30 THE WINGS THEIR BONY FEAMEWOEK. 



closure. Commissure (L. commiltere, 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 Ave say, "commissure straight," or "commissure 

 curved ; " also " commissural edge " of either mandible (equivalent to 

 " tomial edge") in distinction from culmen or gonj's. But it would be 

 well to have more precision in this matter. Let, then, tomia (fig. 5,7) be 

 the true cutting edges of either mandible from tip to opposite base of bill 

 proper, rictus (fig. ^, g) be their edges thence to the point commissure 

 (fig. 5, h) where they join when the bill is open; the line commissure (fig. 

 5,/) 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 inider family Fringillidcc in the 

 Synopsis.) 



The Wings. 



§ 54. Definition. Pair of anterior or pectorcd limbs organized for 

 flight by means of dermal outgrowths. Used for this pux'pose by birds in 

 general ; but by ostriches and their allies only as outriggers to aid running ; 

 by iDcnguins 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 iu a few. To understand their structure we must notice 



§ 55. Theie Bony Feamewoek. (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, tdna and radius, of about 

 equal lengths, reaching from elbow to wrist, forming the forearm, cubit or 

 antihrachium. 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), 

 Avhich 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 (cxe. Archcmpteryx, Struthio, BJiea) ; and no little 

 finger. The third liand-bone is joined to the second, and bears no finger- 

 bone. 



