NOTE ON THE DEVELOPMENT OF AMPHIBIANS. 309 
and middle dilations, and immediately behind the ear arises 
the root of the ninth nerve ( n . IX). These dilated parts of 
the hind-brain in Amblystoma resemble in some degree what 
I have described as the neuromeres in the hind-brain of the 
Lizard, except that in Amblystoma they are fewer in number, 
and certain intermediate neuromeres appear to have been sup- 
pressed. I am inclined to think that the large quantity of 
yolk present in these parts in Amblystoma has considerably 
changed their appearance and development. These dilations 
of the hind-brain have disappeared in Amblystoma, as in the 
Lizard, by the time the nerve-fibres of the brain have appeared. 
It will be seen in fig. 14 f that the cranial nerves meet and 
fuse with the epiblast. This fusion I think corresponds with 
what has been described by Miss Johnson and Miss 
Sheldon 5 as the first or dorsal fusion of the cranial nerves 
with the epiblast. These authors have described this fusion 
for the fifth, seventh, and ninth nerves, and supposed it for 
the vagus. My section shows the correctness of their suppo- 
sition. The vagus retains for some time this fusion with the 
epiblast, and from the point, of fusion there soon grows poste- 
riorly a large linear thickening of the epiblast, which forms 
the lateral nerve. This in its earlier stage is very conspicuous, 
but soon becomes much smaller. I have not been able to trace 
the different steps between what the above-named authors have 
called the “ first (dorsal) fusion” and the “ second (ventral) 
fusion.” One of my series of sections of Triton alpinus 
shows the condition described by them as the “ second (ventral) 
fusion.” In this series the distal ends of the two primary 
branches of the fifth nerve touch the epiblast and appear to be 
fused with the same. 
The further development of the brain is shown in figs. 17 g 
and 18. The irregular appearance of these sections is due to 
the fact that they are neither exactly median nor exactly vertical ; 
they cross the median vertical plane in a line drawn through 
the epiphysis ( Eph .) and the region of the optic chiasma ( Ch .) 
1 Johnson and Sheldon, “Notes on the Development of the Newt (Triton 
cristatus),” ‘ Quart. Journ. Micr. Sci.,’ vol. xxvi, N. S., 18S6. 
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