22 
Northcutt 
Figure 7. Transverse sections through rostral (A) to caudal (C) levels of the right telencephalic hemisphere 
of the Indian monitor, Varantis bengalensis, stained to demonstrate neuron cell bodies. A-D, sensory zones 
of the anterior dorsal ventricular ridge; aot, accessory olfactory tract; cd {Cl-3), dorsal cortex and its 
subdivisions; cl, lateral cortex; cm (Cl-2), medial cortex and its dorsal (Cl) and ventral (C2) subdivi- 
sions; dvr,p, posterior division of the dorsal ventricular ridge; na, nucleus accumbens; ndb, nucleus of the 
diagonal band of Broca; ns, nucleus sphericus; ot, olfactory tubercle; s, septal nuclei; st, striatum. 
Dorsal ventricular ridge. The dorsal ven- 
tricular ridge (DVR) of lizards is the single 
largest pallial unit, and more has been writ- 
ten about it than any other single brain 
region in reptiles. Until recently, most com- 
parative neuroanatomists (Kappers, Huber, 
and Crosby, 1936; Crosby, deJonge and 
Schneider, 1967) regarded the dorsal ven- 
tricular ridge as homologous to the caudate 
and putamen nuclei of mammals. These nuclei 
constitute the dorsal half of the corpus 
striatum which occupies the ventrolateral 
wall of the telencephalon in mammals. The 
corpus striatum was believed to be the 
highest center for the correlation of sensory 
information in nonmammals, and a center 
mediating instinctual behavior (Herrick, 
1948; Krieg, 1953). The hypertrophy of the 
DVR in reptiles and birds was thus corre- 
lated with their supposedly highly developed 
instinctual behavior, and it was concluded 
that reptiles possessed only a rudimentary 
dorsal cortex, homologous to the greatly ex- 
panded mammalian isocortex (neocortex). 
In the last few years, three lines of evi- 
dence have converged to overthrow the view 
