DISSECTION OF THE BRAIN. 83 
Note tts extensive course, sweeping around downward 
and forward to the bottom of the temporal lobe of the 
hemisphere. 
f. Tue Hiprocampus. Major is the prominent con- 
vex ridge lying along the floor of the descending 
cornu. 
ge. THE Fornix. The fosterzor pillar of the fornix 
is the narrow band of white fibres lying along the 
anterior border of the hippocampus major. The pos- 
terior pillars on each side followed forward meet just 
at the posterior edge of the septum lucidum, and unite 
for a short distance to form the dody of the fornix; 
then bending downward they diverge again, forming 
the azterzor pillars of the fornix, which run toward 
the base of the brain. 
Cut away the outer wall of the anterior cornu on 
the same stde on which the wall of the postertor cornu 
was removed. 
h. THE FORAMEN OF Monro, one on each side, is 
the slit-like opening underneath the body and anterior 
pillar of the fornix. It leads into the 3d ventricle, 
and is the passage of communication between the 3d 
and the lateral ventricles. 
To expose the 3d ventricle lift up carefully the pos- 
terior pillars of the fornix where they converge and 
tear them away with the forceps Remove in the same 
way the portion of the corpus callosum still left be- 
tween the posterior pillars of the fornix and forming 
the roof of the 3d ventricle. 
Properly speaking, the corpus callosum does not 
form the tootver the .3d ventricle. Whe true roof of 
the ventricle is a portion of the pia mater known as 
the velum wnterposttum which lies immediately be- 
neath the corpus callosum. The velum interpositum 
