230 G. W. BARTELMEZ 
4. The otic plate has been identified earlier in man than in 
any other vertebrate of which we have accurate data, and in this 
form only does it precede the optic anlage. 
5. Isolated thickenings (growth centers) of the cranial neural 
folds appear at a stage of seven to eight somites, which promptly 
fuse to form a continuous ridge, the ‘optic-crest primordium.’ 
An associated ventricular sulcus in the forebrain levels of the 
ridge indicates the position of the optic anlage. This is the 
earliest stage of this anlage which has been recognized in a 
mammal. 
6. The non-optic part of this primordium proliferates mesecto- 
derm and a large part of the trigeminal ganglion. 
7. The optic anlage appears laterally in the neural fold, but 
between it and the ectoderm there is an intervening zone which 
gives rise to part of the alar and roof plates of the future dien- 
cephalon. The optic vesicle is therefore derived entirely from the 
central nervous system. 
8. At a stage of sixteen somites the optic vesicle is in contact 
with the overlying ectoderm. 
LITERATURE CITED 
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1845 Entwicklungsgeschichte des Hundeeies. Braunschweig. 
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Danpy, W. 1910 A human embryo with seven pairs of somites measuring about 
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