28o 



C. U. Ariens Kappers 



W'hilst the nucleus trochlearis holds a dorsal position in the cerebel- 

 lar píate of Lampreys owing to the numerous primary and secundary 

 equilibrium fibres (of the X. Vestibularis and X. X. laterales) which cnd 

 here or pass it, its subventricular place in higher animáis is apparently 

 defined by the fasciculus longitudinalis posterior (figs. 9, 10, II, 12), the 

 same refíex-tract, on which in most other animáis, the place of the nucleus 



V 



i-í. • ■■ ■ 



nucí, trochl. 

 posterior sinister 



fase. Ion. 

 post. 



ÍÍ^S*:'2 



Fig. II. — Position of the 



trochlearis nucleus in a bird 



(Ciconia) on the fase. long. 



posterior. 



Fig. 12. — Position of a caudal 

 rest of the trochlearis nucleus 

 (nu. trochl. posterior) on the 

 fase. long. posterior in man. 



abducens depends and from which the nucí, trochlearis receives nume- 

 rous collaterals (Beccari) 1. 



That the nucleus makes a frontal shifting, must be ascribed to fibres 

 in this bundle starting from £he roof of the mid-brain and carrying light- 

 reflexes, as has been confirmed specially by Tretjakoff dina van dcr Horst^ 

 the stimuli proceeding from the mid-brain to the nucleus trochlearis, 

 being far more important in higher animáis than in the lamprey -. 



In the lamprey the X. Opticus is only poorly developed and 

 the tectum opticum for a large part is a mere ependymal membra- 

 ne. In sharks and bony-fishes on the contrary the tectum opticum 

 is very strongly developed and gives origin to a large quantity of re- 

 flectory fibres in a caudal direction to the nuclei oculomotorius and 

 trochlearis. 



' Beccari: Monitore Zoológico italiano. Anno 20, 1909. 

 - Compare also Efisio Orru. 



