BIRDS. 20* 



tliem with membranous air-cells, which occupy a very considerable 

 portion of the chest and abdomen, and have direct and uninter- 

 rupted communication with the lungs. The long cylindrical bones 

 are so many air-tubes, and even the flat bones are occupied by a 

 cellular bony net-work, filled with air. In certain birds, the large 

 bills, even the very quill feathers, are in receipt of more or less 

 air from the lungs, at the pleasure of the animal. Lightness of 

 the body being indispensable, the birds which fly highest and 

 most rapidly, have the largest supply of air-cells. 



In these particulars, birds pretty much resemble each other 

 in their internal conformation ; but there are some varieties which 

 we should more attentively observe. All birds have, properly 

 speaking, but one stomach ; but this is very different in different 

 kinds. In all the rapacious kinds, that live upon animal food, as 

 well as in some of the fish-feeding tribe, the stomach is peculiarly 

 formed. The oesophagus, or gullet, in them, is found replete with 

 glandulous bodies, which serve to dilate and macerate the food, as 

 it passes into the stomach, which is always very large in proportion 

 to the size of the bird, and generally wrapped round with fat, in 

 order to increase its warmth and powers of digestion. 



Granivorous birds, or such as live upon fruits, corn, and 

 other vegetables, have their intestines differently formed from those 

 of the rapacious kind. Their gullet dilates just above the breast 

 bone, and forms itself into a pouch or bag, called the crop. This 

 is replete with salivary glands, which serve to moisten and soften 

 the grain and other food which it contains. These glands are very 

 numerous, with longitudinal openings, which emit a whitish and 

 a viscous substance. After the dry food of the bird has been 

 macerated for a convenient time, it then passes into the belly, 

 where, instead of a soft, moist stomach, as in the rapacious kind, 

 it is ground between two pair of muscles, commonly called the 

 gizzard, covered on the one side with a stony, ridgy coat, and 

 almost cartilaginous. These coats rubbing against each other, are 

 capable of bruising and attenuating the hardest substances, their 

 action being often compared to that of the grinding teeth in man 

 and other animals. Thus the organs of digestion are in a manner 



