732 OF THE FUNCTIONS OF THE NERVOUS SYSTEM. 



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 Cerebellum ; and those 

 Vhich most approach Man in the tendency to preserve habitually the erect 

 posture, also come nearest to him in the dimensions of this organ. 



762. 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 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 actively 

 concerned in it ; some being engaged in performing the necessary 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 muscular movements 

 are individually numerous, but they do not require nearly the same perfect co- 

 ordination. And in the Bird, the number of muscles employed in the move- 

 ments 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 with 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 automatic 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 facts already mentioned, 

 which experimental research has disclosed ( 734). 



763. We have next to inquire what evidence can be drawn from Experimental 

 investigations on the same subject : and in reference to this it is desirable 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 Encephalon ; inasmuch as it can 

 be altogether removed, with little disturbance of the actions immediately essen- 

 tial to life ; and the animals soon recover from the shock of the operation, and 

 seem but little affected, except in some easily recognized particulars. The prin- 

 cipal experimenters upon this subject have been llolando, Flourens, Magendie, 

 Hertwig, and Longet. It is not to be expected that there should be an exact 

 conformity among the results obtained by all. Every one who has been en- 

 gaged 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 differ- 

 ences are yet more likely to occur in experiments made upon its centres than 

 in those which concern its trunks. The investigations of Flourens are the 

 most clear and decisive in their results ; and of these we shall accordingly take 

 a general survey. He found that, when the Cerebellum was mechanically in- 

 jured, the animals gave no signs of sensibility, nor were they affected with 

 convulsions. When the Cerebellum was being removed by successive slices, 

 the animals became restless, and their movements were irregular ; and by the 

 time that the last portion of the organ was cut away, the animals had entirely 

 lost the power of springing, flying, walking, standing, and preserving their 

 equilibrium, in short, of performing any combined muscular movements which 

 are not of a simply reflex character. When an animal in this state was laid 

 upon the back, it could not recover its former posture ; but it fluttered its wings, 

 and did not lie in a state of stupor. When placed in the erect position, it 

 staggered and fell like a drunken man not, however, without making efforts 

 to maintain its balance. When threatened with a blow, it evidently saw it, and 

 endeavored to avoid it. It did not seem that the animal had in any degree 

 lost voluntary power over its several muscles ; nor did sensation appear to be 

 impaired. The faculty of combining the actions of the muscles in groups, 



