VERTEBRATA. 27 



powers of flight, it reaches to the last rib. while in the emeu it covers 

 only two. This bone is broad and flat in the penguins. 



The coracoid. or posterior clavicle, is a strong bone, broad in- 

 feriorly. where it is received in a transverse groove in the sternum ; 

 it extends upwards, outwards, and forwards", to articulate with the 

 scapula and clavicle. The glenoid cavity thus resulting from the 

 union of this bone with the scapula, is often unequal to^the recep- 

 tion of the head of the humerus ; hence, in the raptores and inses- 

 sores, a small but distinct bone extends between the coracoid and 

 scapula, over the superior part of the cavity,|which it here completes. 

 It was discovered by Nitzsch, who called it the capsular bone. 



The clavicles are subject to considerable variety. In the ground 

 parrots of Australia, for instance, they present only a rudimentary 

 type, while in the psittacus mitratus, &c, they are wholly absent; 

 they are feebly developed in the emeu, rhea, and cassowary. When 

 these bones are enchylosed together at their sternal extremities, as 

 they ordinarily are, they constitute a single bone, named furculum. 

 In the ostrich they do not come in contact inferiorly, although they 

 reach the sternum ; and in the toucans, they neither come "in con- 

 tact below, nor reach the sternum. It is remarkable that in the 

 ostrich they are anchylosed above with the coracoid and scapula, 

 whilst almost in every other species they either continue separate, 

 or are movably jointed superiorly. 



The humerus attains its greatest length in the albatross, and is 

 shortest in the struthious birds and penguins, whilst in the swifts 

 and humming birds it is characterised by its thickness, strength, 

 and the development of its muscular processes. In the cursores it 

 is short and attenuated, resembling the corresponding part in the 

 paddle of the turtle. Its head is oblong transversely, and enlarged 

 by two lateral crests, under one of which are to be found the air 

 passages leading into the bone. The lower extremity of the hu- 

 merus is formed after the manner of a hinge, consisting of an in- 

 ternal spherical portion to articulate with the ulna, and an external 

 oblong portion for the radius. 



The radius and ulna are straight and slender bones, enlarged at 

 their extremities, and placed one in front of the other, so as scarcely 

 to admit of any pronation or supination. In the penguins the bones 

 of the fore-arm are flattened, and articulated with the anterior edge, 

 and not the extremity of the humerus. 



The carpus is composed of two bones only, and so wedged in 

 between the metacarpus and fore-arm, as to limit the motionsof the 

 hand to adduction and abduction. 



The metacarpus is chiefly formed of two bones, a small ulnar 

 one, which supports a single phalanx, and a large radial one, which 

 sustains two phalanges. A small rudimental bone is usually an- 

 chylosed to the outer side of the proximal extremity of the radial 

 metacarpal bone. 



Lower extremity. — The pelvic bones, like those of the shoulder, 

 are three in number: the ilium represents the scapula, the ishium 



