THE CEREBELLUM. 249 



which serves to bring optic stimuli into relation with cutaneous. 

 The cerebellum is no longer a purely cutaneous center, but im- 

 pulses may be sent out from it in response to retinal stimuli also. 

 The development of special functions has not gone far in the 

 selachians, for removal of the cerebellum alone in the dogfish does 

 not produce visible effects on locomotion (Bethe). In combined 

 operations on the cerebellum and other parts of the brain, how- 

 ever, it is shown that the cerebellum plays some part in the 

 coordination of movement. 



With the disappearance of lateral line organs in land amphibia 

 the cerebellum is greatly reduced in size. The reduction affects 

 chiefly the primary sensory center, and from the amphibia onward 

 the relations of the cerebellum with other brain centers increase. 

 The fibers from other brain centers end chiefly in the dorso-median 

 and cephalic regions of the cerebellum and in higher vertebrates 

 the vermis and adjacent parts of the hemispheres are developed 

 from these regions. Fibers come to these parts from the primary 

 and secondary nuclei of the cutaneous, vestibular and cochlear 

 nerves, and from the inferior olive, the nuclei of the pons and 

 perhaps other sources. The fibers which go out from the cere- 

 bellum make direct or indirect connections with nearly the whole 

 range of motor nuclei^ probably both somatic and visceral. 



It is reasonable to suppose that the presence of the somatic 

 pallium in mammals has influenced the evolution of function of 

 the cerebellum. In fishes and perhaps in amphibia and reptiles 

 the cerebellum and the roof of the mesencephalon share between 

 them the functions of higher centers to which somatic sensory 

 impulses of the second and third orders are sent and from which 

 impulses go out to control complex motor responses. In mammals 

 these impulses are carried to the neopallium, which has taken on 

 the direction of all voluntary movement. What then is the 

 function of the cerebellar cortex? Disease of the cerebellum 

 in man and its extirpation in animals always results in disturbances 

 of voluntary muscular action. Animals from which one hemi- 

 sphere or the whole cerebellum has been removed are unable to 

 stand or walk until they have learned to make compensatory 

 efforts. Does the cerebellum have the special function of main- 



