56 Journal of Comparative Neurology. 



sal horns. The more primitive Petromyzon brain gives strong 

 additional support to this interpretation. 



It is interesting to note, first that the cutaneous centers are 

 nearly as large, although not so well differentiated, in Petromyzon 

 as in Acipenser. Strong was led into error regarding the relative 

 development of the cutaneous and visceral centers in Petromy- 

 zon by Ahlborn's imperfect description of the VII nerve. Fol- 

 lowing the quotation given above, Strong says : " If the charac- 

 ter of the so-called N. lateralis be as above supposed, the most 

 dorlal nucleus of the Acustico facialis center, from which the 

 •Facialis emerges, would correspond to the lobus trigemini." 

 Here Strong uses the term lobus trigemini in the sense in which 

 it was applied in Teleosts, i. e. the cephalic part of the com- 

 munis center. In that sense there is no lobus trigemini in 

 Petromyzon, but only a very slender pre-auditory fasciculus 

 which is distinguished with difficulty. In the sense in which 

 the term is used in Ganoids aud Selachians, howeved, there is a 

 very well developed k)bus trigemini (i. e. lobus lineae lateralis) 

 which is the most dorsal acusticum nucleus and receives the dor- 

 sal lateral line VII root. This fact alone is sufficient to indicate 

 the great development of the cutaneous centers. 



The argument for the unity of the cutaneous centers was 

 supported by the following evidence from Acipenser ('oi c, 

 p. 117): 



(i) Continuity of tissue between the acusticum and cere- 

 bellum, the acusticum and cerebellar crest being exact equival- 

 ents respectively of the granular and molecular layers of the 

 cerebellum. 



(2) The fact that the root fibers of each of the cutaneous 

 nerves, V, lateral hne, and VIII, end in all three centers, nu- 

 cleus funiculi, acusticum, and cerebellum. 



(3) Identity of the nerve elements in all three centers, — 

 large or Purkinje, granule, and II type cells. 



(4) The origin and development of the Purkinje cells from 

 the large cells of the acusticum and dorsal horns. This differ- 

 entiation is in actual progress in Acipenser and the Purkinje 



