Johnston, TJie Bi'ain of Petfomyzon. 6i 



acusticum, and the entrance of sensory fibers into the acusticum 

 only through a narrow neck between the cerebellar crest and 

 the ventricle. These peculiarities together with the general 

 appearance of the structures concerned, as far as they can be 

 made out from Houser's few figures, have led me to think that 

 HousER has given the name "general cutaneous nucleus" to 

 the body which has been known to other authors as the tuber- 

 culum acusticum, and has given this latter name to the structure 

 usually known as the iobus trigemini of selachians and ganoids 

 (my Iobus lineae lateralis). Houser makes no mention of this 

 latter lobe, although its presence has been indicated by Stan- 

 Nius ('49) in Raja, Spinax, Carcharias ; by Gegenbaur ('71) in 

 Hexanchus ; by Jackson and Clarke ('76) in Echinorhinus j 

 and by Ewart ('89) in Laemargus. The general relations of 

 the body which Houser calls the tuberculum acusticum, as far 

 as they are shown in his Figs, i and 2, closely correspond to 

 those of the Iobus lineae lateralis in Raja, while all the sensory 

 structures resemble those in Acipenser. If the names which I 

 have suggested are applied to these structures, the peculiarities 

 noted above no longer require explanation. Some other con- 

 siderations also point to this interpretation. It was suggested 

 by Goronowitsch ('88) and again by Kingsbury ('97) that 

 the posi'.ion of the cerebellar crest in ganoids, between the 

 acusticum and the Iobus lineae lateralis, is to be explained by 

 supposing that there has been a longitudinal infolding along the 

 line of the crest resulting in turning the dendrites of the Pur- 

 KiNjE cells which originally were directed toward the outer 

 surface, toward each other from the acusticum and Iobus re- 

 spectively. This suggestion is the most obvious and plausible 

 explanation of the position of the Purkinje cells in Acipenser 

 and it finds beautiful confirmation in the brain of Mustelus as 

 represented by Houser in his Fig. 2. Here the cerebellar crest 

 covers the outer surtace of the Iobus lineae lateralis and acusti- 

 cum (Houser's /. a. and g. c. n. respectively) and the lateral 

 surface is deeply infolded so as to form a partly fused molecular 

 mass like that in Acipenser between the acusticum and Iobus 

 lineae lateralis, which are almost completely separated in both 



