FUNCTIONS OF THE CEREBELLUM. 190 



scarcely discoverable : their motion being, like that of the Articulata, almost 

 entirely of a reflex character, each segment being influenced by its own 

 ganglionic centre, and the Spinal Cord constituting by far the largest propor- 

 tion of the nervous centres. On looking at the class of Birds, we observe 

 that the active predaceous Falcons, and the swift-winged Swallows (the per- 

 fect control possessed by which over their complicated movements must hav% 

 been observed by every one), have a Cerebellum much larger in proportion, 

 than that of the Gallinaceous birds, \vhose powers of flight are small, or than 

 that of the Struthious tribe, in which they are altogether absent. Lastly, on 

 comparing its proportional size in the different orders of Mammalia, with the 

 number and variety of muscular actions requiring combined movements, of 

 which they are respectively capable, we observe an even more remarkable 

 correspondence. In the hoofed Quadrupeds, in which the muscular appara- 

 tus of the extremities is reduced to its greatest simplicity, and in which the 

 movements of progression are simple, the Cerebellum is relatively smaller 

 than it is found to be in some Birds ; but in proportion as the extremities 

 acquire the power of prehension, and together with this a power of applica- 

 tion to a great variety of purposes, still more, in proportion as the animal 

 becomes capable of maintaining the erect posture, in which a constant mus- 

 cular exertion, consisting of a number of most elaborately combined parts, is 

 required, do AVC 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 any thing 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 

 habitually the erect posture, also come nearest to him in the dimensions of 

 this organ. Now it is evident that Man, although far inferior to many of the 

 lower animals, in the power of performing various particular kinds of move- 

 ment, far surpasses them all in the number and variety of the combinations 

 which he is capable of executing, and in the complexity of the combinations 

 themselves. Thus, if we attentively consider the act of walking in man, we 

 shall find that there is scarcely a muscle of the trunk or extremities which is 

 not actually concerned in it, some being engaged in performing the neces- 

 sary movements, and others in maintaining the equilibrium of the body, which 

 is disturbed by them. On the other hand, in the Horse or Camel, the mus- 

 cular movements are individually numerous, but they do not require nearly 

 the same perfect co-ordination. And in the Bird, the number of muscles em- 

 ployed in the movements of flight, and in 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 w r ith that of Man, and by 

 remembering the complete 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 directly voluntary : 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 fact already mentioned, wfiich experimental research has dis- 

 closed ( 284). It is seen, then, that Comparative Anatomy fully confirms 

 the idea, which Experimental physiology suggests, respecting the chief func- 

 tions of the Cerebellum. 



271. Some of Magendie's experiments indicate a further connection of this 

 organ with the motor function, the nature of which is still obscure. This phy- 

 siologist asserts that, if a wound be inflicted on the Cerebellum, the animal 

 seems compelled by an inward force to retrograde movement, although making 



