496 PROF. MILNES MARSHALL AND W. B. SPENCER. 
ther make up the ramus ophthalmicus profundus of zootomists, a 
nerve which seems to have escaped Balfour’s notice both in the 
adult and in the embryo. Balfour does, indeed, in his descrip- 
tion of the nerves of the adult Scy/lium, speak of a ramus 
ophthalmicus profundus, but imasmuch as he says concerning it 
that “ this latter nerve arises from the anterior root of the fifth, 
separately pierces the wall of the orbit, and takes a course slightly 
ventral to the superior ophthalmic nerve, dwt does not (as is 
usual in Elasmobranchs) run below the superior rectus and 
superior oblique muscle of the eye,’ itis clear that he is describ- 
ing the ophthalmic branch of the fifth and not the true profundus, 
whose existence he has overlooked. There appears to be con- 
siderable confusion in the use of the terms ramus ophthalmicus 
superficialis and ramus ophthalmicus profundus by different 
writers, a confusion which our observations on Scyllium may 
help to remove. We find, as already stated, three perfectly dis- 
tinct nerves to which the term ophthalmic nerve can be, and is, 
applied; of these the two dorsal ones (v a and vita of our figures) 
are the rami dorsales of the fifth and seventh nerves, and may be 
spoken of as the ophthalmic branches of the fifth and seventh 
nerves respectively. Both these nerves are very superficial along 
their whole course, and doth lie dorsad of all the eye muscles 
and other contents of the orbit. The two nerves are at first per- 
fectly distinct, but in the adult unite more or less closely toge- 
ther, the extent of their union varying much in different Hlasmo- 
branchs; the two together constitute the ramus ophthalmicus 
superficialis. 
The third of the ophthalmic nerves, the ramus ophthalmicus 
profundus, has a very different course, and is of a totaily different 
nature ; it is formed in Scyddiwm by the union of the connecting 
branch between the fifth and third nerve (NV. c.) with the branch 
n of the third nerve. It is very definitely characterised by its 
course ventrad of the superior rectus, superior oblique, and internal 
rectus muscles, by its close relation with the inner wall of the 
eyeball, by the fact that the ciliary ganglion is either in its trunk 
or is connected with it directly, by its having at first no branches 
and by its close connection with the olfactory nerve. 
We believe that the ophthalmicus superficialis and ophthal- 
micus profundus always maintain these relations; that the pro- 
Fundus, which is clearly the nasal nerve of Mammaiia, is a primi- 
tive and very constant nerve, and that it uever shifts its position 
so as to lie dorsad of all the eye muscles, as supposed by 
Balfour. 
The two divisions of the ophthalmicus superficialis, on the 
other hand, appear to be very variable indeed in different Verte- 
1 Op. cit., p. 194: the italics are our own. 
