OBSERVATIONS ON THE CRANIAL NERVES OF SCYLLIUM. 479 
extend some little distance beyond the point of junction with the 
communicating branch from the seventh. 
In figs. 14 and 15 some of these branches (va, v4, vc) 
are seen at a stage between o and rp: except that the roots of 
v and vir are much more closely approximated, there is no 
difference of importance between this stage and the earlier one 
which we have more fully described. We have traced all these 
nerves up to what is practically the adult condition, and have 
identified them with the branches bearing the same names in 
the adult. Our observations show that in the fifth, as in the 
third nerve, all the main branches of the adult nerve are fully 
established by stage L, and that the after changes are comparatively 
unimportant. 
The Seventh, or Facial Nerve. 
A. The roots of origin.—Fig. 2 represents a transverse section 
through the roots of origin of the seventh nerve of an embryo 
between stages 1 and k, the same, in fact, of which fig. 1 repre- 
sents the roots of the fifth nerve. The two nerves (vit) are 
seen to arise from the extreme dorsal summit of the hind brain, 
the roots of origin of the two nerves (vita) being continuous 
with one another across the top of the brain. It will also be 
noticed, as contrasted with figure 1, that the two sides of the 
hind brain are close together, both above and below, and that 
the cavity of the hind brain is a mere vertical slit; that, in fact, 
the growth of the roof of the brain, which we have seen is the 
first cause of the separation of the roots of the fifth, has not yet 
commenced in the part of the brain from which the seventh 
nerves arise. ‘The section further shows that the nerve on either 
side extends down as a somewhat club-shaped mass of compactly 
arranged polygonal cells lying between the external epiblast and 
the neural canal, but distinct from both, its ventral end having a 
tendency to pass to the outer side of the third head cavity (fig. 
2, %), just as the fifth nerve passed to the outer side of the 
second cavity (fig. 1, °). 
The next stage is represented in fig. 3, a section through the 
hind brain and roots of the seventh nerve of an embryo of stage 
K, of the same age, though not from the same specimen as fig. 
4. The figure shows that very important changes have occurred; 
the roof of the hind brain has grown rapidly and considerably, 
so as to separate widely the two primary roots of the seventh 
nerves (vila). On the right side only this dorsal primary root 
is seen, but on the left side a considerable portion of the nerve 
is shown, and it is seen that, in addition to the primary root 
(viI a), which is still present, the nerve has acquired a new or 
secondary root (vii 8), about half way down the sides of the 
brain. Both roots of attachment are perfectly clear and unmis- 
