CHAPTER II. 
Tur ExtTeERNAL STRUCTURE OF BIRDS. 
(pee 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 skull, 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- 
