270 ON THE BRAIN OF LIZARDS. [June 6, 



some little interest to what is already 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 

 Ohelonia, on the other hand, it has been recognised that some 

 forms show an overlap of the corpora bigemina by the cerebral 

 hemispheres. 



I have found this lobe very obvious in a brain of the large 

 Testudo vicina, the vascular system of which I have recently 

 described f. The overlap, however, is lateral and not dorsal. It 

 is quite different with Trojndums. Thei-e is a 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 Iguana tuhercidata 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, Tropidurtis. 

 mm. mm. 



Length of brain to end of cerebellum ... 16 11 



Length of cerebral hemispheres 9 6 



Breadth of cerebral hemispheres 11*5 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 Trojndurus is rendered necessary b}^ the skull 

 formation and consequent lack of room for increased lateral 

 growth of the hemispheres. By gi-owing over the corpora 

 bigemina, the hemispheres have been able to attain to the 

 proper size necessai-y 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 cerebi'al 

 hemispheres. 



Nevertheless, it is impossible to overlook the fact that there is 

 an appi'oximation in the brain of this Lizai-d, to whatever cause 

 it may be due, to those of higher Vertebrates. 



* See Bronn's Klassen u. Ordnungen des Tliierreiclis, Ed. vi., and Mej'er, Zeitsclir. 

 wiss. Zool., Bd. Iv. (1893). 

 f Supra, p. 67. 



