FUNDAMENTAL PLAN OF VERTEBRATE BRAIN 463 
section, 2) of the brain plate (figs. 1 and 2). The latter series is 
essential in the comparison, inasmuch as it is the cephalic portion 
of the neural plate which by growth and folding produces the 
brain. It should, of course, be appreciated that these diagrams 
are purely schematic and intended merely to present the respec- 
tive interpretations. The critical landmarks in the comparison 
of these interpretations are the mammillary recess (V/), the 
primitive infundibular recess (J), the preoptic recess (optic recess) 
(O), and the extent of the floor plate (Ff). These points are 
designated in both series of diagrams by the significant letter. 
The floor plate is cross-lined, lamina basalis sparsely dotted, the 
lamina alaris is clear, while the line of secondary closure con- 
verting the brain plate into the vesicular brain is outlined by 
heavy dots. 
The His interpretation (B of figs. 1 and 2) requires little ex- 
planatory comment. ‘The floor plate (/’) and his sutura neuro- 
chordalis terminated at the primitive infundibular recess (J) 
which marked the anterior medial limit of the brain plate. 
Anterior to this the sutura terminalis closed the neural tube in 
front, meeting the sutura dorsalis (roof plate). The line of 
demarcation (sulcus limitans) between the primary motor zone 
(B) and the primary sensory zone (A) terminates at the preoptic 
recess (O). His’ own diagrams which are, of course, well known 
were copied in my earlier paper and may be compared. 
Johnston (’09), entirely correctly as I think will be adequately 
shown later, placed the anterior limit of the brain plate at the 
preoptic recess.2_ C of figures 1 and 2 conveys his interpretation. 
Apparently he conceived the floor plate as extending throughout 
the brain plate, i.e., to the preoptic recess (cf. Kingsbury, ’20, 
Weg). 
Schulte and Tilney (’15), from a study based on twenty-six 
models of the brain in embryo cats, came to conclusions unique 
in two respects: a) the brain plate (and the floor plate) were 
believed to extend no farther forward than the mammillary 
? Mrs. 8. P. Gage (’05) earlier came to the same conclusion (p. 426): ‘The 
natural corollary follows that the optic chiasma crosses the original margin or 
dorso-mesal line.” 
