410 



-: DIGESTIVE APPARATUS IN MAMMALIA. 



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

 already given \\hen speaking of the attachments proper to tlie e;ermu. The 

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

 bands, which maintain the organ in transverse folds. The ///, -<,i/.s- ini-niliriiin- 

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

 by the absence of the Srunnerian and aggregated ylandti. 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 

 li/Hijrftatics pass to the sublumbar receptacle; and the nerves are derived 

 from the great mesenteric plexus. 



FUNCTIONS. The ctecum 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 crecum, 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. 



TIIK rou>\ OK TIM: IIOKSI:. 



1, First portion ascending to form tin: sii|>r.-ist.-rn.il flexure; 2, Second portion 

 descending to form the pelvic flexure, 7; 3, G, Longitudinal muscular bands; 

 4, Point of the ca-cuin, 5; 8, Duodenum; 9, Small intestine. 



volume, and in the disposition they affect in the ulxlominal cavity. The 

 first is the large or donl>b' <<//<>;/ ; the second, the xnuill or Jl<>nfiii</ colon. 



TIIK I. \ii.i: OK DOUBLK COLON (Figs. 20-1, 205, 206). This intestine 



