Relations of Mind and Organization
We may safely assume, as an established fact, that it is only through the instrumentality of the central parts of the nervous system that the Mind maintains its communication with the external world. The eye is necessary to sight, and the ear to hearing; and so with the other organs of sense. But the eye does not see, and the ear does not hear; and if the nerve which forms the communication between any one organ of sense and the brain be divided, the corresponding sense is destroyed. In like manner it is from the brain that all those impulses proceed by which the mind influences the phenomena of the external world. The division of the nerves which extend from the brain to the larynx destroys the voice. The division of the nerves of a limb causes the muscles of the limb to be paralysed, or, in other words, withdraws them from the influence of the will; the division of the spinal cord destroys at once the sensibility and the power of voluntary motion in all the parts below that at which the division has been made.
The brain has a central organ, which is a continuation of the spinal cord, and to which anatomists have given the name of medulla oblongata. In connexion with this there are other bodies placed in pairs. That each of these bodies has its peculiar functions there cannot be the smallest doubt; and it is, indeed, sufficiently probable that each of them is not a single organ, but a congeries of organs having distinct and separate uses.
Experimental physiology, joined with the observation of the changes produced by disease, has thrown some light on this mysterious subject. There is reason to believe that, whatever it may do besides, one office of the cerebellum is to combine the action of the voluntary muscles for the purpose of locomotion. The corpora quadrigemina are four tubercles which connect the cerebrum, cerebellum, and medulla oblongata to each other. If one of the uppermost of these bodies be removed, blindness of the eye of the opposite side is the consequence. If the upper part of the cerebrum be removed, the animal becomes blind, and apparently stupified, but not so much so but that he can walk with steadiness and precision. The most important part of the whole brain seems to be one particular part of the central organ, or medulla oblongata. While this remains entire, the animal retains its sensibility, breathes, and performs instinctive motions. But if this very minute portion of the nervous system be injured, there is an end of these several functions, and death immediately ensues.
These facts, and some others of the same kind, for a knowledge of which we are indebted to modern physiologists, and more especially to M. Magendie and M. Flourens, are satisfactory as far as they go; and warrant the conclusion that there are various other organs in the brain, designed for other purposes, and that if we cannot point out their locality, it is not because such organs do not exist, but because our means of research into so intricate a matter are very limited.—Sir B. Brodie’s Psychological Inquiries.