REPTILIA. 



297 



is empty, the pyloric portion may be distin- 

 guished from the " sack " by the thinness of 

 its walls and the absence of longitudinal folds 

 in its mucous membrane, which latter be- 

 come gradually obliterated as they approach 

 the pylorus. At its termination, this portion 

 of the stomach can hardly be distinguished 

 from the commencement of the intestine, 

 which it resembles both in the transparency 

 of its coats and i in its uniform diameter ; 

 generally, however, the walls of the intestine 

 are thinner and more transparent than that 

 of the pyloric portion of the stomach, and 

 its diameter sensibly increased. Internally, 

 there is a very perceptible difference in the 

 structure of the mucous membrane lining 

 the two, which, in the pyloric portion of the 

 stomach, is arranged in small longitudinal 

 rugae, but in the duodenum has a shaggy or 

 villous appearance. Generally there is a valve 

 or circular fold separating the stomach from 

 the intestine, but this is sometimes only re- 

 presented by a prominent ring formed by the 

 mucous and cellular coats, and occasionally is 

 altogether wanting. 



It is in that part of the stomach which 

 Cuvier calls the " sack " that the digestion of 

 food is accomplished. The pyloric portion 

 forms a first obstacle to stop the prey, which 

 descends to the bottom of the stomachal 

 " sack," where the digestive process is most 

 rapidly carried on, for it is here that the dis- 

 solution of the animal swallowed always com- 

 mences. In proportion as this dissolution goes 

 on, the pyloric canal, the diameter of which is 

 always very small, allows the digested portions 

 of food to pass successively into the intestine. 



The intestinal canal in the common of ring- 

 snake runs in an undulating manner from the 

 pylorus to the rectum, preserving pretty nearly 

 ihe same diameter throughout its whole ex- 

 tent, except that it dilates a little to form the 

 colon. The lining membrane of the small 

 intestine forms broad longitudinal lamince, 

 folded like a shirt-sleeve. In the large intes- 

 tine, which runs straight to the cloaca, the 

 folds are thick and irregular. 



In the true serpents the arrangement is 

 different : the first portion of the intestine 

 forms numerous loops, more or less closely 

 bent upon each other, and retained in position 

 by bands of peritoneum passing between 

 them. The whole is enveloped in a long 

 cylindrical cell formed by the peritoneum. 



This disposition of a part of the alimentary 

 canal in the true serpents, distinguishes them 

 from all other vertebrate animals ; it seems 

 to be rendered necessary by their manner of 

 progressing upon their belly, which, without 

 this precaution, might injure their intestines : 

 it must, however, render slower the peri- 

 staltic movements, and thus contribute to 

 produce the extreme lentor of all their di- 

 gestive functions. This seems to be proved 

 by the fact, that in water serpents (Hydrus, 

 P/aturus, Chersydrus) the intestine is a con- 

 tinuous cavity, and not divided into several 

 loops, their movement in the water not re- 

 quiring such arrangement. 



In the Ophidian reptiles we may always 

 distinguish a large and a small intestine ; the 



Fig. 217. 



Viscera of the Rattlesnake. 



a, the trachea ; B, the right lung ; c, bladder-like 

 termination of ditto ; d, e, f, the oesophagus ; g, the 

 stomach ; h, commencement of the intestine, 1 ; I, 

 the heart ; m, large arterial trunks ; , n, anterior 

 and posterior venaa-cavas ; o, the liver ; p, the gall- 

 bladder, situated at some distance from the liver. 



latter generally terminates end to end in the 

 former, and it is rare to find anything like 

 a cul-de-sac or caecum at the place of 

 their union. The small intestine preserves 

 nearly the same diameter throughout. The 

 large intestine, which is shorter, is generally 

 divided into two or sometimes three com- 

 partments by one or more sets of valves, 

 or even by one or two partitions, through 

 which there is only a small opening leading 

 from one compartment to another. The first 

 compartment is generally smooth, or only 

 presents internally a few simple folds ; whilst 

 the last compartment, or the rectum, pro- 

 perly so called, has its cavity divided by 

 irregular transverse plicae, or even by very 

 broad valvulae conniventes. When there is 

 an intermediate compartment, its sides are 



