A BIRD’S FORE LEG. Lo 
man the muscles that open the arms or fore legs away 
from the body lie mostly between the shoulders. But 
suspended by the wings, the bird might be too top- 
heavy if the region between them were piled high 

Skeleton of duck’s wing (after Coues). 
h, humerus; 7d, radius; wl, ulna, showing pits, pts, where the secondary 
flight quills enter slightly; se and cu, carpals, forming the wrist; 
d?, so-called thumb ; mc, mc, the hand bone, composed of three bones 
fused into one girder-shaped piece, one for each digit; the “thumb” 
abutting against a short one at the base; d8, the middle and longest 
digit; d4, outer digit, inclosed in tissue with 3. 
with muscles. So these muscles are placed below 
upon the chest, and by their weight help to keep the 
bird in proper position during flight ; and they effect 
their lifting power upon the wing by means of ten- 
dons that run up over a pulley. Perhaps in all the 
modifications of the bird’s fore leg this is the greatest. 
