lf)8 THE VITAL FUNCTIONS. 



are employed with the apparent intention of pre- 

 venting theircontents from passing along too hastily : 

 these contrivances are most effectual in animals 

 whose food is vegetable, and contains little nourish- 

 ment ; so that the whole of what the food is capable 

 of yielding is extracted from them. Sir E. Home 

 observes that the colon, or large intestine of animals 

 which live upon the same species of food, is of 

 greater length in proportion to the scantiness of the 

 supply. Thus the length of the colon of the Ele- 

 phant, which inhabits the fertile woods of Asia, is 

 only 26i feet ; while in the Dromedary, which 

 dwells in the arid deserts of Arabia, it is 42 feet. 

 This contrast is still more strongly marked in birds. 

 The Cassowary of Java, which lives amidst a most 

 luxuriant supply of food, has a colon of one foot in 

 length, and two caeca, each of which is six inches 

 long, and one quarter of an inch in diameter. The 

 African ostrich, on the other hand, which inhabits a 

 country where the supply of food is very scanty, has 

 a colon forty-five feet long ; each of tliB cseca is two 

 feet nine inches in length, and, at the widest part, 

 three inches in diameter ; in addition to which there 

 are broad valves in the interior of both these 

 cavities.* 



On comparing the structure of the digestive 

 organs of Man with those of other animals belong- 

 ing to the class Mammalia, we find them holding a 

 place in the series intermediate between those of 

 the purely carnivorous, and exclusively herbivorous 



* Lectures, &c. I. 470. In tlie account above given of the di- 

 gestive organs I have purposely omitted all mention of the spleen ; 

 because, although this organ is probably in some way related to 

 digestion, the exact nature of its functions lias not yet been deter- 

 mined with any certainty. 



