CENTRAL NERVOUS SYSTEM IN VERTEBRATE ANIMALS. 
739 
pierces the auditory apparatus obliquely, passes backward and outward through a 
channel in the cartilage of the skull, and supplies the first branchial arch. 
In Scyllium (fig. 1) also this nerve arises independently of the vagus, but nearer to 
it than the corresponding one in Acanthias; it pursues a course through the auditory 
apparatus resembling that in Acanthias, and like it is distributed to the first branchial 
arch. 
In the Rays it has a similar distribution, but arises beneath the anterior roots of the 
vagus. 
In Rhina (fig. 2) this nerve has a somewhat different arrangement. It arises in 
connexion with the anterior side of the anterior root of the vagus, and after having 
passed through the chamber containing the otolithic vesicle, enters a long channel in 
the postero-external angle of the skull, in which it enlarges into an elongated fusiform 
ganglion, and continuing in the same outward and backward direction eventually 
divides into two branches, of which the anterior supplies the membrane bounding the 
gill cavity, and runs along the anterior surface of the branchia attached to it; the 
other supplies the anterior border of the first branchial arch and passes round its outer 
edge towards the pharynx. 
Tenth pair (fig. 2).—Vagus.—In Rhina this nerve rises by seven roots. The two 
anterior roots are thickest; they arise close together and join immediately. The third 
root, which was only found on one side, comes out close behind the posterior of these. 
Then follows an interval, after which occur three fine roots, which immediately join 
together to form a single fine cord, which after a short course joins the third root in 
the foramen of exit ; so that the nerve emerges from the skull in two divisions, which 
close outside and, under cover of the projecting process containing the glosso¬ 
pharyngeal, develop a large ganglion. Close outside the foramen a large branch, 
which appears as a continuation of the two anterior roots, is given off from the outer 
edge of the proximal end of the ganglion, and passing outward and backward, bifur¬ 
cates at the edge of the branchial arches ; one branch goes along the posterior border 
of the first and the other to the anterior border of the second branchial arch. 
The ganglion at its distal end divides into three branches; the outer of these passes 
backward and divides into two nerves, which are distributed in the same manner as 
the last, one going to the posterior border of the second, and the other to the anterior 
edge of the third branchial arch. The middle one of the three terminal branches of 
the ganglion is the largest, and passes backward to form the ramus intestinalis of the 
vagus ; before entering the abdominal cavity it gives rise to a branch, which goes 
towards the outside and, dividing into two, supplies the posterior border of the third 
branchial arch and the anterior border of the fourth, precisely in the same manner as 
the others. The ramus intestinalis gives off another branch beyond, but this I failed 
to trace to the posterior border of the fourth branchial arch, which it probably 
supplies. The remaining division of the ganglion passes down the back between the 
muscles and forms the ramus lateralis. 
5 B 2 
