18 
Northcutt 
an ascending pathway in Butler and Ebner’s 
study. 
The medial cortex of gekkonids, pygopo- 
dids, and xantusiids has hypertrophied. In 
the gekkonids and xantusiids the medial 
cortex is so expanded that it forms a distinct 
outpocketing of cortex that overlaps the 
dorsal surface of the olfactory peduncles. 
These taxa should prove extremely useful in 
experimental studies directed toward under- 
standing the organization and function of 
medial cortex in lizards. 
Dorsal cortex. The dorsal cortex of lizards 
has been variably defined and subdivided by 
different workers (P. Ramon, 1896; Unger, 
1906; de Lange, 1911; Shanklin, 1930; 
Frederikse, 1931 ; Dart, 1934 ; Goldby, 1934 ; 
Curwen, 1937 ; Goldby and Gamble, 1957 ; 
Filimonoff, 1964; Minelli, 1966; Northcutt, 
1967 ; Ebbesson and Voneida, 1969 ; Platel, 
1969 ; Lohman and Mentink, 1972 ; Senn and 
Northcutt, 1973). Opinions range from those 
of Minelli (1966) and Platel (1969), who 
claim that no dorsal cortex exists as a dis- 
tinct cortical division, to those of Lohman 
and Mentink (1972), who recognize three 
subdivisions within dorsal cortex. Three 
distinct neural populations (Figs. 2,3) can 
be recognized in the dorsal roof of the telen- 
cephalon in most lizards. The nomenclatural 
arguments really depend on whether or not 
any or all of these dorsal subdivisions are 
homologous to isocortical (neocortex) com- 
ponents or to the hippocampal complex in 
mammals. 
An examination of the AChE and SDH 
enzyme distributions in the dorsal cortex of 
Iguana (Figs. 4, 5) clearly reveals that this 
area is distinct from the medial roof com- 
ponents. The SDH dense regions are due to 
high concentrations of mitochondria and 
usually coincide with terminal sites of major 
ascending pathways (Friede, 1960; North- 
cutt, 1973, 1974; Kicliter and Northcutt, 
1975). Butler and Ebner (1972) have re- 
ported thalamic projections to the dorsal 
cortex in Iguana, but did not specify which 
subdivisions were involved. 
In turtles and crocodiles, electrical poten- 
tials in the dorsal cortex can be evoked by 
photic stimulation (Kruger and Berkowitz, 
1960 ; Orrego, 1961 ; Moore and Tschirgi, 
1962; Belekhova and Kosareva, 1971). Addi- 
tionally, Hall and Ebner (1970) reported 
direct lateral geniculate projections to a 
portion of dorsal cortex in Pseudemys that 
is responsive to photic stimulation. These re- 
sults suggest that at least part of the dorsal 
cortex in turtles should be considered 
homologous to striate isocortex (primary 
visual cortex) in mammals. Thus, it is likely 
that at least part of the dorsal cortex in 
lizards also receives a visual projection from 
the lateral geniculate nucleus of the thalamus 
since this pathway is widely present in other 
land vertebrates. However, Gusel’nikov and 
Supin (1964) could evoke visual responses 
from only the dorsal half of the medial cor- 
tex (Cl) and not from the dorsal cortex in 
Agama caucasica. If this observation is cor- 
roborated by other studies, it poses a serious 
problem regarding the homologs of the dorsal 
and medial cortices among reptiles. 
Northcutt (1968), Lohman and Mentink 
(1972), and Butler (1975) have reported on 
the efferent projections of the dorsal cortex 
in lizards. While the exact details of these 
studies are not in accord, projections to the 
medial cortex, septum, and preoptic area of 
the hypothalamus have been reported. There 
is considerable variation in the development 
of the dorsal cortex in lizards, and my analy- 
sis to date suggests that this character has 
low taxanomic value since most of the varia- 
tion falls within the category of regressive 
changes. The most common pattern observed 
is that in which three subdivisions can be 
recognized (Figs. 2,3). In Anniella and 
Sphaerodactylus only two subdivisions can 
be recognized, and in taxa such as Anely- 
tropsis and Dibamus the dorsal cortex is 
barely recognizable and is less than a quarter 
of the cross-sectional width of either of the 
other cortices. This is clearly not due to a 
scaling factor, as other small lizards such 
as Scinella and Anolis possess all three sub- 
divisions, and in Scinella these are even 
hypertrophied with regard to the thickness 
of the cortical plate as seen in cross section. 
