30 INTRODUCTION. 



greatly enlarged and flattened at its anterior end, at the ex- 

 tremity of which is the articular surface corresponding to the 

 glenoid cavity, /, ?w, in Fig. 4. The upper edge or crest of this 

 enlarged part is curved a little forwards, and affords insertion 

 to the pectoral muscle, wdiich pulls the wing downwards ; while 

 its lower edge is rounded and curved backwards. Behind this 

 part is an orifice by w^hich the air gains access to its cavity. 

 The outer extremity of the bone is also flattened, curved a little 

 outwards, and presents two rounded surfaces, the lower, larger 

 for the ulna, the other for the radius. This bone varies ex- 

 tremely in length, being very short in the Sw^allows, of moderate 

 length in the Gallinaceous birds, longer in the Crows, very long 

 in the Gannets, and excessively elongated in the Albatross. In 

 the Golden Eagle, it is also seen to be of great length. As the 

 power of the wing depends partly upon the size of the quills, 

 the elongation of the humeral bone does not correspond with 

 the velocity of the bird ; but in those species which have a 

 buoyant flight, produced by a slow^ motion of the wings, it is 

 always long. 



The cubitus, or fore-arm, is composed of tAVO bones, the ulna, 

 «, T, and the radius, u\ w. The former is a cylindrical bone, 

 enlarged at both extremities, and generally marked by the at- 

 tachment of the cubital quills, or those usually termed secon- 

 daries. The radius is nearly of the same form, but more 

 slender. 



The carpus, betw^een t, %*, and x, is formed of two small 

 bones, intervening betwixt the anterior extremity of the radius 

 and ulna, and the metacarpus, so as to confine the motion to 

 flexion and extension. The metacarpus, ^, is usually formed 

 of two bones, united at both extremities. At its base externally 

 is a single small bone, y, free or anchylosed, w^hich is analogous 

 to the thumb, and to which are attached the feathers of the 

 pinion, alula, or bastard wing. Appended to the outer meta- 

 carpal bone are usually two digital bones, z ; and generally 

 to the inner a smaller bone of the same nature. The quills 

 named primaries, usually ten in number, correspond to the 

 metacarpus and digits. 



The inferior extremity is attached to the pelvis, which in 



