BIRDS. 



INTRODUCTION. 



BIRDS are the spoilt children of Nature the favourites of creation. 

 Their plumage often assumes the most resplendent colours. They 

 have the happy privilege of moving in space now fluttering through 

 the air, hunting the insect which flits from flower to flower ; or 

 soaring high aloft, to swoop upon the victim marked for its prey ; 

 again cleaving the atmosphere, and performing journeys of vast 

 extent with great rapidity. Mankind cannot fail to admire these 

 winged beings, which charm at once by the elegance of their form, 

 the melody of their song, and the graceful impetuosity of their 

 movements. 



Anatomically speaking, Birds, by their internal structure, are 

 connected with the Mammalia, as their skeletons are nearly 

 the same, only modified slightly for the purpose of flight. How- 

 ever, in them there is a double circulation. The heart consists 

 of two moieties, or lobes, known as the auricle and ventricle. 

 It is conical in form, and occupies the anterior part of the thorax, 

 its apex passing between the lobes of the liver ; but there is little 

 perceptible distinction between auricles and ventricles. Their 

 blood is richer in globules than that of the Mammalia, being more 

 thoroughly permeated by air ; the respiratory function is also more 

 energetic, from the same cause in fact, they consume a larger 

 quantity of oxygen, and produce a proportionately greater degree 

 of heat; for while their lungs are small, and placed~in the upper 

 part of the thorax only, where they are confined on each side to a 

 cavity, bounded above by the ribs, and below by an imperfect 

 diaphragm, they are perforated by tubes, which communicate 

 with membranous cells, distributed over the thoracic and abdo- 

 minal cavities, between the muscles, and beneath the skin often 



