Ee, 
INTERNAL STRUCTURE OF THE MESENCEPHALON. 495 
remainder make their way through the optic thalamus, enter the posterior limb 
of the internal capsule, and, through this, are carried upwards to the cerebral cortex of 
the Rolandic area (Flechsig; Ferrier, and Turner). The superior cerebellar peduncle 
is, therefore, to be regarded as a great efferent tract which issues from the lateral 
hemisphere of the cerebellum, crosses the mesial plane in the lower part of the 
mesencephalon, and ends in the red nucleus, the ventral part of the optic thalamus 
and the Rolandic area of the cerebral cortex of the opposite side. 
Superior quadrigeminal 
body 
; Zee 
=== Sylvian gray matter 
External geniculate____-__ 
be ly 5 
f > Sylvian aqueduct 
Inferior brachiun 
++ Teementum 
Internal geniculate Se = 
body 
i) 
= Nucleus of third nerve 
i 
—- 
Posterior longitudinal 
Mesial fillet bundle 
as 
= th 
Sm 
; Red nucleus 
| Fibres of superior 
cerebellar peduncle 
Crusta 
Optic tract —— gigs a RAN .\: ——— Third nerve 
~~ ——Substantia nigra 
4 a 
fOr 
WT 2 
i } 
f i 
Corpus mamiiillare 
Fic. 366.—TRANSVERSE SECTION THROUGH THE HUMAN MESENCEPHALON AT THE LEVEL OF THE SUPERIOR 
QUADRIGEMINAL Bopy. 
Red Nucleus (nucleus ruber).—This is an elongated nuclear mass, of a reddish 
tint in the fresh brain, which lies in the upper part of the tegmentum, and in 
transverse section presents a circular outline. It begins at the level of the lower 
border of the superior quadrigeminal body and it extends upwards into the sub- 
thalamic tegmental region. At first it is small and is placed at a little distance from 
the mesial plane; but as it proceeds towards the subthalamic region, it increases in bulk 
and approaches more nearly to the mesial raphe, and its neighbour of the opposite 
side. The curved emerging bundles of the third nerve pass through it on their way 
to the surface. The relation which the fibres of the opposite superior cerebellar 
peduncle present to it has been described. These fibres traverse its lower part in 
such numbers that in Weigert-Pal specimens it presents a very dark colour; but 
higher up, as the fibres are gradually absorbed by the nuclear mass, they become 
less numerous in its midst, and the nucleus assumes a paler tint. 
The posterior longitudinal fasciculus is a very conspicuous tract of longi- 
tudinal fibres which extends throughout the whole length of the medulla, pons, and 
mesencephalon, in the formatio reticularis or tegmental part of each. Below, at the 
level of the decussation of the pyramids, it becomes continuous with the anterior 
basis-bundle of the spinal cord (p. 455), whilst, by its opposite or upper end, it 
establishes intricate connexions in the region immediately above the mesencephalon. 
Throughout its whole length it lies close to the mesial plane and its fellow of the 
opposite side. In the mesencephalon it is applied to the ventral aspect of the 
Sylvian gray matter, whilst in the pons and medulla it is situated immediately 
subjacent to the gray matter of the floor of the fourth ventricle. One of its most 
