446 



ANATOMY OF VERTEBRATES. 



projecting into the caecum, which is continued beyond, spirally, 

 and contracting to open into the colon by a rounded puckered 

 aperture, at the end of a conical valvular prominence. Valvular 

 folds of the mucous membrane project into the colon from its 

 concave side, decreasing in breadth as they descend. The coats 

 of the intestine make smaller indentations from the convex side, 

 opposite the intervals of the larger folds. Beyond these folds the 

 colon diminishes in diameter, and makes a sudden turn upon 

 itself before becoming the ' rectum.' The ca3cum is, here, not a 

 mere ( caput coli,' but a distinct segment of the alimentary canal, 

 having an orifice for ingress, and a second for egress, of contents, 

 analogous to the carclia and pylorus of the stomach, with parietes 

 more muscular than either of the intestines with which it com- 

 municates. 1 



It would seem, from petrified contents or excretions of the 

 intestine, that some part, probably the terminal one, of this canal 

 had been provided, in the extinct Ichthyosaur, with a spiral valve, 

 fig. 105 ('coprolite' figured below the pelvis). 



The rectum does not open directly upon the exterior of the 

 body in any Reptile, but into a cavity, or ' cloaca,' common to it 



1 The following Table (CCXLV. p. 92) gives the weight of the body, in grains, and 

 the lengths of the alimentary canal, in inches, in various Reptiles. 



