28 Dixon—On the Development of the Branches of the Fifth Cranial Nerve in Man. 
towards the surface. These communicate with the infratrochlear branch of the 
nasal. The rest of the frontal nerve—supraorbital—passes outwards and upwards, 
and ends above the outer part of the eyeball. The twigs of the supraorbital do 
not seem to reach much higher than those of the supratrochlear, but are much 
more external. This nerve was probably not traced to its very termination. 
In this embryo, notwithstanding its beautiful state of preservation, I was not 
able to make out with certainty anything about the ciliary ganglion. Large 
numbers of nuclei are present all round the different nerves as they lie close 
behind the eyeball, but no collection of these into a distinct isolated ganglion was 
discovered. I am inclined to believe that two collections of these nuclei, which, 
however, are continuous by a narrow neck of cells, but at no point sharply 
marked off from the tissue round, represent the ciliary ganglion. The first of 
these is present about the frontal branch, near its origin, while the other is 
placed between the inferior part of the third nerve and the nasal nerve. The 
fourth nerve is close to the upper collection. 
In the orbital region it is exceedingly difficult to make out with certainty the 
outlines of the different structures which are here so crowded together. The 
muscles of the eyeball, which are now beginning to appear, increase this difficulty 
greatly, and the branches of the different motor nerves to these muscles also add 
to the confusion. 
F.M.—Ophthalmic trunk, . . 0°32 mm. 
Nasal nerve, . : 2°22" mm. 
Frontal nerve, . :  L2mm: 
Lachrymal nerve, . = 20:8" mam, 
Supraorbital, . . . 1:2 mm. not fully traced. 
Supratrochlear, ‘ = 4 nim: 
Infratrochlear, : oO mama: 
Emsryo Mr. (8th week). 
In this embryo the nerves and muscles in the orbital region have practically, 
as we shall see, the disposition that obtains in the adult. The ophthalmic nerve 
springs from the anterior end of the Gasserian ganglion, and almost immediately 
divides into its branches. Indeed, the common trunk is so short that it can 
hardly be said to exist. The plane of the section is such that it cuts frontal and 
nasal branches transversely, and in section the transverse diameter of the frontal is 
at least double that of the nasal nerve. In this embryo the muscles of the eyeball 
are easily made out, and the termination of the motor nerves in the muscles are 
distinctly visible. As the nasal and frontal nerves pass forwards, the large third 
nerve passes downwards and forwards to their inner side. The sixth nerve, on 
