270 ON THE BRAIN OF LIZARDS, [June 6, 
some little interest to what isalready known about the Lacertilian 
brain, as a result of the examination of two brains of this Lizard. 
In the Lacertilian brain generally, so far as my own knowledge 
and the inspection of published figures* enable me to state, the 
optic lobes lie behind the cerebral hemispheres, the furrow between. 
them being practically vertical; there is, in fact, no trace of an 
overlap of the corpora bigemina by the hemispheres. In the 
Chelonia, on the other hand, it has been recognised that some 
forms show an overlap of the corpora bigemina by the cerebral 
hemispheres, 
IT have found this lobe very obvious in a brain of the large 
Testudo vicina, the vascular system of which I have recently 
described. The overlap, however, is lateral and not dorsal. It 
is quite different with Zropidurus. There isa very distinct overlap 
of the corpora bigemina by the hemispheres dorsally. The 
corpora bigemina are thus partly hidden when the entire brain 
is viewed on the dorsal aspect. 
A comparison of the measurements of the brain in this species 
and in Jguana tuberculata seems to throw some light upon the 
causation of this overgrowth of the cerebral hemispheres over the 
corpora bigemina, dorsally. 
The following are the measurements to which I desire to 
refer : 
Iguana. Tropidurus. 
mm. mm. 
Length of brain to end of cerebellum ... 16 11 
Length of cerebral hemispheres ......... i) 6 
Breadth of cerebral hemispheres ......... 115 6:5 
It will be observed, from a comparison of these figures, that the 
proportions between the total length of the brain in the two 
Lizards, and both the breadth and length of the cerebral hemi- 
spheres, are about equal. It therefore results that the overlap of 
the hemispheres in Z'ropidwrus is rendered necessary by the skull 
formation and consequent lack of room for increased lateral 
growth of the hemispheres. By growing over the corpora 
bigemina, the hemispheres have been able to attain to the 
proper size necessary to the equilibrium of their possessor. 
These considerations may be regarded, perhaps, as discounting 
the morphological importance of the partial covering over of the 
corpora bigemina by an extension backwards of the cerebral 
hemispheres. 
Nevertheless, it is impossible to overlook the fact that there is 
an approximation in the brain of this Lizard, to whatever cause 
it may be due, to those of higher Vertebrates. 
* See Bronn’s Klassen u. Ordnungen des Thierreichs, Bd. vi., and Meyer, Zeitschr. 
wiss. Zool., Bd. lv. (1898). 
+ Supra, p. 67. 
