1035 



In Acipenser (lie III nerve enters the brain us usual directly behind 

 the lobi interiores. Its nucleus has a dorsal position, dorso-Uiterally 

 from and l)et\veen the fasciculi longiludinales dorsales ; but very 

 few cells reach a somewliat more venti-al position than in scyllium, 

 thus slightly indicating the jn-ocess which in Teleosts gives rise to 

 the formatio]! of a real ventro-inedian nucleus. The same was the 

 case in Amia. The dorso-lateral part of the nucleus extends some 

 distance in front of the entrance of the III root. 



Some distance in front of it, new cells of a much larger tyj)e 

 appear, belonging to the large reticular type and probably con- 

 stituting the homologue of Cajals ^) "foco intersticial" in mammals 

 and birds, also described by dk Langk ") in Reptilia, which sends its 

 axones in the posterior longitudinal fascicle. 



The III nucleus finishes caudallj^ near the |)Osterior limit of its 

 root entrance. 



The IV nucleus lies some distance behind the III, separated 

 from it by the tractus cerebello-mesencefalicus dorsalis, which ])asses 

 here from the valvula cerebelli into the mesencephalon. 



Such a separation has never yet been found in Selachii, but occurs 

 rather often in Teleosts. The nucleus is small and its root lies a 

 good deal farther caudad, as is also the case in Amia. 



In the region of the trochlear luicleus large reticular cells are 

 rarely found, and I get the impression that these large cells in Aci- 

 penser, as in other animals (v. Höevell) ^), tend to group together 

 in definite regions. 



Also the position of the motor V nucleus shows a great resem- 

 blance with that of Amia, in so far as in both the nucleus retains 

 a dorsal position over its entire length. The nucleus has moreover 

 the same length in the two, though in x\mia it begins a little caudad 

 from the frontal line of entrance of its root and extends a little 

 behind the VII root entrance. 



Next to the trigeminus nucleus, along the lateral border of the 

 fasciculus iongitudinalis posterior, we find a great quantity of large 



^ El s.islema nervoso del liombre y de los verle brados, Tomo II p. 551, Fig. 505 

 and Trabajos, Tomo VH: Ganglios de la subslancia reticular del bulbo p 279 Fig. 9. 



~) Das Zwischenhirn und das Miltelhirn der Reptilia. Folia Neurobiologica Vol. 

 VJII p. 134, Fig. 57 and p. 135 Fig. 58. 



Gyclostomes these large reticular cells have been found in front of tlie 

 Oculomotor nucleus (comp. a. others Tuetjakoff Arch. f. mikr. Anal. 1909, End. 74). 



3) J. .1. L. Ü. Barun v. Höevkll. Remarks on the reticular cells of the oblon- 

 gata in dilVerent vertebrates. Proc. of the Kon. Akad. v. VVel. Amsterdam ; 

 April, 1911. 



