NOTES ON THE DEVELOPMENT OF THE NEWT. 579 
the 5th nerve (fig. 24). At the same time a nerve grows 
down from the ganglion, which soon divides into two branches, 
a posterior, the inferior maxillary, shown in figs. 24 and 26, 
and an anterior, the superior maxillary, shown in fig. 24. 
The Facio-auditory nerve grows downwards towards 
its corresponding sensory thickening, and fuses with it at two 
points, one behind the other. The anterior of these we 
interpret as the sense organ belonging to the 7th nerve, and 
the posterior as the ear. There is only a very short distance 
between them, along which the nerve is not fused. In a later 
stage, shown in fig. 37, the ear is seen to be clearly distin- 
guishable from the sense organ of the 7th nerve, the ganglion 
of which is still fused with the skin, while the ear itself is 
completely separate, forming a simple closed vesicle (fig. 36). 
The main trunk of the 7th passes on downwards, and fuses 
with the epiblast of the dorsal wall of the first visceral cleft 
(figs. 837 and 36). Afterwards, this second connection with 
the epiblast is lost, and the nerve divides into two branches, 
one behind and one in front of the first cleft (figs. 26, 31, and 
32). At the same time the ganglion on the upper part of the 
trunk has sunk deeper into the body, remaining attached to 
the sensory thickening by a cord of cells constituting the 
dorsal branch (ophthalmic) of the 7th nerve (fig. 31). 
The facio-auditory nerve is now attached to the brain by 
two roots, one behind the other; the anterior is shown in 
fig. 26, and its connection with the ganglion and pre- and 
post-branchial branches shows it to be the 7th nerve-root ; 
the posterior p’ sses into the walls of the auditory vesicle 
(fig. 31), and 7 herefore the 8th nerve. 
The 9th ner e fuses with its corresponding sensory epithe- 
lium soon after its origin (fig. 27). The main trunk then 
passes on and fuses with the epiblast of the 2nd gill-cleft, as 
shown at a later stage in fig. 28. The root by this time has 
shifted downwards from the dorsal surface of the brain. The 
subsequent course of events is exactly the same as in the case 
of the 7th nerve. The ganglion retreats further from the 
-surface of the body, remaining attached by the dorsal nerve to 
