176 LECTURE vnr- 



and the Sturgeon. The relative size of tlie cerebellnm, accord- 

 inglj, varies greatly in different bony fishes : it is very small in the 

 lazy Lump-fish, and extremely large in the active and warm- 

 blooded Tunny, where also its surface shows transverse groovings. 

 The cerebellum is unsymmetrically placed in the Pike and Flat- 

 fish {FleuronectidcE), and is unsymmetrically shaped in the Sharks ; 

 it presents a posterior notch in the Hei'ring, a transverse notch 

 dividing it into an anterior and posterior lobe in the Lophius, and 

 a crucial impression in the Skate. The cerebellum presents in 

 many fishes a small cavity or fossa at its under part, continued from 

 the fourth ventricle {Jig.5\. c) ; it is solid in the Tench, the Gar- 

 Pike, and the common Eel ; some grey matter is usually found in 

 its interior, with feeble indications of white strice, but thei'e is no 

 'arboi vita?,' except in the Tunny and the Sharks. 



c The posterior 'crura cerebelli' 



■51 - ^'"^fWy^^jl^ h ^^® formed, as we have seen, by 



B^^-^^ _____ t]^e posterior pyramids in con- 



'y^s^ '^ junction with part of the resti- 



Section of Brain, Carp. n , , j.- i /•! „, i* 



^ lorm tracts : vertical fibres Irom 



the side of the cerebellum continue to attach it to the sides of the 

 restiform or trigeminal lobes, and some of these are continued, as 

 arciform filaments, upon the under surface of the medulla oblongata : 

 they answer to the ' crura cerebelli ad pontem ' of mammalia ; but, 

 as there are no lateral lobes to the cerebellum in Fishes, these crura 

 are rudimentary, and the ' pons ' is absent. In the Shark they con- 

 nect the sides of the base of the cerebellum with the ' restiform 

 commissure' (^figs. 48 and 55. I.). In most Fishes two fasciculi of 

 medullary fibres proceed, as ' anterior crura,' from the under and 

 fore part of the cerebellum, or converge from the lateral and fore 

 part forwards, to foi-m the inner wall or septum (^fig. 52. r) of the 

 oj)tic lobes : these answer to the ' processus a cerebello ad testes ' of 

 the human brain : they are connected below their origin at the under 

 part of the cerebellum by one or two tranverse fasciculi of white 

 fibres, forming the ' commissura ansulata,' which crosses the pre- 

 pyramids just behind the 'hypoaria' {^fig. 53. 7i). The inferior white 

 surface of the cerebellum which forms the roof of the fourth ven- 

 tricle is called ' discus cerebelli,' and from this part small tubercles 

 project in a few fishes (e. g. Blennuis). 



The restiform columns, quitting the postpyramidal crura of the 

 cerebellum, and having effected by their previous confluence therewith 

 some interchange of filaments, swell out at the anterior lateral parts 

 of the medulla oblongata, and give origin to the great trigeminal 

 nerve. They here form considerable ' trigeminal lobes ' in the 



