GENERAL CHARACTERISTICS. 
299 
Ornithologists have devised a number of terms to indicate the different parts 
of a body of a bird, several of which are located in the accompanying diagram; 
the others it will be unnecessary to mention here. It may be observed, however, 
that the ears of Birds are unprovided with external conchs, merely opening flat on 
the sides of the head, usually a little behind and below the eyes. The eyes, which 
are in most cases placed laterally and near the middle of the head, are provided 
with a third eyelid, or nictitating membrane, which can be drawn obliquely like a 
shutter over the eyeball, while the proper eyelids remain open; as may be observed 
in a captive owl or eagle, when the glistening white membrane will be seen from 
time to time to sweep across the eye with extreme rapidity. 
The beaks of birds, which, as we have said, are always encased in horn or 
leathery skin, have different terms applied to them, according to their relative 
length and form ; the meaning of most of such terms, as jissirostral, dentirostrcil , 
conirostral, etc., being self-apparent. A horny investment is also generally 
present on such portions of the lower part of the legs as are devoid of feathers; 
although in some cases, as in the ducks, this is replaced by a more or less leathery 
skin. The horny covering of the metatarsus may consist of small pieces, with the 
edges in apposition, as in the plovers, when it is said to be reticulate ; but frequently 
the front surface, as in the fowls, has a number of broad overlapping plates, when 
it is termed scutate. Occasionally each side is invested by a single greave-like 
plate, meeting its fellow in a prominent ridge at the back. 
The feathers of birds, being all-important, need a somewhat fuller 
Plumstg'6. , , . ^ ^ 
notice. A feather in its most complete state of development consists 
of a main stem, and a secondary stem, or after-shaft ; but the latter is frequently 
wanting. The base of the main stem is formed by the hollow horny quill, the 
lower end of which is pointed and inserted into the skin. The upper part of the 
quill passes into the shaft, or rachis, at a point marked by a small aperture termed 
the upper umbilicus. The shaft is four-sided, elastic, pithy, and less horny than 
the quill; and gradually tapers at its extremity to a tine point. On either side of 
the shaft are the two webs, collectively forming the vane of the feather. Each 
web or half of the vane, one of which is generally considerably wider than the 
other, is composed of a series of flattened plates closely applied to one another, and 
diverging from the shaft at an open angle, each plate terminating in a point. 
These plates form the barbs, and they are held together by barbules, given off in 
the same manner as are the barbs from the stem; while the barbules may again 
give off booklets. The after-shaft is, when fully developed, a miniature of the main 
stem, from which it is given off* at the junction of the quill with the shaft. Such 
is the structure of a typical feather; but the soft feathers known as down have 
the stem short and weak, or even wanting, while the barbs are soft and not held 
together by fully-formed barbules and hooklets. Sometimes the ends of such 
feathers break up into powder, and they may then be spoken of as jpoivder-down 
feathers. In another type of feather the vane is rudimentary, and the whole 
structure then becomes more or less hair-like; to such the term thread-feathers is 
applicable. Finally, the feathers covering the body and concealing the underlying 
down are conveniently referred to as the contour-feathers. 
Instead of being evenly distributed over the body of a bird, the feathers grow 
