22 Journal of Comparative Neurology. 



gus, (2) gelatinous substance, (3) secondary vagus tract, (4) 

 motor nidus, (5) endyma. Between (1) and (2) might be inter- 

 polated the zone of small cells. Of these five layers only the 

 first two would belong to the communis system ; the others are 

 involved because of the modification of this region. The tract 

 recognized by Mayser and termed the "secondary vago-trigem- 

 inal tract " appears quite constantly in the teleosts (examined). 

 It is a tract ventrad or ventro-mesad of the spinal Vth tract, 

 formed by fibers coming from the fasciculus communis and go- 

 ing cephalad to a nidus at the base of the cerebellum (Rinden- 

 knoten, Mayser) which communicates with its fellow by a dor- 

 sal commissure through the cerebellum.^ 



The relation the issuing vagal fibers bear to the spinal Vth 

 is clearly due to mechanical advantage and the course they take 

 is regulated by the position and development of their oblon- • 

 gatal center. 



The communication of the two fasciculus communis sys- 

 tems caudad of the metatela, spoken of as the " conmiissura 

 itifima Halleri" appears constant. The caudal limit of the com- 

 munis system was not always easy to determine. In most how- 

 ever (especially Ainiurus and Perca)^ its limit was apparent, and 

 Mayser's view that this as well as the spinal Vth was continuous 

 with the gelatinosa of the myel, is questionable. 



The distribution of the fibers of the root spoken of as the 

 " lateral line nerve " has not been determined for any of the 

 teleosts. It is, however, the undoubted homologue of the lat- 

 eral line nerve in Amia and Acipenser in which its distribution 

 has been shown. There is constantly found an isolated root 

 from the fasciculus communis near or slightly caudad of the 

 lateral line nerve, which I am inclined to think represents the 

 sensory portion of the IXth. The relation in Atniurus rescm- 



' Mayser believed the secondary vago-trigemiiial tracts decussated through 

 the cerebellum. From the conditions in Amiurus, which has been more espec- 

 ially studied, this does not seem to be the case ; the two tracts terminate and 

 the nidi in which they terminate are connected by a dorsal commissure through 

 the cerebellum. 



