Forebrain and Midbrain of Lizards 
55 
organism where stimuli exist relative to 
the organism. This tectal function appears 
common to all vertebrates. The relevant 
literature has recently been reviewed by 
Ingle (1973). Numerous studies implicate 
these midbrain centers in pattern recogni- 
tion as well. Even in mammals, considerable 
color vision and pattern vision remain in 
the absence of isocortical sensory centers 
(Humphrey, 1970; Ware et al., 1972, 1974; 
Spear and Barbas, 1975; Cranford et al., 
1976). 
The ability of turtles to perform pattern 
discriminations in the absence of telenceph- 
alic visual centers (Bass et al., 1973), or 
geckos to feed on small moving insects fol- 
lowing ablation of telencephalic visual cen- 
ters (unpublished observations), indicates 
that the tectum of reptiles also possesses 
“perceptual” functions. What is not clear is 
whether the tectum in reptiles is sensitive to 
only a few sets of visual objects, or performs 
complex visual discriminations as well. 
It is possible that the evolution of the 
dorsal ventricular ridge in lizards underlies 
complex discriminations. Increased analysis 
of sensory information and fine motor con- 
trol characterizes the evolution of mammal- 
ian isocortex, and a similar evolutionary 
phenomenon may have occurred in parallel 
in living lizards. That lizards with the larg- 
est brain-body ratios and the most differen- 
tiated dorsal ventricular ridges also possess 
the most complicated behavior is probably 
not a coincidence, particularly if the dorsal 
ventricular ridge of lizards is homologous to 
most of mammalian isocortex. As noted ear- 
lier, the dorsal ventricular ridge receives 
information from many different sensory 
modalities and, in turn, projects massively 
upon the striatum. In these respects, it pos- 
sesses functional similarities to mammalian 
isocortex and may perform complex sensory 
integrations and exert final control upon the 
functions of the striatum and other lower 
brain centers. The evolution of the dorsal 
ventricular ridge is the single most striking 
change in the CNS of lizards and most likely 
underlies much of their complex behavior. 
Phylogenetic Considerations 
In 1923, Charles L. Camp published his 
now famous study of the “Classification of 
Lizards.” Prior to Camp’s synopsis a num- 
ber of widely different phylogenetic schemes 
had been proposed (Cope, 1864; Boulenger, 
1884; Fiirbringer, 1900). Nearly 50 years 
later, most of Camp’s families and their phy- 
letic placement remains firm, and his analysis 
stands as the major landmark in lizard sys- 
tematics. Camp divided lizards into two 
major divisions, the Ascalabota and the 
Autarchoglossa (Fig. 21). He based this 
division on four characters: presence or ab- 
sence of superficial rectus muscles, number 
of transverse rows of ventral scales, width of 
scale free margin, and external form of the 
copulatory organs or hemipenes. Camp him- 
self noted the differences in locomotion re- 
flected by his two divisions. It is very likely 
that three of his four sorting characters are 
tied to locomotor adaptations, and their 
combined occurrence may have evolved a 
number of times independently. 
Recently it has been argued that the py- 
gopodids and xantusiids, which possess well- 
developed superficial rectus muscles, are 
closely related to gekkonids (McDowell and 
Bogert, 1954; Hoffstetter, 1962). This view 
was supported by Romer, (1956) who sug- 
gested that the placing of the pygopodids and 
xantusiids near the gekkonids destroyed 
Camp’s divisions, and that these divisions 
should be abandoned or redefined. 
Underwood (19711, in a recent review of 
lizard affinities, suggested that the pygopo- 
dids and xantusiids are derivatives of the pre- 
cusors of the Ascalabota and argued for the 
retention of Camp’s divisions. He presents 
an updating of Camp’s scheme which I have 
interpreted as a dendrogram in Figure 22A. 
The major changes in Underwood’s updating 
of Camp’s scheme, besides the transfer of 
the pygopodids and xantusiids to the Gek- 
kota, relate to the placement of the cordylids 
and dibamids. Camp placed the Cordylidae 
within the anguimorphs, but noted that they 
possessed more ascalabotan characters than 
the anguimorphs. Underwood has accepted 
