DEVELOPMhlNT OF THE HEAD IN GOBI US OAPITO. 341 



recent paper (14) on the development of the sturgeon. Von 

 Baer, Dursy, and His regarded the infundibulum as the 

 terminal point. Reichert, Kolliker, and Mihalkovics sought the 

 point in the region of the optic stalks. Goette concluded that 

 the pineal organ represented the ueuropore. Van Wijhe found 

 that in birds the last point of connection of the ectoderm and 

 brain representing the neuropore lay at the middle of the sac 

 of the fore-brain. 



Orr (17) found that in the frog the " anterior medullary 

 fold^' representing the end of the floor of the neural canal lay 

 above the optic chisma in later stages. Kupffer himself 

 describes in the sturgeon a very definite structure, the lobus 

 olfactorius impar, at first hollow, and communicating with the 

 exterior, and in all respects resembling the neuropore of 

 Amphioxus ; and from the agreement of his conclusions with 

 those of Van Wijhe he regards the question as settled for all 

 Vertebrates. 



In Teleostei, however, as we have seen, there is no definite 

 structure corresponding to the lobus olfactorius impar. The 

 wall of the brain passes continuously over the spot, and only 

 comparatively late (fig. 4, x) can it be determined which 

 region is identical with that structure. In Teleostei the 

 neuropore and end of neural axis seem to have been 

 situated at the level of the optic stalks, and below the 

 subsequently formed anterior commissure. This con- 

 clusion is confirmed by the exact observations of Orr on the 

 frog. 



In his latest writings (8 and 9) His speaks of the neuropore 

 as a " Nabelartige Unterbrechung der vordere oder frontale 

 End-nath. " Further he says, '' The total extent of the 

 neuroporic cleft stretches in all craniate Vertebrata from the 

 position of the basilar ridge through the region of the sub- 

 sequently formed recessus infundibuli, chiasma, and recessus 

 opticus, between the nasal organs and along the lamina 

 terminalis to its dorsal extremity.^' Considering the several 

 conflicting and yet exact observations, this view of His seems 

 the only reasonable one to take. 



