BIRDS OF OLD 85 
evident that Hesperornis was not an ordinary 
bird, and that he could not have swum in the 
usual manner, since this would have brought his 
great knee-caps up into his body, which would 
have been uncomfortable. And so, at the cost 
of some little time and trouble,* the mount- 
ings were so changed that the legs stood out at 
the sides of the body, as shown in the picture. 
A final word remains to be said about 
toothed birds, which is, that the visitor who 
looks upon one for the first time will probably 
be disappointed. The teeth are so loosely im- 
planted in the jaw that most of them fall out 
shortly after death, while the few that remain 
are so small as not to attract observation. 
By the time the Eocene Period was reached, 
even before that, birds had become pretty 
much what we now see them, and very little 
* The mounting of fossil bones is quite a different matter 
from the niring of an ordinary skeleton, since the bones are not 
only so hard that they cannot be bored and mired like those of a 
recent animal, but they are so brittle and heavy that often they 
mill not sustain their onn weight. Hence such bones must be 
supported from the outside, aud to do this so that the mountings 
will be strong enough to support their weight, allow the bones to 
be removed for study, and yet be inconspicuous, is a difficult task. 
