174 
will be described in my full paper. No further description, however, 
is necessary here. Further, there is a largish nerve given off from 
TR. much at about the same place, which, on being carefully dis- 
sected, is found to arise mostly from the mandibular nerve, and which 
constitutes the principal nerve supply of the masseter muscle of the 
lower jaw. On the other hand the posterior division B is seen soon 
after entering the orbit to be composed of two bundles, which ulti- 
mately separate to form the inner and outer buccal nerves supplying 
two groups of ampullae and the whole of the infraorbital sensory 
canal (see my paper above). So far then TR looks much like the 
trigeminal nerve. If it be followed back to the brain it will be found 
to have a large ganglion (Gasserian) which extends into the orbit (2). 
From this ganglion a small nerve (S.0. V) will be seen to arise, which, 
in the typical condition (?), takes a dorsal curve, crosses, but does 
not fuse with, 8.0.VII, and is ultimately distributed to the skin 
over and in front of the orbital region. Here we obviously have a 
superficial ophthalmic division. After this point TR. comes to lie 
under B but is always easily separable from it (see fig.). 
Whilst passing through the canal in the cranium it gives off a large 
profundus nerve (P) which swells into a ganglion shortly after its 
origin (3). Further back still TR. is found to arise from the medulla 
by two ventral roots (V), which however do not remain distinct. 
I had expected that the smaller anterior one was the root of the pro- 
fundus, but neither the profundus nor the root could be separated 
from the main trunk of the nerve. Both the roots of TR. and its trunk 
in passing through the cranium lie under cover of B (see fig.), but 
the latter can easily be separated from it and does not in any way 
fuse with it. Here then, quite apart from embryological 
considerations, we have a perfect trigeminal nerve, in so far it 
has: — 
a) ventral roots ] 
b) a ganglion on the trunk | 
c) a profundus branch \ 
d) an ophthalmic branch | 
e) maxillary and mandibular branches | 
Now if B and S.0. VII be followed back to the brain they will 
be found to arise respectively by single large dorsal and ventral roots. 
S.O.VII crosses over B and arises mostly from the ventral surface 
of the medulla (VII), but receives a fairy large anastomosing branch 
(4 from B, and hence may be described as having both dorsal and 
ventral roots. Bon the other hand apparently consists of dorsal fibres 
Except a twig from the pro- 
fundus supply no sense or- 
gans of lateral line (see my 
Royal Society Edin. paper). 
