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 
alond, 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 Yertebrated 
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 - 
