THE MAMMALIAN BRAIN 
83 
the various bundles of fibers from below into the cerebellum, is 
reached. Cut away the middle region or vermis of the cerebellum, 
which lies over the fourth ventricle, and carefully detach it, 
leaving in place as much as possible of the anterior and posterior 
medullary vela which form the actual roof of the cavity. Separate 
and identify the three bundles of fibers which enter the cerebellum 
upon each side as follows: (a) the brachium conjunctivum,which 
enters it from the dorsal portion of the peduncle of the cerebrum; 
(b) the brachium pontis which enters it from the pons; ( c ) the 
corpus restiforme which enters it from the lateral funiculus of the 
medulla. 
4. The Brain Stem. 
The dissection of the cerebral hemispheres and the cerebellum, 
as above directed, leaves that portion of the brain which cor¬ 
responds to practically the whole of the primitive vertebrate 
brain and is known as the brain stem. In the study of this, 
distinguish with care between those portions which are external 
surfaces, those which are interior surfaces of cavities, and those 
which are cut surfaces. Draw a dorsal view showing the parts 
identified; also , if time permits , a lateral view. 
In the telencephalon note the corpora striata which lie in the 
floor of the lateral ventricles; the thickness of the lateral wall of 
the ventricle, the cut surface of which displays a gray cortical 
layer and a converging mass of white substance adjoining the 
corpus striatum. This white substance consists largely of the 
system of projection fibers known as the corona radiata, which 
extends from the cerebral cortex through the corpus striatum to 
enter the cerebral peduncles and thus reach the more posterior 
portions of the nervous system. By making an oblique longi¬ 
tudinal section through one of the corpora striata, the course of 
these fibers through it may be seen, forming the “inner capsule” 
of the organ, and giving it the peculiar appearance from which it 
has derived its name. 
In the diencephalon note that the external surface of the optic 
thalami, which form its thick lateral walls, is exposed to view, and 
that between these rounded eminences the removal of the anterior 
chorioid plexus has disclosed anterior to the pineal body the slit- 
