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



scarcely less valuable or suggestive on this account, since the 

 functions of the Cerebellum, like its ultimate structure, are pro- 

 bably uniform in kind throughout all classes of the Yertebrata. 



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

 that the Optic Lobes of Fishes are brought into immediate relation 

 with their rudimentary Cerebellum. 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 Cms, 

 decussate beneath the Corpora Quadrigemina, and thence proceed 

 in a slightly divergent direction to the anterior portion of the 

 Cerebellum. It is highly probable, therefore, that in Man also 

 these Upper Peduncles in part serve to bring the Optic Centres 

 into relation with the Cerebellum. 



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

 the Fifth Nerve or * Trigeminus,' lies on the iipper and outer 

 border of this Upper Peduncle, and a portion of the root of the 

 Auditory 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 

 Auditory) come into relation with the Cerebellum through its 

 Upper Peduncles. 



But it seerns possible that the various cortic al ' 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 Tegmentuui and the Upper Cerebellu r 

 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. 



