352 FUNCTIONS OF THE NERVOUS SYSTEM. 



taming the equilibrium, being remarkably preserved after the loss of them 

 (435). 



461. Upon comparing these results with the preceding table, a remarkable 

 correspondence will be observed between them. The classes which have the 

 greatest variety of movements, and which require for them the most perfect 

 combination of a large number of separate muscular actions, have, taken col- 

 lectively, the largest Cerebellum. Of all classes of Vertebrata, Reptiles are 

 the most inert ; and their motions require the least co-ordination. The active 

 predaceous Fishes far surpass them in this respect ; and may be compared 

 with Birds, in the energy of their passage through the water, and in their 

 facility of changing their direction during the most rapid progression. The 

 Cerebellum, accordingly, bears to the Spinal Cord in them, very much the 

 same proportion as it does in Birds. On the other hand, the Flat Fish, which 

 lie near the bottom of the ocean, and which have a much less variety of move- 

 ment, have a very much smaller cerebellum : and the Vermiform Fishes, which 

 are almost all completely destitute of fins, and whose progression is accom- 

 plished by flexion of the body, have a Cerebellum so small as to be scarcely 

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

 a reflex character, each segment being influenced by its own ganglionic cen- 

 tre, and the Spinal Cord constituting by far the largest proportion of the nervous 

 centres. On looking at the class of Birds, we observe that the active preda- 

 ceous Falcons, and the Swift-winged Swallows (the perfect control possessed 

 by which over their complicated movements must have been observed by every 

 one), have a Cerebellum much larger in proportion than that of the Gallina- 

 ceous birds, whose powers of flight are small, or than that of the Struthious 

 tribe, in which they are altogether absent. Lastly, on comparing its propor- 

 tional size in the different orders of Mammalia, with the number and variety 

 of muscular actions requiring combined movements, of which they are respect- 

 ively capable, we observe an even more remarkable correspondence. In the 

 hoofed Quadrupeds, in which the muscular apparatus 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 application to a great variety of purposes, 

 still more, in proportion as the animal becomes capable of maintaining the 

 erect posture, in which a constant muscular exertion, consisting of a number 

 of most elaborately-combined parts, is required, 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 Cerebellum ; and those which most approach Man in the tendency 

 to preserve habitually the erect posture, also come nearest to him in the di- 

 mensions of this organ. 



462. 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 tea Ik in ^ 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 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 



