MR. A. SANDERS ON THE ANATOMY OF THE 
746 
Stannius (38) gives an account of this nerve in the Gadus callarias, in which 
species it also developes a ganglion on the outside of the skull ; but that author does 
not mention any connexion between it and either the acusticus (for as in the Mugil 
it has a separate origin from the brain) or the trifacial. 
I would suggest that the branch of the acusticus just described homologises with 
the facial and not with the glossopharyngeal. From this point of view, the ganglion 
in the course of this nerve would be the ganglion geniculare or intumescentia, which 
on account of the non-development of the tympanum in Teleostei, comes to be placed 
outside the skull. The branch to the first branchial arch would be the twig of commu- 
nication between the facial and the glossopharyngeal, and the anterior branch joining the 
casserian ganglion would be the auriculo temporal, or, perhaps, the main trunk. The true 
glossopharyngeal would be found in the branch of the vagus to be presently described. 
In the evolution of the higher Vertebrate animals, when the glossopharyngeal and 
the facial become independent nerves, I should imagine, on the supposition that the 
above considerations were well founded, that the posterior branch of the ganglion 
in question would degenerate into the communicating twig between the facial and the 
glossopharyngeal ; while the anterior branch would increase in size, pari passu with 
the increasing development of the muscles of the face, and at the same time become 
detached from immediate connexion with the trifacial. 
The vagus arises here also by two roots as in Mugil cephalus, but they join before 
arriving at the foramen of exit, instead of outside the skull as in that sjoecies. The 
ganglion of the vagus is formed partly in the foramen, but the greater part of it is 
situated outside. From the upper edge of the ganglion, two nerves are given off : one 
to the lateral line, the other to the skin over the dorsal part of the branchial chamber 
at the point where it makes a fold to line the operculum. Two branches are given off 
from the distal and outer side of the vagal ganglion, which supply the second and 
third branchial arches ; then the greater part of the ganglion tapers off at its distal 
extremity into the main trunk of the vagus, which after giving a branch to the 
fourth branchial arch, follows the oesophagus. 
It seems quite as reasonable to consider as the glossopharyngeal all the above- 
mentioned nerves to the branchial arches, which appear to a great extent to be 
distinct from the main trunk of the vagus ; as to confine the interpretation to the 
branch which supplies the first branchial arch alone, which is usually the custom. 
The nerve which is situated behind the vagus is generally looked upon as a spinal 
nerve, although in many Teleostei, in the present species among the number, it passes 
out of the skull through a special foramen in the exoccipital bone; here it is clearly 
a double nerve. It arises by two dorsal and two ventral roots ; these all join into 
one trunk, which has a ganglionic enlargement as it emerges through the foramen. 
Immediately outside it gives off a dorsal branch like a spinal nerve ; after which it 
divides into two trunks, which run a parallel course dorsad of the kidney, and then 
unite together and with the main trunk of the succeeding nerve, which is the first 
