54 I'NTRODUCTION. 



deed, there are very few Birds, generally esteemed grarii- 

 vorous, that are wholly so. The common Cock and Hen, 

 although devouring much grain, devour also many worms 

 and flies ; and, unquestionably, if left to themselves, would 

 direct the attention of their young to such food. And 

 although the chicken of the common hen will pick up and 

 digest grain, yet, it may be stated, generally, that animal 

 food is most suitable to very young birds. The reason for 

 this is apparent : animal food most readily assimilates with 

 the fluids of their bodies with the least eff'orts of the digestive 

 powers. In this respect, therefore, birds do not difler very 

 essentially from the mammalia. 



In connexion with this subject, it may be mentioned here, 

 that, in most birds, the canal between the crop and gizzard 

 enlarges considerably before it opens into the last-named re- 

 ceptable : this enlargement is named the Proventriculus ; 

 its shape varies greatly in difi"erent birds; but, in all, it con- 

 tains numerous glands, in which is secreted an acid liquor 

 that mixes with the food, and, doubtless, greatly assists the 

 process of digestion ; and is of course analogous to, if not 

 identically the same as, the gastric juice found in the stomach 

 of the mammalia. 



The structure of the trachea of birds is also, particularly 

 in those of the songsters, peculiar ; there being a larynx both 

 at the top, or opening, into the mouth, and another at the 

 bottom, just before the trachea separates into two divisions, 

 to communicate with the right and left lung ; it is in the 

 lower larynx that the chief arrangement is found by which 

 those varieties and niceties in sound are produced, so 

 beautifully exemplified in the notes of our singing birds, 

 and for which it is so ingeniously and curiously 

 adapted, but which it is not necessary here to describe. 

 The trachea is also, in some others of the tribe, pe- 



