108 GENERAL ORNITHOLOGY. 



elbow." The third segment of the wing is the wrist or carpus. In adult life, this normally 

 consists of two little knohhy carpal bones, extromely irregular in shape,oalled the seapholunar, 

 sc, and (yimeiform, cu. One being at the end of the radius, the other at that of the ulna, they 

 are also called radiate and ulmare. In the embryo, there is at least another carpal bone, that 

 early fuses with the next segment. This fourth segment is the hamd proper, or metacarpus, 

 mc, C to E (exclusive of d'i). The single metacarpal or hand-bone is very composite; that 

 is, compounded of several; for, besides including certain carpal elements, as already said, it 

 consists of three bones fused (in all recent birds) in one, corresponding to the three digits or 

 fingers that birds possess. In fact it is three metacarpals in one. The metacarpal corre- 

 sponding to the principal finger is much the largest of the three ; that of the first finger is very 

 short, being only the expanded part seen in the figure just above the bone marked d 2 ; that 

 of the third finger is nearly as long as the main metacarpal, but much slenderer, and usually 

 fused only at its two ends, leaving between itself and the main metacarpal a considerable 

 space, as seen opposite the letters mc in the figure. The wing is finished off with three 

 fingers or digits, marked d 2, dZ, ci 4. The niiddle one of these, E Xo D in the figure, is 

 much the largest, and forms the main continuation of the hand. This digit, d 3, ordinarily 

 consists of two bones, called phalanges, placed end to end, as in the example before us ; but 

 occasionally thiere is found a third phalanx. The outer or radial digit, d 2, ordinarily con- 

 sists of two bones, of which the terminal one is small, and may be wanting. The inner or 

 ulnar digit, d 4, consists of a single small phalanx, closely bound to the side of the middle 

 finger. Corresponding to the compactness and consolidation of these terminal segments, the 

 digits enjoy little individual motion. The outer or radial digit is the most independent one. 

 In the Ardheopteryx the three metacarpals were free bones, and the whole hand more like 

 that of a lizard. No bird now has free metacarpals in adult life; none has more than thi'ee 

 digits. These three are supposed by some to 'correspond to the thumb and fore and middle 

 fingers of our hands ; by others, to the fore, middle, and ring fingers, and being consequently 

 the second, third, and fourth digits, as marked in the figure. The digit marked <? 3 is com- 

 monly called a bird's thumb ov pollex. The Apteryx and the cassowary have but one complete 

 digit. The resemblance to a lizard's or quadruped's digits is increased by the claws 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 CatharUdee ; both on 

 this and on the terminal phalanx of d 3 id" in fig. 29), as iii 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 xa Archteopteryx. The whole segment, 

 C to B, is commonly called " the hand," " pinion," or manMs, though, as we have seen, it consists 

 of hand proper (metacarpus), and fingers (digits) with their respective phalanges. (Fig. 112 ter.) 

 Some other bones are observed in birds' wings. As already said, there is a little ossicle in 

 the shoulder-joint of many birds ; it is called the scapula aecessoria (fig. 56, ohs). At the con- 

 vexity of the elbow there may be one or more ossicles, not pertaining 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 birds are all supposed to be 

 carpal elements, the exa«t homologies of which may be stiU 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 abduction), 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-bones have little individual motion. The construction of the wrist-joint is 



