303 



place on or near the level of its root entrance as has also been 

 described by Kappers for his specimen of Rana. (fig. 8). 



In connection herewith it Is interesting to notice that the sensory 

 VIl^'^ and conseqnently the candal mixed VII — IX sensory nncleus 

 is less developed in anura than in the arodela. 



I further fonnd that the abdncens nnclens lies behind the rooten- 

 trance of the VIP'', in Necturus and Bnfo a little closer to the 

 VIP'' than in Cryptobranchns and Rana. 



The position and extension of the V and III nucleus, the size 

 and arrangement of the III, IV, V, VI, VII, IX, K and XII roots, 

 as also the slight variations which these exhibit are clearly demon- 

 strated in the sagittal schemes. 



My series of Necturus and Rana were not continued sufiiciently 

 backward to state the limit of the spino-occipital column and the 

 position of the spino-occipital roots. 



The relation found in Bufo however shows a striking resemblance 

 to the condition represented in Kappers' Rana. In Cryptobranches 

 however this column does not extend as far frontally as in Molge. 



The trochlear nucleus extends in my Rana and Bufo much more 

 in a caudal direction than in Kappers Rana. 



This large backward extension of the IV nucleus induces me to 

 add the following remarks concerning the phylogenetic development 

 of this nucleus : 



In Petromyzon this nucleus has a position dorsal to the ventricle 

 (Schilling^), Tretjakopf-), Huet'), Kappers^)) in the velum anticum 

 cerebelli frontally from but close to the level of the trigeminus 

 nucleus at a great distance behind the oculomotor nucleus (compare 

 fig. 1). 



Contrary to this in most other mammals the nucleus has a 

 much more frontal position, directly behind the oculomotor nucleus 

 and ventrally from the ventricle. 



The phenomena observed in the frontal shifting of another eye- 

 muscle nucleus, the VI nucleus (Kappers, I.e. p. 118) prove that the 

 first form in which this frontal shifting can take place consists in its 

 elongation in a frontal direction. So does the abducens nucleus of 

 Chelone and Alligator extend from the giossopharyngeus to the 

 facialis level (I.e. fig. 105]. 



In the higher Reptilia (Varanus and Lizard e. g.) also the rest of 



1) Abhandl. der Senckenb. Naturf. Gesellsch. 1907, Vol. 30, p. 441. 



2) 1. c. p. 713. 



3) Proceedings of the Kon. Akad. v. Wetensch. Amsterdam, February 25, 1911. 

 *) 1. c. p. 9. 



