matter and cellular substance. The nervous matter exists in distinct threads, which are bound together by the cellular membrane. They may be likened to a bundle of hairs or threads, enclosed in a sheath composed of the finest membrane.

The figure represents a nerve greatly magnified, for the sake of illustra tion, and consisting of distinct filaments. A, the nerve, enveloped in its membranous sheath; B, one of the threads dissected out. The nerves vary in thickness from the diameter of a small thread to that of a whip-cord. They are dispersed through the body, and extend to every part which enjoys sensibility or motion, or which has a concatenated action with another part. The matter of a nerve in health and in the full exercise of its influence, is of an opaque white hue; it is soft and pulpy, between fluid and solid, and drops from the probe. When putrid, it acquires a green colour; when dried, it is transparent. Corrosive sublimate and muriate of soda harden it; alkalis dissolve it. Each fibril of a nerve is convoluted, and runs not in a straight line, but zigzag, like a thread drawn from a worsted stocking, which has by its form acquired elasticity that it would not otherwise have possessed. By want of use the matter of a nerve is either not secreted in due proportion, or changes its appearance; for the nerve then acquires a degree of transparency.

There is no evidence that any fluid or spirit circulates in the nerves; nor is there any that the nervous fibrils are tubes.

Nerves are supplied with arteries and veins, and their dependence on the supply of blood is proved by the fact, that, if a limb be deprived of blood, the nerves lose their powers, and sensibility is lost. If a nerve be partially compressed, so as to interrupt the free entrance of the blood into it, both the power over the muscles and the reception of sensation through it are interrupted; and when the blood is admitted again, painful tingling accompanies the change. It is not the compression of the tubes of a nerve, but the obstruction of its blood vessels, which produces the loss of power consequent on tying it. The brain, the nerves of the eye and the ear, the nerves of sense and motion, are all affected by changes in the circulation; and each organ, according to its natural function, is variously influenced by the same cause-the rushing of blood into it, or the privation of its proper quantity.

A nerve consists of distinct filaments; but there is nothing perceptible in these filaments to distinguish them from each other. One filament serves for the purpose of sensation; another for muscular motion; a third for combining the muscles when in the act of respiration. But the subserviency of any of all these filaments to its proper office must be discovered by following it out, and observing its relations, and especially its origin in the brain and spinal marrow. In their substance there is nothing particular. They all seem equally to contain a soft pulpy matter, enveloped in cellular membrane, and so surrounded with a tube of this membrane as to present a continuous track of pulpy nervous matter, from the nearest extremity in the brain to the extremity which ends in a muscle or in the skin. The key to the system will be found in the simple proposition, that each

filament or track of nervous matter has its peculiar endowment, independently of the others which are bound up along with it; and that it continues to have the same endowment throughout its whole length. There is no interchange of powers between the different filaments; but a minute filament of one kind may be found accompanying a filament of a different kind, each giving a particular power to the part in which it is ultimately distributed. Some nerves give sensibility; but there are others, as perfectly and delicately constituted, which possess no sensibility whatever. Sensibility results from the particular part of the brain which is affected by the nerve. If the eyeball is pressed, the outward integuments feel pain; but the retina gives no pain-only rings of light or fire appear before the eye. In the operation of couching the cataract, the needle must pierce the retina; the effect, however, is not pain, but to produce, as it were, a spark of fire and so an impression on the nerve of hearing, the papilla of taste, or the organ of any sense except feeling, does not produce pain. The sensation excited has its character determined by the part of the brain to which the nerve is related at its root. But there are nerves which have no relation to outward impression. There are nerves purely for governing the muscular frame these being constituted for conveying the mandate of the will, do not stand related to an organ of sense in the brain; hence no sensibility and no pain will be produced by them. Each of these may be said to be a nerve of exquisite feeling in one sense; that is, it may be a cord which unites two organs in intimate sympathies, so as to cause them to act in unison; yet, being bruised or injured, it will give rise to no perception of any kind, because it does not stand related to a part of the brain whose office it is to produce either the general impression of pain, or heat, or cold, or vision, or hearing: it is not the office of that part of the brain to which it is related to produce perception at all.

