GENERAL CHARACTERISTICS. 290 



Ornithologists have devised a number of terms to indicate the different parts 

 of a body of a bird, several of which arc 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 fiat on 



the sides of the head, usually a little behind and below the eyes. The ryes, which 

 are in most eases placed laterally and near the middle of the head, are provided 

 with a third eyelid, or nictitating membrane, which can lie 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 he 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 fissirostral, dentirostral, 

 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 replace, I by a more or less leathery 

 skin. The horny covering of the metatarsus may consisi of small pieces, with the 

 edges in apposition, as in the plovers, when it is said to 1»- 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 



notice. A feather in its most c plete 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 wnibilicus. The shaft is four-sided, elastic, pithy, and less horny than 

 the quill ; and gradually tapers at its extremity to a fine 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 bj' 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 atypical 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 poivder-down 

 /•"fliers. 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 o T ow 



