Drxon—On the Development of the Branches of the Fifth Cranial Nerve in Man. 35 
out. If this be a correct explanation, we would expect that the fibres which will 
ultimately form an independent branch would take, in the first instance, the same 
direction as the parent trunk, and further, that these fibres would leave the main 
trunk to form the branch at the point where the trunk is sharply bent. The 
branch when formed, will at first be, as far as direction goes, the continuation of 
the undivided nerve. Examples of this are afforded by the infratrochlear branch 
of nasal, the supratrochlear branch of frontal, and by the frontal itself. We have 
here another cause for the branching of nerves besides those enumerated in the 
paper already referred to, in which Professor His lays stress on the fact that 
nerves meeting with such obstacles as small vessels, cartilages, &c., must neces- 
sarily divide or be deflected, as well as on the fact that in any nerve the fibres 
from the beginning do not run parallel to one another, and so in their growth 
outwards may separate, and thus give rise to branches. 
Professor His* has called attention to the fact, that although the nasal or 
nervus ethmoidalis is the special nerve of the fronto-nasal process, yet it is not 
distributed in the adult to the whole region derived from this part of the embryo, 
but that branches of other nerves encroach upon its domain. Thus we find 
branches of the infraorbital nerve supplying not only the lateral but also the 
central part of the upper lip, which owes its origin to the fronto-nasal process. 
Professor His also points out that the ophthalmic nerve fails to completely fulfil 
the rdle of a dorsal branch rightly ascribed to it by Gegenbaur, and that it is 
assisted by branches from the second and third cervical nerves. 
The comparatively late development of the frontal nerves probably corre- 
sponds with the late appearance of the cerebral hemispheres, the protective 
coverings of which they supply. 
Marshall and Spencer first directed attention to a ganglion which they dis- 
covered on the ramus ophthalmicus profundus in Seyllium.+ This ganglion they 
consider represents the ciliary ganglion, and seeing that they followed Schwalbe 
in referring the ciliary ganglion to the third nerve, they are forced to consider 
the ramus ophthalmicus profundus a part of the third nerve. They point out 
that the proximal part of the ramus profundus is from the first simply a connect- 
ing nerve between the ciliary ganglion and the Gasserian; and that therefore 
‘there is no reason whatever in the early stages for considering it as_belong- 
ing to the fifth rather than to the third nerve.” These authors do not 
describe any stage early enough to show whether the fibres of this connecting 
nerve start from the “ciliary”? ganglion and grow towards the Gasserian, oz 
* « Die Morphologische Betrachtung der Kopfnerven.’”’ Archiy fiir Anatomie und Physiologie. Anat. 
Abtheilung, 1887. Heft vi., p. 447. 
+ ‘‘ Observations on the Cranial Nerves of Scyllium.” Quarterly Journal of Microscopical Science, 1881, 
vol, xxi. 
TRANS. ROY. DUB. SOC., N.S. VOL, VI., PART LI. G 
