158 ELEMENTS OF ORNITHOLOGY. 
avillary feathers, because they are nearest to the arm-pit. They 
lie close to the body at the inner margin of the under surface of 
the wing, and are generally longer and firmer than the rest of 
the under wing-coverts. They correspond below with the 
humeral coverts above, and may be well seen in the Duck, the 
Snipe, and the Plover. 
Claws.—In some birds a claw exists at the end of the thumb ; 
in others one at the end of the thumb and one towards the 
apex of the pinion or there only. Besides these claws, claw- 
like structures termed spurs may be borne, one on the side of 
the pinion; and in one bird, the Screamer (Palamedea), there 
are two of them. Such a structure is called a calcar. 
The Legs.—We must now pass to the hind, or posterior, pair 
of limbs—the legs—which are called pelvic limbs, or append- 
ages, because they are attached, as we shall shortly see, to a 
portion of the skeleton called the “ pelvis.” 
As has been said, all birds have a pair of legs, and these 
organs have a general, essential resemblance to our own lower 
limbs, having three distinct parts :—(1) the part corresponding 
to our thigh, (2) the part answering to our leg and called the 
crus, and (3) parts which correspond with our foot, the straight 
upper part of which is called in Ornithology the tarsus. 
There is a knee-jomt between the thigh and the leg which is 
like our own joint in its direction and essential particulars. 
There is also a joint between the crus and the tarsus which 
roughly answers to our own ankle-joint, but (as we shall see 
when we study the bones) does not entirely or accurately 
correspond therewith. 
The foot—pes—(using that term as the equivalent to our 
foot) includes the straight and sometimes greatly elongated 
segment of the limb called the “ tarsus,” and also the toes, or 
digits, which diverge from the lower end of that segment, 
though the toes alone are commonly called the “ foot.” 
The foot, using that term in its wide sense, is of course 
always a conspicuous part of the limb, while more or less of 
the leg and all the thigh are concealed by the plumage, or even 
enclosed within the general envelope of the skin of the trunk. 
Thus the knee is never externally apparent, and this circum- 
stance, together with the conspicuous ankle and long upper 
part of the foot, give rise to popular misapprehensions about 
the nature of the lower limbs of birds. 
The thigh is always very thick. The next segment, or true 
