490 



ABDOMEN 



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

 above and below by a protruding lip 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-cacal 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 the frenula of the valve. 



The peritoneum and the longitudinal muscular bands are in no way 

 involved in the infoldings which form the valve-flaps ; but the other 



Upper segment 



Orifice 



Frenulum 



Lower segment 



Orifice of vermiform 

 process 



FIG. 189. Ileo-Caecal Opening and Valve from a subject hardened 

 by formalin injection (Birmingham.) 



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 this 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 regurgitation, the frenula of the valve are put upon the stretch 

 and the free borders of the segments are brought into firm contact. In this 

 way reflux of the contents of the caecum into the ileum is prevented, although 

 it is well to note that the obliquity of the entrance of the ileum into the 

 caecum also exercises a very important influence in the same direction. 



The position of the ileo-caecal orifice is marked on the 

 anterior surface of the abdomen by the medial angle between 

 the intertubercular and the right lateral lines. About an inch 

 below the ileo-caecal orifice, and on a posterior plane, is the 



