Forebrain and Midbrain of Lizards 
33 
Thalamus. Most workers since the turn of 
the century have divided the thalamus of 
reptiles into dorsal and ventral divisions. 
These divisions have been assumed to be the 
homologs of the similarly named thalamic 
divisions in mammals. However, to date 
there is no experimental evidence either to 
support or reject this hypothesis. 
The ventral thalamus of lizards can be 
divided into the following nuclei: area tri- 
angularis, nucleus ventrolateralis, nucleus 
ventromedialis, nucleus entopeduncularis, 
and nucleus geniculatus lateralis (Figs. 10- 
13). The ventral thalamus begins just caudal 
to the preoptic recess of the hypothalamus. 
At this level the ventral thalamus consists 
of a plate of cells (area triangularis) arch- 
ing over the forebrain bundles (Fig. 12). At 
more caudal levels the area triangularis is 
split into lateral and medial divisions by the 
dorsal peduncle of the lateral forebrain bun- 
dle. The caudal continuation of the lateral 
Figure 11. Transverse section through the caudal diencephalon of the Tokay gecko. Bar scale represents 
1 mm. dlh, dorsolateral hypothalamic nucleus; gp, nucleus geniculatus pretectalis; lfb,v, ventral peduncle 
of the lateral forebrain bundle; Im, nucleus lentiformis mesencephali ; m, nucleus medialis; mfb, medial 
forebrain bundle; mp, nucleus medialis posterior; npd, nucleus posterodorsalis ; ot, optic tract; p, periven- 
tricular hypothalamic nucleus; pe, pars extensa of nucleus lentiformis thalami; pp, pars plicata of nucleus 
lentiformis thalami; so, subcommissural organ; vh, ventral hypothalamic nucleus; vi, ventrolateral nucleus; 
vm, ventromedial nucleus. 
