STRUCTURE OF BIRDS. 33 



the extremity of the cubitus) " is generally termed the 

 shoulder; ikiQ fleximi^^ (pointing to the wrist) " is the shoul- 

 der joint; and the aa;///a "' (reference to the pollex), "which 

 corresponds to the cubitus^ is commonly called the shoulder 

 margin." Errors like these are deplorable, more especially as 

 their author is in many respects an estimable writer. To 

 mistake the wrist joint for the shoulder joint is a blunder 

 which might have been avoided by inspecting a skeleton, or 

 even feeling for the bones in the wing of any common bird. 



The Muscles of birds are generally of a deep red colour, their 

 fasciculi remarkably distinct, their tendons glistening and pecu- 

 liarly liable to become ossified, especially those of the inferior 

 extremities. In the Gallinaceous species, however, and some 

 others, the muscles are often very white. It is not necessary 

 here to enter into a particular description of these organs of 

 motion ; but as the mechanism of the wings is of especial inte- 

 rest, and as I shall often have occasion to speak of the flight of 

 birds, it may be well to endeavour to afford some general de- 

 scription of it. 



The bones of the wing have already been pointed out in the 

 skeleton of the Golden Eagle, and are again represented in 

 Plate III, Fig. I. It may here be further stated with re- 

 spect to them that the frame-work of the wing is composed 

 of a series of bones fixed by a joint to the solid apparatus of 

 the scapula and clavicles, and folding up by hinges into three 

 pieces, the humerus, the cubitus, and the hand, so as, wdiea 

 not in use, to be conveniently disposed of by the side of the 

 body. The first bone, the os humeri, or bone of the arm, or 

 brachial bone, ^, c, is articulated by a small rounded surface to 

 a corresponding cavity formed betw^een the coracoid bone, ^, and 

 the scapula, a, in such a manner as to allow great freedom of 

 motion. When at rest this bone is directed backwards, more or 

 less parallel to the spine. Its distal extremity forms, w^th the 

 proximal extremity of the cubital bones, the ulna and radius, c, 

 d^ an oblique hinge-like joint, c^ which allows the cubitus to 

 be folded up parallel to the brachium, and nearly in the same 

 plane. The third portion, the hand, d^ e^ /, on the contrary, is 

 jointed so as to fold under the cubitus in a perpendicular 



