496 
salient features is the intimate association which it presents with the three motor — 
nuclei from which the nerves for the supply of the muscles of the eyeball take 
igi the oculo- motor or 
third nucleus, the trochlear or 
fourth nucleus, and the abducent 
The first two 
of these are closely applied to its 
inner and dorsal aspect, whilst 
the abducent nucleus is placed on 
Into each of these 
nuclei it sends many collaterals, 
and probably also some of its 
constituent fibres, and these end 
arborisations around 
the nuclear cells. It would appear, 
therefore, that one of the most im- 
portant functions of this strand is 
to bind together these nuclei, and 
thus enable them to act in harmony 
Fibres also enter 
Decussation of 
lateral fillet 
fibres 
Inferior 
quadrigeminal ——— 
nucleus 
Mesencephalic 
root of fifth 
nerve 
Fourth nerve 
Posterior 
longitudinal 
bundle 
i 
Lateral fillet Hh 
Decussating 
superior_ \ 
cerebellar 
peduncles 
THE NERVOUS SYSTEM. 
origin, Viz. 
or sixth nucleus. 
its outer side. 
in terminal 
with each other. 
Fic. 367.—SECTION THROUGH THE INFERIOR QUADRIGEMINAL 
Boby AND THE TEGMENTUM OF THE MESENCEPHALON 
BELOW THE LEVEL OF THE NUCLEUS OF THE FOURTH 
(The decussation of the superior 
cerebellar peduncles and the course of the fourth nerve 
NERVE IN THE ORANG. 
in the Sylvian gray matter is seen.) 
and other motor nuclei. 
large extent, it is formed of fibres which run a short course within it. 
In spite of the large amount of attention which has been given to the study of the posterior 
longitudinal bundle, it must be admitted that there is little unanimity of opinion regarding its 
That it is a brain tract of high importance is evident from the fact 
that it is present in all vertebrates, and, further, that its fibres assume their medullary sheaths 
In fish, amphibians, and reptiles, it is one of the most powerful 
In man its fibres medullate between the sixth and seventh months of 
foetal life, and at the same time as the fibres of the anterior basis-bundle of the cord, with which 
connexions and functions. 
at an extremely early period. 
bundles of the medulla. 
it stands in connexion. 
According to Van Gehuchten and Edinger, it extends upwards beyond the level of the 
oculomotor nucleus, and in the subthalamic region its fibres take origin from a special nucleus of 
its own in the gray matter of the third 
ventricle, immediately below the level 
of the corpora mamimillaria. Held asserts 
that numerous fibres, arising from cells 
in the superior quadrigeminal body, 
curve in an arcuate manner in the teg- 
mentum outside the Sylvian gray matter, 
to take part on the ventral aspect of this 
in what is called the “ fountain decussa- 
tion.” Reaching the opposite side these 
fibres turn downwards and join the 
posterior longitudinal fasciculus. The 
same authority considers that fibres 
from the ventral part of the posterior 
commissure can also be traced down- 
wards into the posterior longitudinal 
bundle. Edinger, on the other hand, 
places these fibres as a distinct tract on 
the ventral and lateral aspect of the 
posterior longitudinal bundle, although 
In apposition with it. 
Mendel believes that fibres from the 
oculo-motor nucleus are carried down in 
the posterior longitudinal bundle, and, 
from this, into the facial nerve for the 
supply of the orbicularis palpebrarum 
and the corrugator supercilii, bringing these muscles therefore under the control of the same 
nucleus as the levator palpebrze superioris muscle. 
the hands of Tooth and Turner. 
Fic. 368. 
———= S55 
AT A SLIGHTLY LOWER LEVEL THAN Fic. 367. 
the posterior longitudinal fasci- 
culus from the auditory system 
and perhaps, also, from the facial 
results obtained by degeneration 
would seem to indicate that, toa 
Decussating 
lateral fillet 
<5] uLbres 
Nucleus of in- 
ferior quadri- 
geminal body 
Se Mesencephalic 
root of fifth 
e 
sa nerve 
baa 
“7, —Fourth nerve 
Posterior 
longitudinal 
bundle 
Lateral fillet 
Superior 
cerebellar 
peduncle 
-—— Mesial fillet 
SECTION THROUGH THE INFERIOR QUADRIGEMINAL 
Bopy AND THE TEGMENTUM OF THE MESENCEPHALON, 
This view has received corroboration at 
It has been further suggested that fibres from the hypoglossal 
