OBSERVATIONS ON THE CRANIAL NERVES OF SCYLLIUM. 493 
they also, as shown in fig. 16, lie at a deeper level than at 
the earlier stages. 
The fourth nerve bears, as already noticed, a very close rela- 
tion to these branches. As shown in figs. 1] (av) and 16 (1y) it 
crosses the ophthalmic branches at right angles, lymg at a 
slightly deeper level but turning outwards immediately beneath 
them, to end in the superior oblique muscle (0. s.). At the point 
of crossing the branches of the two nerves are in very close rela- 
tion with one another, and we are inclined to believe that a 
communication exists between the fourth nerve and the ophthal- 
mic branch of the fifth at this point, though we have failed to 
determine this with certainty. ; 
In determining the morphological value of these ophthalmic 
branches of the fifth and seventh nerve, very valuable evidence, 
by which we have been much influenced, is afforded by the con- 
dition of the glossopharyngeal nerve. ‘This nerve, at stage L, 
gives off, just beyond its root of origin, a slender dorsal branch 
(fig. 10, rx @), which, at first passing upwards and backwards, 
soon curves round the hinder end of the auditory vesicle (aud.), 
and reaching the dorsal surface of the head, runs forward a 
short distance, lying immediately beneath the superficial epiblast. 
It gives off branches along its whole course, which are distributed, 
as shown in the figure, to the integument of the top of the head. 
At stage N this nerve (fig. 12, 1x a) has the same course and 
appearance, the only differences being that it extends rather 
further forwards than at the earlier stage, so as to reach some 
distance in front of the middle of the auditory vesicle; and, 
secondly, that its branches are now seen to be in connection with 
the commencing mucous canals of this region. This branch of 
the ninth nerve is clearly the ramus dorsalis, and an examina- 
tion of the figures 11 and 12 will, we think, leave no doubt that. 
the nerves vit a and v a, which have a similarly superficial course 
and a like distribution to mucous canals, must be viewed as the 
equivalent branches of the seventh and fifth nerves. We are, 
therefore, led to adopt the view put forward by Balfour, that 
the ophthalmic branches v @ and vit a of the fifth and seventh 
nerves are the rami dorsales of these nerves. Stannius and 
_) In my paper on the head cavities of Elasmobranchs I abandoned the 
view previously put forward (this Journal, Jan., 1878, p. 30), that the 
ophthalmics were persistent remains of the commissure connecting to- 
gether the roots of the nerves at their first appearance, but did not expressly 
adopt the view that they were rami dorsales. I have been led to adopt 
this view mainly because it now appears that, instead of being perfectly 
exceptional in their course, as I had previously supposed them to be, the 
ophthalmics merely express an exaggerated condition of a state of things 
shown in a less extreme form by the ramus dorsalis of the glossopharyn- 
geal.—A. M. M. 
