160 THE HUMAN SPECIES 



As to the proportion of the Rons Varoli (Fig. 82) to the 

 cerebellum, the higher the mammal stands in the organic scale 

 the narrower and shorter is the Pons Varoli in proportion to the 

 cerebellum. 1 Man possesses the broadest cerebellum, the next 

 in order being the cats, and then, although at some distance, 

 the ruminants. 



Each lobe of the cerebellum in man as in the animals 

 consists of six parts. The difference between man and the 

 mammals consists in the medulla being much less extensive in 

 man than in the animals, and the central lobe in man occupies 

 a more central position. In man, too, the vermis is somewhat 

 triangular in shape, the apex of the triangle being posterior. 



A further study of comparative anatomy shows that the 

 vermis and the cerebellar hemispheres in man develop in 

 inverse ratio to the same in the animals. In fishes the 

 cerebellum begins with the formation of the vermis, while in 

 birds and mammals the hemispheres are developed at the cost 

 of the vermis. In the lower mammals the cerebellum gradually 

 becomes circular in shape, owing to the increasingly lateral 

 position of the hemispheres ; in the higher mammals it in- 

 creases in breadth, and finally, in the apes and man, attains 

 its characteristic transverse expansion. Huschke 2 gives the 

 following figures for the proportion of the vermis to the 

 hemispheres : 



Otter . . 2 5 '6 / vermis 74-4 / hemispheres. 



Pig 32'8 67-2 



Dog . 39-42 61-58 



Fox . . 437 56-3 



Horse . 45-54 55-46 



Cat . 47-51 53-49 



Goat . 50 50 



In the anthropoids the cerebellum usually projects from under 

 the margins of the occipital lobes, owing to the cerebellum being 

 particularly broad, but in man this rarely occurs. On the other 

 hand, the vermis of the human cerebellum is invariably more 

 perfectly developed than that of the anthropoids. 



The thickness and curve of the corpus callosum (see Fig. 81) 

 bears an exact proportion to the height and curve of the cere- 



1 Huschke, loc. cit., p. 85. *Ibid., p. 77. 



