i6o GENERAL ORNITHOLOGY 



fore, middle, and ring fingers, and being consequently the second, 

 third, and fourth digits, as marked in the figure. The digit marked 

 d 2 is commonly called a bird's thumb or pollex. The A'pteryx and 

 the cassowaries have but one complete digit. The resemblance to 

 a lizard's or quadruped's digits is increased by the claivs which many 

 birds possess, These may be borne on the enlarged terminal 

 phalanx of d 2 (k, in Fig. 29), as is very well shown in the turkey- 

 buzzard and other American Cathartidce ; both on this and on the 

 terminal phalanx of d 3 (d" in Fig. 29), as in the ostrich ; on the 

 latter alone, as in- the Apteryx, cassowary, American ostrich, and 

 swan. The inner finger, d 4 {d'" in Fig. 29) is not known to ever 

 bear a claw, excepting in Archceopteri/x. The whole segment, C to 

 D, is commonly called " the hand," " pinion," or manics, though, as 

 we have seen, it consists of hand proper (metacarpus), and fingers 

 (digits) with their respective phalanges. (Fig. 29 his.) 



Some other bones are observed in birds' wings. As already 

 said, there is a supplementary'' ossicle in the shoulder-joint of many 

 birds ; it is badly called the scajnda accessoria (Fig. 56, ohs). At the 

 convexity of the elbow there may be one or more ossicles, not per- 

 taining properly to the wing-skeleton, but developed in the tendons 

 of muscles passing over the joint ; they are sesamoids, like the 

 human patella, or knee-cap. In various birds there is found at 

 the convexity of the wrist, on the head of the metacarpal, an 

 ossicle called the os prominens ; apparently a sesamoid. Some other 

 ossicles observed in the wrists of young or embryonic birds are all 

 supposed to be carpal elements, the exact homologies of which may 

 be still questioned. 



The Mechanism of these Bones is admirable. The shoulder- 

 joint is free, much like our own, permitting the humerus to swing 

 all about ; though the principal motions are to and from the side of 

 the body {adduction and ahduction), and up and down in a vertical 

 plane. The elbow-joint is a very strict hinge, permitting motion in 

 one plane, nearly that of the wing itself. The finger-l)ones have 

 little individual motion. The construction of the wrist-joint is 

 quite peculiar. In the first place the two bones of the forearm are 

 so fixed in relation to each other, that the radius cannot roll over 

 the ulna, like ours. If you stretch your arm upon the table, you 

 can, without moving the elbow, turn the hand over so that either 

 the palm or the knuckles are downward. This is a rotary motion 

 of the bones of the forearm, called pronation and supination; the 

 hand is prone when the palm touches the table, supine when the 

 knuckles are downward. This rotation is absent from the bird's 

 arm ; if it could occur, the action of the air upon the pinion- 

 feathers would throw them all " at sea " during the strokes of the 

 wing, rendering flight difficult or impossible. The hinging of the 



