4G4 Leland Griggs. 



the remaining one being entirely hidden from view in a deep 

 furrow at the anterior end of the neural plate. The sections 

 illustrated in fig. 7 show the process of infolding. In section A 

 there is not yet any appearance of the infundibular depression. 

 The three succeeding sections show the origin and development 

 of the depression and the flexure that is produced in the neural 

 plate by the infolding. The neuromeres cannot be readily 

 observed in sections A and B but in C and D the raised proce- 

 phalic lobes are easily recognized and in the latter it is possible 

 to identify the neuromeres particularly the fourth. The rela- 

 tion of the infundibular depression to the neuromeres will be 

 shown again in the next stage. 



This infolding involves also the anterior pit which represents 

 the original anterior germinal depression (agd, fig. 6, C). The 

 pit may be seen for a short time lying on the floor of the infun- 

 dibular depression but it sooq disappears and it cannot be seen at 

 all in embryos after the closing of the neural canal, even by a 

 careful dissection of the brain to uncover this region. The 

 infundibular depression itself, however, persists as a very impor- 

 tant landmark. 



Kupffer ('04) has given a very good account of this region of 

 the embryonic brain, the hypencephalon, as he calls it, in a series 

 of vertebrates. According to him it is bounded behind by a 

 transverse ridge, evidently the anterior edge of the first neuromere 

 as seen in Amblystoma, w^hich he calls the tuberculum posterior, 

 but in front in the earlier stages there is no definite boundary. 

 He observes that the infundibulum develops from the posterior 

 ventral part of the hypencephalon while the optic chiasma forms 

 in front of the infundibulum on the floor of the hypencephalon. 

 It should be noted that he failed entirely to trace the neuromeres 

 of the open neural plate into this stage. The determination of 

 the exact relation of the first neuromere to this infundibular 

 depression would certainly form an important contribution to 

 the history of this region. 



Behind the procephalic lobes there appears a new series of 

 neuromeres, the postcephalic neuromeres (pen, fig. 6), which 

 apparently develop in order from before backward. They 



