THE CEREBELLUM, AND ITS FUNCTIONS. 675 



great variety of purposes, still more, in proportion as the animal becomes 

 capable of maintaining the erect posture, in which a constant muscular ex- 

 ertion, consisting of a number of most elaborately combined actions, is re- 

 quired, do we find the size of the Cerebellum, and the complexity of its 

 structure, undergoing a rapid increase. Thus, even between the Dog and 

 the Bear there is a marked difference ; the latter being capable of remaining 

 for some time in the erect posture, and often spontaneously assuming it; 

 whilst to the former it is anything but natural. In the semi-erect Apes, 

 again, there is a very great advance in the proportional size of the Cerebel- 

 lum ; and those which most approach Man in the tendency to preserve ha- 

 bitually the erect posture also come nearest to him in the dimensions of this 

 organ. Thus on looking at the size of the Cerebellum, in relation to the 

 general motor activity of the Vertebrated classes respectively, and especially 

 taking into account the variety of their respective movements, and the num- 

 ber of separate muscular actions which are combined in each, we can scarcely 

 help noticing that it is in the tribes which are most distinguished in these 

 respects, that the largest Cerebellum is usually found. Now it is evident 

 that Man, although far inferior to many of the lower animals in the power 

 of performing various particular kinds of movement, far surpasses them all 

 in the number and variety of the combinations which he is capable of exe- 

 cuting, and in the complexity of the combinations themselves. Thus, if we 

 attentively consider the act of walking, we shall find that there is scarcely a 

 muscle of the trunk or extremities which is not actively concerned in it; 

 some being engaged in performing the necessary movements, and others iu 

 maintaining the equilibrium of the body which is disturbed by them. Ou 

 the other hand, in the Horse or Camel, the muscular movements are indi- 

 vidually numerous, but they do not require nearly the same perfect co-ordi- 

 nation. And in the Bird, the number of muscles employed in the movements 

 of flight, and iu directing the course of these, is really comparatively small ; 

 as may at once be perceived, by comparing the rigidity of the skeleton of the 

 trunk of the Bird with that of Man, and by remembering the almost com- 

 plete inactivity of the lower extremities during the active condition of the 

 upper. In fact, the motions of the wings are so simple and regular, as to 

 suggest the idea, that, as in Insects, their character is more reflex than vol- 

 untary, an idea which is supported by the length of time during which 

 they can be kept up without apparent fatigue, and also by the important 

 facts already mentioned ( 524), which experimental research has disclosed. 

 548. We have next to inquire what evidence can be drawn from Experi- 

 mental investigations on the same subject; and in reference to this it is de- 

 sirable to remark, in the first place, that the experimental mode of inquiry is 

 perhaps more applicable to this organ than to other parts of the Encephalou, 

 inasmuch as it can be altogether removed with little disturbance of the ac- 

 tions immediately essential to life, the animals soon recovering from the 

 shock of the operation, and seeming but little affected except in some easily 

 recognized particulars. The principal experimenters upon this subject have 

 been Rolando, Flourens, Magendie, Hertwig, Louget, Schiff, Browu-Sequard, 

 and Wagner. It is not to be expected that there should be an exact con- 

 formity among the results obtained by all. Every one who has been engaged 

 in physiological experiments is aware of the amount of difference caused by 

 very minute variations in their circumstances; in no department of inquiry 

 is this more the case, than in regard to the Nervous System ; and such dif- 

 ferences are yet more likely to occur in experiments made upon its centres, 

 than in those which concern its trunks. The investigations of Flourens 1 



1 Kecherches Experim. sur les Proprietes et les Fonctions du Systferne Nerveux. 



