OR OSSEOUS SYSTEM. 93 



plane, as in mammalia. In the arm of the bird there is a 

 great development of the proximate bones, which by their 

 magnitude and strength are best able to withstand the re- 

 sistance to which they are so frequently opposed, while the 

 more delicate and the more distant bones of the hand are 

 few and less perfectly developed. The humerus (Fig. 45. e,) 

 has a broad, compressed, and curved head, the large articular 

 surface of which plays freely in the shallow glenoid cavity 

 formed by the scapular and coracoid bones. In the con- 

 cavity at the back part of the head of the humerus, are the 

 large apertures by which the air from the axillary cells gains 

 admission into the capacious interior cavity of this bone. 

 The distal extremity of the humerus is curved forwards, and 

 presents a broad articular surface with a double condyle, on 

 which chiefly rotates the large ulna (Fig. 45. h,) the radius 

 being a more slender bone. The radius and the ulna are 

 so articulated as to resist pronation and supination of the 

 hand, these motions being partially admitted at the head of 

 the humerus. The arm of the bird is fixed in a state of 

 pronation, the position best suited to strike the air with 

 effect, and the hand moves upon the arm, not in the 

 common mode of flexion and extension, but 

 by abduction and adduction. At the ex- 

 tremity of the radius (Fig. 50. ,) and the 

 ulna (b,) there are two carpal bones (c, ?,) 

 which are succeeded by a single long meta- 

 carpal bone (y,} composed of three pieces an- 

 chylosed together. One of these pieces (e,) on 

 the radial side of the hand is very short, and 

 supports the single small phalanx of the radial 

 or fore finger (h.) The middle meta-carpal 

 piece (/*,) is by much the largest, and supports 

 at its extremity generally three phalanges of 

 the middle finger (k, I, m,) the last of which is 

 very short and slender. The first phalanx (k,) 

 of the middle finger has a flat compressed 

 form, like the meta-carpal bone. At the ulnar 

 side of the distal termination of the meta-car- 

 pal bone is a small single phalanx of the outer 

 or little finger (i,) which is more immediately 

 connected with the exterior slender portion (g,) 



FIG. 50. 



