BIRDS. 391 



restore them to their proper situations, after they have been 

 disturbed by any violent impulse. 



The wing of a bird does not, at first view, present much 

 analogy with the fore extremity of a quadruped: but on a 

 closer examination we find it to contain all the principal 

 bones of the latter, though somewhat altered in shape, and 

 still more changed in their functions. Yet still the same 

 unity of plan, and perfect harmony of execution may be 

 discerned in the mechanism of this refined instrument of a 

 higher mode of progression. 



The head of the humerus (h) has a compressed form; and 

 in order to obtain great extent of motion, it is made to play 

 by a very small cylindrical surface upon the scapula; thus 

 admitting of the complete descent of the wing, unobstructed 

 by any opposing process, but at the same time limiting its 

 motion to one plane. It is connected below, by broad at- 

 tachm.ents, to the radius and ulna, forming with them a hinge 

 joint. These latter bones are separate, and of great length, 

 but so firmly united together by ligament as scarcely to have 

 any motion on one another. The carpus (w,) consists of 

 two bones only, the one articulated with the radius, the 

 other with the ulna. They move together as one piece; 

 but, contrary to what takes place in quadrupeds, the move- 

 ments are made from side to side, instead of their consistino- 

 of flexion and extension; this variation from the usual struc- 

 ture being for the purpose of folding down the joints of the 

 wing, and bringing them close to the bod}^ .The metacar- 

 pus (m) consists originally of two bones, which soon become 

 united into one at the upper part. On the radial side it has 

 a process, derived perhaps from a third metacarpal bone, 

 which is anchylosed at a still earlier period of ossification; 

 and to this process a small pointed bone is connected, cor- 

 responding to a rudimental thumb (t.) There are generally 

 two fingers, of which the first exhibits traces of having been 

 originally two bones: the inner finger consists of two or 

 three long phalanges, and the outer one of a single phalanx: 

 there is sometimes also a rudimental bone corresponding to 



