FATE OF NEURAL CREST IN HEAD OF URODELES 2S 
THE ORAL ECTODERM 
Lastly, the oral region in the urodeles presents a curious con- 
dition with reference to the positions of ectoderm and endoderm. 
None of the authors interested primarily in the origin of head 
mesenchyme has described this region carefully. This is all the 
more striking, since, on superficial examination, it would seem 
to furnish the best evidence for the derivation of mesenchyme 
from the lateral ectoderm. Johnston (’10), working on the fate 
of the oral entoderm in Amblystoma, gives an accurate descrip- 
tion of the oral region. He does not, however, follow the fate 
of the mesenchyme. My results agree with his, except in one 
particular. 
I find, in agreement with Johnston, that the anterior end of 
the archenteron is open at first well forward to the position of the 
future oral opening. ‘This open oral and pharyngeal cavity next 
becomes closed and forms a solid, flat column of entoderm abut- 
ting cephalad against the oral ectoderm, which at this point 
consists of the usual two layers, a superficial epithelium and a 
deeper layer of nervous ectoderm. The next change consists 
in the formation of a collar of ectoderm around the solid column 
of oral entoderm. ‘This collar grows caudally from the anterior 
oral region and mesially from the lateral oral region as far as the 
position of the vomerine teeth, which is approximately the 
posterior boundary of the solid column of the oral entoderm. 
This ectodermic collar is derived from lateral ectoderm as distinct 
from neural crest. During the formation of the ectodermal col- 
lar the nervous layer of the ectoderm disappears at the line of the 
future opening, but we are unable to verify Johnston’s statement 
that the ectoderm disappears entirely, leaving the endodermal 
column exposed at the oral region. In our preparations the 
surface ectoderm is never absent at this point before its rupture 
to form the oral opening. 
- The next change consists in the formation of a definite oral 
cavity in the previously solid column of oral endoderm. It 
splits from behind forward, and after the endodermal column 
splits, the thin layer of superficial ectoderm ruptures, thus forming 
