429 
C. J. Sundevall on the Wings of Birds. 
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 humeri condylus ext emus 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 ext emus ; 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 turberculum 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 here given are those employed in human anatomy, in 
order to show the analogy more distinctly. As, however, the same part 
often performs different 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 , pronator, &c. 
