Forebrain and Midbrain of Lizards 
29 
the plate when seen in the transverse plane. 
Because of the similarity in cell size, it is 
difficult to be certain of the exact boundaries 
of the plate and core in the rostral ridge. 
More caudally there is no difficulty in sepa- 
rating plate and core in these taxa as the 
plate assumes a packing density 2-3 times 
higher than the core, and the plate cells be- 
come far more clustered than the core cells. 
The ridge of Lanthanotus (Fig. 6), while 
clearly differentiated into a peripheral plate 
and core, appears slightly reduced in volume 
when compared to gekkonids and lacertids. 
The plate is half the thickness of the core 
and, while some of the core cells appear as 
large as the plate cells, the majority are 
clearly smaller than the plate cells. The plate 
possesses a cell density twice that of the 
core, and giant cells are particularly pro- 
nounced in the rostral lateral plate. Nucleus 
sphericus is well developed in Lanthanotus. 
Heloderma (Fig. 6) possesses a highly 
distorted ridge due to a greatly expanded 
nucleus sphericus. Yet the ridge clearly pos- 
sesses a peripheral plate and a central core. 
The plate cells are distinctly larger, and 
their density is twice as high as that of the 
core. Both Heloderma and Lanthanotus ap- 
pear to have slightly reduced ridges. How- 
ever, this impression may be biased by the 
extensive development of nucleus sphericus 
in both taxa. 
The DVR’s of agamids, iguanids, teiids, 
and varanids are much enlarged and can be 
characterized by large cells scattered 
throughout the entire ridge area. The cell 
density, peripherally, is the same or slightly 
lower than the cell density centrally. No dis- 
tinct cell plate and core can be recognized. 
All of these taxa possess some cell clustering, 
particularly in the medial ridge area (area 
A, Figs. 3,7,8), which may represent the 
last trace of a peripheral cell plate. It is far 
more difficult to recognize cytological subdi- 
visions of the rostral ridge in these taxa 
than in gekkonids or lacertids. The nonex- 
perimental criteria are poorly developed cell 
free zones marking the edges of areas with 
differential densities in cell packing. These 
differences are so slight that, without the 
observed differences in SDH activity and the 
experimental results of Foster (1974) and 
Distel and Ebbesson (1975), it would be 
foolhardy to recognize subdivisions in these 
taxa with greatly expanded ridges. Thus, 
more detailed comparisons among these taxa 
must await further experimental results. 
Subpallium 
The striatum. No general agreement exists 
in the literature regarding the extent and 
subdivisions of the reptilian striatum. Platel 
(1971) has recently summarized much of the 
literature on this topic. Most workers have 
recognized a medial division, nucleus accum- 
bens, believed to be homologous to the same 
named nucleus in mammals based on its 
topographical position. Nucleus accumbens 
in lizards, as in mammals, can be character- 
ized histochemically by high concentrations 
of SDH and AChE (Figs. 4,5). Distel and 
Ebbesson (1975, personal communication) 
report that nucleus accumbens receives pro- 
jections from the dorsolateral thalamic nu- 
cleus, but not from nucleus rotundus nor 
reunions. At present, nothing is known re- 
garding the efferents of nucleus accumbens. 
The lateral division of the striatum has 
been frequently subdivided into dorsal and 
ventral components (Crosby, 1917 ; North- 
cutt, 1967 ; Distel and Ebbesson, 1975, per- 
sonal communication). The distribution of 
AChE in the striatum of Gekko and Iguana 
(Fig. 5) supports such a division. A dorsal 
component with moderate AChE concentra- 
tions and a more ventral high density com- 
ponent can be recognized. 
However, these striatal components do not 
constitute homogeneous cell populations. The 
striatum can be separated from the dorsal 
ventricular ridge by the dorsal medullary 
lamina. This lamina consists of a dense layer 
of fibers with small neurons scattered 
throughout the fibrous plate. The lamina is 
easily recognized in Nissl stains, and in 
AChE preparations it is characterized by 
moderate to dense activity. 
