30 THE WINGS—THEIR BONY FRAMEWORK. 
closure. Commissure (i. committere, to put or join together) means the 
point where the gape ends behind, that is, the angle of the mouth, where 
the opposed edges of the mandibles join each other; but as in the last case, 
it is loosely applied to the whole line of closure, from true commissure 
to tip of the bill. So we say, “commissure straight,” or “commissure 
curved;” also “commissural edge” of either mandible (equivalent to 
“tomial edge”) in distinction from culmen or gonys. But it would be 
well to have more precision in this matter. Let, then, toma (fig. 5,7) be 
the true cutting edges of either mandible from tip to opposite base of bill 
proper, rictus (fig. 5, 7) be their edges thence to the PomnT commissure 
(fig. 5, 2) where they join when the bill is open; the LINE commissure (fig. 
5, f) to include both when the bill is closed. The gape is straight, when 
rictus and tomia are both straight and lie in the same line; curved, sinuate, 
when they lie in the same curved or waved line; angulated, when they are 
straight, or nearly so, but do not lie in the same line, and therefore meet at 
an angle. (An important distinction. See under family /ringillide in the 
Synopsis. ) 
THe WINGS. 
§ 54. Deriirion. Pair of anterior or pectoral limbs organized for 
flight by means of dermal outgrowths. Used for this purpose by birds in 
general; but by ostriches and their allies only as outriggers to aid running ; 
by penguins as fins for swimming under water; used also in the latter 
capacity by some birds that fly too, as divers. Wanting in no recent birds, 
but imperfect in a few. To understand their structure we must notice 
§ 55. Tuerr Bony Frameworrn. (Fig. 6.) This ordinarily consists 
of nine actually separate bones; but there are several more that fuse 
together. The arm-bone, humerus, a single bone, reaches from shoulder to 
elbow; it is succeeded by two parallel bones, wna and radius, of about 
equal lengths, reaching from elbow to wrist, forming the forearm, cubit or 
antibrachium. The wrist (carpus) has two little knobby carpal bones, called 
scapholunar and cuneiform; very early in life there is another, the mag- 
num, that soon fuses with the hand-bone, or metacarpal. At first, this last 
is of three bones, corresponding to those of our hand that support our fore, 
middle and ring finger respectively ; afterwards they all run together. The 
one corresponding to the middle finger is much the largest of the three, and 
it supports two finger-bones (phalanges) placed end to end, just as our 
‘three similar finger-bones are placed one after the other at the end of their 
own hand-bone. The forefinger hand-bone sticks out a little from the side 
of the principal one, and bears on its end one finger-bone (sometimes two), 
which is commonly, but wrongly, called the bird’s “thumb.” For although 
on the extreme border of the hand, it is homological with the forefinger ; 
birds have no thumb (exe. Archewopteryx, Struthio, Rhea); and no little 
finger. The third hand-bone is joined to the second, and bears no finger- 
bone. 
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