744 
MR. A. SANDERS ON THE ANATOMY OF THE 
The optic nerve (fig. 1, n. 2) is folded on itself transversely several times, so as 
to give its section a pectinated appearance, — a fact which was first mentioned by 
Malpighii (2). 
The motores oculorum (fig. 5, n. 3) invariably arise from the point of junction of the 
hypo aria with the ventral edge of the medulla, where a band of transverse fibres exist, 
which were described by Gottsche under the name of “ commissura ansulata these 
nerves pass outwards, and appear in the groove between those bodies and the lower 
edge of the optic lobes at about the centre of their length. 
The trochlea, res (fig. 6, n. 4) arise from the valvula-cerebelli, whence they pass out 
behind the optic lobe, and curving round the posterior edge of that body pass 
forward towards their destination 
Desmoulins (26) ha,s given the origin of this nerve from the ventral surface of the 
medulla oblongata, where, he says, the filaments of the root of one nerve were contiguous 
to those of the nerve on the opposite side. What could have induced this author to 
make such a mistake it is impossible to imagine. No nerve, except the motores 
oculorum, and that not strictly, answers to his description ; and that nerve is precluded 
by the context. 
The remainder of the cranial nerves vary in origin in different species of Teleostei. 
The trifacial (fig. 2, n. 5 ; fig. 7, n. 5 ; fig. 8, l.c. 5 ; fig. 9, l.c. 5 and u.c. 5) in Mugil 
cephalus has the following arrangement : it arises by three closely contiguous roots 
from the side of the medulla oblongata, beneath the anterior edge of the crura cerebelli; 
the casserian ganglion is developed on the middle root only ; the anterior passes for- 
ward over the ganglion, and joins the middle root in the foramen of exit, which in this 
species is through bone ; the posterior root passes forward to a separate foramen, 
through which it emerges as an independent nerve, having first received a branch from 
the under surface of the ganglion ; it then pursues its course obliquely through the 
palato-quadrate arch, and its fibres are lost on the outer surface of the quadrate bone. 
It is this root which is considered by anatomists to be the facial nerve. In the Pleuro- 
nectes, according to Stannius, there are four or five roots to the trifacial, and more 
than one of them contribute to the formation of the facial. 
The abducens (fig. 8, n. 6 ; fig. 9, n. 6) has a very constant origin; each root arises 
by two small cords from the ventral surface of the medulla, beneath the anterior root 
of the vagus. 
The acusticus arises from the medulla oblongata, on a lower level than the trifacial ; 
the anterior end of its root is placed exactly ventrad of the posterior root of the tri- 
facial, while its posterior edge is in front of the anterior root of the vagus. This 
nerve immediately divides into two branches : one, the anterior, goes to the anterior 
and horizontal semicircular canals, while the posterior goes backwards to be distributed 
to the sac of the otolithes ; in its course the latter gives off a small branch, which 
supplies the ampulla of the posterior semicircular canal. 
There is a small nerve which is often merely a branch from the posterior division of 
