Forebrain and Midbrain of Lizards 
23 
of the DVR as the homolog of mammalian 
corpus striatum. 
(1) Kallen (1951) examined the embry- 
onic development of the telencephalon of a 
number of reptiles including the lizards 
Lacerta and Chamaeleo. He concluded that 
the DVR was of pallial, rather than sub- 
pallial, origin. Kallen further noted that part 
of mammalian isocortex arises from the same 
pallial field that gives rise to the dorsal 
ventricular ridge in reptiles. 
(2) In mammals the corpus striatum can 
be characterized by the highest concentra- 
tions of acetylcholinesterase and dopamine 
of any telencephalic region (Friede, 1966; 
Cooper, Bloom, and Roth, 1974). Similarly, 
in reptiles the ventrolateral wall — ^beneath 
the dorsal ventricular ridge, but not the 
ridge itself — possesses high concentrations 
of these chemicals (Parent and Olivier, 
1970 ; Kusunoki, 1971 ; Parent, 1973a, 
19736; and see Fig. 4). The distribution of 
AChE is phylogenetically very stable, as the 
ventrolateral telencephalic wall of fish, 
amphibians, and birds also possesses similar 
distributions (Karten, 1969; Braak, 1970; 
Northcutt, 1973, 1974; Parent, 1975). 
(3) Finally, in both birds and reptiles, 
the DVR has been shown to be the major 
target of ascending sensory projections from 
the dorsal thalamus (Karten, 1969; Hall 
and Ebner, 1970; Butler and Ebner, 1972; 
Pritz, 1973, 1974a, 1975). These same 
thalamic projections terminate in sensory 
parts of isocortex in mammals. Thus, all 
available embryological, histochemical, and 
connectional evidence argues that the DVR 
of reptiles should be considered homologous 
to parts of mammalian isocortex, rather than 
to mammalian corpus striatum. 
The dorsal ventricular ridge of lizards has 
frequently been divided into anterior and 
posterior parts (Unger, 1906; deLange, 
1911; Rose, 1923; Shanklin, 1930; Goldby, 
1934; Curwen, 1938, 1939; Kallen, 1951; 
Northcutt, 1967 ; Senn and Northcutt, 1973). 
However, there has been little consistency 
in recognizing the boundary between these 
two divisions or the cellular populations 
forming either division. Several authors 
have based their divisions on the sulcus neo- 
archistriaticus of Kappers (1921), a sulcus 
on the posterodorsal edge of the DVR that 
lies just rostral to the nucleus sphericus in 
many lizards (de Lange, 1911; Frederikse, 
1931; Goldby, 1934; Filimonoff, 1963). If 
this boundary is used, the anterior division 
of the DVR includes all neural populations 
except nucleus sphericus and the populations 
immediately lateral to it, which then con- 
stitute a posterior division (e.g., Curwen, 
1938, 1939). Kallen (1951) argued that the 
cytological differentiation into anterior and 
posterior divisions was a late embryonic 
event and of minor morphological signifi- 
cance. Certainly many lizards do not possess 
a recognizable sulcus neo-archistriaticus, and 
the presence of this feature may be corre- 
lated with the development of the nucleus 
sphericus, since both are particularly pro- 
nounced in varanids and teiids. 
An examination of AChE and SDH distri- 
butions in the DVR of Iguana (Figs. 4, 5) 
clearly reveals that this area is heterogen- 
ous, even excluding nucleus sphericus as a 
subdivision of the ridge. The ridge can be 
divided into anterior and posterior subdivi- 
sions based on the density and distribution 
of SDH (Fig. 4). The ridge rostral to the 
level of the anterior commissure is charac- 
terized by at least three dense areas of SDH 
activity (Fig. 45). As noted earlier, these 
dense areas are due to high concentrations 
of mitochondria and have been correlated 
with terminal sites of major pathways in a 
number of vertebrate species. In Iguana, 
the terminal targets of ascending thalamic 
pathways to the anterior DVR closely match 
the SDH dense areas (Butler and Ebner, 
1972; Butler, personal communication). 
While Butler and Ebner established that the 
thalamus does project to the anterior DVR, 
they did not report on discrete lesions of 
individual thalamic nuclei. However, a num- 
ber of other reptilian taxa have been exam- 
ined, and it now appears that at least three 
different pathways, representing three sepa- 
rate sensory modalities, project to the an- 
terior DVR. In Pseudemys (Hall and Ebner, 
