CHAPTER: Tit 
A BIRD’S FORE LEG. 
Or course, it is apparent that the wing of a bird 
corresponds to the front leg of a quadruped, but it is 
not so evident at a glance that it 2s a leg or the result 
of a leg’s modification. Yet, to the student of the 
skeletons of birds as an entire group, taken in con- 
nection with the skeletons of reptiles, especially liz- 
ards, no other opinion can well prevail. 
The modifications of limbs by loss of digits from 
the twenty rays of the fish’s fin to the single toe of 
the horse is interesting. This degeneration soon 
reached five digits normally in the reptiles, especially 
in the rear; but in those that were most birdlike, of 
which the fossils are known, it ran lower both on 
hand and foot. 
The earliest bird we know had four toes and three 
fingers, and this is the normal yet. 
In this half-reptilian Archwopteryx already noted 
all the bones of the fingers were free from each other, 
and if a thumb were present it was alongside the others 
and of about equal length with them. In all later birds 
the thumb, so called, is much shorter than the other 
fingers and has fewer number of joints, and, except in 
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