470 Leland Griggs. 



evidence, therefore, seems fairly conclusive that the region of 

 the procephalic lobes includes the fore-brain, mid-brain and 

 that part of the hind-brain in which the anlage of the cerebellum 

 is found. 



The determination of the relation of the individual neuromeres 

 to landmarks of the adult brain is a more difficult problem. It 

 should be borne in mind that this is the last stage in which it is 

 possible to identify the neuromeres with certainty since they 

 very quickly disappear as the neural crests close over into the 

 neural tube. The only trustworthy evidence then must come 

 from the embryos of this stage. It will be best to consider the 

 neuromeres separately beginning with the first or most anterior. 

 This neuromere very clearly lies on the floor of the fore-brain 

 vesicle (nl, fig. 8, A, fig. 9, C). A small portion of the second 

 neuromere is bent down with the first until it may perhaps be 

 considered to be involved with the infolding (n2, fig. 9, C). 

 Johnston's ('05) statement that 'Hhe fore-brain is formed by a 

 relatively enormous growth of the first neuromere especially of 

 its dorsal part" seems to go considerably beyond the facts as 

 they appear in Amblystoma. All chat can actually be observed 

 here is that the first neuromere forms the floor of the infundi- 

 bular depression wJiich at this stage constitutes the ventral por- 

 tion of the primary fore-brain vesicle. That the cells of the first 

 neuromere actually contribute to the formation of the sides and 

 roof of the adult fore-brain may be very probable but other 

 structures may very likely be involved also. The second and 

 third neuromeres in the same way form the floor of the primary 

 mid-brain vesicle (n2, n3, fig. 8A, fig. 9, C). The second neuro- 

 mere as has been stated sometimes appears to extend slightly 

 into the fore- brain region, but the third lies wholly in the mid- 

 brain. The fourth neuromere covers a region on the floor of 

 the hind-brain vesicle lying directly below the cerebellar crests 

 (n4, fig. 9, A, C). All these various relations nay be summed up 

 by the statement that the first neuromere contributes to the for- 

 mation of the fore-brain, the second and third to the formation 

 of the mid-brain, and the fourth to the formation of the anterior 

 part of the hind-brain. It should be borne in mind, however, 



