82 
MAMMALIAN ANATOMY 
elevation in the floor of the descending cornu is the hippo¬ 
campus. 
Forming a part of the medial wall of each ventricle is the body 
of the fornix, the two halves of which join in the midline (cf. 
median sagittal section) to form a triangular mass. Anteriorly 
the fornix takes the form of two columns of fibers which curve 
ventrally and disappear (since they pass into the thick mass 
which forms the floor of the cavity, and then curve posteriorly to 
reach the mammillary bodies, from which they pass dorsally to 
reach the optic thalami in the lateral walls of the diencephalon). 
✓ 
Posterior to the body of the fornix, its two crura diverge rapidly, 
and each forms the thin border, or fimbria, of the corresponding 
hippocampus. This may be disclosed upon one side by removal 
of the chorioid plexus which supplies the interior of the lateral 
ventricles, entering along the line between the corpus striatum 
and the fimbria where there is only a thin epithelial lamina. 
Draw the brain thus dissected to show the floor of the lateral ventricles , 
dorsal view. 
By gently detaching the ventral ends of the temporal lobes, 
the hippocampus and the adjacent remaining portions of the 
temporal and occipital lobes may be lifted in one piece and turned 
forward, displaying beneath them the dorsal surface of the dien¬ 
cephalon and the mesencephalon which this portion of the cerebral 
hemisphere overlaps. Note that in the middle of the diencephalon 
anterior to the pineal body there may be seen the chorioid plexus 
which forms the thin roof of the third ventricle. By removing 
this the narrow slit of the third ventricle is disclosed from above, 
between the thick walls formed by the optic thalami. If the 
reflected portion of the cerebral hemispheres be pulled well for¬ 
ward, the Y-shaped foramen interventriculare will now be seen 
beneath the body of the fornix connecting the lateral ventricles 
with the third ventricle. Cut through the body of the fornix and 
thus remove entirely the reflected portion of the cerebral 
hemispheres. 
3. Dissection of the Cerebellum. 
By a series of horizontal slices, remove the dorsal portion of 
the cerebellum until the level of the entrance, upon each side, of 
