THE BRAIN OR ENCEPHALON. 439 
the brain becomes continuous with the spinal cord. The bulb hes on the ventral 
aspect of the cerebellum, and occupies the vallecula or hollow which intervenes 
between the two cerebellar hemispheres. The cerebellum is a mass of considerable 
size which is placed below the hinder portions of the two cerebral hemispheres. It 
Olfactory bulb 
Olfactory tract 
Broca’s area 
Olfactory tubercle 
\ Mesial root of olfactory 
jnerve 
Lateral root 
Optic chiasma 
>= \ y- Ant. perforated spot 
ee ef - aii lobe (cut) 
ij Optic tract 
Trochlear nerve! Ta ere | </>, —~ Jeulo-motor nerve 
Trigeminal nervy Trochlear nerve 
( 
bh M 
i] enia semicircularis 
‘ j Trigeminal nerve 
i t _— eZ Wes IDES | Z Ext. geniculate body 
\\\ a = . AN E==SS S fi L A, 
\\ —= SV) ZZ oe. DES Ze Abducent nerve 
j } Z] Int. geniculate body 
ZY Pulvinar 
ij Facial nerve 
Pars intermedia 
Auditory nerve 
Lateral ventricle 
Mid. cerebellar peduncle 
Abducent nerve 
ae 
Facial nerve 
Pars intermedia 
Auditory nerve 
TE nerve 
Vagus nerve 
Spinal accessory nerve 
(accessory) 
Spinal accessory nerve 
(spinal) 
Vecipital lobe (cut) 
Glosso-pharyngeal nerv j 
Jaous 
<a ; ies fad + Hypoglossal nerve 
Spinal accessory nerve (accessory) Spinal cord 
Spinal accessory nerve (spinal) Vermis of cerebellum (cut) 
Hypoglossal nerve 
| Fic. 325. 
The under part of the left temporal and occipital lobes has been sliced off so as to open into the lateral 
ventricle. The left hemisphere of the cerebellum has also been removed. 
THe Base OF THE BratN (A. M. Paterson). 
is easily recognised on account of the closely-set, curved, and parallel fissures which 
traverse its surface. Above the medulla, and in close connexion with it, is a 
: prominent white elevation called the pons Varolii. Immediately in front of the 
pons there is a deep hollow or recess. This is bounded behind by the pons Varolii, 
_ on either side by the projecting temporal lobe of the cerebral hemisphere, and in 
_ front by the orbital portions of the frontal lobes of the cerebral hemispheres. 
Passing out from either side of the fore-part of this recess is the deep Sylvian 
fissure which intervenes between the pointed and projecting extremity of the 
temporal lobe and the frontal lobe of the cerebrum, whilst in the middle line in 
front the great longitudinal fissure, which separates the frontal portions of the 
cerebral hemispheres, opens into it. 
Within the limits of this deep hollow, in the base of the brain, two large rope- 
like strands, the crura cerebri, may be seen issuing from the upper aspect of the 
pons Varolii. Placed close together as they emerge from the pons, these crura 
diverge as they proceed upwards and forwards, and finally each disappears by 
plunging into the corresponding side of the cerebrum. Turning round the outer 
side of each crus, where it enters the cerebrum, a flattened band termed the optic 
tract may be observed. These bands converge in the fore-part of the hollow, and 
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J 
P 
b, 
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