760 
MR. A. SANDERS ON THE ANATOMY OF THE 
There are extensive commissures or arcuate fibres in the region of this nerve, 
which cross the ventral surface and other parts in the formatio reticularis; they 
appear to join the restiform bodies. 
Sixth nerve.—The abducentes arise by about four small bundles from each side of 
the raphe. They can be traced from the external surface of the ventral side of the 
medulla oblongata at about the middle of its length to the lower edge of the ventral 
columns, where they are lost. They resemble in their arrangement the oculomotor 
nerves, but unlike them they could not be traced to any nerve cells, unless they have 
anything to do with some large cells which are sparingly scattered through the 
formatio reticularis in this region. 
Seventh (figs. 6, 7, 8).—The facialis, which in Rhina and Scyllium is a branch 
of the trifacial, and in A cantinas has a separate root, arises from a bundle which 
comes forward from the spinal cord. This fasciculus appears above the central canal, 
between the dorsal and ventral cornua ; in its course forward it lies internal to the 
ascending root of the trifacial. This bundle is described by Rohon # (who apparently 
missed its connexion with the facial) as the fasciculus longitudinalis lateralis, which 
he considers as a new formation especially confined to the Plagiostomata, but it 
corresponds to the root of the facial in the Teleostei ; it was described in my paper 
on the brain of the Teleostei t under the name of the upper column of the trifacial. 
Eighth.—The Acusticus appears to arise from the grey matter of the floor of the 
fourth ventricle. 
Ninth pair.—The glossopharyngeal also appears to arise from the grey substance of 
the floor of this same ventricle. 
Tenth pair.—The vagus arises from the series of rounded tubercles which are 
situated on the floor of the fourth ventricle. Gegenbatjr j compares these tubercles 
to the swellings on the surface of the medulla oblongata in Trigla, and explains the 
fact that they are situated outside, by supposing that the sinus rhomboidalis in that 
species is too small to receive them, whereas in Hexanthus the presence of a larger 
ventricle affords space for them within it. 
These tubercles contain a few cells of medium size, from which the roots of the 
nerve appear to be derived; each tubercle seems to give rise to a separate root, which, 
passing out of the medulla, joins the others to form the nerve in a manner formerly 
described. 
Notion, § who has gone minutely into the relations of the roots of this nerve, has 
come to the following conclusions. The lobus vagi corresponds to a collection of nerve 
ganglia, and each root, arising from a single ganglion, corresponds to a posterior 
(dorsal) root of a spinal nerve; and, further, the roots that emerge behind the lobus 
* Op. cit., p. 101. 
f ‘ Phil. Ti'ans.,’ 1878, vol. 169, p. 765, fig. 9. 
f Op. cit., p. 520. 
§ “ Ueber den Ursprung des Nervus Vagus.” ‘ Wien, Zool. Instil. Arbeiten,’ Heft 1, 1878. 
