Forebrain and Midbrain of Lizards 
49 
A B 
Figure 18 . Representative transverse sections through the left telencephalic hemisphere of an anuran 
amphibian, Rana catesbeiana, (A) and a gekkonid lizard, Gekko gecko, (B) illustrating the diiferences in 
the development of the lateral hemispheric wall and the migration of neuronal populations from a peri- 
ventricular position, dc, dorsal cortex; dp, dorsal pallium; dvr, dorsal ventricular ridge; Ic, lateral cortex; 
Ip, lateral pallium; Is, lateral septal nucleus; me, medial cortex; mp, medial pallium; ms, medial septal 
nucleus, na, nucleus accumbens; st, striatum. 
oped lateral pallial areas for sensory and 
motor processing. 
A persistent riddle regarding telencepha- 
lic evolution in modern reptiles and therop- 
sids is why both groups elaborated a lateral 
pallial field rather than simply expanding the 
striatum which already received the vast 
bulk of the dorsal thalamic projections. Sev- 
eral possibilities should be considered. First, 
the vomeronasal system probably arose with 
land vertebrates and, while clearly recog- 
nizable in amphibians, became increasingly 
well developed in terrestrial reptiles and most 
mammals. Since the sole target of the 
vomeronasal system is located in the caudal 
lateral pallial wall (Scalia, 1972; Northeutt 
and Royce, 1975), it is possible that, with 
increased importance of this chemoreceptive 
system in land vertebrates, additional sen- 
sory modalities were linked with this telen- 
cephalic system. This would seem particu- 
larly likely since the lateral pallium and cor- 
tical amygdala (vomeronasal target) offer 
a direct pathway descending out of the telen- 
cephalon to hypothalamic and tegmental 
centers (at least in mammals; the efferents 
of these telencephalic centers in reptiles have 
not been determined). 
However, Hoogland’s (1975) experimental 
analysis of the efferents of the rostral dorsal 
ventricular ridge in Tupinambis reveals that 
the striatum is the primary, if not the sole. 
