FATE OF NEURAL CREST IN HEAD OF URODELES 20 
or lymphatic-vessel formation. However, when the ectodermal 
collar forms, its distinctness from the mesenchyme is quite evi- 
dent, since the mesenchyme is loose in structure, while the 
ectodermal collar is dense and continuous with the deeper layer 
of the surface ectoderm. As to the later differentiation of the 
ectodermic collar, we find ourselves in agreement with Johnston 
(10), who states that it gives rise to the dental ridges and teeth, 
while the endodermal lining of the oral cavity gives rise to the 
taste buds and oral epithelium. 
Concerning the fate of the remaining cells of the ectodermic 
collar, we cannot make such definite statements. Aside from 
the teeth, the ectoderm gives rise to the dense tissue in which 
the teeth are imbedded. ‘The dental ridges and teeth, however, 
disarrange the cells of the ectodermic collar where it comes into 
contact with mesenchyme, and the collar may possibly contribute 
to the mesenchyme, but the indications are against such an 
interpretation. We have followed the ectodermic collar up to 
the time when membrane bone begins to form around Meckel’s 
cartilage and about the bases of the teeth. At this late stage 
one is forced to the uncertain method of tracing derivation by 
position mainly. Based on this criterion, the bone that forms 
about Meckel’s cartilage comes from the mesenchyme of both 
ectodermal and endodermal origin, while the membrane sur- 
rounding the teeth seems to come from ectoderm only. It is 
certainly formed in the same dense tissue of the collar from 
which the teeth arise, although we cannot exclude the possibility 
of the migration of mesenchyme cells of mixed origin into the 
ectodermal collar. The late stage at which true membrane bone 
forms renders it unsafe to make definite statements concerning 
its derivation from ectodermal mesenchyme as distinct from 
entodermal mesenchyme because of the fact that both types 
are similar in structure, owing to the loss of yolk granules by the 
endoderm and the reduction in size of entodermal mesenchyme 
cells. 
_ My conclusion, therefore, concerning the contribution of the 
lateral ectoderm to mesenchyme is that the lateral ectoderm, 
aside from the oral ectodermic collar and its derivations, is not 
