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ANNALS NEW YORK ACADEMY OF SCIENCES 



cephalic structure which by its derivatives can be assigned to the basal 

 plate. A second furrow, not connected with the foregoing, extends 

 across the wall of the thalamencephalon, nearly horizontally, to the fora- 

 men of Monro. This sulcus of Monro, His interpreted as the continuation 

 of the sulcus limitans. The interpretation we have suggested is at least 

 as concordant with his observations and dges not entail morphologic im- 

 possibilities. 



In order to facilitate the comparison of these divergent interpretations 

 we subjoin two schemata; the first (Fig. 1) is based on the well-known 



Fig. 1. — Schema of the composition of Hie encephalon in terms of basal and alar plates 



of His 



1. Basal plate. 2. Alar plate. 3. Sulcus limitans. 



figure of His; the second (Fig. 2) iilusti-ates the region of the neuraxis 

 which must be assigned to the ganglionic crest on the basis of our in- 

 terpretation. We have retained from His's figure the sulcus limitans 

 as it appears in later stages of development for the pur])ose of defining 

 the basal plate, although in the period of development of the cat covered 

 by our series of embryos this furrow is not even indicated. 



Prosexcephalon 



The elevation of the neural folds at their cephalic extremity is accom- 

 plished in two phases, affecting first their basal, later their alar portions 



