464 THE NERVOUS SYSTEM. 
into the other. In opposition to this view, Klimoff holds that the middle peduncle is 
composed solely of centripetal or afferent fibres, which pass from the nucleus pontis to the 
cerebellum. Some of these fibres are crossed and others direct. 
Certain of the transverse fibres of the pons turn backwards and enter the dorsal or 
tegmental part of the pons, but the precise connexions of these are doubtful. 
Corpus Trapezoides.—This name is applied to a group of transverse fibres 
which traverse the lower part of the pons. They are quite distinct from those 
which have been just described as entering the middle peduncle of the cerebellum, 
and they lie in the boundary between the dorsal and ventral parts of the pons, but 
encroaching considerably into the ground of the former. They arise from the 
cells of the terminal nucleus of the cochlear division of the auditory nerve, and con- 
stitute a tract which establishes certain central connexions for that nerve. They 
will be more fully described when we treat of the cerebral connexions of the 
auditory nerve. 
Dorsal or Tegmental Part of the Pons (pars dorsalis pontis)—On the dorsal 
surface of the tegmental part of the pons there is spread a thick layer of gray 
matter, covered by ependyma, which forms the floor of the upper or pontine 
part of the fourth ventricle. Beneath this the mesial raphe of the medulla is 
continued up into the pons, so as to divide its tegmental part into two symmetrical 
halves. 
In the lower part of the pons, immediately beyond the medulla, the restiform 
body is placed on the outer side of the tegmental part. In transverse sections 
through the pons it appears as a large, massive oval strand of fibres which gradually 
inclines backwards into the cerebellum, and thus leaves the pons. Between the 
restiform body and the median raphe the tegmental part of the pons is composed 
of formatio reticularis, continuous with the same material in the medulla. Thus 
arcuate or transverse fibres, curving in towards the raphe, and also longitudinal 
fibres, are seen breaking through a mass of gray matter which occupies the inter- 
stices of the intersecting fibres. To the naked eye the formatio reticularis presents 
a uniform gray appearance, but its constituent parts are revealed by low powers of 
the microscope in properly-stained and prepared specimens. Embedded in this 
formatio reticularis are various clumps of compact gray matter and certain definite 
strands of fibres. These we shall describe as we pass from the restiform body 
inwards towards the median raphe. 
(1) Spinal root of the trigeminal nerve and the substantia gelatinosa Rolandi— 
Close to the inner side of the restiform body, but separated from it by the vesti- 
bular root of the auditory nerve as it passes backwards through the pons, is seen a 
large crescentic group of coarse transversely-divided bundles of fibres. This is the 
spinal root of the fifth nerve, and applied to its inner concave side is a small mass 
of gray matter, which is the direct continuation upwards of the substantia gelatinosa 
tolandi. 
(2) The nucleus of the facial or seventh nerve comes next. It is sunk deeply 
in the tegmental part of the pons and lies close to the transverse fibres of the 
corpus trapezoides. It is a conspicuous, obliquely placed, ovoid clump of gray 
matter. From its outer and dorsal aspect the root-fibres of the facial nerve 
stream backwards and inwards towards the gray matter on the floor of the fourth 
ventricle. Passing forwards between this nucleus and the substantia Rolandi a 
solid nerve-bundle may be observed. This is the facial nerve, traversing the pons 
towards its place of emergence from the brain. 
(3) Immediately internal to the facial nucleus, but placed more deeply in the 
tegmental part of the pons, is the superior olivary nucleus (nucleus olivaris superior). 
It lies in a bay formed for it by the transverse fibres of the corpus trapezoides. 
These fibres curve round its ventral aspect, and many of them may be observed pene- 
trating into its substance. In man it is a very small mass of gray matter, and 
presents little resemblance to the inferior olivary nucleus, except in the size and 
shape of its constituent cells. In sections through the part of the pons where it 
attains its greatest size, it appears in the form of two, or it may be three, small 
isolated clumps of gray matter. It is intimately connected with the trapezial 
fibres, many of which end in it, whilst others take origin within it. 
