Phenomena of ncurobiotaxis in the optic system 



279 



In higher fishes Sharks and Teleosts (ñg. 9), this position is altered 

 in two respects, the nucleus lying iinder the floor of the ventricle and 

 besides on a more frontal level, either very near or cióse behind the nucí, 

 oculomotorius, often in front of the level of its own root, and consequent- 

 ly at a great distance from the trigeminus. This position is almost 



Fig. 10. — Position of the trochlearis nucleus in.aturtle (Chelone midas) on the 

 fase. long. post., after ó", de Lange. 



constant ^ in al! higher animáis: Amphibia, Reptiles, Birds (comp. fig. 10 

 and 11) and Mainnials. 



In some primitive Amphibia Rothig, found transitor}'^ stages between the caudal 

 and frontal position of this nucleus, demonstrated by a frontal extensión, only its 

 posterior pole remaining on a more caudal level, as also occurred with the nu- 

 cleus abducens in Reptiles. \Ve sometimes find a caudal rcst of the nucleus tro- 

 chlearis.; as an isolated, asymmetrical group of cells behind the main part. as has 

 been described by Tsucliida, van Valkcnbiirg and myself, undcr the namr o{ nu- 

 cleus trochlearis posterior- (compare fig. 12). 



• Only in some Ungulates (Horse f. i.) the nucleus is found underneath the 

 fase. long. post. 



