Forebrain and Midbrain of Lizards 
15 
contrast, Johnston (1923) argued that the 
amygdala consisted of pallial and basal com- 
ponents. Johnston believed the pallial com- 
ponent represented a ventral continuation 
of the olfactory cortices, while the basal 
component represented a group of nuclei 
situated medial to the septal nuclei and 
dorsal to the striatum. In Johnston’s analy- 
sis the amygdaloid complex has neither 
embryonic nor topographical continuity 
with the corpus striatum. My own observa- 
tions (Northcutt, 1974) support Johnston’s 
interpretation of the amygdala, but detailed 
embryological, histochemical, and connec- 
tional studies of the caudal telencephalon in 
reptiles are required to determine which of 
the nuclei in this region are homologous to 
the amygdaloid nuclei of other vertebrates. 
For these reasons I have not discussed the 
caudal telencephalic nuclei as a single group, 
and no comparison with the amygdala of 
other vertebrates has been attempted. 
The telencephalon medium consists of a 
nucleus interstitialis and the preoptic nu- 
cleus, as well as the lateral and medial fore- 
brain bundles which interconnect the tel- 
encephalon with the diencephalon and 
medulla. 
Few experimental neuroanatomical 
studies on lizards have been reported, and a 
rudimentary overview is possible only by 
utilizing clues provided by experimental 
studies on other reptiles and by examining 
the variation in brain structure in lizards. 
The organization and variation of the major 
telencephalic components in lizards are 
described beginning at the dorsomedial edge 
of the roof, or pallium, and moving laterally, 
ventrally, and then medially to end the 
description of the telencephalon with the 
septal nuclei. Each cytological area is de- 
scribed, its afferent and efferent connections 
(where known) are summarized, and the 
variation among taxa is noted. 
Pallium 
Medial cortex. The exact extent of medial 
cortex in lizards has been variously defined 
by different workers (Edinger, 1896 ; Goldby 
and Gamble, 1957 ; Northcutt, 1967 ; Lohman 
and Mentink, 1972; see section on dorsal 
cortex for a more detailed discussion of 
problem). However, at least two distinct 
cytological fields have usually been included 
in descriptions of the medial cortex (Figs. 
2, 3) : a ventral small-celled component (C2) 
and a dorsal large-celled component (Cl). 
The cellular organization of these com- 
ponents has been described in Chamaeleo 
(P. Ramon, 1896), Iguana (Northcutt, 
1967), and Tupinambis (Ebbesson and 
Voneida, 1969). The most common neurons 
forming the C2 division of the medial cortex 
are termed double pyramidal cells (Crosby, 
1917; Northcutt, 1967). These cells are 
fusiform or pyramidal in shape with bipolar 
dendrites that extend into the medial and 
lateral fibrous laminae of the medial wall. 
Their axons arise from the cell soma and 
pass into the lateral (alvear) lamina where 
they frequently bifurcate. P. Ramon and 
most subsequent workers have been able to 
trace axons of these cells as far centrally 
as the septal nuclei. 
The most common neurons forming the 
Cl division of the medial cortex can be 
described as small projection or pyramidal 
cells. These cells possess both apical and basal 
dendrites. The apical dendrite (s) passes 
dorsally and branches throughout the extent 
of the superficial neuropil. The basal den- 
drites branch in the deep neuropil, and the 
axons of these cells arise from the somata 
and pass into the deep neuropil. Their 
axons, like those of the C2 neurons, bifur- 
cate, and branches can be traced ventro- 
medially as well as laterally within the deep 
fibrous lamina. 
At present the only data on afferents to 
the medial cortex in lizards relate to inter- 
hemispheric connections. Northcutt (1968), 
Voneida and Ebbesson (1969), Lohman and 
Mentink (1972), and Butler (1975) have 
reported that the medial cortices in Phryno- 
soma, Tupinambis, and Gekko receive re- 
ciprocal connections. Additionally these 
studies have also revealed medial cortical 
projections to the septal nuclei. This projec- 
