EXTERNAL PARTS OF BIRDS. — THE WINGS. 



107 



structed, by loss of some of the digits tliat five-fiiigered acimals possess, and by the compres- 

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

 freely upon the shoulder, in a shalhiw sncltct foniied cmijointly by the shoulder-Made or 

 scapula, and by the coracokl 

 bone ; these two, with the 

 clavicles, collar-bones or mer- 

 ry-thought, fnrcidum, form- 

 ing the shoulder-girdle, or 

 pectoral arch (figs. 56, 59). 



The wing ordinarily con- \^|\ 

 sists, in adult life, of teyi 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 Fig. 28. ^Mechanism of elbow-joint. (See e.xplaTiation of tig. 27.) 



the shoulder-joint (fig. 56, olis), sometimes one at the wrist-joint, occasionally an extra bone at 

 the end of the principal finger. Tlie normal or usual numlier is shown in fig. 37, taken from 

 a duck (Clani/ula islandka), in whicli there arc eleven. 



Tlie upper arm -bone, /*, reaching from the shoulder A 

 to the elbow B, is the humerus. In the closed wing, the 

 humerus lies nearly in the position (.if the same bone in man 

 when the elbow is against the side f>f the Ixidy; in extension 

 of the wing, the elbow is borne away from tlie Viody, 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 /-shaped, with a globular head to fit the socket 

 of the shoulder, a strong pectoral ridge for insertiun of the 

 breast muscles, and at the bottom t^'o condyles (fig. 28, re, 

 tic,) or joint -surfaces for articulation "VAdth a pair of succeed- 

 ing bones. The fore-arm, cuhit or antihrachium, extending 

 from elbow to wrfst, 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 oi the 



Fig. 29, from a young grouse [Centrocercits nrophaslanuf.-, six montlis old), is designed to show tlie composi- 

 tion of tlie carpus ami metacarpus before the elements of these bones fuse together ; r, radius ; u, ulna ; s. scaph- 

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

 metacarpus; s, 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 tlie metacarpus; 7, radial or outer metacarpal 

 bone, bearing the pollex or outer digit, consisting of two phalanges, d and 1: : 9', 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, (!"'. Tlie pieces marked om, z, 7, 8, 9. all fuse with 9'. (From nature by Dr. E. W. Shufeldt, 

 U.S.A.) 



