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most of those nerves which confer motion and bestow sensibility. To confirm this opinion, he cut across the posterior branch, or that which has a ganglion, on the face of an ass, and it was found that the sensibility of the parts to which it was distributed was entirely destroyed. Again, he exposed the anterior branch of the fifth pair at its root, in an ass, the moment the animal was killed ; and on irritating the nerve, the muscles of the jaw acted, and the jaw was closed with a snap. On dividing the root of the aerve in a living animal, the jaw fell relaxed. Thus its functions were no longer matter of doubt : it was at once a muscular nerve and a nerve of sensibility. And thus the opinion was confirmed, that the fifth nerve was to the head, what the spinal nerves were to the other parts of the body.
The muscles have two nerves, which fact had not been noticed previously to Mr. Bell's investigations, because they are commonly bound up together ; but whenever the nerves, as about the head, go in a separate course, we find that there is a sensitive nerve and a motor nerve distributed to the muscular fibre, and we have reason to conclude that those branches of the spinal nerves which go to the muscles, consist of a motor and a sensitive filament. The nerve of touch or feeling, ramified on the skin, is distinct from both.
It was formerly supposed that the office of a muscular nerve is only to carry out the mandate of the will, and to excite the muscle to action; but this betrays a very inaccurate knowledge of the action of the muscular system ; for before the muscular system can be controlled under the influence of the will, there must be a consciousness or knowledge of the condition of the muscle.
When we admit that the various conditions of the muscle must be estimated or perceived, in order to be under the due control of the will, the natural question arises, Is that nerve which carries out the mandate of the will, capable of conveying, at the sarne moment, an impression retrograde to the course of that influence, which, obviously, is going from the brain towards the muscle ? If we had no facts of anatomy to proceed upon, still reason would declare to us, that the same filament of a nerve could not convey
a motion, of whatever nature that motion may be, whether vibration or motion of spirits, in opposite directions, at the same moment of time.
Mr. Bell has found, that, to the full operation of the muscular power, two distinct filaments of nerves are necessary, and that a circle is established between the sensorium and the muscle : that one filament or simple nerve carries the influence of the will towards the muscle, which nerve has no power to convey an impression backwards to the brain ; and that another nerve connects the muscle with the brain, and, acting as a sentient nerve, conveys the impression of the condition of the muscle to the mind, but has no operation in a direction outward from the brain towards the muscle, and does not therefore excite the muscle, however irritated.
There are four nerves coming out of a track or column of the spinal marrow, from which neither the nerves of sensation, nor of common voluntary inotion, take their departure. Experiment proves that these nerves excite motions dependent on the act of respiration.
Under the class of respiratory motions, we have to distinguish two kinds: first, the involuntary, or instinctive ; secondly, those which accompany an act of volition. We are unconscious of that state of alternation of activity and rest which characterises the instinctive act of breathing in sleep; and this condition of activity of the respiratory organs, we know by experiment, is independent of the brain. But, on the other hand, we see that the act of respiration is sometimes an act of volition, intended to accomplish some other operation, as that of smelling or speaking. Mr. Bell apprehends that it is this compound operation of the organs of breathing which introduces a certain degree of complexity into the system of respiratory nerves. A concurrence of the nerves of distinct systems will be found necessary to actions, which, at first sight, appear to be very simple.
If we cut the division of the fifth nerve, which goes to the lips of an ass, we deprive the lips of sensibility; so that, when the animal presses the lips to the ground, and against the oats lying
there, it does not feel them; and consequently there is no effort made to gather them. If, on the other hand, we cut the seventh nerve, where it goes to the lips, the animal feels the oats, but it can make no effort to gather them, the power of muscular motion being cut off by the division of the nerve. Thus we perceive that, in feeding, just as in gathering any thing with the hand, the feeling directs the effort; and two properties of the nervous system are necessary to a very simple action.
After the investigation of the regular system of nerves of sensation and voluntary motion, the question that had so long occupied Mr. Bell, viz. What is the explanation of the excessive intricacy of the nerves of the face, jaws, throat, and breast? became of easy solution. These nerves are agents of distinct powers, and they combine the muscles in subserviency to different functions.
As animals rise in the scale of being, new organs are bestowed upon them ; and, as new organs and new functions are superadded to the original constitution of the frame, new nerves are given also, and new sensibilities, and new powers of activity.
Mr. Bell remarks, that we understand the use of all the intricate nerves of the body, with the exception of the sixth perve, which stands connected with another system of nerves altogether, namely, the system hitherto called the Sympathetic, or sometimes the Ganglionic System of Nerves; and of this system we know so little, that it cannot be matter of surprise, if we reason ignorantly of the connexion of ihe sixth with it.
PRINCIPLES OF PHRENOLOGY.
In the Introduction, I have shown that the Brain is admitted by Physiologists in general, to be the organ of the Mind; but that two obstacles have impeded the discovery of the uses of its particular parts. lst, Dissection alone does not reveal the functions of any organ. No person, by dissecting the optic nerve, could predicate that its office is to minister to vision; or, by dissecting the tongue, could discover that it is the organ of taste. Anatomists, therefore, could not, by the mere practice of their art, discover the functions of the different portions of the brain. 2dly, The mind is not directly conscious of acting by means of organs ; and hence the material instruments, by means of which it performs its operations in this life, and communicates with the external world, cannot be discovered by reflection on consciousness.
The phrenologist compares developement of brain with manifestations of mental power, for the purpose of discovering the functions of the brain, and the organs of the mind. This course is adopted, in consequence of the accidental discovery made by Dr. Gall, that certain mental powers are vigorously manifested, when certain portions of the brain are large, and vice versa, as detailed in the Introduction. It is free from the objections attending the anatomical and metaphysical modes of research, and conformable to the principles of inductive philosophy.
No inquiry is instituted into the substance of the Mind, or into the question, Whether the mind fashions the organs, or the organs constitute the mind ? If dissection of organs does not reveal their functions, and if reflection on consciousness does not disclose the nature of the mind's connexion with matter, no means remain of arriving at philosophical conclusions on these points ; and specula