476 PROF, MILNES MARSHALL AND W. B. SPENCER, 
observations on these stages, when considered in connection 
with our much more complete series of observations on the 
seventh nerve, leave no room for doubt that the root of origin 
(v a) shown in fig. 1 is the primary root, the one which at 
Stage G was situated at the top of the brain, and which has 
acquired its present position merely in consequence of the rapid 
growth of the roof of the brain pushing its two lateral halves 
apart, and so separating the roots of the nerves. 
Concerning the root of attachment (V (6) shown at stage x in 
fig. 3 there is more room for dispute. Balfour appears to hold? that 
this further change in position is due to the same cause as the 
former one, 2. e. to growth of the roof of the brain ; but this ex- 
planation, while it would fully account for the first change, would 
im no way explain such a shifting of the root down the thickened 
sides of the brain, as is clearly seen to have occurred on com- 
paring fig. 3 with fig. 1. We believe that what really happens 
is that about the commencement of stage K the nerve acquires a 
new and secondary connection with the brain at the point (v (3) 
opposite the projection already noticed, that the primary attach- 
ment (v a) is lost, and that the part of the nerve left above the 
secondary root rapidly diminishes and ultimately disappears 
altogether, the slight dorsal projection already noticed in fig. 3 
being the last rudiment of it. As our arguments in support of 
this view depend almost entirely on our own observations on the 
development of the roots of the seventh nerve, we postpone 
further consideration of the point till a later portion of this 
aper. 
Tt the commencemént of stage x then, the fifth nerve arises 
about half way up the sides of the hind brain by a single large 
root in which ganglion cells are abundant, and opposite to which 
there is a well-marked external bulging of the walls of the 
brain ;? beyond this root the nerve expands suddenly into a very 
arge ganglionic swelling, the future Gasserian ganglion. 
Before the close of stage K additional roots appear; a long, 
slender process runs forward from the anterior-superior angle of 
the Gasserian ganglion, and becomes connected with the brain 
some distance in front of the main root; in addition to which 
one, two, or more roots of a similar kind appear in intermediate 
situations. 
These anterior roots of the fifth nerve are well shown at 
the next stage (L) in fig. 10, v y, which shows that the fifth nerve 
at this time arises from the brain by three distinct roots, of 
which the posterior one is much the largest, and is the ganglionic 
root (v (3) of fig. 3, while the two anterior slender non- 
1 Op. cit., p. 196. ° 
Marshall, loc. cit., p. 84. 
