MOTOR NUCLEI IN PHYLOGENY 



389 



In addition, in the latter animals the lagena becomes further 

 constricted off from the sacculus than in urodeles, and the papilla 

 acustica basilaris lagenae which appears for the first time in 

 phylogeny in amphibians, attains a higher stage of development 

 in anm"ans than in urodeles (Retzius, 48; Wiedersheim, 58). 



Nerve V 



The motor V nucleus in R. catesbeana lies a short distance 

 rostrad of the motor VII nucleus and occupies a similar position 



-Tr.Vlll 



Fig. 5 Rana catesbeana. Transverse section through the medulla at. the 

 exit level of the motor trigeminal root. Abbreviations: Cb., cerebellum; Nu.V. 

 TO., motor trigeminal nucleus; B.V.m., motor trigeminal root; R.V.s., sensory 

 trigeminal root. Other abbreviations as before. 



in the periependymal gray. The motor V nucleus is at least 

 double the size of the motor VII nucleus and its limits are more 

 sharply circumscribed. It extends approximately from the 

 rostral border of the emergent motor V root to that of the 

 motor VII root, so that its chief bulk lies caudad of its root 

 exit. The motor fibers arising in the caudal part of the nucleus 

 course a short distance rostrad as separate strands through the 

 nucleus and then, together with those arising further forward, 

 pass laterad and slightly ventrad in small fascicles to emerge 

 below the large sensory trigeminus root (fig. 5). 



