The Anatomy of Birds 



in 



FIG. 9. Wing bones of a young Ostrich. 

 Parker'.) 



(After 



I, II, III, digits; i, 2, 3, metacarpals; a, b, c, carpal bones. 



Professor Seeley has thought that the resemblances between birds and ptero- 

 dactyls was more than superficial, but he stands practically alone in this view, 

 the most commonly accepted working theory being that birds and dinosaurs have 

 had a common ancestry. 



The extent to which the skeleton of a bird is permeated by air usually bears 

 a direct and apparent ratio to its mode of life. Thus the Condor and other soar- 

 ing birds, such as the Frigate-birds, Cranes, and Screamers, have very lightly 

 built skeletons, and Ducks and other 

 water fowls have the cavities of the 

 long bones filled with marrow, while 

 the bones of the strictly aquatic Pen- 

 guins are filled with bony tissue. 



That the lightness of the skeleton 

 does not necessarily appear in con- 

 nection with the power of flight is 

 shown by the Hornbills and especially 

 by the larger species, for in these birds of heavy, lumbering flight, the air 

 penetrates to the very tips of the toes. On the other hand, in birds like the 

 Condor and Frigate-bird this pneumaticity, or presence of air in the bones, is 

 believed to aid in oxygenizing the blood and in adjusting the air pressure when 

 a bird descends rapidly from a great height. It may also be connected with 



lessening the sudden shock that 

 takes place when a Gannet or 

 Brown Pelican plunges headlong 

 into the sea. 



It is usual to commence the 

 description of a skeleton with the 

 skull, but while the skull is of 

 the utmost importance to the 

 systematist, it is a complicated 

 structure whose topography is by 

 no means easy to understand, 

 and whose numerous parts bear 

 equally numerous and unfamiliar 

 technical names. So we may 

 slight this, leaving it to be briefly 

 described later on, and begin 



with the wings, which, next to the feathers, are the most obvious features of 

 a bird. 



The wings of a bird comprise the same parts as the fore limb of a mammal or 

 reptile, and save in the hand, we can readily recognize these various parts, the 

 upper arm (humcrus), forearm (radius and ulna), wrist, and hand. 



The bones of the fore limb are modified for the support of the large feathers 

 forming the wing, the hand being reduced to three fingers, while only two of 

 these, those to which the primaries are fastened, are of much use. 



FIG. 10. Wing bones of a young Chicken. (From 

 Coues's " Key.") 



A, shoulder; B, elbow; C, wrist or carpus; D, tip of third finger; 

 a, humerus; b, ulna; c, radius; d, scapholunar bone; e, cuneiform 

 bone; /, g, epiphyses of metacarpal bones /, k, respectively; h, meta- 

 carpal and its digit i. 



