248 BIRDS. 



As regards the structure of the wing proper, the humerus 

 is short and strong, and articulates superiorly with an arti- 

 cular cavity formed partly by the coracoid and partly by the 

 scapula. The fore-arm is composed of a radius and ulna, of 

 which the former is the smallest and most slender. The 

 carpus is reduced to two small bones wedged in between the 

 distal end of the fore-arm and the metacarpus. One other 

 bone of the normal carpus (namely, the " os magnum ") is 

 present, but this is anchylosed with one of the metacarpals. 

 There are thus really three carj)al bones, though only two 

 appear to be present. (According to Morse, there is a fourtli 

 carpal, which early anchyloses with the base of the meta- 

 carpal of the middle finger). The carpus is followed by the 

 metacarpus, the condition of which agrees with that of the 

 carpal bones. The two outermost of the normal five meta- 

 carpals are absent, and the remaining three are anchylosed — 

 together with the os magnum — so as to form a single bone 

 (fig. 582, A, m). This bone, however, appears externally as if 

 formed of Uoo metacarpals united to one another at their 

 extremities, but free in their median portion. The meta- 

 carpal bone which corresponds to the radius is always the 

 larger of the two (as being really composed of two meta- 

 carpals), and it carries the digit which has the greatest num- 

 ber of phalanges. This digit corresponds with the " index " 

 finger, and it is composed of two, or sometimes three, pha- 

 langes. At the proximal end of this metacarpal, at its outer 

 side, there is generally attached a single phalanx, constitut- 

 ing the so-called " thumb," which carries the " bastard- wing," 

 and is sometimes furnished with a claw. The digit which is 

 attached to the ulnar metacarpal corresponds to the middle 

 finger, and never consists of more than a single phalanx. 



As regards the structure of the posterior extremity or hind- 

 limb, the pieces which compose the innominate bones (namely, 

 the ilium, ischium, and jjubes) are always anchylosed with 

 one another ; and the two innominate bones are also always 

 anchylosed, by the medium of the greatly-elongated ilia, with 

 the sacral region of the spine. In no living bird, however, 

 with the single exception of the Ostrich, are the innominate 

 bones united in the middle line in front by a symphysis 



