1905. ] BRAIN OF LIZARDS. 269 
by them. It is faintly grooved in the middle line and laterally 
on each side is a flattened process extending backward rather 
beyond the rest of the cerebellum. Its insignificant proportions 
are shown by the fact that the transverse (antero-posterior) 
diameter of this thin plate is 2 mm., while the corresponding 
measurement of the optic lobe is 8 mm. 
As will be seen from text-figs. 39, 40 (p. 268), the cerebellum 
of Varanus exanthematicus is a much more important structure. 
Not only the actual but the relative size of the cerebellum is 
greater. The corresponding measurements to those given above 
for Tupinambis are for Varanus—diameter of cerebellum 4:5 mm., 
diameter of optic lobes 45 mm. They are thus equal. 
The difference in dimensions between the cerebella of the two 
Lacertilia is due to the exaggeration in Varanus of the boss-like 
eminence upon the cerebellum of Zupinambis and Iguana. Not 
only is the cerebellum of Varanus exanthematicus much greater 
in bulk than that of Tupinambis or Iguana, but it is more 
complicated in structure owing to furrows. 
The dorsal furrow, continuous with that dividing from each other 
the corpora bigemina, is more deeply marked in Varanws and more 
definitely circumscribed than in Zupinambis ; in Iguana I did not 
find any traces of it. Im the second place, the cerebellum of 
Varanus exanthematicus has an equally deeply marked lateral 
furrow, which runs obliquely upwards and forwards. Thirdly, the 
lateral process of the cerebellum is much more sharply marked 
off from the cerebellum itself than in Zupinambis, and runs 
downwards rather than backwards, thus distinctly suggesting 
the flocculus in the cerebellum of the higher forms. It is, indeed, 
not at all unlike the cerebellar flocculus in Alligator. 
It is plain therefore that the cerebellum of this Lizard is not 
‘‘a mere transverse plate,” but an organ of some dimensions, and, 
indeed, not very far, in point of relative size, from that of the 
Crocodilia. 
A large cerebellum has been associated in reptiles with the 
swimming habit. And it is true that the Monitor Lizards are 
often largely aquatic in habit. Curiously enough, however, 
the present species, with its large cerebellum, is stated by 
Dr. Giinther* not to take to the water. 
More likely, as it appears to me, is this advance in structural 
complexity of the brain to be associated with the not only isolated 
but high position which the Monitors occupy among the 
Lacertilia. 
(2) On the Cerebral Hemispheres in Tropidurus hispidus. 
T imagine that I am right in believing that the brain of this 
TIguanoid Lizard has not up to the present been submitted to 
anatomical examination. I am able, therefore, to add a fact of 
* “On the Anatomy of Regenia ocellata,” P. Z.S. 1861, p. 60. 
