27G 



ANATOMY OF VERTEBRATES. 



179 



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

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

 connect the sides of tlie liase of the cerebellum with the ' restiform 

 commissure,' figs. 172 & 187, 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 forward, to form the inner wall or septum, fig. 184, r, of the 

 optic lobes : these answer to the ' processus ii cerebello ad testes ' 

 of the himiau brain : tliey are connected below their origin at the 

 under part of the ccreljellum by one or two trans%'erse fasciculi of 

 white fibres, forming the ' commissura ansulata,' which crosses the 

 pre-pyramids just behind the ' hypoaria,' fig. 185, n. The inferior 

 white surface of the cerebellum, which forms the roof of the fourth 

 ventricle, is called ' discus cerebelli,' and from this part small tuljer- 

 cles project in a few fishes (e. g. Blennius and Sturio, fig. 173, c). 

 The restiform columns, quitting the post-pyramidal crura of 

 the ccreliellum, and liaving elfected hj their previous confluence 

 therewith some interchange of filaments, swell 

 out at the anterior lateral parts of the medulla 

 oblontrata, and cive orifrin to the ajreat trio-eminal 

 nerve. They here form considerable 'trigeminal 

 lobes' in the Loach and Herring, fig. 184, /, and 

 are folded or 'fimbriate 'in C/H'mffir«,fig. 179, dd, 

 and most Plagiostomes, where they are closely 

 connected with a thick vascular mass of pia 

 mater and arachnoid. The trigeminal lobes are 

 convolute in the Skate ; enormous and blended 

 with the vagal lobes in the Torpedo ; but in most 

 Osseous Fishes (Lepidosteus, Cod) they are not 

 developed so as to merit tlie name of lobes. In 

 the Cod the inner surfaces of the restiform bodies 

 project into the fourth ventricle, and obliterate 

 the fore part of the calamus by meeting above 

 it ; this commissure, which is beneath the cere- 

 bellum, is the ' commissura restiformis,' fig. 182. 

 It is remarkably developed in Carcharias, where 

 it seems to form a small supplemental cerebellum 

 "' '" '" '""■ beneath the larc;e normal one: in fio-. 172 



the medulla oblongata is cut across, the fourth 

 ventricle cxjioscd from behind, and tlie restiform eonnnissure, /, is 

 raised: it has an anterior and posterior median notch. 



The priuiary division of the brain, which consists of tlie medidla 

 oblongata with the cerebellum and other less constant appendages 



