EXTERNAL PARTS OF BIRDS. — THE WINGS. 



107 



striicted, by loss of some of the digits that five-fingered animals possess, and liy the compres- 

 sion of those that are left. The wing proper begins at the shoulder-joint, where it hingee 

 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, furcuhim, form- 

 ing the shoulder-girdle, or 

 Xtectoral 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 Pig. 28. — Meclianiam of elbow-joint. (See exjjlanation 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. 37, 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 ciuter aspect in the 

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

 what italic /-shaped, mth 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, cuhit or antihracMum, extending 

 fi-om elbow to wrist, B to C, in fig. 37, 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 antericjr. The enlarged proximal 

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



Fig. 29, from a young grouse (Centrocercus urophasianus, 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 radiate; c, 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 pentosteon, later fusing with the metacarpus; 7. radial or outer metacarpal 

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

 bone, bearing the middle finger, consisting of the two phalanges, di, d^' ; 9, inner or ulnar metacarpal, bearing a 

 iligit of one phalanx, dlf. The pieces marked om, z, 7, 8, 9. all fuse with 9'. (From nature by Dr. E. W. Shufeldt, 

 U.S.A.) 



0>f^, 



