ICHTHYOSAURUS. 175 
A further advantage resulting from this curious 
apparatus of bony plates, was to give strength 
to the surface of so large an eye-ball, enabling 
it the better to resist the pressure of deep vrater, 
to which it must often have been exposed ; it 
would also have protected this important organ 
from injury by the waves of the sea, to which an 
eye, sometimes larger than a man's head, must 
frequently have been subject, when the nose was 
brought to the surface, for the necessary purpose 
of breathing air : the position of the nostrils, 
close to the anterior angle of the eye, rendered 
it impossible for the Ichthyosaurus to breathe 
without raising its eye to the surface of the 
water. 
Jaws, 
The Jaws of the Ichthyosauri, like those of 
Crocodiles and Lizards, which are all more or 
less elongated into projecting beaks, are com- 
posed of many thin plates, so arranged as to 
combine strength with elasticity and lightness, 
in a greater degree than could have been ef- 
fected by single bones, like those in the jaws of 
Mammalia. It is obvious that an under jaw so 
slender, and so much elongated as that of a 
Crocodile or Ichthyosaurus, and employed in 
seizing and retaining the large and powerful 
animals which formed their prey, would have 
been comparatively weak and liable to fracture 
