578 ALICE JOHNSON AND LILIAN SHELDON. 
brain, and the nerve is directed forwards towards the eye. 
We have not ascertained whether or no there is any sensory 
thickening of the epiblast corresponding to it, but it seems 
possible that the ciliary ganglion may be fused with the 
Gasserian, as is stated by Mr. Beard (4) to be the case in the 
Frog. It would thus not have a separate sense organ of 
its own, 
The Trigeminal nerve grows downwards from the brain 
till it reaches the level of the sensory epiblastic thickening, 
and then fuses with it (fig. 21). The point of fusion con- 
stitutes the Gasserian ganglion together with the sensory 
thickening. It is not possible to decide if the epiblast actually 
takes part in the formation of the ganglion. The mere 
presence of dividing nuclei in this region, as insisted on by 
Mr. Beard, seems to us to prove nothing, since all the tissues 
of the body are actively growing, and consequently contain 
numbers of such nuclei. We are inclined, therefore, to think 
that the fusion of the nerve with the epiblast is merely a case 
of innervation of a sense organ, exactly comparable to what 
occurs in the nose and ear, and that, in all such cases, the 
nerve-elements are derived from the brain and the sense 
elements from the epiblast. Professor Marshall has shown 
how early this fusion occurs in the case of the ear in the 
Chick (16). 
The root of the 5th nerve is at first attached to the dorsal 
surface of the brain (fig. 18). Later, the surface of attach- 
ment widens out and extends further down the side (fig. 22), 
and then gradually becomes confined to a small area situated 
about half way down the brain (fig. 23). The point of 
attachment is thus shifted downwards, no secondary attach- 
ment being formed in this case while the first is lost, as has 
been described by Professor Marshall in the Chick (16) and in 
Scyllium (17). 
The Gasserian ganglion is for a short time fused into one 
mass with the sensory epiblast. Soon it begins to sink deeper 
into the body, but remains attached to the surface by a cord 
of cells, which constitutes the dorsal branch (ophthalmic) of 
