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BOOK II. 

 THE DIGESTIVE APPARATUS. 



CHAPTER I. 



GENERAL CONSIDERATIONS ON THE DIGESTIVE APPARATUS. 



WE Lave considered the animal as a machine composed of various 

 levers and susceptible of various movements ; but it will bo easily under- 

 stood that the working of this machine will cause the wear or decomposition 

 of the molecules which enter into the construction of its organs, and 

 that these springs or animated wheels demand for their maintenance an 

 incessant supply of new materials, destined to repair their continual losses. 

 Animals, therefore, are under the necessity of taking aliment, from which 

 they extract those reparative principles which, distributed to all the organs, 

 are assimilated into their proper substance. 



The organs in which this work of preparation and absorption of the 

 organisablo material is carried on are collectively named the digestive 

 <i]>l><iratu8 : one of the most important of those which, as we will see, suc- 

 cessively complicate and perfect the animal machine. This apparatus does not, 

 properly speaking, constitute an essentially distinctive characteristic of 

 animality, as there are animals without a digestive cavity ; but it is yet ono 

 of the most salient attributes, for tho exceptions just mentioned are ex- 

 tremely rare. Considered in tho vertebrata, this apparatus appears as a 

 long tube, most frequently doubled on itself many times, bulging at intervals, 

 and provided along its course with several supplementary organs, tho 

 majority of which are of a glandular nature. This tube extends tho wholo 

 length of tho animal s body, and opens externally by two orifices, ono of 

 these serving for tho introduction of aliment, tho other for tho expulsion of 

 tho residue of digestion. These openings are at the extremities of tho 

 alimentary canal. 



The conformation of this apparatus is not identically tho samo in all 

 tho individuals composing tho sub-kingdom of vnrtohrata ; on the contrary, 

 it presents very numerous varieties, according to the habits and mode of 

 life of these individuals, and this makes its study interesting from two 

 points of view : in relation to tho science of zoology, and to that of veterinary 

 hygiene, which derives from this study valuable indications concerning tho 



me of tho domesticated animals. 



But this diversity of characters docs not suffice to establish sharply- 



<;d limits between tho conformations that ore distinguished by it. There 



is, in reality, but ono typical form for tho digestive apparatus, and tho samo 



1'i-inri],],' prevails in its construction throughout tho entire series. Thus, 



whichever of tho vertebrata wo may bo studying, its alimentary tube will 



bo found composed of a collection of bulging or tubnliform cavities, which 



succeed each other from boforo to behind in tho following order : tho mouth, 



JHJT, tesophfitjus, slomach, and interim-. 



