1894 - 5 .] Cranial and Spinal Nerves of Elasmobranchs. 477 
Lcvmarrjus, as shown in fig. 1, there is a further twig which, run- 
ning posteriorly, curves round, and is closely applied to the inner- 
postero wall of the cranium, coursing slightly downwards, and 
being distributed to the fibrous tissue between the muscles and the 
cranium. 
X. The Vagus . — In Loemargus the vagus consists of six main 
trunks, each provided with a ganglion. Of these only one — the 
lateralis — supplies sense organs. No dorsal branches were observed 
passing either from the four hranchials or from the visceral trunk. 
On the other hand, the lateralis receives fibres (probably sensory) 
from the rest of the Xth as it passes through the vagus canal, and 
the first branch, in addition to innervating the anterior sense organs 
of the lateral line, sends twigs to the skin immediately behind the 
auditory capsule. In Torpedo the most anterior branch of the 
lateralis not only springs from the lateralis trunk proximal to its 
ganglion, but presents a distinct swelling near its origin, in which lie 
a number of ganglion cells. This is evidently the result of split- 
ting, and resembles the condition of things found in the facial. This 
branch sends fibres to the skin, and probably also to the sense 
organs of the lateral canal. In addition to the branch to the skin 
from the lateralis, the two first branchial nerves apparently sent deli- 
cate branches to the skin on a level with their corresponding clefts. 
These, however, on careful examination were found to arise from 
the lateralis. It is worth mentioning that each of the four branchial 
nerves of the Torpedo arises by a distinct root, and possesses a 
well-marked ganglion — there being, as in Loemargus and Raia, six 
ganglia in connection with the vagus. 
VII. The Facial . — The facial used to be described as consisting 
of two equal portions — the portio dura and the portio mollis or 
auditory nerve. Gegenbaur on morphological, and Balfour and 
Marshall on embryological grounds, looked upon the auditory nerve as 
a dorsal branch of the facial, and not as the equivalent of the portio 
dura. Others have considered the auditory nerve as of segmental 
value, for the following reasons : — (1) because of the presence of 
a ganglion ; (2) the supposed existence of a cleft between the 
spiracular and first branchial clefts ; and (3) because it develops 
like an ordinary segmental nerve. If, as is probable, the auditory 
organ is derived from a lateral sense organ, the auditory nerve will 
