10 F. L. LANDACRE 
extends dorsal to the upper border of the vesicle and the posterior 
end lies at a lower level. The nerve trunk (ophthalmicus profun- 
dus) which arises at the anterior end of the ganglion can 
be followed forward at this stage to a point over the anterior 
end of the lens where it becomes so attenuated that it cannot be 
followed further. 
The nerve forms a gentle curve corresponding to the dorsal 
surface of the optic vesicle and maintains a constant position 
over the middle of the optic vesicle. The ophthalmicus profun- 
dus does not at this stage come into contact with either the 
ophthalmicus superficialis VII or the ophthalmicus superficialis 
V and is presumably a pure general somatic nerve, although in 
the early stages of the formation of the ganglion (82 hours) there 
is a pronounced contact with the epidermis, but whether this 
is placodal in nature or not has not been determined. The root 
of the profundus arises from the posterior end of the ganglion 
and passes back and down arching under the lateral lobes of the 
metencephalon which it enters from the ventral surface. The 
root forms a gentle curve down and back reversing the relations 
of the trunk. At the middle of its course the root comes into 
intimate relations with the third nerve, and somewhat further 
posterior, with the ciliary ganglion also. 
The Gasserian ganglion (trigeminus IT) 
This ganglion (fig. 1) in the 10 mm. embryo is a large oblong 
ganglion placed diagonally in the mesoderm with its anterior end 
at the side of the oral cavity and above the level of the roof of the 
oral cavity. It is nowhere in contact with the epidermis. It 
extends from a point just anterior to the pituitary body, where it 
is located under the posterior portion of the optic vesicle, back to 
a point at the level of the anterior end of the dorso-lateral por- 
tion of the lateralis VII ganglion. It is not in contact with either 
the profundus (trigeminus I), or the geniculate ganglion of the 
VII, nor with the dorso-lateral VII. The ganglion is compact 
and definitely outlined. Its root is at the posterior end and is 
quite short, the ganglion cells at this point being closely attached 
