THE CEREBELLUM. 



2 3 I 



ary gustatory nucleus and it is probable that the nucleus has 

 invaded the valvula along the commissure. The dorsal limb of 

 the valvula is thin and belongs to the tectum mesencephali. The 

 arrangement of tracts related to the gustatory nucleus in a ganoid 

 is shown in Figure 117. 



The cerebellum in the higher classes of vertebrates does not 

 continue to increase in size and complexity as it does through 

 the several classes of fishes. On the contrary, in amphibia and 

 reptiles it is relatively very small, owing to the comparatively 



^^omm.inf.cerebelli 

 Valvula, 



Tectun V-vn :.^ A/, , 



:. gustatory nuc. 



,Rad. mesenc. V 



! Tr. spin.V 

 Sec. gust, tract 



Jrachium a^uTS^-^ sys ' 



L. inferior) Tertiary gustatory tract 



FIG. 117. The relations of the cerebellum, brachium conjunctivum and gusta- 

 tory tracts in a ganoid fish (Acipenser). Projection on the median plane. 



sluggish habits of these animals and the consequent reduction 

 in the number of cutaneous and gustatory sense organs. The 

 reduction of the cerebellum in amphibia as compared with selach- 

 ians is chiefly a decrease in size only. The somatic sensory portion 

 constitutes lateral lobes which are simply arched over the ventricle, 

 not folded, but in these the typical granular and molecular layers 

 and Purkinje cells are as clearly marked as in selachians. Simi- 

 larly the secondary visceral nuclei are present in the lateral walls 

 but no valvula is developed. The size of the cerebellum is closely 

 related to the degree of activity of the animals. In active forms 



