478 THE NERVOUS SYSTEM. 
cells leave the dorsal aspect of the nucleus in converging groups to form the root- 
bundles of the nerve. These, in the first place, proceed straight backwards in the 
anterior horn of gray matter. Reaching the bay between the two horns of gray 
matter, they turn sharply outwards into the white matter and traverse the lateral 
column to gain their points of exit from the cord. At the decussation of the 
pyramids, root-bundles, which join the spinal accessory nerve, are seen to proceed 
from the detached head of the anterior horn of gray matter. 
The medullary part of the spinal accessory nerve has its nucleus of origin in the 
medulla; and its root-bundles, as they proceed outwards from this, can be distin- 
euished by the fact that they pursue a course on the ventral side of the spinal root 
of the trigeminal nerve, whereas the vagus roots, with which they are apt to be 
confused, pass through or lie on the dorsal aspect of the trigeminal root (Kolliker). 
The nucleus of origin of the medullary part of the accessory nerve is formed by the 
same column of cells which constitutes the nucleus ambiguus, and which, at a higher 
level, gives motor fibres to the vagus and glosso-pharyngeal nerves. 
It is usual to describe the medullary part of the spinal accessory nerve as arising in the 
nucleus of termination of the afferent part of the vagus. In the present state of our knowledge 
this is inconsistent with the fact that the medullary part of the spinal accessory is a motor nerve 
which supplies the muscles of the larynx, etc. Collaterals and fibres of the opposite pyramidal 
tract end in connexion with the cells of origin of the accessory nerve, and thus bring its nucleus 
into connexion with the motor area of the cerebral cortex. Fibres also from the posterior roots 
of the spinal nerves (afferent or sensory fibres) end in the nucleus. 
Vagus and Glosso-pharyngeal Nerves (nervus vagus, nervus glosso-pharyngeus). 
—These nerves present similar connexions with the brain, and they may theretore 
be studied together. The greater part of both nerves is composed of afferent fibres, 
which arise outside the brain-stem from ganglionic cells placed in relation to the 
nerve-trunks. Both nerves likewise possess motor or efferent fibres, which spring 
from a special nucleus of origin situated within the medulla and termed the 
nucleus ambiguus. The afferent ganglionic fibres of the vagus and glosso-pharyngeal 
enter the brain by a series of roots which penetrate the medulla along the outer or 
ventral side of the restiform body. Within the medulla they separate into two 
sets, viz. a series of bundles (chiefly composed of vagus fibres), which end in the 
nucleus of termination of the vagus and glosso-pharyngeal nerves, and another series 
of bundles (chiefly composed of glosso-pharyngeal fibres), which join a conspicuous 
longitudinal tract of fibres called the fasciculus solitarius. 
The nucleus of termination (Figs. 341, p. 458, and 545, p. 460) of the vagus 
and glosso- pharyngeal nerves very nearly equals in length the nucleus of the 
hypoglossal nerve, with which it is closely related. Above, it reaches as high as 
the strive acusticee, whilst below its lower end falls slightly short of that of the 
hypoglossal nucleus. Jn specimens stained by the Weigert-Pal method the two 
nuclei offer a marked contrast. The hypoglossal nucleus presents a dark hue, 
owing to the enormous numbers of fine fibres which twine in and out amidst its 
cells; the vago-glosso-pharyngeal nucleus is pale from the scarcity of such fibres 
within it. In the closed part of the medulla the vago-glosso-pharyngeal nucleus 
lies in the central gray matter immediately behind the hypoglossal nucleus; in 
the open part of the medulla it lies in the gray matter of the floor of the fourth 
ventricle, immediately to the outer side of the hypoglossal nucleus and subjacent 
to the surface area termed the trigonum vagi. Its cells are spindle-shaped in 
form and very similar to those found in the posterior horn of gray matter in 
the cord. In connexion with these cells, the greater number of the afferent fibres 
of the vagus nerve, and a small proportion of the afferent fibres of the glosso- 
pharyngeal nerve end in fine terminal arborisations. A small part of the upper 
portion of the nucleus may be said to belong to the glosso-pharyngeal nerve and 
the remainder of the nucleus to the vagus nerve. 
Several authorities consider the nucleus which we have described as the terminal 
nucleus of the vagus and glosso-pharyngeal to be in reality a nucleus of origin, and to give 
off motor fibres, which enter these nerves. Quite recently Dr. A. Bruce has lent to this 
theory the weight of his name and experience. - 
The fasciculus solitarius (Figs. 340, p 457; 341, p. 458; and 345, p. 460) is a 
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