24 Dixon—On the Development of the Branches of the Fifth Cranial Nerve in Man. 
The third nerve, passing from above and behind, downwards, forwards, and a 
little outwards, ends close to the inner side of the origin of the ophthalmic 
nerve. 
Emsryo Ru.—(5th week, 9'1 mm.). Figure 6, Plate I. 
In this embryo the ophthalmic trunk, rising from the upper and anterior 
part of the Gasserian ganglion, passes upwards and slightly inwards, and soon 
divides into anterior and posterior branches. 
Among the fibres of the nerve, near its origin, a number of nuclei are present, 
which are seen to be more numerous in the section of the posterior part of the 
trunk. Of the two branches into which the ophthalmic nerve divides the posterior, 
although the shorter, is more the direct continuation of the main trunk, as far as 
direction goes, than the anterior branch. Further, as seen in section, the two 
branches differ from one another; thus, the fibres of the posterior branch are not 
so distinct, and, throughout its whole length, it stains more deeply than the 
anterior branch, and nuclei are present in greater numbers among its fibres. 
These points of difference can be made out in the nerves of both sides. 
The common trunk of the ophthalmic, before its division into anterior and 
posterior branches, is only about 0:08 mm. long. 
The posterior branch of the ophthalmic passes upwards, inwards, and slightly 
backwards, behind the eye-ball; its length is 0°16 mm. 
The anterior and longer of the two branches of the ophthalmic is directed 
forwards, and a little upwards, across the optic stalk; near its termination, 
however, it turns a little outwards. The anterior, or distal extremity of this 
nerve, reaches farther forwards than the front part of the eyeball, and lies only 
0-2 mm. from the inferior surface of the front part of the brain. The place 
where this nerve crosses the optic stalk is just at the point where the latter joins 
the eyeball. The length of this nerve is 0°84 mm. From a comparison of these 
two branches with those of later embryos it is found that the anterior branch 
represents the nasal, and the posterior the frontal nerve of the adult. 
In this embryo, also, no defined collection of nuclei was found in connection 
with the fifth nerve, which might be considered to represent a ciliary ganglion. 
The third nerve, coming from above and behind, passes downwards, forwards 
and outwards, some distance to the inner side of the posterior (frontal) branch of 
the ophthalmic. Having passed along the inner side of the Gasserian ganglion, 
it ends below the optic stalk, at the level of the origin of the superior maxillary 
nerve. The third nerve gives off no branch, and from its course it is evident 
that it is the inferior division of the third nerve of the adult that is represented 
in this embryo. No aggregation of cells into a distinct ganglion was found 
connected with the third nerve. 
