154 ELEMENTS OF ORNITHOLOGY. 
which answers to our fore-arm, these being united by a joint like 
our elbow. These portions of the arm are further held together 
by a very elastic and extensible fold of skin, which is of course 
widest opposite the elbow-joint. Another fold extends from the 
trunk tothe upper arm ; each of these folds is sometimes called 
a patagium. ‘'hirdly, there is a part which answers to our 
hand, and which is termed the pinion. Within this “ hand” — 
or manus—there are, as we shall see when we study the skele- 
ton, parts which represent, more or less imperfectly, our first 
and second (index and middle) fingers, but they are all enclosed 
in one solid structure invested by skin, so that no finger can 
be externally recognized as free and separate like our own. 
There is, however, a short and small thumb—or pollew—which 
shows itself externally as a separate part. Thus the thumb 
and fingers (or digits) of the hand are enclosed as ours are 
when we have put on a pair of boxing-gloves. The thumb is 
a separate and distinct part of the pinion, but the other digits 
are enclosed, together with what answers to the middle part of 
our hand, in one continuous pad. 
The relative proportions of the three solid parts of the wing 
differ in different birds. Thus the upper arm is relatively, as 
well as absolutely, very long in the Albatross; while in the 
Humming-birds it is relatively, as well as absolutely, very 
short. The fore-arm is longer than usual in the Apteryx, while 
in the Humming-birds and Swifts the pinion is relatively very 
much elongated. 
The feathers which clothe the wing belong to three divisions, 
two of which correspond to those of the two divisions of the tail- 
feathers. 
There are, first, the effective feathers of flight, which are 
called remiges or rowers; and there are, secondly, the covering 
feathers or tectrices, which invest the bases of the effective 
feathers of the wing, as the covering feathers of the tail invest 
the bases of the effective feathers of that part—the “ rectrices.” 
The third division consists of a small group of feathers which 
are implanted on the thumb. 
Thumb-feathers—The feathers of the pollex are a small 
group which constitute what is called the <Alula (“little 
wing”) or the Ala spuria (bastard wing). This little group of 
feathers is placed on the front and outer side of the pinion, and 
lies on the dorsum of the wing along its front or outer 
border. 
