384 HABITUAL ACTIONS : FUNCTION OF CEREBELLUM. 



tically conducted to a place very different from that to 

 which, he had intended going. So, again, we may read 

 aloud, or play on a musical instrument, without being at all 

 aware of what we are about, the whole attention being ab- 

 sorbed by some engrossing thoughts or feelings within. And 

 it seems to be in this manner that the movements of Som- 

 nambulists are guided; their Cerebrum being, as it were, 

 cut-off from communication with the outer world, and their 

 Sensory Ganglia acting independently of it. 



Function of the Cerebellum. Combination of Muscular Actions. 



480. Much discussion has taken place of late years respect- 

 ing the uses of the Cerebellum ; and many experiments have 

 been made to determine them. That it is in some way con- 

 nected with the powers of motion, is now generally admitted. 

 Its size in the different tribes of Yertebrated animals bears a 

 pretty close correspondence with the variety and energy of 

 the movements performed by them ; being greatest in those 

 animals which require the constant united effort of a large 

 number of muscles to maintain their usual position, whilst it 

 is least in those which require no muscular exertion for this 

 purpose. Thus in animals that habitually rest and move upon 

 four legs, there is but little occasion for any organ to combine 

 and harmonize the actions of their several muscles ; and in 

 these the Cerebellum is small. But among the more active 

 predaceous Fishes (as the Shark), Birds of most powerful 

 and varied flight (as the Swallow, which not only flies rapidly, 

 but executes the most complicated evolutions in pursuit of its 

 Insect prey with the greatest facility), and Mammals which 

 can maintain the erect position and use their extremities for 

 other purposes than support and motion, we find the Cere- 

 bellum of much greater size : whilst in Man, who surpasses 

 all other animals in the number and variety of the combina- 

 tions of muscular movement which he is capable of executing, 

 it attains its largest dimensions and its greatest complexity of 

 structure. 



481. From experiments upon all classes of Vertebrated 

 Animals, it has been found that, when the Cerebellum was 

 removed, the power of walking, springing, flying, standing, 

 or maintaining the equilibrium of the body, was destroyed. 

 It did not seem that the animal had in any degree lost volun- 



