Forebrain and Midbrain of Lizards 
43 
processes which pass dorsally through all of 
the tectal laminae and terminate as over- 
lapping endfeet at the pial surface (Leg- 
hissa, 1962). 
Laminae 2 and U consist of nonmyelinated 
and poorly myelinated axons whose origin is 
unknown. These laminae also contain the 
basal dendrites of the neurons of laminae 3 
and 5 (Ramon, 1896; Leghissa, 1962; Butler 
and Ebbesson, 1975). 
Laminae 3 and 5 are formed by the cell 
bodies of piriform neurons that Ramon 
(1896) divided into three populations: (1) 
cells whose apical dendrites terminate in 
zone 7 ; (2) cells whose apical dendrites 
extend into lamina 14, but also possess 
dendritic ramifications in laminae 7, 9, 10, 
and 13 with axons directed superficially and 
entering lamina 13; and (3) cells whose 
apical dendrites ramify in laminae 10, 12, 
and 14 with axons entering lamina 6. All 
three piriform populations possess dendrites 
which ramify in retinal terminal zones, with 
the possible exception that the first popula- 
tion terminates in lamina 7. It is probable 
that the major extent of the apical dendrites 
of all three piriform populations are related 
to nonvisual inputs or to multisynaptic visual 
inputs. Both telencephalic and contralateral 
tectal pathways are known to terminate 
among the dendritic processes of these piri- 
form cells (Butler and Ebbesson, 1975). 
Lamina 6 is composed primarily of my- 
elinated axons among which a few cell bodies 
can be identified. The most common cell type 
has been termed giant fusiform or pyramidal 
cells by Butler and Ebbesson (1975). Such 
cells have been recognized in the tecta of 
most vertebrates (Leghissa, 1962; Potter, 
1969). These neurons ramify primarily with- 
in lamina 6 with occasional dendrites directed 
toward the level of lamina 5. Their axons 
have not been described. 
Lamina 7 consists primarily of cell bodies. 
Two basic patterns in the distribution of 
these cell bodies are seen in lizards. In one 
case there is a clear separation of laminae 6 
and 7 with few, if any, cell bodies located in 
lamina 6, as in Lacerta (Fig. 16). In the 
second case, the cells of lamina 7 form an 
outer or dorsal subdivision and an inner or 
ventral subdivision, with some being scat- 
tered between the fibrous columns of zone 6, 
as in Iguana (Fig. 15) ; a distinct division 
into laminae 6 and 7 is impossible. Ramon 
(1896) recognized at least four neuronal 
populations in lamina 7. All of these neurons 
possess dendrites that ramify in the super- 
ficial tectal laminae that receive retinal 
terminals. In addition, many of these cells 
are bipolar and possess dendrites that ramify 
in deeper layers (laminae 6 and 5). The 
segregation of neurons of lamina 7 into two 
subdivisions may reflect differences in af- 
ferent connections. Unfortunately, little 
experimental data are available concerning 
the afferents to the central tectal region. 
Butler and Ebbesson (1975) have reviewed 
the known projections which include visual 
afferents to the superficial apical dendrites 
of cells of lamina 7, telencephalic input to 
the deep half of lamina 7, and intertectal 
projections to laminae 3 through 5. Similar 
intertectal projections have been reported in 
Iguana by Foster and Hall (1975). The deep 
dendrites of cells in lamina 7 extend into 
lamina 5 and perhaps form synapses with 
intertectal projections. 
Spinal hemisections reveal few, if any, 
projections directly to the tectum (Ebbesson, 
1967). However, the degeneration after 
isthmal hemisections reveals ascending pro- 
jections to at least the deep and central 
tectal regions in Gekko (unpublished obser- 
vations). 
Laminae 8 through H. These laminae con- 
sist primarily of layers of retinofugal fibers 
and their terminal neuropils. Laminae 9, 
12, and 14 are composed of retinal fibers that 
terminate in laminae 8, 11 and 13 (Northcutt 
and Butler, 1974; Cruce and Cruce, 1975). 
The bulk of these retinal fibers issue from 
the contralateral eye, but ipsilateral retino- 
tectal fibers to the rostral tectum in Gekko, 
Tupinambis, and Xantusia are now known 
to exist. At present considerable work re- 
mains to be done in order to characterize 
the cell types and dendritic ramifications of 
laminae 8 through 14. Leghissa’s descrip- 
tions (1962) are not sufficiently detailed to 
