Forebrain and Midbrain of Lizards 
35 
Figure 13. Transverse section through the caudal diencephalon of the green iguana. Bar scale represents 
1 mm. dlh, dorsolateral hypothalamic nucleus; dm, dorsomedial nucleus; e, nucleus entopeduncularis; gp, 
nucleus geniculatus pretectalis; If, lateral forebrain bundle; Im, nucleus lentiformis mesencephali ; m, 
nucleus medialis; mf, medial forebrain bundle; n, neuropil of the pars ventralis of the lateral geniculate 
nucleus; p, periventricular hypothalamic nucleus; pb, perirotundal belt; pc, posterior commissure; pe, pars 
extensa of the nucleus lentiformis thalami; pp, pars plicata of the nucleus lentiformis thalami; r, nucleus 
rotundus; rn, retinal neuropil of the ventrolateral nucleus; so, subcommissural organ; vh, ventral hypotha- 
lamic nucleus; -uW, pars dorsalis of the ventrolateral nucleus; vlv, pars ventralis of the ventrolateral nu- 
cleus; vm, ventromedial nucleus. 
division of area triangularis is termed nu- 
cleus ventrolateralis, and the caudal contin- 
uation of the medial division is termed nu- 
cleus ventromedialis. These ttvo nuclei extend 
throughout the entire diencephalon, reaching 
the level of the nucleus interstitialis which 
marks the beginning of the mesencephalic 
tegmentum. 
Nucleus ventrolateralis can be divided into 
dorsal and ventral components. The ventral 
component consists of a medial cell plate and 
a lateral neuropil. This ventral component 
receives direct contralateral retinal and ipsi- 
lateral tectal projections (Butler and North- 
cutt, 1971a, 19716; Ebbesson, 1972; North- 
cutt and Butler, 1974). Nucleus ventrolater- 
alis also appears to receive projections from 
an ascending spinothalamic pathway (un- 
published observations). Nothing is known 
regarding the efferent projections of this 
nucleus. 
At present, the only known projection to 
nucleus ventromedialis arises from the me- 
dial part of the striatum (Hoogland, 1975). 
This pathway constitutes part of the ventral 
peduncle of the lateral forebrain bundle and 
probably is homologous to part of the ansa 
lenticularis complex of mammals. Nucleus 
entopeduncularis (Fig. 12) also receives a 
projection from the striatum in Tupinamhis 
(Hoogland, 1975) ; this nucleus is a collec- 
tion of cells scattered along the dorsal edge 
