410 



THE DIGESTIVE APPARATUS IN MAMMALIA. 



STRUCTURE. The serous tunic does not call for any notice beyond that 

 already given when speaking of the attachments proper to the caecum. The 

 muscular tunic is formed of circular fibres, crossed externally by longitudinal 

 bands, which maintain the organ in transverse folds. The mucous membrane 

 is thicker than that of the small intestine, and is also distinguished from it 

 by the absence of the Brunnerian and aggregated glands. It has, however, 

 the solitary follicles and crypts of Lieberkiihn, as well as some few 

 intestinal villi. The blood-vessels are the ccecal arteries and veins. The 

 lymphatics pass to the sublumbar receptacle; and the nerves are derived 

 from the great mesenteric plexus. 



FUNCTIONS. The caecum serves as a reservoir for the enormous quantities 

 of fluid ingested by herbivorous animals. The greater part of this fluid, in 

 its rapid passage through the stomach and small intestine, escapes the 

 absorbent action of the villi and accumulates in the caecum, where it may be 

 said to wash the alimentary mass with which it comes in contact ; thus 

 dissolving the soluble and assimilable matters this mass may yet contain, 

 and favouring their entrance into the circulation through the immense 

 absorbing surface formed by the mucous membrane of the large intestine. 



It does not appear that the aliment is submitted in the caecum to any 

 transformation, all the molecular changes of the digestive process, properly 

 speaking, having been accomplished when the mass reached the interior of 

 this viscus. 



B. Colon. 

 The colon is divided into two portions, which differ from each other in 



Fig 206. 



THE COLON OF THE HORSE. 



1, First portion ascending to form the suprasternal flexure; 2, Second portion 

 descending to foi-m the pelvic flexure, 7 ; 3, 6, Longitudinal muscular bands ; 

 4, Point of the csecum, 5 ; 8, Duodenum ; 9, Small intestine. 



volume, and in the disposition they afl'ect in the abdominal cavity. The 

 first is the large or double colon ; the second, the small or floating colon. 



THE LARGE OR DOUBLE COLON (Figs. 204, 205, 206). This intestine 



