IP THE CEREBELLUM 867 



replaced by those of an entirely different nature. The pigeon may r< 

 qnire the power of flying straight, or and this is particularly importanl 

 the dog may reacquire the power of apparently normal pr< ion, al- 

 though, it' its muscular movements are carefully examined by physiological 

 methods, it will be found that at leasl three changes hav< 

 late resull of the extirpation; namely, a weakness of co tion, a tremor 

 during the contraction, and a want of tone when at pest. Th< mdi- 

 tiona have been called asthenia; atonia and astasia, res] tively. <>n su- 

 perficial examination it may often be difficult to make out these three con- 

 ditions, but they can readily be observed in animals in which tli pebellar 



extirpation has been performed on one side, so that the abnormal may be 

 compared with the normal Bide. In a dog that has had one Mar 



hemisphere removed some time previously, the muscles "-, the correspond- 

 ing side are so much weaker than those on the opp side that the 

 animal, in order to retain his equilibrium, lias to prop himself up 

 by leaning against whatever objecl may he convenient, or by extending 

 his legs so as to increase his base of support. In other words, 1.-' constantly 

 lends to fall to the side of the lesion, but tries to prevent this either by 

 increased muscular effort or by taking advantage of artificial support. 

 The effect which this weakening has on his <_rait ran he very clearly demon- 

 strated by comparing the footprints produced by the normal with those of 

 the abnormal side, these footprints being obtained by making the animal 

 trut along a piece of glazed paper blackened with a carbon de] - in 

 taking tracings (Fig. 222). 



Localization of Function in the Cerebellum 



Although these facts in themselves would tend to indicate a certain de- 

 gree of localization of function in the cerebellum, or at least that certain 

 parts of the cerebellar cortex have to do with certain groups of muse 

 yet for many years it was considered that the cerebellum did not show in 

 any marked degree the same kind of localization that we find in the e 

 bral cortex. One cause for the backward state of our knowledgi jern- 

 ing cerebellar localization is that, unlike I rebrum, its cortex is 



practically inexcitable. In recent years, however, on account partly of 



anatomic and partly of experimental and clinical work a high d« _ 

 localization has 1 n found to exist in th pcbellum. Prom the anatomical 



point of view it has been found that in certain groups of animals, such as 



the nngulata, the postero-medial lobule of the cerebellum is very la 



whereas the lobuli ansiformes are small. In another grou] earnivi 



the opposite obtains, the lobuli ansiformes being oped and 

 postero medial lobule quite small. 



