108 GENERAL ORNITHOLOGY. 



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

 consists of two little knobby carpal b(.jnes, extremely irregular in shape, called the scaplioluiiar, 

 . ,vc, and cuneiform, cu. One being at the end of the radius, the other at that of the ulna, they 

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

 early fuses with the next segment. This fourth segment is the hand piroper, or metacarjju.'i, 

 mc, C to E (exclusive of d 2). 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 tlirec 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 

 sliort, 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, d 3, d i. The middle one of these, E to D in the figure, is 

 nmch the largest, and forms tlie main continuation of the hand. This digit, d3, ordinarily 

 consists of two l)ones, called jjl'ahivges, placed end to end, as in the example before us ; but 

 occasionally there is found a third ])halanx. Tlie outer or radial digit, d 2, ordinaiHy 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 Arclifcopteryx the three metacarpals were free bones, and tlie whole hand more like 

 that of a lizard. No bird now has free metacarpals in adult life; none has mfire than three 

 digits. These tliree are supposed by some to correspond to the tliurab 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 d 2 is com- 

 monly called a bird's thumb ox poUex. 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 fi 2 (Tc, in 

 fig. 29), as is very well shown in the turkey-buzzard and other American Catluirtidee ; 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 Icnown to ever bear a claw, excepting in Archccopteryx. The whole segment, 

 C to D, is commonly called " the hand," " pinion," o-rmanus, 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 shouldor-joiut of many birds ; it is called the scapula accessoria (fig. 56, ohs). At the con- 

 vexity of the elbow there may be one or more ossicles, not p)ertaining piroperly 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 ; apiparently a 

 sesamoid. Some other ossicles observed in the wrists of young 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 

 .Mir 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 



