128 B. F. KINGSBURY 



lare). The partial decussation of the oculomotor nerve (crossed 

 origin) might also express a primitive continuity across from side 

 to side in this region. 



5. I venture again to call attention to the conclusion of John- 

 ston that what His termed the recessus infundibuli (Basilarleiste) 

 should more appropriately be termed the primitive optic furrow 

 and that the recessus infundibuli was a secondary out-pocketing 

 of the wall of the neural tube. Under the conception of the 

 brain-plate here outlined, this would occur medially between the 

 alar and basal plates separating the sensory zone in the floor (the 

 optic chiasma) from the motor (the floor of the midbrain) ; but 

 whether at the expense of the sensory zone or of the motor zone 

 or as an essential separation of them, cannot be said. The de- 

 velopment of the infundibulum is, I think, unquestionably 

 bound up with the development of the hypophysis, and until the 

 early morphogenesis of the latter is clarified and its morpho- 

 logical significance better estimated, nothing can be added to a 

 mere statement of fact. 



6. Such a conception as this of the cephalic portion of the 

 neural plate, it must be conceded, contradicts certain generally 

 accepted doctrines of fundamental brain morphology. Thus, 

 the boundary between primary motor and sensory zones, which 

 appears in the more caudal portion of the neural tube as the sul- 

 cus limitans, frequently to be seen, particularly in the mammahan 

 neural tube and in the rhombencephalon, would not terminate at 

 the preoptic recess as is generally thought to be the case, but 

 would terminate in the primitive infundibular recess, primarily 

 continuous across from side to side. In the His models of the 

 developing human brain, as Schulte and Tilney point out, the 

 sulcus limitans does so terminate anterior to the midbrain floor 

 (i.e., in the mammillary region). It is in my opinion a valid ob- 

 jection to the generally accepted interpretation that it includes 

 in the basal, primary motor lamina optic chiasma and hypothala- 

 mus — regions which possess no such significance. The motor 

 zone ceases with the floor of the midbrain. This is, I think, 

 more striking in the brain of a lower vertebrate than it is in that 

 of a higher form. The divisions of the brain would lose their 



