EXTERNAL PARTS OF BIRDS.—THE WINGS. 107 
structed, by loss of some of the digits that five-fingered animals possess, and by the compres- 
sion of those that are left. The wing proper begins at the shoulder-joint, where it hinges 
freely upon the’ shoulder, in a shallow socket formed conjointly by the shoulder-blade or 
scapula, and by the coracoid 
bone; these two, with the 
clavicles, collar-bones or mer- 
ry-thought, furculum, form- 
ing the shoulder-girdle, or 
pectoral arch (figs. 56, 59). 
The wing ordinarily con- 
sists,’in adult life, of ten or } 
eleven actually separate bones ; 
in the embryo (see fig. 29) 
there are indications of several 
more at the wrist-joint, which 
speedily lose their individual 
identity by fusing together 
and with bones of the hand. 
Aside from these, there is S 
often an accessory ossicle at Fie. 28.— Mechanism of elbow-joint. (See explanation of tig. 27.) 
the shoulder-joint (fig. 56, ohs), sometimes one at the wrist-joint, occasionally an extra bone at 
the end of the principal finger. The normal or usual number is shown in fig. 27, taken from 
a duck (Clangula islandica), in which there are eleven. 
The upper arm-bone, h, reaching from the shoulder A 
to the elbow B, is the humerus. In the closed wing, the 
humerus lies nearly in the position of the same bone in man 
when the elbow is against the side of the body; in extension 
of the wing, the elbow is borne away from the body, as when 
we raise the arm, but carry it neither forward nor backward. 
A peculiarity of the bird’s humerus is, that it is rotated on 
its axis through about the quadrant of a circle, so that what 
is the front of the human bone is the outer aspect in the 
bird. The humerus is a cylindric bone, straightish or some- 
what italic f-shaped, with a globular head to fit the socket 
of the shoulder, a strong pectoral ridge for insertion of the 
breast muscles, and at the bottom two condyles (fig. 28, re, 
uc,) or joint-surfaces for articulation with a pair of succeed- 
ing bones. The fore-arm, cubit or antibrachium, extending 
from elbow to wrist, B to C, in fig. 27, has two parallel 
bones of about equal lengths. These are the ulna, ul, and 
the radius, rd; the former, inner and posterior, the larger 
of the two, bearing the quills of the secondary series ; the 
Zr. we latter, slenderer, outer and anterior. The enlarged proximal 
extremity of the ulna is called the olecranon, or “head of the 
Fig. 29, from a young grouse (Centrocercus wrophasianus, 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, scaph- 
olunar or radiale; ¢, cuneiform or ulnare; om, a carpal bone believed to he os magnum, later fusing with the 
metacarpus; z, 2 carpal bone, supposed to be unciform, later fusing with metacarpus; 8, an unidentified fifth 
carpal bone, which may be called pentosteon, later fusing with the metacarpus; 7, radial or outer metacarpal 
bone, bearing the pollex or outer digit, consisting of two phalanges, d and /; 91, principal (median) metacarpal 
bone, bearing the middle finger, consisting of the two phalanges, d/, d// ; 9, inner or ulnar metacarpal, bearing a 
digit of one phalanx, d///, The pieces marked om, z, 7, 8, 9. all fuse with 9’. (From nature by Dr. R. W. Shufeldt, 
U.S. A.) 
