70 
Butler 
pern and Frumin, 1973 ; Northcutt and But- 
ler, 1974a., 6; Cruce and Cruce, 1975). Tecto- 
thalamic projections to nucleus rotundus 
have also been demonstrated in turtles 
(Hall and Ebner, 1970a), lizards (Ebbesson, 
1970a; Butler and Northcutt, 1971b), and 
crocodiles (Braford, 1972a). 
Unilateral transections at the thalamic 
level in the lizard, Igimna iguana, have been 
found to result in a complex pattern of de- 
generation in the telencephalon (Butler and 
Ebner, 1972). Fibers travel rostrally in the 
superficially lying stratum moleculare (dor- 
sal to the dorsomedical cortex) and terminate 
in peridendritic fields in this layer and 
among the cell somas of the dorsomedial and 
dorsal cortices. Another group of degener- 
ated fibers enter the dorsal ventricular ridge 
and terminate in several discrete fields. 
Other studies have shown that thalamotelen- 
cephalic fibers project (1) from the dorsal 
lateral geniculate nucleus to the general 
(dorsal) cortex in turtles (Hall and Ebner, 
19706; Foster et al., 1976), and (2) from 
nucleus rotundus to a discrete region of the 
dorsal ventricular ridge in turtles (Hall and 
Ebner, 19706), crocodiles (Fritz, 1975), and 
lizards (Distel and Ebbesson, 1975). Thus, 
there appear to be two separate visual path- 
ways to the telecephalon in reptiles, as there 
are in birds (Karten et al., 1973) and mam- 
mals (Schneider, 1969). 
Auditory System 
An auditory projection pathway to the 
telencephalon has also been described in rep- 
tiles. Fibers arising from the torus semi- 
circularis (inferior colliculus) in the mesen- 
cephalon project to nucleus reuniens (medial 
geniculate nucleus) in the dorsal thalamus 
(Foster, 1974; Fritz, 1974a). From nucleus 
reuniens, projections have been traced in 
caiman (Fritz, 19746) and in lizards (Distel 
and Ebbesson, 1975) to a discrete region in 
the DVR, medial to and distinct from the 
visual target of nucleus rotundus. 
Somesthetic System 
Of the three major ascending sensory sys- 
tems, the somesthetic system has received 
the least study in reptiles. 
Ascending spinal projections to the dorsal 
thalamus in Tupinambis (Ebbesson, 1967) 
have been described. Recent data on this sys- 
tem are discussed by Ebbesson (this con- 
ference). 
It is mainly on the basis of these findings 
of ascending sensory projections relayed 
from dorsal thalamic nuclei that the dorsal 
ventricular ridge is now considered to corre- 
spond to parts of mammalian neocortex. 
While the finding in turtles of a projection 
of the dorsal lateral geniculate nucleus to 
dorsal cortex (Hall and Ebner, 19706; 
Foster et al., 1976) strongly supports the 
classical idea that this pallial region is also 
a homolog of neocortex, other connections 
of this area, which will be discussed below, 
suggest that its nature may be more complex. 
A study of telencephalic connections which 
was recently completed in the lizard Gekko 
gecko (Butler, 1976) will now be reviewed 
before returning to a discussion of the nature 
of the reptilian dorsal pallium and dorsal 
ventricular ridge. 
ORGANIZATION OF 
TELENCEPHALON IN GEKKO 
While the ascending projections from nu- 
clei in and caudal to the dorsal thalamus 
have not yet been worked out in detail in 
Gekko gecko unilateral brainstem transec- 
tions result in a pattern of degeneration in 
the telencephalon similar to that seen in the 
green iguana (Butler and Ebner, 1972). The 
dorsal and dorsomedial cortices are targets 
of these projections, as are the DVR and 
basal forebrain. 
A series of ablations made by suction that 
variously involved part or all of the lateral, 
dorsal, and medial walls of the telencephalon, 
and the dorsal ventricular ridge was carried 
out in Gekko gecko. Survival times ranged 
between 14 and 32 days, after which the 
