileo-ccecal valve]. At the 

 extremities of the orifice the segments of the valve unite 

 together and become continuous with a ridge of the wall of 

 the gut which is prolonged around the cavity. The anterior 

 and posterior parts of the ridge, immediately adjacent to 

 and connected with the lips of the valves, are spoken of as 

 thefrenu/a of the valve. 



The peritoneum and the longitudinal muscular bands are 



Upper segment 



Orifice 



Frenulum 



Lower segment 



Orifice of vermiform 

 process 



FIG. 154. Ileo-Caecal Opening and Valve of the Colon from a 

 subject hardened by formalin injection. (Birmingham.) 



in no way involved in the infoldings which form the valve- 

 flaps ; but some of the other constituents of the gut-wall (viz., 

 the mucous membrane, the submucous coat, and the circular 

 muscular fibres) take part in their formation. Villi are 

 present on the ileal but not on the caecal aspect of each 

 valve-flap. 



The function of the valve is obvious. It is so arranged 

 that the free passage of materials from the ileum into the 

 caecum is in no way impeded ; but when the caecum becomes 

 distended, and there is, consequently, a tendency to regurgita- 

 tion, the frenula of the valve are put upon the stretch, and 

 the free borders of the segments are brought into firm contact. 

 In that way reflux of the contents of the caecum into the 



