498 PROF, MILNES MARSHALL AND W. B. SPENCER, 
Balfour! describes the mandibular branch of the seventh as 
being large in the embryo, so large in fact that he feels difficulty 
about identifying it with the adult spiracular nerve. His 
figures,' however, show perfectly clearly that what he describes as 
the mandibular branch of the seventh is really the nerve we have 
shown to be the buccal.? 
The maxillary nerve (v 4) is, from its time and mode of 
development, almost certainly to be regarded as the true anterior 
branch of the fifth corresponding to the mandibular branch of 
the seventh, although in the absence of a visceral cleft in this 
region this determination cannot be considered absolutely proved. 
Whether there is any equivalent branch of the third nerve is 
very doubtful; at any rate no such branch can be pointed out 
with certainty. 
There now remains for consideration the buccal nerve, the 
determination of which, as a branch of the seventh, is one of 
the most striking points we have brought to light. Whether 
this remarkable nerve has any homologue among the branches of 
the fifth is a point our investigations have not yet enabled us 
to determine. It is perhaps worth while pointing out that there 
are many points of resemblance between this nerve and the ramus 
ophthalmicus profundus, points of sufficient importance to render 
a comparison between the two nerves at any rate a possible and 
suggestive one. In each case the proximal portion of the nerves 
in question connects together directly the ganglion of one seg- 
mental nerve with that of the nerve next in front, while the 
distal portion passes forward into the segment anterior to that 
in which the main branches of the nerve are contained. The 
early origin, the curiously straizht course, and the absence of 
branches until close to their termination, are features common to 
the two nerves, and ones in which they stand in marked contrast 
to most other branches. The deep course of the profundus as 
contrasted with the very superficial one of the buccal nerve may 
perhaps be attributed to the great development of the eye: in 
front of the orbit the profundus is a superficial nerve, and like 
the buccal, is purely sensory in its distribution. 
On the other hand, it must be noticed that, as already pointed 
out, the evidence is distinctly in favour of the distal portion of 
the profundus (beyond the ciliary ganglion) being a branch of the 
third rather than of the fifth nerve. Another point of distinction 
between them lies in the fact, that the former (the profundus) 
is distributed to what is, morphologically, the dorsal surface, the 
buccal to the ventral. 
In the present paper we have purposely refrained from 
| Op. cit., p. 202. 
2 Op. cit., Pl. XIV, fig. 2 and fig. 15 a. 
