Cranial neural crest extirpation and cyclopian development.

Extirpation of cranial neural crest cells in presomite to 5 somite chick embryos produces monsters which in all essential respects are identical to human cyclopias. The primary lesion involves damage to the forebrain and consequently the inhibition of the nasal placode and nasal organ development as well as the destruction of the anterior neural crest cells, with the resultant absence of the nasal and interobital septa and of the facial dermal skeleton.