722 AVES. 



wise the air freely penetrates to the interior of the body, and, as we 

 shall afterwards find, is there most extensively diffused. 



(2045.) In the construction of the alimentary system, there are many 

 interesting peculiarities to invite our notice. Their mouth constitutes 

 the apparatus whereby the prehension of food is accomplished ; it is in 

 no instance provided with teeth, or adapted to masticate food, but forms 

 a beak encased in a dense, horny sheath, which, from the varieties of 

 form that it assumes in different genera, becomes adapted to very various 

 purposes. 9 



(2046.) In the Rapacious tribes, for instance, the bill is a strong and 

 formidable hook, calculated to tear in pieces the animals devoured. In 

 Granivorous birds, it is a simple forceps for picking up the seeds of 

 vegetables. In the Snipe and the Curlew it forms a probe, whereby 

 insects are extracted from the soft and marshy ground. In the Parrot 

 it is partially an assistant in climbing, as well as an organ for seizing 

 food; and, not to mention innumerable other modifications, in the 

 Flamingo and Duck tribes it constitutes a shovel, by the aid of which 

 alimentary matters are obtained. 



(2047.) The sense of taste, even in these highly-gifted animals, is as 

 yet but very imperfectly developed ; and their tongue, instead of being 

 soft and flexible, as in the Mammalia, is supported by one or two bony 

 pieces, derived from the os hyoides (fig. 357), and covered with a horny 



Fig. 357. 



Hyoid apparatus of a bird. 



sheath, obviously ill adapted to gustation, but simply assisting in the 

 deglutition of food. We must not be at all surprised, therefore, if even 

 in birds the tongue is convertible into various instruments assisting in 

 the apprehension or preparation of nourishment : thus, in the Parrot 

 it is a thumb opposable to the upper mandible, and eminently serviceable 

 in holding and turning nuts or morsels of fruit ; in the honey-eating 

 tribes the tongue is armed at its extremity with a tuft of horny filaments, 

 resembling a camel-hair pencil, which, being plunged into the bell of a 

 flower, sucks up the nectar from the bottom ; and in the Woodpecker 

 it is absolutely converted into a harpoon, whereby the insect is speared 

 in its lurking-place and dragged into the mouth. 