:

At the conflux of the nervous filaments small reddish tumours appear, which are named GANGLIONS-(See D, in fig., p. 67.) A ganglion resemples in form the circular swellings which appear on the stalk of a straw or of a cane; but ganglions do not rise at regular intervals on the nerves like these swellings. Ganglions are laid in a regular succession in the whole length of the body, and, in the vertebral animals, form a regular series down each side of the spinal marrow; the nerve of communication among them is the great sympathetic nerve. There are other ganglions seated in the head, neck, and cavities of the chest and belly, which are very irregular in their situation and form.

The colour of the ganglions differs from that of the nerves; it is redder, which is owing to the greater number of blood vessels: they consist of the same matter with the brain.

Wherever we trace nerves of motion, we find that, before entering the muscles, they interchange branches, and form an intricate mass of nerves, which is termed a PLEXUS. A plexus is intricate in proportion to the number of muscles to be supplied, and the variety of combinations into which they enter. The filaments of nerves which go to the skin, and have the simple function of sensation, regularly diverge to their destination without forming a plexus. From the fin of a fish to the arm of a man, the plexus increases in complexity in proportion to the variety or extent of motions to be performed in the extremity. It is by the interchange of filaments that combination among the muscles is formed.

Different columns of nervous matter combine to form the SPINAL MAR. ROW, (AB, p. 67.) Each lateral portion of the spinal marrow consists of three tracks or columns; one for voluntary motion, one for sensation, and one for the act of respiration. So that the spinal marrow comprehends in all six rods, intimately bound together, but distinct in office; and the capital of this compound column is the medulla oblongata.

The anterior column of each lateral division of the spinal marrow is for motion; the posterior column is for sensation; and the middle one is for respiration. The former two extend up into the brain, and are dispersed or lost in it; for their functions stand related to the sensorium: but the last stops short in the medulla oblongata, being in function independent of reason, and capable of its office independently of the brain, or when separated from it.

A B the spinal marrow seen in front; the division into lateral portions appearing at the line A B. The nervous cord C arises from the posterior lateral division, and gives sensibility. The swelling D is its ganglion. The nervous cord E arises from the anterior lateral division, and gives motion. It has no ganglion. These two cords combine at F, and proceed under one sheath to their destination.

Sir C. Bell struck a rabbit behind the ear, so as to deprive it of sensibility by the concussion, and then exposed the spinal marrow. On irritating the posterior roots of the nerve, he could perceive no motion consequent in any part of the muscular frame; but on irritating the anterior roots of the nerve, at each touch of the forceps there was a corresponding motion of the muscles to which the nerve was distributed. These experiments satisfied him that the different roots, and different columns from which those roots arose, were devoted to distinct offices, and that the notions drawn from the anatomy were correct.

He also performed certain interesting experiments on the fifth pair of nerves, which originates from the brain. In his Plate I. he represents this nerve rising from two roots, one of them coming from the crus cerebri, corresponding to the anterior column of the spinal marrow; and the other from the crus cerebelli, corresponding to the posterior column of the spinal marrow. There is a ganglion on the latter branch, and none on the former; which circumstance also is in exact correspondence with the nerves rising from the spinal marrow. The two branches combine at a short distance from their origin, and are universally distributed to the head and face. Sir C. Bell conceived that this nerve is the uppermost 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, 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 nerve 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 Sir C. 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 fibres; 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 same moment, an impression retrograde to the course of that influence, which, obviously, is going from the brain toward 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.

Sir C. Bell has found that, to the full operation of the muscular power, two distinct nervous filaments 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 toward the muscle, which nerve has no power to convey an impression backward 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 toward 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 those of common voluntary motion take their departure. Experiment proves that these nerves excite motions connected with the act of respiration.

Under the class of respiratory motions we have to distinguish two kinds; first, the involuntary or instinctive; and, secondly, those which accompany an act of volition. We are unconscious of that state of alternation of activity and rest which characterizes 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. Sir C. 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 that 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 anything 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 Sir C. 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, with new sensibili ties and new powers of activity.

Sir C. Bell remarks, that we understand the use of all the intricate nerves of the body, with the exception of the sixth nerve, 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 the 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. In the first place, dissection alone does not reveal the vital 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. Secondly, the mind is unconscious of acting by means of organs; and hence the material instruments, by means of which, in this life, it performs its operations and communicates with the external world, cannot be dis covered 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,