BIRDS ORGANIZATION DIAGRAM 4. 



59 



when looking at pigeons flying, to see how they use it to guide 

 themselves. 



However, all birds do not fly equally well. There are some, 

 like fowls, which have much trouble to rise from the ground, 

 and others, like the ostrich, which cannot fly at all. Others, 

 instead of wings, have a kind of flat oars, with which it would 

 be impossible for them to fly, but which they use for swimming ; 

 among these are the penguins and the auks. 



The bones of birds are not filled with 

 marrow, like those of the ox and other 

 mammals, but are hollow and full of 

 air, which makes them lighter, and renders 

 flight easier. 



Birds generally swallow their prey at 

 a single gulp. The oesophagus often 

 exhibit a fold throughout the length of 

 the neck, well known to fanciers as the 

 crop. When a pigeon is killed which 

 has just been feeding, the crop is found 

 to be filled with corn. When pigeons 

 coo and inflate the neck, it is because the 

 crop is filled with air. The food then 

 passes into the gizzard, a stomach with a 

 very thick, shining, and almost silvery 

 surface. The two outlets of this stomach 

 are very near to each other ; so that it 

 requires a little attention to distinguish the oesophagus by which 

 the food enters the gizzard, from the orifice through which it 

 passes out. 



The gizzard is nearly always found filled both with corn and 

 small stones, which the bird swallows at the same time. The 

 sides of the gizzard are formed of an exceedingly strong muscle ; 

 and they contract, and bruise the corn among these stones. 

 The product of this kind of mastication then passes into a third 

 stomach, and into the intestine. 



Pengi 



