CHAPTEE 11. 



The Extebnal Stetjcttiee of Bieds. 



TPHE body of every Bird consists of a compact central part, or 

 -*- trunk; a very moveable neck, bearing a rounded head 

 with a more or less prolonged beak ; a pair of wings ; a pair of 

 legs, and a short solid tail. It is always clothed with feathers 

 and the wings and tail almost always support long ones. The 

 legs end in from two to four toes terminated by claws. There 

 are always a pair of eyes plainly visible, but the equally constant 

 pair of ears generally give no external indications of their 

 presence. 



The leading facts of the internal structure of, a Bird are, like 

 those of our own internal structure, matters of common know- 

 ledge. Thus it is almost superfluous to say that immediately 

 beneath the skin of a Bird is . the " flesh " of its body, which 

 more or less amply wraps round its bones — the bones of the 

 head, neck, trunk, tail, and limbs. Within the trunk is a 

 cavity wherein lie a variety of parts known as the heart, lungs, 

 kidneys, crop, stomach. Intestine, liver, &c. 



Inside the skuU, and its continuation posteriorly, the back- 

 bone, is a mass of white substance — the brain and spinal 

 marrow. Delicate threads of similar substance (nerves) and 

 tubes of various sizes (vessels) traverse the body in all directions. 



Each considerable and more or less distinct part is called an 

 " organ " — as e. g. the heart is an organ of circulation. Each 

 connected set of organs is called a system — as the heart and the 

 vessels called " arteries " and " veins " form the " circulating 

 system," and the brain, spinal cord, and nerves form the "nervous 

 system." The flesh is composed of muscle, and all the muscles 

 taken together constitute the " muscular system," and we shall 

 presently have to notice the " alimentary," " respiratory," " uri- 



