only a few artists are versed in this science, they will be apt to caricature nature; they are learned above their rivals; it is their forte, and they are solicitous to display it. But were the study of anatomy more general, the same spirit and love of originality, which tempt them to a style bordering on deformity, would make those very men seek distinction by combining grace, and the other qualities of fine painting, with truth and expression.

It is not enough, however, that the painter should improve himself in the knowledge of anatomy: public attention must also be directed to its importance. For as necessity precedes invention in the origin of the arts, so must general good taste precede or accompany their improvement. The mere conviction in the mind of the painter, that anatomy is essential to the perfection of his art, will seldom be sufficient to insure his application to a very difficult and somewhat repulsive study. The knowledge and opinion of the public must force him to the task, and encourage his labour by the assurance of its merited reward.

APPENDIX.

ON

THE NERVOUS SYSTEM.

BY

ALEXANDER SHAW.

In many parts of this work references are made to an Essay upon the Nervous System; and the last edition contained such an essay. But on examining the copy intended for the present edition, it was found that the author had drawn his pen through the essay, and had not composed another to supply its place. It cannot be doubted that he intended to reconstruct that part of the work; and as some account of his observations on the Nervous System, which bear upon the questions discussed in the volume, may be interesting, I have been requested to give a short review of his opinions. I enter upon the task with much diffidence.

It is stated, in various parts of the essays, that a distinct Class of Nerves is provided, in the human body, for controlling the organ of Respiration; and that it is that class which is principally affected by passion and emotion, so as to give rise to the phenomena of Expression.

In Man, the organ of Breathing is constructed in such a manner, that besides ministering to the oxygenation of the blood, its primary office in the economy, it is the instrument of Voice and of Expression,-two properties which bear relation to his Intellectual nature. In order to adapt the organ to these endow.

P

ments, it is necessary that the mechanism should have a form and arrangement distinct from that in the lower animals, where it serves for purifying the blood alone: and as a correspondence always exists between the structure of the moving parts of the frame, and the nervous system, which regulates their actions, the change in the construction of the organ is accompanied with a change in the arrangement of the nerves. Accordingly, by comparing the nervous system in the inferior animals, with its order and distribution in man, the author found that a distinct class of nerves is appropriated, in the human frame, to the organ of Respiration: and to that class he gave the name Respiratory Nerves.

But that conclusion was not arrived at till many other important observations had been previously made on the functions of the Nervous System. Medical science has been indebted to the author of this volume for improvements in our knowledge of the Nerves, only to be compared, for their extent and value, with those introduced by Harvey, by his discovery of the Circulation of the Blood. Although no parts of the living body have excited greater interest, since anatomy was first studied, than the Brain and the Nerves; yet when Sir Charles Bell entered upon his researches into the subject, he found it involved in so much confusion, and surrounded by so many difficulties apparently insurmountable, that physiologists had almost ceased to prosecute it. Errors on points which bore on the first elements of the inquiry, had taken deep root. He succeeded in removing these errors, and in establishing a new principle of investigation. By adopting that principle as his guide, he was rewarded not only by making discoveries of the utmost value to medicine, but by communicating a fresh impulse to the labours of other physiologists in the same field.

The error which formerly prevailed, and had the greatest effect in retarding improvement, was this:-It was taken for granted that all parts of the nervous system had certain general properties belonging to them in common; so that all were considered alike in function. The Brain, including the Spinal Marrow, was looked upon as a common store, from which certain powers, such as that of motion, were issued to the body, and into which others, such as sensation, were received, the nerves being regarded as the conductors; and, in conformity

with that view, it was further supposed that any part of the brain, or any single nerve, had equal power with all the rest of bestowing the numerous properties commonly assigned to the nervous system. For the sake of illustration, let us take the nerves of the lower extremities; which come off from the spinal marrow. It was conceived that these nerves were all simple in structure; and that, nevertheless, they had the double property of conveying the power of motion and of sensation, to the limbs and the spinal marrow, being regarded as a prolongation of the Brain, was believed to transmit the powers of motion and of sensation along the nerves, by all its parts promiscuously.

Certain facts probably diverted the minds of physiologists from perceiving the correct views. When we examine the structure of a Nerve, it is found to consist of a number of distinct fibrils, like threads, laid parallel, connected loosely together, and contained in a common sheath; and when the fibrils are inspected narrowly it is impossible to perceive any difference between them; all are exactly alike in size, colour, and consistence. This similarity of structure, it may be supposed, would lead to the inference, that the functions of the fibrils were the same. Then, as to the Brain; although subdivided into several masses of different forms and textures, which give the appearance at first sight of its being composed of separate organs, yet a remarkable uniformity prevails in the general structure of the brain; the distinct substances of which it consists (the medullary and cineritious) are so variously intermingled and diffused, that it seems unavoidable to conclude that its powers are held in common, and are exercised by a combined operation of all its component parts. Again, the phenomena of certain diseases and accidents would probably give strength to the mistaken views. When a person is wounded in the leg, and a principal nerve cut across, the lower part of the limb, isolated from the brain, is deprived both of motion and sensation. If the spinal marrow be crushed, or disorganised by disease, so that the communication between the brain and the nerves beyond the seat of injury, is destroyed, total paralysis ensues, that is, the limbs lose both motion and sensation. When a man is struck down by apoplexy, owing to sudden effusion of blood into the brain from a ruptured vessel, he is deprived instantaneously of both motion and sensation. These occurrences,

met with daily, would naturally lead to the belief that sensation and motion were inseparably united in all the different forms of the nervous system; and when it was imagined that two such distinct functions could belong to the same part, it would not be inconsistent to believe that other powers could be combined with them.

But Sir Charles Bell had not long commenced his investigations, when it occurred to him that it was contrary to reason to suppose that two functions so essentially distinct from each other as motion and sensation, could belong to the same nerve. Let us consider the direction in which the nervous agency which gives rise to motion, must necessarily be conveyed along a nerve to produce muscular contraction. As the volition originates in the brain, and the force, whatever it is, which acts upon the nerve must be propagated to the muscle, it is obvious that the force will proceed outwardly or centrifugally. But when a sensation is felt, as the effect must be produced by an impression being made upon the extremity of the nerve expanded on the skin, and by that being conveyed to the sensorium, it follows that the course of the nervous agency must be inwardly, or centripetally. Hence the force which causes muscular contraction passes along a nerve in one direction, and that which causes sensation in a contrary direction: and it is inconsistent to suppose that the same nerve, or same portion of the nervous centres, could minister to both functions at once.

The fundamental principle of the author's discoveries was originally announced in nearly the following terms :-The nerves of the body possess distinct and appropriate functions, corresponding with the parts of the brain and spinal marrow with which they are connected at their roots; and when a nerve, which appears simple, is found to bestow more than one endowment, it is a sign that that nerve has more than one origin from the brain, and consists in reality of several nerves joined together. The mode by which this principle was demonstrated and established to be a law in physiology, was as follows :—

The author first directed attention to the nerves of the Organs of the Senses. These nerves were formerly conceived to be so closely allied to each other, that their functions were regarded rather as modifications of one common property, than as distinct and specific. Thus it was supposed that the nerve of one organ