70 J. B. JOHNSTON, 
(Phot. 4) the lateral surface of the fore brain presents one fact of 
interest, namely that the corpus striatum rises much higher at the 
cephalic than at the caudal end. From the dorsal aspect (Phots. 6 
and 7) the cavity appears narrower than that of the ‘tween brain, 
but at about its middle there goes off to either side on the surface 
of the epistriatum, a groove which deeply marks the epistriatum 
and ends in a Y-division. In the young fish which were used for 
the greater part of the microscopic study, the epistriatum is re- 
latively much smaller and the groove just mentioned is not present. 
The minute structure shows that we have here nothing to do with 
cerebral hemispheres, and these grooves can not be regarded as 
lateral ventricles as some recent writers would probably regard them. 
(Compare discussion of origin of cortex, page 235 and following.) 
They are due merely to unequal growth of parts of the epistriata in 
their later development. At the caudal end of the fore brain the 
floor is abruptly depressed near the middle line just in front of 
the chiasma (Phot. 3), forming the preoptic recess, the walls of which 
constitute the nucleus taeniae. At the cephalic end the dorsal 
membranous wall extends downward between the lobi olfactorii to 
the ventral surface. At either side of this membrane the cavity 
communicates with the cavity of one of the olfactory lobes (Phots. 3, 
6, and 7). These lobes extend forward, diverging, as two bluntly 
spindle-shaped bodies whose surfaces are rough and longitudinally 
striated by the olfactory nerve fibres. 
III. Minute Anatomy. 
1. Description. 
A. The Hind Brain. 
a) Medulla oblongata. 
On the basis of its minute structure the medulla may be divided 
into two parts, a basal portion and a dorso-lateral portion (Phots. 8 
—11). The basal portion is bounded laterally and dorsally by the 
spinal V tract, and corresponds to that part of the spinal cord lying 
lateral and ventral to the dorsal horns. The dorso-lateral portion 
ies dorsal to the spinal V tract and corresponds to the dorsal 
horns and tracts of the cord together with structures mesial to the 
dorsal horns. (Compare sections on the lobus vagi below, page 83 
and 177—186.) 
