472 THE NERVOUS SYSTEM. 
peduncle are both afferent and efferent. The connexions which they establish in the 
pons are described on p. 463. The efferent fibres arise from cells in the gray cortex of the 
lateral hemisphere (also probably to some small extent in the cortex of the vermis), and 
end in connexion with the cells of the nucleus pontis, and likewise in the tegmental part 
of the pons. The afferent fibres, arising in the pons, end in the gray cortex of the lateral 
hemisphere of the cerebellum, and perhaps also in the cortex of the worm. 
The inferior peduncle is also composed of afferent and efferent fibres (see p. 459); only 
the more important connexions which these establish in the cerebellum can be touched on 
here. The principal afferent strand is the direct cerebellar tract. The fibres of this 
strand end in the cortex of the superior worm on both sides of the mesial plane, but 
chiefly on the opposite side. The principal efferent tract consists of the cerebello-olivary 
Jibres, and the precise origin of these is doubtful. It appears probable that they come 
from cells in the cortex of both the worm and hemisphere, and also from cells in the 
nucleus dentatus. The numerous arcuate fibres which enter the inferior peduncle establish 
connexions with cells in the cortex of the lateral hemisphere and of the worm. 
The superior peduncle is an efferent tract. The majority of its fibres come from 
the cells of the nucleus dentatus, whilst a small proportion appear to come from the cere- 
bellar cortex. According to Risien Russell, the fibres which form the dorsal edge of the 
band come from the opposite side of the cerebellum and cross the mesial plane to join the 
peduncle. 
Our knowledge of the connexions of the peduncles of the cerebellum has been greatly 
extended by Ferrier and Aldren Turner ; and the account which is given above, and also at 
p. +63, is largely derived from their memoir on this subject. 
As already mentioned, the views of Klimoff upon the cerebellar connexions do not coincide 
with those expressed above. He believes that the efferent tracts to the parts above (viz. the 
mesencephalon and cerebrum) are the superior cerebellar tracts; whilst the efferent tracts to the 
parts below are the direct sensory cerebellar tracts of Edinger (vide p. 482), which spring from 
the vermis and pass down to Deiters’s nuclei. From these internodes tracts proceed downwards 
in the antero-lateral columns of the cord as far as the lumbar region. These latter are termed 
Lowenthal’s anterior marginal bundles. Further, according to Klimoff, the middle and inferior 
peduncles are entirely afferent—the former binding the cerebellum to the cerebral cortex through 
the nucleus pontis as an internode, and the latter binding it to the medulla and cord. 
Commissural and Association Fibres.—In addition to those fibres of the white 
medullary centre which belong to the system of peduncles, there are others which have 
exclusively cerebellar connexions. Thus the various folia are bound together by numerous 
association fibres, which pass from one folium into another around the bottom of the inter- 
vening fissure. Tracts of transversely-directed commissural fibres cross the mesial plane 
in the white centre of the vermis, connecting corresponding parts of opposite sides. These, 
in some measure, are analogous to the corpus callosum of the cerebrum. The roof nuclei 
are also closely bound by connecting fibres with the cortex. 
Medullary Vela.—The medullary vela are closely associated with the cerebellar 
peduncles. They consist of two thin laminee of white matter, which are projected 
out from the white central core of the cerebellum. 
The superior medullary velum is described on p. 451. Laterally, it is continuous 
with the dorsal edges of the superior cerebellar peduncles; whilst, inferiorly, it 
is prolonged downwards and backwards under the lingula and the central lobule of 
the superior worm, to become continuous with the central white matter or corpus 
trapezoides of the worm. 
The inferior medullary velum is more complicated in its connexions. It presents 
much the same relations to the nodule of the inferior vermiform process that the 
superior velum presents to the lingula of the superior vermiform process. It is a 
wide thin lamina of white matter—so thin that it is translucent—which is pro- 
longed out from the white centre of the cerebellum above the nodule. From the 
nodule it stretches outwards to the flocculus on each side, thereby bringing these 
three small portions of the cerebellum into association with each other (Fig. 349). 
Where it issues from the white matter of the cerebellum it is in contact with the 
superior medullary velum, but, as the two lamin are traced forwards, they 
immediately diverge from each other. The superior velum is carried upwards 
between the two superior cerebellar peduncles, whilst the inferior medullary velum 
is curved forwards and then downwards round the nodule, and ends at a variable 
point in a free, slightly thickened, crescentic edge. The cavity of the fourth 
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