EXTEENAL PARTS OF BIIWS. — THE WINGS. 



107 



Fig. 28. — Mechanism of elbow-joint. See explanation of tig. 27.) 

 , sometimes <>ne at the wrist-joint, occasionally an extra bone at 



strncteil, by loss of some of the digits that fivo-fiiigcred 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; the.se two, with the 

 clavicles, collar-bones or mer- 

 ry-thought, furculum, form- 

 iiiiT 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 

 often an accessory ossicle at 

 the shoulder-joint (fig. 56, ohs) 

 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 ann, 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 fi-ont of the human bone is the outer aspect in the 

 bird. The humerus is a cyliudric bone, straightish or some- 

 what italic /-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, 

 u<;,) or joint-surfaces for articulation \A-ith a pair of succeed- 

 ing bones. The fore-arm, cuhit 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 

 latter, slenderer, outer and anterior. The enlarged proximal 

 extremity of the ulna is called the olecranon, or " head of the 



Fifs. 29, from a young grouse (Centrocercus nrophasianux. six months old), is designed to show the composi- 

 tion <if the carpus and metacarpus before the elements of these bones fuse together: r, radius; v, ulna; s, scaph- 

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

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

 carpal bone, which may be called pentostean, later fusing with the metacarpus; 7, radial or outer metacarpal 

 bone, bearing the j>ollex or outer digit, consisting of two phalanges, d and k; 9', principal (median) metacarpal 

 bone, bearing the middle finger, consisting of the two phalanges. d>, (W ; 9, inner or ulnar metacarpal, bearing a, 

 digit of one phalanx, H'". The pieces marked om, z, 7, 8, 9. all fuse wi Ji 9'. (From nature by Dr. R. W. Shufeldt, 

 U.S.A.) 



