396 J. B. JOHNSTON 
ally until it was driven down nearly upon the basal surface and 
until the migrated general pallium itself had covered over the 
striatum, there would be produced a fairly exact counterpart of 
the primitive mammalian brain. This is the condition of the 
brain of an opossum or rabbit, in both of which the lateral (Syl- 
vian) fissure is little deeper than the analogous striatal depres- 
sion in the turtle’s brain. The further expansion of the frontal 
and caudal poles produces the opercula bounding the lateral 
fissure. 
On the dorsal surface just behind the olfactory peduncle 
occurs a slight rounded elevation (figs. 3, 25) which forms a part 
of the pallial thickening to be described below. 
On the medial surface of a brain from which the stem has been 
cut away and the choroid plexus removed (fig. 3) it is seen that 
a wide chorioid fissure extends caudad in a simple curve from the 
interventricular foramen into the temporal pole. On removing 
the medial wall of the hemisphere there are exposed certain ridges 
which constitute some of the most characteristic features of the 
reptilian brain (figs. 4, 10). Three main bodies are to be dis- 
tinguished: a dorsal ventricular ridge, the largest and most prom- 
inent; beneath it.and extending farther rostrad, the striatum; 
and rostrally in the dorsal wall a smaller pallial thickening. 
Three longitudinal ventricular grooves are to be distinguished: 
dorsal, middle and ventral. The dorsal ventricular groove is a 
very deep groove between the dorsal ridge and the pallium (figs. 
4, 11 to 22). The middle groove runs beneath the dorsal ridge 
from the amygdaloid region forward into the olfactory bulb. 
A bifurcation of the caudal end of this groove and its significance 
will be mentioned later. The ventral groove is medial to the 
striatum. It dips very deep into the olfactory tubercle but is 
shallow rostral and caudal to this level. 
The term epistriatum was first used by Edinger to designate a 
body in the reptilian forebrain to which C. L. Herrick had traced 
a large part of the olfactory tract. In the 1904 edition of Edin- 
ger’s textbook this body is labelled epistriatum in figures 117, 
Varanus; 122 and 123, Schemata; 125b, lizard. This usage is 
followed by de Lange in a recent paper on Varanus. In Edin- 
