658 THE NERVOUS SYSTEM. . " 
Becoming separated from the brain, the cellular mass separates into three portions, of 
which the middle part is associated with the facial nerve and pars intermedia (as the 
geniculate ganglion), while the mesial and lateral parts are converted into the mesial 
(vestibular) and lateral (cochlear) ganglia and roots of the auditory nerve. The cells 
becoming bipolar, their central processes are secondarily connected with the brain on 
the dorsal (lateral) aspect of the facial nerve ; the peripheral processes proceed to the 
auditory vesicle, to which they are distributed as the vestibular and cochlear nerves. 
Numerous cells are carried along with the nerve trunks into relation with the auditory 
capsule, and constitute the vestibular and cochlear ganglia. 
The glosso-pharyngeal and pneumogastric nerves are developed from the side 
of the hind-brain, both in the same way, and each by two roots. <A collection of 
cells separates itself from the alar lamina of the hind-brain behind the auditory vesicle to 
form the ganglionic afferent root. The ganglion of the pneumogastric is much larger 
than that of the glosso-pharyngeal. Each ganglion becomes divided into two parts, a 
proximal and a distal portion, connected together by a commissural band of fibres. The 
proximal ganglion (jugular ganglion of the glosso- pharyngeal ; ganglion of the root of the 
pneumogastric) is secondarily connected by centripetal fibres to the hind-brain. From the 
distal ganglion (petrous ganglion of the elosso-pharyngeal ; ; ganglion of the trunk of the 
pheumogastric) peripheral fibres grow outwards to form the nerve trunk. 
Each nerve is also provided ‘with a small efferent root, consisting of nerve fibres, 
arising from a collection of neuroblasts in the lateral part of the basal lamina of the hind- 
VENTRAL ROOT 
DORSAL ROOT V.VILVIIL.IX. X. 
IX. XX 7 
A B 
Fic, 472.—CoMPARISON OF SPINAL CorD AND Hinp-Brarn ; ORIGIN OF NERVE Roots (after His). 
A. Spinal cord ; B. Hind-brain. 
ALAR LAMINA ALAR LAMINA 
BASAL LAMINA 
LATERAL AREA 
BASAL 
LAMINA 
MESIAL AREA 
im 
@) 
Y 
1. 1V. VIX 
brain, and emerging beneath the ganglionic root at the junction of the alar and basal 
laminze (in series with the fibres of the efferent root of the facial nerve above and of the 
spinal accessory nerve below). 
The spinal accessory nerve arises in two pi medullary, the other spinal. 
The medullary (accessory) portion develops as the processes of a series of neuroblasts in 
the lateral portion of the basal lamina of the hind-brain, which emerge in series with the 
efferent roots of the glosso-pharyngeal and pneumogastric nerves. The spinal portion 
arises as the processes of a group of neuroblasts in the ventral part of the medullary tube, 
which at first are directed dorsally in the side of the primitive spinal cord, and, turning 
outwards, emerge as a series of roots on its lateral aspect. 
The hypoglossal nerve is developed, not in series with the nerves above- 
mentioned, but like the third, fourth, and sixth nerves, from the mesial part of the basal 
lamina of the hind-brain, in the space between the glosso-pharyngeal and nerves above 
and the first cervical nerve below. It is formed as a series of peripheral processes from a 
collection of neuroblasts occupying the hind-brain. Froriep’s ganglion is a transitory 
collection of nerve-cells developed from the alar lamina of the hind-brain on the dorsal 
aspect of the nerve, and represents in a rudimentary condition its dorsal ganglionic root. 
It gives off no branches and soon disappears. 
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