738 
MR, A. SANDERS ON THE ANATOMY OF THE 
ganglion, and passing directly downward supplies the integument about the angle of 
the mouth. 
In Rhina (fig. 2) the trifacial has a corresponding origin and distribution to that in 
Acanthias, except that it arises by two roots. 
In Scyllium (fig. 1) the arrangement of this nerve is somewhat different, it arises 
by a single root opposite the posterior end of the crura cerebelli ad medullam. While 
still within the skull it gives off two branches, each of which passes through its own 
separate foramen ; outside these join together and pursue a course comparable to that 
of the ophthalmic in Acanthias and Rhina. The root, having given off these branches, 
passes on through another foramen, and immediately outside it forms the Gasserian 
ganglion, which gives off the superior maxillary branch from its distal extremity; 
from the proximal end of the ganglion is given off a trunk which at once divides into 
two branches, of which one passes beneath the trunk of the superior maxillary nerve, 
and piercing the floor of the orbit supplies the muscles situated beneath that part, viz., 
the masticatory muscles. The other branch follows the usual course of the facial; it 
passes obliquely backward and outward behind the spiracle to the outer margin of the 
body in front of the branchial chamber. 
Sixth pair—Abducentes—arise near the central line of the medulla oblongata on the 
ventral surface by four bundles, which soon unite into a single strand on each side. 
Ahlborn* describes a small nerve in the Petfomyzon, which he thinks is this nerve, 
but it is evidently only an unusual branch of the trifacial. If it were the abducens, 
Petromyzon w r ould be an exception to all other vertebrata. 
Seventh pair.—Facial.—In the Rays this is inseparably united to the under part 
of the upper root of the trifacial; it emerges through a separate foramen immediately 
in front of the ear capsule and, passing over the muscles of the jaws, supplies the 
cheek. 
In Acanthias (fig. 3) also the facial has a separate root, which arises in close juxta¬ 
position to the posterior side of the trifacial. It passes through a foramen separated 
from that of the former by a very thin plate of cartilage ; it supplies the region of the 
spiracle. In Rhina and Scyllium this nerve is a branch from the Gasserian ganglion. 
Rohon t describes it as a branch of the acusticus, but in all specimens that have been 
examined by me there have been none in which the two nerves could be said to be 
joined either at their origins or elsewhere. 
Eighth, pair—Acusticus.—In all these species this is in juxtaposition to the posterior 
side of the facial, and arises beneath the upper root of the trifacial. 
Ninth pair (fig. 3).— Glossopharyngeal.—In Acanthias this nerve arises from the 
side of the medulla oblongata on about the same level as the trifacial. It is a small 
o 
nerve, but is quite independent of the trifacial in front and of the vagus behind; it 
* “ Untersuahungen iiber das Gehirn der Petromyzonten.” ‘ Zeitschr. f. Wissensch. Zool.,’ vol. 39,1883, 
p. 211 . 
t Loc. cit., p. 63. 
