278 H. SAXTON BURR 
cephalic evagination. In all the cases studied the outpouching 
of the wall of the neural tube has been closely associated with the 
olfactory placode. Beginning first in the cyclostomes as an 
evagination of the olfactory bulb, the further phylogenetic history 
has involved progressively more and more olfactory association 
material (Herrick, ’21). The relation of the evaginated portions 
to the rest of the tube assumes, therefore, a prime importance. 
The following communication deals with an experimental study 
of the fate of the neuropore in Amblystoma and the subsequent 
history of the relations of the longitudinal columns of the neural 
tube in this region. 
THE FATE OF THE NEUROPORE 
The work of Johnston (’09), based on a comparative study of 
the forebrain vesicle in vertebrates, showed clearly that the ven- 
tral lip of the neuropore was incorporated into the brain as the 
terminal ridge lying between the lamina terminalis anteriorly 
and the chiasmatic ridge posteriorly through the fusion of the 
lateral lips of the blastopore. He concluded that the preoptic 
recess, marking the termination of the sulcus limitans and separa- 
ting the terminal ridge from the chiasmatic ridge, represented 
the meeting-point of the roof and floor plate and hence the ante- 
rior end of the neural tube. Hatschek (’09) confirmed in the 
main Johnston’s researches, but stated that the terminal ridge 
or ‘Basilarlippe’ marked the primary anterior wall of the neural 
canal. In any event, it seems evident that this terminal ridge 
is subsequently occupied by decussating fibers of the anterior 
commissure. 
To determine experimentally the above facts, a number of 
operations were performed on Amblystoma larvae. At the sug- 
gestion of Doctor Harrison, fine hairs were inserted into the 
neuropore for a short distance and watched during subsequent 
development in the hope that the ultimate position of the hair 
would indicate the final position of the neuropore in the embryo. 
Difficulties were at once encountered, since a fine hair, unless 
inserted for a considerable distance into the embryo, would not 
remain there, but would be extruded. If, on the other hand, the 
