72 
Butler 
animals were perfused transcardially with 
saline and 10 percent formalin. The brains 
were then embedded in egg yolk, frozen and 
sectioned at 30;^. Sections were processed 
with various modifications of the Nauta 
silver impregnation technique, including 
those of Fink and Heimer (1967), Roth 
(Ebbesson, 1970&), and Eager (1970). In 
Gekko gecko, the Eager modification pro- 
duced the most successful impregnation of 
degenerated fibers and terminals. 
The pattern of degeneration seen follow- 
ing one of the larger lesions, which involved 
dorsal cortex, parts of the medial wall, and 
the dorsal ventricular ridge is shown in 
Figure 2. Ipsilaterally degeneration extends 
throughout the cortices and the dorsal ven- 
tricular ridge, and into the septum and 
striatum. The majority of degenerated fibers 
traced into the contralateral hemisphere 
travel via the hippocampal (dorsal pallial) 
commissure (HC). Some fibers pass into and 
terminate in the contralateral septum (S), 
while the rest turn dorsally in the alveus, 
a fiber tract deep to medial cortex. Terminal 
degeneration associated with the medial cor- 
tex (MC) is confined to two bands on either 
side of the cell plate, leaving the outer por- 
tion of the stratum moleculare free of de- 
generation. Ventral to the dorsomedial cor- 
tex (DMC) some degenerated fibers turn 
dorsally and others continue laterally into 
the region of the ventral cell plate (CP) and 
medial part of dorsal cortex (DCm). 
Terminal debris extends throughout the dor- 
sal cortex; in the lateral part of dorsal cor- 
tex (DCl), the degeneration is primarily 
concentrated in the superficial molecular 
layer. Sparse degeneration extends into the 
region of the lateral cortex (LCd) and the 
lateral edge of the DVR. Finally, a fairly 
sparse amount of degeneration is found in 
the contralateral basal forebrain, ventro- 
lateral to the ventral recess of the lateral 
ventricle. 
A series of more restricted lesions of por- 
tions of the cortex enables some dissection 
of this pattern of projections. A lesion which 
involved the lateral cortex and the lateral 
edges of the DVR and basal forebrain gave 
rise to degeneration in the contralateral 
hemisphere, mostly via the anterior com- 
missure, in the striatum, lateral cortex, and 
more sparsely in the lateral edge of the DVR. 
Lesions restricted to the dorsal cortex, how- 
ever, result in degenerated fibers which 
travel via the hippocampal commissure and 
alveus to terminate in the contralateral 
medial, dorsomedial, and dorsal cortices, and 
very sparsely in the lateral edge of the DVR. 
This distribution is similar to that seen 
following the more extensive lesions as 
described above. Further studies utilizing 
intra-axonal anterograde transport of tri- 
tiated amino acids and retrograde transport 
of horseradish peroxidase are presently be- 
ing initiated to dissect further the details 
of these projections. 
REPTILIAN DORSAL CORTEX AND DVR 
Figure 3 summarizes some of the data 
from recent anatomical studies on the con- 
nections of the dorsal cortex and DVR in 
reptiles and birds. While being oversimpli- 
fied for illustration, it provides an outline of 
current information. 
Dorsal Ventricular Ridge 
In turtles, lizards, and crocodiles the DVR 
has been found to receive an ascending visual 
pathway. The optic tectum projects to nu- 
cleus rotundus in the dorsal thalamus (Eb- 
besson, 1970a; Hall and Ebner, 1970a; 
Butler and Northcutt, 19716; Braford, 
1972a), and nucleus rotundus, in turn then 
projects to a lateral area in the anterior 
dorsal ventricular ridge (Hall and Ebner, 
19706; Pritz, 1975; Distel and Ebbesson, 
1975). In lizards and crocodiles an ascending 
auditory pathway from the torus semicircu- 
laris (inferior colliculus), via nucleus re- 
uniens in the dorsal thalamus (Foster, 1974; 
Pritz, 1974a), projects to a medial area in the 
anterior DVR (Pritz, 19746) ; Distel and 
Ebbesson, 1975). As discussed above, these 
pathways in reptiles and similar ones in birds 
