FUNCTIONS OF THE CEREBELLUM 867 



replaced by those of an entirely different nature. The pigeon may reac- 

 quire the power of flying straight, or and this is particularly important 

 the dog mav reacquire the power of apparently normal progression, al- 

 though, if its muscular movements are carefully examined by physiological 

 methods, it will be found that at least three changes have developed as a 

 late result of the extirpation ; namely, a weakness of contraction, a tremor 

 during the contraction, and a want of tone when at rest. These condi- 

 tions have been called asthenia, atonia and astasia, respectively. On 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 the cerebellar 

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

 compared with the normal side. In a dog that has had one cerebellar 

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

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

 ianimal, in order to retain his equilibrium, has to prop himself up either 

 by leaning against whatever object may be convenient, or by extending 

 his legs so as to increase his base of support. In other words, he constantly 

 tends 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 gait can be 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 

 trot along a piece of glazed paper blackened with a carbon deposit as 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 muscles, 

 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 cere- 

 bral cortex. One cause for the backward state of our knowledge concern- 

 ing cerebellar localization is that, unlike the cerebrum, its cortex is 

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

 anatomic and partly of experimental and clinical work a high degree of 

 localization has been found to exist in the cerebellum. From the anatomical 

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

 the ungulata, the postero-medial lobule of the cerebellum is very large, 

 whereas the lobuli ansiformes are small. In another group, the carnivora, 

 the opposite obtains, the lobuli ansiformes being greatly developed and the 

 postero-medial lobule quite small. 



