484 THE NERVOUS SYSTEM. 
emergent portion (Figs. 358 and 359). The facial nerve thus forms a curved loop 
over the dorsal aspect of the abducent nucleus. The emergent part of the nerve 
takes an oblique course through the pons to reach the surface. It inclines out- 
wards and downwards as it proceeds towards the ventral aspect of the pons, 
and on its way it passes between 
its own nucleus and the spinal root 
of the fifth nerve. 
ENTIA 7 
Men ERe ‘3 
Entering the facial nucleus, and end- 
ing in fine terminal arborisations around 
its cells, are many fibres from the op- 
posite pyramidal tract; fibres from the 
spinal root of the fifth nerve ; fibres from 
the corpus trapezoides, etc. The nucleus 
is thus brought into connexion with the 
motor area of the cerebral cortex, with 
the trigeminal nerve or sensory nerve of 
the face, and with the auditory nerve, ete. 
The fibres of the pars intermedia 
of Wrisberg arise from the cells of 
the geniculate ganglion of the facial 
nerve. These, like the cells of a 
spinal ganglion, are unipolar, the 
single process in each case dividing 
into a peripheral and a central 
branch. The group of peripheral 
fibres represent the chorda tympani 
branch of the facial nerve, whilst 
the central fibres form the pars 
intermedia. The latter penetrate 
the brain, and, passing either 
through or on the dorsal side of 
the spinal root of the fifth nerve, 
they finally reach the upper part 
of the column of gray matter in connexion with the fasciculus solitarius, and in 
this they end. The pars intermedia presents, therefore, the same terminal con- 
nexions within the brain as the glosso-pharyngeal nerve. 
Fia. 359.—DIAGRAM OF THE INTRAPONTINE COURSE PURSUED 
BY THE FactAL NERVE. 
Abducent or Sixth Nerve (nervus abducens) (Figs. 358 and 359).—This is a 
small motor nerve, which emerges from the brain at the lower border of the pons 
on the outer side of the pyramid of the medulla. It is the nerve of supply to 
the external rectus muscle of the eyeball. Its nucleus of origin is a small 
spherical mass of gray matter, containing large multipolar cells, which hes in 
the dorsal part of the tegmental portion of the pons, close to the mesial plane and 
immediately subjacent to the gray matter of the floor of the fourth ventricle. Its 
position can be easily indicated on the ventricular floor, seeing that it is placed 
subjacent to the emenentia teres and immediately above the level of the strize 
acustice. Its peculiar and intimate relation to the intrapontine portion of the 
facial nerve has already been indicated. It lies on the ventral aspect of, and within 
the concavity formed by, the two limbs of the loop of that nerve. 
The axons of the multipolar cells of this nucleus emerge from the inner aspect 
of the nucleus in the form of several bundles, which proceed through the whole 
antero-posterior thickness of the pons towards the place of exit. In this course 
they incline downwards and slightly outwards as they pass forwards. In the 
tegmental part of the pons they proceed forwards on the inner side of the superior 
olive, whilst in the ventral part of the pons they keep for the most part to the 
outer side of the pyramidal bundles, although several of the nerve fasciculi pierce 
these on their way to the surface. 
It would appear probable that certain of the axons of the cells of the abducent nucleus enter 
the posterior longitudinal fasciculus and proceed upwards in it to join the ;third or oculo- 
motor nerve of the opposite side. Further mention of these will be made later on. Fibres 
