Kingsbury, Oblongata in Fishes. 27 



responsible. Goronowitsch, in the readiness with which he re- 

 cognized the fibers arising from the so-called lobus trigemini in 

 Acipenser as fine as compared with the fibers from the dorsal 

 tracts, favored by his determination to find in the cranial nerves 

 the dorsal and ventral roots of the spinal nerves ; and Mayser, 

 in applying ( first ) the name lobus trigemini previously used in 

 the elasmobranch brain to a structure in the cyprinoid brain 

 without determining their complete homology. 



Under such circumstances attempts to completely homolo- 

 gize the nerves in Ichthyopsida must fail without a recognition 

 of this trouble, and as soon as it is recognized many points be- 

 fore inexplicable are cleared up. 



In Elasmobranchs there exists upon the dorsal side of the 

 oblongata an elevated region which is simply a continuation caud- 

 ad of the corpus restiforme, and to this the name of lobus trigemini 

 was quite generally applied ( by Miklucho-Maclay ; Viault, 

 Rohon, Gegenbaur). Since it is a direct continuation of the 

 corpus restiforme, that name, as used by some ( Stannius ) also 

 includes it. It is partially covered by a caudal extension of the 

 molecular layer of the cerebellum which also covers the dorsal 

 tracts laterad of it. Beneath it a large nerve root arises, the 

 most dorsal of the nerves of the V-VII complex. This is un- 

 doubtedly the nerve from the corpus restiforme of Stannius in- 

 nervating the 'mucous' canals. Ewart describes the most dor- 

 sal of the nerves distributed to the lateral line system in Lae- 

 margus as the ophthalmicus superficialis. ' ' This nerve arises by 

 a large root from the so-called trigeminal nucleus which occu- 

 pies the most dorsal portion of the medulla." It communicates 

 freely with the buccal. VIIc of Strong '94 in Galeocerdo seems 

 to be the same root. 



It seems probable that the "lobus trigemini" of Acipenser 

 ( and other sturgeons, probably ) is the same structure found in 

 sharks and the nerves are homologous. In examining transec- 

 tions through this region of the Acipenser brain, the impression 

 was strong that there had been a partial folding in of the cere- 

 bellar crest and fusion of the two surfaces. The occurrence of 

 large (Purkinje) cells on both sides of the cerebellar crest 



