84 
Cruce & Cruce 
Pretectum 
The rostral cell groups of the pretectum 
are first seen in Figure 1-7. A small patch 
of label is associated with nucleus postero- 
dorsalis (PD) (Figs. 1-7 and 1-8). Nucleus 
geniculatus pretectalis (GP) (Figs. 1-8 and 
1-9) receives a bilateral projection from the 
retina. The ipsilateral connection is to a much 
more limited portion of the nucleus than the 
contralateral projection. Like the nucleus 
geniculatus lateralis ventralis, the nucleus 
geniculatus pretectalis consists of a lateral 
cell-sparse neuropil and a medial cell plate. 
The retinal projection is concentrated in the 
lateral neuropil. 
A bilateral projection leads to the nucleus 
lentiformis mesencephali (LM) (Figs. 1-8) ; 
contralaterally the projection fills the 
nucleus but on the ipsilateral side the 
projection is outside the nuclear boundaries. 
The nucleus pretectalis (NPT) has not been 
separately described in a previous cyto- 
architectonic study (Cruce 1974). In the 
present study, a distinctive area receiving a 
contralateral retinal projection has been 
identified and named the nucleus pretectalis 
(Fig. 1-9 and 1-10). Finally, in the caudal 
pretectum a small patch of terminal labeling 
appears on the contralateral side in a position 
dorsomedial to the cells of nucleus pretectalis 
dorsalis (PRD) (Figs. 1-10). 
Tectum 
The optic tectum is illustrated at both high 
and low power magnification in Figure 3. 
The projection of retinal ganglion cells to the 
tectum is bilateral. The contralateral tectum 
receives a heavy projection which goes pri- 
marily to layers 9, 11, and 13 (Fig. 4) ; these 
are layers which are relatively cell-free, and 
presumably the terminals in these layers are 
contacting dendrites of cells in adjacent lay- 
ers. The ipsilateral retinotectal projection is 
much sparser than the contralateral one. 
Retinal fibers terminate in the rostral 300/i 
of the ipsilateral tectum in layer 9 only (Fig. 
5). 
Hypothalamus 
Within the hypothalamus retinal fibers 
terminate in relation to the supraoptic nu- 
cleus (SO) (Figs. 1-1 and 1-2) ; this hypo- 
thalamic connection is to the contralateral 
side only. 
Nucleus of the Basal Optic Tract 
The cells of the nucleus of the basal optic 
tract are interspersed within the fibers of the 
basal optic tract (bot) and are located in the 
ventromedial part of the brain (Figs. 1-9 and 
1-10). They receive contralateral optic 
terminations. 
DISCUSSION 
The pattern of connections from the retinal 
ganglion cells to the brain seen in the Tegu 
lizard conforms to the basic vertebrate plan 
as outlined by Ebbesson (1970). The regions 
of the brain that receive retinal fibers are 
the dorsal thalamus, ventral thalamus, pre- 
tectum, tectum, hypothalamus, and basal 
optic nucleus. The same pattern of organiza- 
tion has been seen in all reptile species 
studied, although there are certain variations 
present. 
The uncrossed retinal projections seen in 
the present study, do not seem to be uni- 
versally observed in the various reptiles 
studied. By the use of modern experimental 
techniques, ipsilateral projections have been 
well documented in lizards and snakes, 
whereas turtles and crocodiles seem to have 
completely crossed retinal fibers. In all the 
lizards and snakes which have been studied 
to date the thalamus seems to be the recipient 
of ipsilateral as well as contralateral retinal 
projections. In addition to the present study 
bilateral retinotectal projections have been 
reported in three other articles (Reperant, 
1973; Butler, 1974; Northcutt and Butler, 
1974a). 
The findings with respect to the six major 
regions will now be discussed in the light of 
