C. J. Sundevall on the Wings of Birds. 429 



must therefore commence with its description^ for where it is 

 strongly developed, flat, and broad, it fills the whole space 

 between the sinews, which, in the Song-birds, is occupied by 

 the above-mentioned sinus cutaneus ulnaris, in consequence 

 of which this entirely disappears. 

 The muscles are as follows : — 



A. On the outer (extensor) side of the cubitus, springing 

 from the humei'i condylus externus and the radius. They 

 are in general extensors, and form together in Birds a 

 large mass of flesh. 



a. Long muscles (for the hand). 



1. Extensor carpi radialis longus *, usually the largest on 

 the forearm ; lies usually foremost on the radius ; springs 

 from the humerus above the condylus externus; the sinew 

 terminates at the tuber baseos metacarpi quite in the margin 

 of the wing, below the thumb. It is the principal extensor 

 muscle of the hand and the largest remiges. 



2. Extensor carpi radialis brevis, concealed between the 

 radius and No. 4 ; springs from the posterior (ulnar) side of 

 the radius ; is often very small, always much narrowed to a 

 point, with a slender sinew, which comes from near the end 

 of the radius, and is attached beneath the preceding muscle. 



3. Extensor digitorum communis, from the condylus ex- 

 ternus close upon the radius, visible externally beside No. 1. 

 — Sinew long, runs to and along the front margin of the 

 OS metacarpi to the base of the first phalange, forming there 

 a sort of trochlea ; thus it goes from the outer side across 

 the fore margin of the bone to the inner side, where it is 

 attached to the turberculuni marginis antici. The sinew 

 gives off a strong branch, like a filiform ligament, to the 

 base of the thumb, as it passes by the latter. It extends 



* The names liere given are those employed in human anatomy, in 

 order to show the analogy more distinctly. As, however, the same part 

 often performs ditlerent functions in different animals, the names derived 

 from the functions are often unsuitable, e. g. No. 5, which in birds is not 

 an extensor. So also with supinator, lironator, &c. 



