378 J. B. JOHNSTON 



dor sally by the neuroporic recess. Other authors have defined the 

 lamina terminalis as the closing 7ne7nhra7ie which is hounded above 

 by the choroid plexus. Both groups of workers believe that they 

 are following His. The result has been the greatest confusion. 

 In some eases even the tela chorioidea has been included in the 

 lamina terminalis. The writer holds the view that the lamina 

 terminalis is coextensive with the primitive neuropore and is 

 bounded above by the neuroporic recess, but insists that the 

 locus of this recess shall be accurately determined. It will appear 

 below that His was in error in locating the neuroporic recess at 

 his angulus terminalis. 



Conclusive evidence as to the location of the neuroporic recess 

 in reptiles and mammals is to be obtained only by following that 

 recess from the open neuropore through successive stages of de- 

 velopment until its relation to the telencephalio commissures is 

 established. The accompanying figures 1 to 6 show the contour 

 of the dorsal seam of the forebrain in embryos of Chelydra ser- 

 pentina from the stage of the open neuropore to a stage possess- 

 ing a carapace 8 mm. in length. For the opportunity to study 

 this material the writer is indebted to Dr. C. E. Johnson. The 

 locus of the neuroporic recess is entirely clear throughout these 

 stages. In the latest stage drawn (fig. 6) there appears between 

 the preoptic recess below and the beginning of the tela chorioidea 

 above (m) a somewhat S-shaped thickening of the roof-plate. 

 In the lower part of this thickening the fibers of the anterior 

 commissure are present. Above this the neuroporic recess ap- 

 pears as a ventricular pit. The upper part of the thickening is 

 the lamina supraneuroporica. 



The same relations are seen in figure 7 which shows the out- 

 line of the median section of the brain of a slightly more advanced 

 embryo of Emys lutaria. For the opportunity of studying this 

 embryo I am indebted to Dr. G. Carl Huber. In this the 

 recessus neuroporicus separates widely the lamina supraneuro- 

 porica from the thickening in the lamina terminalis which con- 

 tains the anterior commissure. The lighter outlines numbered 

 1, 2, 3, 4> are the outlines of successive parasagittal sections 

 of the medial wall of the right hemisphere. The contours 1 and 



