MR. A. SANDERS ON THE ANATOMY OF THE 
7GG 
anterior chamber of the fourth ventricle ; the latter comes from the region of grey matter 
which covers over the narrow passage of that ventricle, and partly from the transverse 
commissure at that part. The so-called glossopharyngeal also comes out from beneath 
this root, and is principally derived from the same part and from the lower portion of 
the same transverse commissure. 
The posterior root of the vagus is also derived from two distinct sources. One 
is a conspicuous ganglion which extends beneath the whole length of tire floor 
of the posterior part of the fourth ventricle, and reaches even for a short distance 
behind it. This ganglion is narrower transversely than from above downwards ; it is 
composed of cells of a pyriform shape, the points of which run out into fibres which 
are partly directed outwards and partly outwards and downwards. The fibres from 
the cells situated on the dorsal part of the ganglion join the nerve more directly than 
those which are derived from cells situated nearer the ventral side. The vagus 
receives eight or ten bundles of fibres from this ganglion. 
The other source of origin for this root of the vagus is the vertical row of small cells 
which occurs in the walls of the posterior end of the fourth ventricle or the vagal 
tuberosity. From these cells bundles of fine fibres pass across to the outer edge of 
the medulla; just as in the torus the fibres from the corresponding cells pass through 
to the deep surface of that part. These fibres all join this posterior root of the vagus, 
which also derives some reinforcement from the transverse commissure of the medulla 
at this point. If the idea of Owsjannikow (46) be correct, that the sensory roots of 
the nerves are derived from small cells, while the motor roots come from the larger 
cells — an idea which receives countenance here from the origins of all the nerves 
except that of the trochleares — then these are the origins of the sensory fibres of the 
vagus, while the bundles from the larger-celled ganglion would be motor roots. 
Lockhart Clarke (60) thinks that this ganglion of the vagus properly belongs to 
the hypoglossal, because, he says “that the ganglion in question bears the same relation 
to the floor of the fourth ventricle that the hypoglossal ganglion bears to the central 
canal;” he also remarks that a branch of the vagus supplies the tongue in fishes. 
With regard to the first statement I would point out that the ganglion in question 
is not the only one which bears that relation to the floor of the fourth ventricle or to 
the central canal ; and that from the extent of the territory supplied by the vagus it 
is scarcely probable that its greatest and most important source of origin would be 
devoted to such a comparatively unimportant part (in the fish) as the tongue. With 
regard to the second point, I have never myself found a branch of the vagus going to 
the tongue, neither have I met such a statement in the writings of any author that 
I have consulted. The terminal twigs of the nerves that supply the branchial arches 
are not in point here, as they would belong to the glossopharyngeal nerve and not 
to the hypoglossal. 
The spinal nerves (figs. 12 and 13), including the first spinal, or as some authors call 
it, the hypoglossal, have all dorsal and ventral roots. The ventral root arises by three 
