222 DIGESTION. [CHAP xxv. 



It may further be observed, that as the several portions, whether of small or 

 large intestine, have very definite characters as regards the mucous membrane, 

 we can readily determine the relative length and development of each portion, 

 and thus deduce its proper degree of importance in intestinal digestion. But 

 upon these points it is much to be regretted that we are greatly in want of 

 precise information ; we are persuaded that nothing would tend more to the 

 correct determination of the office performed by each portion of the intestinal 

 canal than a series of careful observations with special reference to anatomical 

 characters on the intestines of a great number of animals. 



Much importance is attached by Physiologists, and apparently with good rea- 

 son, to the size and form of the ccecum. It is difficult, however, and, in the 

 present state of our knewledge, impossible, to determine the law which in- 

 fluences its development. Nevertheless, it may be stated that there appears to 

 be a direct relation between this development of the intestine and the hardness 

 of digestion of the food : in some instances, we find that a large ccecum. com- 

 pensates for a less capacious stomach, as in the Solipeds ; and in these cases 

 there exists even a striking similarity in the forms of these two organs. A 

 large ccecum, then, belongs to the herbivorous classes, as a large stomach does, 

 and a small ccecum would, on the other hand, indicate a diet of animal food. 

 Anatomy would seem to point to the conclusion, that the function of the ccecum 

 is not dissimilar to that of the stomach, and that in it substances hard of diges- 

 tion are subjected a second time to a reducing action resembling that of the 

 stomach. Perhaps the anomaly which we have noticed in the dormouse, in the 

 absence of a ccecum, may be explained on the supposition, that this accessory di- 

 gestive cavity was rendered unnecessary in consequence of the existence of the 

 glandular pouch at the cardiac orifice of the stomach in that animal. 



The subdivision of the intestinal canal in man into the small and 

 large intestine by the difference in calibre of those two portions of 

 that tube as well as by the existence of an ileo-coecal valve, has 

 already been described. There are other characteristics, however, 

 of anatomical constitution which likewise sufficiently distinguish 

 them. The whole of the intestinal tube is composed of certain 

 tunics which, enumerated from within outwards, are as follows : 

 1st., the mucous membrane; 2ndly., the submucous tissue; 3rdly., 

 the muscular coat ; 4thly., the serous coat, which is connected to 

 the tunic last named by a thin layer of very delicate areolar tissue. 

 Of these tunics, the mucous membrane, the muscular coat and the 

 serous coat, exhibit on the whole, very distinctive characters in the 

 two divisions of the intestine. 



The mucous membrane continuous with that of the stomach 

 exhibits very characteristic features in the different portions of 

 the intestine. We shall reserve the description of it until we have 

 spoken of the other tunics. 



The submucous tunic is a layer of very fine areolar tissue, which 

 connects the mucous to the muscular coat ; it is entirely devoid of 



