THE BRAIN 705 



tudinal bundle; (2) in the middle peduncle to the nucleus pontis of 

 the opposite side; (3) in the superior peduncle to the red nucleus, 

 superior corpus quadrigeminum, and third nucleus and optic thalamus 

 of the opposite side (the first neuron of the cerebello-cerebral path). 



The Functions of the Cerebellum. The cerebellum was credited 

 by Gall, the founder of phrenology, with the control of the organs of 

 generation. To this day the bump of philoprogenitiveness is placed 

 in the skull above the cerebellum. We now know that the cerebellum 

 has nothing whatever to do with this function. 



Comparative anatomy indicates the chief function of the cere- 

 bellum. In a variety of skate which lies at the bottom of the sea, 

 and practically does not move, the cerebellum is almost absent; in 

 the common variety, which swims about in search of food, it is well 

 marked. All strong-swimming fish and hard-flying birds have a well- 

 developed cerebellum. The cerebellum is therefore indicated as the co- 

 ordinating centre for muscular movements, especially for those of 

 equilibration. When half the cerebellum is cut away, the animal is 1 

 at first quite unable to stand, any attempt to do so causing it to fall to 

 the side of the lesion. There is only slight loss of power of the muscles 

 (asthenia), but marked loss of tone (atonia). After a week or two 

 it recovers the power to stand, although the limbs droop owing to 

 the loss of power and tone ; but its power of equilibration is so imper- 

 fect that in walking the limbs have to be widely abducted in order 

 to correct the tendency to fall to the side of the lesion. The con- 

 tractions of the muscles during such a purposive movement are 

 attended by tremors (astasia). If such an animal be excited, it will 

 fall toward the side of the lesion, and turn completely over. This is 

 particularly well seen in monkeys. After some weeks the symptoms 

 disappear. This is due to a cerebral compensation. Destruction of 

 the cerebral cortex of the opposite side leads to a reappearance of the 

 symptoms. It takes a much longer time to recover from extirpation 

 of the whole cerebellum, and even then the mode of progression is 

 not normal. Owing to the fear of falling during diagonal movements, 

 the animal performs galloping movements with the limbs wide apart. 

 This ataxia presents marked difference from the high-stepping ataxia 

 due to overaction of the muscles in spinal lesions. 



In man, lesions of the cerebellum may, or may not, show symptoms 

 according to the rapidity of onset. When symptoms are present, 

 there is the staggering ataxia, the marked tremors, and, if placed on 

 all fours, the tendency to turn over on the side of the lesion. In 

 many cases, however, where a cerebellar tumour has been found 

 after death, there have been no marked symptoms, owing probably 

 to the concomitant acquirement of cerebral control. 



Stimulation experiments have also been conducted upon the cere- 

 bellar cortex. This is difficult to excite., but thus far the experiments 

 indicate that the roof nuclei are particularly concerned in the move- 

 ments of the eyes and head, the lateral nuclei with the movements of 

 the trunk and limbs. 



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