Kappers, Teleostean and Selachian Brain. 89 



the fourth ventricle is here larger. There are, however, very 

 many more points of difference between the two kinds of fish. 

 The mode of subdivision of the cerebellum itself is different. 

 The part generally called the valvula cetebelli which, in most 

 bony fishes, extends in so characteristic a way under the roof of 

 the mid-brain and which some older anatomists considered as 

 corpora bigemina is not represented in this form in the sharks. 

 Here the anterior part of the cerebellum overlies the tectum 

 opticum and looks more like the anterior half of the true cere- 

 bellum, while macroscopically the valvula seems more like an 

 appendage of it, at least in Gadus, Lophius, Salmo and the greater 

 number of other bony fishes. From the investigations of C. L. 

 Herrick, in Haploidonotus grunniens and those of Marcusen 

 in Mormyridae it results, however, that the valvula may also be 

 developed into a very strongly plicated organ, as it also appears 

 in Thynnus. Burckhardt considers it as the homologue of the 

 pars anterior cerebelli of the selachians, whose cerebellum, he 

 contends, is always divided into two parts by a dorsal transverse 

 furrow, which in some representatives of these fishes is only feebly 

 marked but which is generally clearly to be seen. I can state that 

 this transverse groove clearly appears in the selachians which I 

 have examined. In Galeus it is far deeper, as a superficial exam- 

 ination could show; in Angelus squatina it is far less clearly seen. 

 Another point of difference lies in the auriculus cerebelli found in 

 the plagiostomes, a continuation of the cerebellum caudad and 

 characterized by the sharp elevation which it causes and the folding 

 of its surface (Figs, c, ci, Plate VII). 



Another part which in the bony fishes is united with other 

 regions is distinct in the selachians and known as the lobus nervi 

 lateralis anteriores, also called lobus facialis sensibilis and formerly 

 generally lobus trigemini, according to the opinion the naturalists 

 had regarding the important geniculated root which terminates 

 there and which some say belongs to the trigeminus and others to 

 the facialis, but which as a static nerve might best be said to belong 

 to the octavus, with whose region this terminal nucleus is united, 

 as is the case in the bony fishes, though in the selachians it has 

 grown out as a separate lobe. 



The fusion of the static regions across the median line, which in 

 bony fishes is caused by the fact that so many roots enter the same 

 region in consequence of which the region is greatly extended, does 



