i6 



The Anatomy of Birds 



The wrist of the adult bird, frequently called shoulder, consists of but two 

 bones; the part corresponding to the palm of the hand comprises three meta- 

 carpals and two carpals solidly fused into one mass, though this can be seen only 

 in a very young bird. Following this is a short finger on the front edge of the 

 wing bearing the so-called bastard wing, one long central bone and one shorter 

 more or less pointed. The stages by which the clawed hand has been trans- 

 formed to a wing may be gathered partly from fossils and partly from a study of 

 the embryo, but it is not quite certain whether the first finger of a bird, that bear- 

 ing the so-called spurious wing, corresponds to the first or second finger of man, 

 with the probability in favor of its being the second. The wing bones are 

 lengthened or shortened in a pretty direct ratio to the rapidity with which the 

 wings are moved, being longest in such sailing birds as the Albatross and 



shortest in the Pigeons and 

 Hummingbirds. The short- 

 ening is greatest in the 

 humerus; for while in the 

 Albatross and Frigate-bird 

 the upper arm and forearm 

 are about equal, in the 

 Pigeons the humerus is 

 somewhat shorter, and in 

 the Hummingbird very 

 much shorter, than the 

 succeeding bones. This 

 relates to the fact that a 



FIG. ii. Wing bones of an embryo Hoactzin. 

 K. Parker.) 



(After W. 



Wing bones of an embryo Hoactzin, when the embryo was about half 



ripe for hatching, showing the claw on the first digit, dg 1 ; on the second Ki r H'c wina ic 

 digit, dg'; the rudimentary claw on the third digit, <fg 3 ; and the rudiment ' Wing 1 > a, 



of a fourth digit, dg*; h, humerus; r, radius; u, ulna; re, radiale; ue, 

 ulnare; i, intermedium; c, centrale; dc l , dc a , distal carpals. 



< v 



shoulder joint representing 



the fulcrum, the muscle the power, the end of the wing the weight. The 

 shorter the wing, the easier it is to move it rapidly; the more rapidly it is 

 moved, the stronger must it be. The wing of a Condor or Albatross would 

 break, were sufficient power applied to move it as fast as that of the Pigeon. 

 The rapidity of the wing stroke is also indicated by the development of the 

 processes about the inner end of the humerus for the attachment of wing 

 muscles, these reaching by far their greatest development in Hummingbirds. 



The wing is supported by the coracoid, a bone abutting on the front of the 

 breast-bone and raking forwards and upwards. This bone, represented in the 

 higher mammals by a mere process on the shoulder, forms half of the shoulder 

 joint in reptiles and also in the Echidna and Platypus, and by far the greater 

 part of the shoulder joint in birds, that part of the shoulder blade being much 

 reduced. 



In perching birds the coracoid is long and slender, and in birds which soar or 

 sail it is shortened and broadened, for it is a rather curious fact that while the 

 amount of muscular power employed in flight is much smaller in sailing birds 

 than in others, the support for the wing is much more strongly built. In the 



