EXTERNAL PARTS OF BIRDS. — THE WINGS. 



113 



axis through about the quadrant of a circle, so that what is the front of the human bone is 



the outer aspect in a bird. The humerus is a cylindric bone, straightish or somewhat italic 



/-shaped, with a globular head to fit the socket of the shoulder, a strong pectoral ridge for 



insertion of breast muscles, 



and at the lower end two 



condyles (fig. 28, re, uc), or 



surfaces for articulation with 



a pair of succeeding bones. 



The second segment is the 



fore-arm, ciihit or antibra- 



chium, extending from elbow 



to wrist, B to C, fig. 27 ; 



this has two parallel bones of 



about equal lengths. These 



are tihui, ul, and radius, rd ; 



the ulna, inner and posterior, 



the larger of the two, bears 



quills of the secondary series ; 



the radius is slenderer, outer, 



aud anterior. The enlare;ed Fm. 28. — Mechanism of elbow-joint. (See explanation of Jig. 27.) 



upper end of tlie ulna is called olecranon, or ''head of the elbow." The third segment of the 



wing is the pinion, hand, or manus, to be considered in its three successive portions : wrist or 



carpus ; hand proper or metacarpus ; and fingers or digits : in all, C to D in fig. 27. In adult 

 life, the carpus almost always consists of 'two small knobby 

 carpal bones, extremely irregular in shape, called scapho- 

 lunar, sc, and cuneiform, cu; or radiale and ulnare, because 

 one of them is at the end of the radius, and the other at the 

 end of the ulna. In embryos, several more cartilaginous 

 or gristly nodules are demonstrable ; their number varies in 

 different birds. The theory is, that birds' ancestors had the 

 following number of carpals : three in a proximal or first 

 row, warned radiale, intermedium, and ulnare; one median, 

 called centrale; and five in a distal row, being one for eacli 

 of the five ancestral digits (though no more than three have 

 ever been demonstrated). It is believed with reason that 

 the actual radiale consists of an ancestral radiale fused with 

 an intermedium ; that the actual ulnare consists of an an- 

 cestral ulnare fused with a centrale; and it is certain that, 

 whatever number of distal carpals can be demonstrated in 

 any case, they all fuse with the metacarpal bones. Thus a 

 bird's carpals are reduced to the two abovesaid, and one of 

 these disappears in some ratite birds. The hand proper or 

 metacarpus, C to E (exclusive of rf2), in all recent adult 

 birds, consists of a single metacarpal bone; but this is a 



from a yonnrj grouse { Centrocercus nrophaxiantix, six months old), is designed to show the composi- 

 tion of the carpus and metacarpus before the elements of these bones fuse together: r. radius; u, ulna; s. seai)h- 

 olunar or radiale; c, cuneiform or ulnare; om, a carpal bone believed to be os magnum, later fusing with the 

 metacarpus; «. a carpal bone, supposed to be unciform, later fusing with metacarpus; 8, an unidentified fifth 

 carpal bone, wliich may be called pentnstemi. later fusing with the metacarpus; 7. r.adial or outer metacarpal 

 bone, bearing the pollex or outer digit, consisting of two plialanges, d and k; 9', principal (median) metacarpal 

 bone, bearing the middle finger, consisting of the two plialanges, di, d" ; 9, inner or ulnar nietacarp.al, bearing a 

 digit of one phalanx, dl'f. The pieces marked om, z, 7, 8, 9. all fuse with 9^ (From nature by Dr. R. W. Shufeldt, 

 U.S.A.) „ 



