The Lacertilian Forebrain 
69 
systems (Ebbesson, 1967, this conference). 
From the dorsal thalamus, ascending 
fibers project to the telencephalon. The 
dorsal lateral geniculate nucleus has been 
shown to project to the dorsal pallium in 
turtles (Hall and Ebner, 1970&, Foster 
et al., 1976) and to a portion of the Wulst 
(a dorsal pallial region) in birds (Karten 
et al., 1973). The thalamic targets of the 
mesencephalic optic tectum and torus semi- 
circularis do not project to cortex but to 
discrete regions in the dorsal ventricular 
ridge (Karten, 1968; Hall and Ebner, 1970b; 
Karten and Hodos, 1970; Pritz, 19746, 
1975). These ascending pathways to the 
dorsal ventricular ridge appear to cor- 
respond in their organization to those of the 
auditory and extrastriate cortex in mammals 
(e.g., Graybiel, 1970, 1972; Mathers, 1971; 
Kaas et al., 1972; Harting et al., 1973; 
Harting and Casagrande, 1974; Rezak and 
Benevento, 1975). As the dorsal ventricular 
ridge (DVR) is the target of these sensory 
projections in reptiles and birds, it is now 
thought that this region of the telencephalon 
is homologous as a field to parts of mam- 
malian neocortex, rather than to basal 
ganglia. This concept is supported by obser- 
vations on the histochemistry and connec- 
tions of several more basilar regions of the 
telencephalon (Karten, 1969; Karten and 
Dubbeldam, 1973) that indicate that only 
the latter correspond to mammalian basal 
ganglia. 
Studies of ascending projections following 
unilateral transections at diencephalic, mes- 
encephalic, and more caudal levels have been 
done in a wider variety of vertebrate species 
(Schroeder and Ebbesson, 1974; Butler and 
Ebner, 1972; Rubinson and Colman, 1972; 
Kicliter and Northcutt, 1975) and likewise 
demonstrate ascending systems that termi- 
nate in nonolfactory portions of the telence- 
phalon. In the shark, it has further been 
shown electrophysiologically that the telen- 
cephalic target of the dorsal thalamus is a 
visual area (Cohen et al., 1973), and that 
visual deficits in pattern discrimination re- 
sult from removal of this area (Ebbesson, 
personal communication). 
Efferent projections. The efferent projec- 
tions of the telencephalon have received less 
attention than the afferent. However, find- 
ings in amphibians and reptiles that the 
medial wall projects to areas which in mam- 
mals comprise parts of the limbic system 
(e.g., Halpern, 1972, 1974, 1976; Lohman 
and Mentink, 1972; Ulinski, 1975) strongly 
support Elliot Smith’s 1910) deduction that 
the medial wall is homologous to the mam- 
malian hippocampal formation. 
In summary, the classical views that the 
medial and lateral telencephalic regions in 
nonmammalian vertebrates are homologous, 
respectively, to mammalian hippocampal and 
piriform cortices are supported by recent 
experimental evidence. The idea that the 
dorsal pallial region is homologous to neo- 
cortex has received some support, but, as 
will be discussed below, the nature of this 
zone may not yet be fully understood. 
Finally, the dorsal ventricular ridge of rep- 
tiles and birds, once thought to be homol- 
ogous to basal ganglia, now appears to be 
homologous as a field (Campbell and Hodos, 
1970) to parts of neocortex. 
THALAMOTELENCEPHALIC 
PROJECTIONS IN REPTILES 
Studies of sensory projections to the 
thalamus and telencephalon in reptiles have 
mainly been concerned with the visual sys- 
tem, although some data are now available 
on the auditory and somatosensory systems 
as well. As a detailed account of the visual 
pathways will be given elsewhere in this 
volume (Cruce and Cruce), I will only 
briefly summarize them here. 
Visual System 
Retinal projections to the dorsal and ven- 
tral lateral geniculate nuclei of the thalamus, 
to pretectal nuclei, and to the tectum have 
been described in a number of reptiles (e.g., 
Armstrong, 1950; Ebbesson, 1970a; Butler 
and Northcutt, 1971a; Braford, 19736; Hal- 
