Drxon— On the Development of the Branches of the Fifth Cranial Nerve in Man. 25 
The fourth nerve ends 0°6 mm. from the termination of the frontal. 
The sixth nerve runs upwards and outwards, and ends near the termination of 
the third nerve. 
Ru.—Ophthalmic nerve = 0-08 
Frontal branch = 016 
Nasal branch 0°84 
Emeryo C.R.—(beginning of 6th week, 13°6 mm.). Figures 7 and 8, Plate I. 
The ophthalmic nerve arises from the upper and anterior part of the Gasserian 
ganglion. ‘The main trunk is short (0°24 mm.), and divides into two well marked 
branches. Both of these branches pass upwards and forwards, one lying behind 
the other. The more anterior branch, which represents the nasal of the adult, 
crosses the optic stalk, just where the latter joins the eyeball. The posterior or 
frontal branch also crosses the optic stalk, but is placed farther above it. From 
the posterior branch, just at its origin, a fine nerve passes outwards, behind the 
eyeball. This represents the lachrymal of the adult. The length of this 
lachrymal nerve is about 0°6 mm. 
The nasal and frontal branches, from their origin, at first pass upwards and 
forwards, nearly parallel to one another, the frontal being not only posterior to, 
but also higher than, the nasal. After a course of about 0:7 mm. they turn in 
different directions, the frontal passing upwards, forwards and outwards, the 
nasal upwards, forwards and inwards. The frontal nerve takes a more distinctly 
ascending course than the nasal. 
The nasal nerve having given off a small branch, which seems to represent the 
infratrochlear nerve of the adult, turns more inwards and comes to lie to the 
outer side of the olfactory nerves. In this part of its course the nasal nerve lies 
between the under surface of the anterior part of the brain above, and the upper 
part of the nasal pit below. Before its termination the nasal nerve turns slightly 
downwards and forwards. The entire length of nasal nerve is 1:5 mm. 
The infratrochlear branch passes forwards from the point where the nasal 
nerve turns inwards: it is not more than 0:2 mm. in length. 
The frontal nerve is larger than the nasal, and lies above and behind it at first ; 
ceasing to run parallel to the nasal nerve, the frontal turns outwards and divides 
into two branches—supratrochlear and supraorbital. The supratrochlear passes 
forwards and upwards, and ends near the infratrochlear branch of nasal. This 
supratrochlear nerve is about 0°5 mm. in length. 
The supraorbital branch of frontal passes backwards as well as upwards and 
outwards, and is abont 0-8 mm. in length. The frontal nerve from its origin to its 
division is 1:0 mm. 
