1815.) Intellectual Functions of Man and Animals. 31 
7. This truth receives new confirmation when we observe, that 
the degrees of voluntary power always bear a close analogy to the 
various magnitudes of the cerebellum. In fishes, for instance, 
which possess amazing locomotive power, the cerebellum is often 
larger than the cerebrum; and they sometimes possess an addi- 
tional tubercle, which seems to Cuvier to form a second cere- 
bellum ! 
In the statement of these reasons, Dr. Leach will find obviated 
any quibble which might be founded on the various meanings of the 
word ‘ opposite’ which, for the sake of brevity, I formerly used. 
They will also enable the reader to correct Dr. Cross’s representation 
of them. 
Dr. Leach, then, endeavours to prove, that there is no propor- 
tion between the various magnitudes of the cerebellum and the 
degrees of voluntary power.—The cerebellum, he says, is propor- 
tionally smaller in children than in the adult, and yet children have 
more of muscular agility than adults. Now, if by agility Dr. 
Leach means that their voluntary powers are stronger, I unhesitat- 
ingly deny it; and if he do not mean this, his example is inappli- 
cable: the truth is, he does not take into consideration the eva- 
nescent action of children and the permanent and sustained action 
of adults.—A shark, he says, which has the greatest locomotive 
power, has a remarkably minute cerebellum. Now this instance is 
as inapplicable as the last ; for I have nowhere asserted the greater 
absolute magnitude of the cerebella of fishes; but have, in distinct 
terms, asserted their greater. proportional magnitude—The same 
answer applies to Dr. Leach’s third example of the swallow. 
That, contrary to Dr. Leach’s assertion, this is a * general prin- 
ciple,” is sufficiently proved by this, that if our considerations be 
general—if we compare the cerebella of birds with those of quad- 
rupeds, we find the former larger in proportion to the brain con- 
sistently with their more intense, frequent, and rapid voluntary 
motion ; and if we compare the cerebella of fishes with those of 
birds, we find the former, in both these respects, excel the latter. 
But if we enter into more particular examinations—if we compare 
these parts in the genera and species of animals, as Cuvier has 
done, our observations must be more particular than his—we must 
attend not only to the general magnitude of the organs, but to their 
particular form; for (L now repeat an important fact which I, prior 
I believe to any other person, announced some years ago,) “ on the 
length of the cerebral organs depends the intensity of their func- 
tion, and on the breadth of these organs the permanence of their 
function.” As liquids pass with greater velocity through the narrow 
portion of a tube than through its wider parts, precisely so must all 
nervous action pass between the parietes of the organs—the tubes 
of the neurilema, whether that action be performed by fluids, by 
liquids, or by globules, as proved by Prochaska and others. That 
the nervous matter is thus laterally confined by the neurilema, is 
proved by the circumstance of the ends of nerves expanding when 
