a new Fossil Animal . 
567 
and the changes they undergo in different parts of the jaw, from its 
anterior to its posterior extremity, and also the manner of their 
application to each other. 
Bones of the upper part of the Head . 
These have the same marked coincidence with those of the croco- 
dile which distinguishes the bones of the lower jaw; they are shewn in 
the accompanying figures (pi. 40) fig. 9, 1 1, 12, marked by the letters 
employed by M. Cuvier. Since to describe them at length would be 
generally to repeat the words of that author, in treating of the 
structure of that animal (the crocodile), we shall confine ourselves 
to a rapid sketch, noticing principally the peculiarities of configura- 
tion by which the Ichthyosaurus differs from this type, most of 
which arise from the adaptation of the parts to the narrow and 
elongated contour of the whole. The eye also is rather lower 
placed than in the crocodile, the bottom of the orbit being nearly 
‘ ona level with the line of the opening of the jaws ; this produces 
some very slight changes in the form of the adjacent bones ; and 
perhaps a still more important deviation occurs in the place of the 
nostrils; but this point still remains involved in some degree of 
obscurity. 
We shall first consider those bones which appear on the sides and 
inner part of the mouth, as exhibited in figures 9, 11, and 12, plate 
40. and in the transverse section fig. 3, of the same plate. 
The general outline of the upper, like that of the lower jaw, is 
much more pointed than in any species of crocodile ; its termina- 
tion resembles that of the porpoise, the bones of the opposite sides 
opening at the end so as to form a narrow angular slit ; this slit re- 
quires an attentive examination from the doubts that have arisen 
Vol.V. 4 c 
