68 ALIMENTARY SYSTEM. 



of which everv thing that nature produces is an 

 example. We know, from our own case, that if even 

 a single muscle of the system, except those which 

 are employed in immediately carrying on the vital 

 functions, be exerted, not one part of the body, far 

 less the whole of it, can be in that state of repose 

 which is necessary for enabling the active system to 

 recover its tone. With us, an easy position on the 

 couch, in the chair, on the grassy sod, or on the bare 

 earth, according to the habit, and the need that there 

 is for rest, is the position for repose ; and if we were 

 to attempt to sleep, clinging by the hands, or in any 

 other way in which our mere weight is not the means 

 by which we retain our position, we should assuredly 

 fall. But birds have to repose in all varieties of 

 situation, and their means of keeping their places are 

 increased and varied accordingly. 



ALIMENTARY SYSTEM. 



In their alimentary system birds are variously 

 formed, according to the general nature of their food. 

 If that food is wholly animal, their stomachs are 

 simple and membranous, and their intestinal canals 

 short, and without csDca. If wholly vegetable, the 

 stomach is more complicated : one part, which is 

 styled the craw, and which is little else than an en- 

 largement of the inferior part of the gullet, being a 

 sort of receptacle into which they can take much 

 more food than the bare stomach can at once receive 

 for the purpose of digestion. In this respect it bears 

 some resemblance to the paunch, or first stomach of 

 the ruminant mammalia ; but as birds have no chewing 

 apparatus in the mouth, the food taken into the craw 

 does not return to the mouth, but proceeds into the 

 stomach portion by portion, as the progress of di- 



