306 
THE IGUANODON 
the Mososaurus.* In tliese bones the body bears 
some resemblance to a vertebra, but the large cells 
or hollows which pervade it tbrougbont, readily 
distinguish it ; it forms a thick pillar or column, 
which is contracted in the middle, and terminates 
at both extremities in an elliptical and nearly flat 
surface : two lateral processes, or alcB, pass off 
obliquely, and are small in proportion to the size 
of the column ; on placing these hones beside the 
os tympani of an Iguana, we at once perceive that 
the relative proportions of these parts are reversed; 
for in the recent animal the pillar is small, and the 
lateral processes large. From the great size of the 
body in the fossil, and the extreme thinness of its 
walls, the tymjyanic cellulce must have been of 
considerable magnitude, and have constituted a 
large portion of the auditory cavities. PI. II. fig. 1. 
accurately represents the most perfect specimen in 
my cabinet ; it is 6 inches high, and 5^ inches 
wide at the longest diameter of the extremity of 
the body. It exceeds in magnitude the corre- 
sponding bone of the Mososaurus, and is 14 times 
as large as the same bone in an Iguana four feet 
long.t 
V^ertebrcB, The somewhat angular vertebrae de- 
* The os tympani is beautifully preserved in the head of the Moso- 
saurus, in the Jardin des Plantes; and its form is perfect in a splendid 
model of that specimen presented to me by the late M. Cuvier : yet 
this bone does not appear in any of the numerous published repre- 
sentations of that celebrated fossil ; and has not, I believe, even been 
described. 
f It is due to my excellent and distinguished friend. Dr. Hodgkin, 
to mention, that he suggested to me long since, that these fossil bones 
approximated, in some respects, to the os quadratum in birds ; but 
