vm THE HIND-BRAIN 451 



in monkeys than in dogs, so that in the tracing the foot- 

 prints of the hind -limbs always fall in front of those of the 

 fore-limbs (Fig. 236). The animal deviates from side to side in 

 walking, making an undulating line, and if it falls to right or left 

 this is always due to the giving way of one or both hind-limbs, 

 in which atony is predominant. In comparison with a normal 

 monkey, it moves more slowly, and from time to time feels obliged 

 to rest, sitting on its buttocks. 



The astasia is most prominent in the neck, but spreads more 

 or less to all the other muscles, as shown by the slight trembling 

 of the limbs each time they are used for isolated movements, as 

 to carry fruit to the mouth, to catch the insects in the hair, etc. 



In monkeys, too, the limbs are raised unduly in walking 

 (dysmetria), owing to disturbed functions of the organs charged 

 with the compensatory processes. This dysmetria is certainly 



FIG. 236. Male Macacus in which nearly the whole of the cerebellum was extirpated at one 

 sitting. (Luciani.) b, tracing obtained one and a half months after the operation ; c, tracing 

 taken after a yeai . 



not sensory in origin, because cutaneous and muscular sensibility 

 are not found, with the various methods of investigation which 

 can be employed on animals, to be appreciably disturbed. If 

 total extirpation of the cerebellum is performed on an animal 

 which has previously been deprived of the signioid gyri, which 

 contain the senso-motor area, or if, vice versa, these are excised 

 in an animal that has already lost its cerebellum, it remains 

 for the rest of its life incapable, not only of walking, but 

 even of supporting itself for a few moments in the erect posture. 

 This depends less on the fact that the motor defect phenomena 

 are much greater in this case, because those which depend on the 

 absence of the cerebellum sum up with the others which are due 

 to deficiency of the two cerebral areas, than on the removal of the 

 sigmoid gyri, which disturbs cutaneous and muscular sensibility ; 

 the animal consequently loses the power of compensation by which 

 it widens its base of support to save itself from falling. 



Between the two extreme typical forms of cerebellar ataxy 

 described, which are due to the total or almost total absence of half 



