OLFACTORY CENTERS IN TELEOSTS 189 
b. The cerebral hemispheres 
(1) Gross morphology. The cerebral hemispheres are of the typi- . 
cal teleostean type (figs. 1 to 4). They consist of paired solid basal 
lobes which contain chiefly the secondary olfactory centers, con- 
tinuing caudo-ventrally over the optic chiasma as the pedunculi 
thalami, or praethalamus of C. L. Herrick. Dorsally and later- 
ally, these are covered by a membranous roof, the so-called pal- 
lium, composed of adjacent layers of ependyma and pia. This 
tela is continuous rostrally with the membranous roof of each 
olfactory crus, the separation into two parts occurring just at 
the rostral margin of the basallobes. This tela is attached at the 
ventro-lateral margin of each hemisphere, at which point its pia 
becomes continuous with that of the base of the brain, while its 
ependyma is reflected over the basal lobes (figs. 1, 2, 3, 4, 34). 
Immediately mesal to the attachment of the tela occurs a fis- 
sure, the fissura endorhinalis (figs. 4, 24, 25, etc.). This is the 
sinus rhinalis of Kappers (’06), the fovea endorhinalis externa of 
Kappers and Theunissen (’08), the fovea limbica of Goldstein 
and Edinger, the fissura ectorhinalis of Owen (’68), the fissura 
endorhinalis of many authors. This fissure holds a constant posi- 
tion throughout the vertebrate series, separating in the higher 
forms the basal olfactory centers from the pyriform lobe; it like- 
wise bears a constant relation to the tractus olfactorius lateralis, 
as will be noted later. 
The ventricle of the forebrain consists of the open space between 
the tela and the basal lobes. This forms a large, but shallow 
cavity, excepting between the two basal lobes where it is of some 
depth (figs. 24, 34, 35, etc.). It extends caudally to the velum 
transversum. Caudal to this velum, occurs a much convoluted 
epithelial sac extending rostrally over the tela proper; this is 
the dorsal sac, and is an evagination of the membranous wall of 
the diencephalon (fig. 68). Ventral to the velum transversum, the 
forebrain ventricle passes over into the third ventricle or dien- 
cephalic cavity. 
Each basal lobe is separated by ependymal sulci on the dorsal, 
lateral and mesal surfaces into regions with characteristic internal 
