Chap. XXIV.] PRINCIPAL PARTS OF THE BRAIN. 505 



scarcely less valuable or suggestive on this account, since the func- 

 tions of the Cerebellum, like its ultimate structure, are probably 

 uniform in kind throughout all classes of the Vertebrata. 



By means of the Upper Peduncles there is good reason to believe 

 that the Optic Lobes of Fishes are brought into immediate relation 

 witli their rudimentary Oerebellum. The fibres constituting these 

 peduncles pass from the septum between the Optic Lobes to the 

 median portion of the Cerebellum. In Man the same peduncles, 

 starting from the ' red nucleus ' in the sensory tract of the Crus, 

 decussate beneath the Corpora Quadrigemina, and thence proceed 

 in a slightly divergent direction to the anterior portion of the Cere- 

 bellum. It is highly probable, therefore, that in Man also these 

 Upper Peduncles in part serve to bring the Optic Centres into rela- 

 tion with the Cerebellum. 



Again, according to Meynert,* a portion of the great root of the 

 Fifth Nerve or ' Trigeminus,' lies on the upper and outer border of 

 this Upper Peduncle, and a portion of the root of the Auditoi-y 

 Nerve is similarly disposed. In some Fishes the ganglion at the 

 root of the Fifth Nerve is, according to Owen, directly connected, 

 by means of some vertical fibres, with the Cerebellum. 



Thus, though almost nothing is known as to any relations of the 

 Olfactory Lobe with the Cerebellum, it seems certain that the next 

 three sensory cranial nerves (viz., the Optic, the Fifth and the Au- 

 ditory) come into relation with the Cerebellum through its Upper 

 Peduncles. 



But it seems possible that the various cortical ' Perceptive Cen- 

 tres ' in the Cerebral Hemispheres, may also be brought into rela- 

 tion with the Cerebellum, by internuncial fibres passing through 

 the 'red nucleus' of the Tegmentum and the Upper Cerebellar 

 Peduncles. In such a case, these fibres might convey ' afferent ' 

 stimuli in relation with Ideo-Motor and Voluntary Movements, 

 whilst those coming to it from Sensory Nerves or their Ganglia 

 may convey 'afferent' stimuli capable of evoking movements which 

 have become ' automatic ' or which are of the ' secondary-automatic ' 

 order. Other fibres, however, next to be referred to, seem also to 

 belong to this latter category. Whether the Upper Peduncles con- 

 tain afferent fibres only, we have no means at present of deciding. 



Each Lower Peduncle of the Cerebellum in Fishes is in close 

 relation with the two ' visceral ' sensory nerves, viz., the Vagus and 

 * Strieker's "Histology," vol. ii. p. 460. 



