122 B. F. KINGSBURY 



evidence that the rostral (cephalic) end of the neural plate in the 

 closed neural tube is marked by the anterior boundary of theoptie 

 chiasma, that is, is located at the preoptic recess. His termed 

 this recess the optic recess as marking on the middle plane the 

 level of the optic evaginations. Johnston points out that the- 

 preoptic recess is secondary and that the basilar furrow of His- 

 (Basilarleiste) , which he regarded as becoming the recessus in- 

 fundibuli, in reality marks the level of the optic evaginations. 

 Johnston therefore calls the basilar furrow of His the primitive- 

 optic furrow, which he concludes may persist as a postoptic re- 

 cess. These points of disagreement with the conclusions of His- 

 do not particularly concern us here, aside from his conclusion 

 that the anterior end of the neural plate includes the optic chi- 

 asma. The experimental results of W. H. Lewis ('12), Spemann 

 ('01) and Stockard ('13), indicating as they do that the anterior 

 end of the neural plate is occupied by the retinal area (or areas), 

 would in a general way confirm this. Johnston further says (p. 

 462) that ''The determination of the anterior end of the brain 

 will fix the extent of the floor-plate and roof-plate of His and will 

 show the point at which the prolongation of the sulcus limitans 

 must end;" and further concludes (p. 504) that ''The optic chi- 

 asma therefore occupies the anterior border of the floor-plate of 

 the brain." Johnston thus extends the floor-plate farther forward 

 than did His, and apparently, like His, regarded it as completely 

 dividing the cranial portion of the neural plate into two halves. 

 His wording in regard to this is not entirely clear, as appears 

 from the above quotation. 



Schulte and Tilney ('15), in a study of the morphogenesis of 

 the neuraxis and the interpretation of the forebrain in terms of 

 the longitudinal zones of the neural tube, have likewise dealt 

 with the problem involved. Their conclusions are based upon 

 the conditions in twenty-six young cat embryos cut in the trans- 

 verse plane as studied in wax-model reconstructions. They find 

 that the anterior end of the neural plate is marked by a swelling, 

 the 'tubercle of the floor,' which is located at the anterior extrem- 

 ity of the floor-plate. This tubercle, according to their interpre- 

 tation, becomes the mammillary region. The medial plane of 



