CENTRES DIAGRAM ILLUSTRATING THE MOTOR AREA AND THE MOTOR TRACT. BY W. H. RILEY, M. D. O. T. Optic Thalamus; L. N. Lenticular Nucleus; C. N. Candato Nucleus; 1. Cortical motor cell; 2, 2, 2, 2, 2. Axis cylinder process of motor cell ending in end brush around the spinal cell at 5; 3, 3. Collateral branch to opposite hemisphere; 3'. Collateral branch to lenticular nucleus; 4, 4. Collateral branches to spinal motor cells; 5. Spinal motor cell; 6. Spinal motor nerve; 7. End brush of same; S. Cell in posterior spinal ganglia; 9. Afferent nerve from skin; 10. Collateral branch of central branch of afferent nerve; 11. End brush of afferent nerve. AND BACTERIOLOGICAL WORLD. VOL. II. BATTLE CREEK, MICH., U. S. A., DECEMBER, 1893. ORIGINAL ARTICLES. THE VOLUNTARY MOTOR MECHANISM AND SOME OF ITS DISEASES, MOTOR PARALYSIS, WITH ILLUSTRATIVE CASES. BY W. H. RILEY, M. D., Member of the American Neurological Association, etc. WHEN we direct our attention to our own body, we recognize certain of our movements as "voluntary, " and we say that they are executed by an effort of the "will." Some of our maneuvers may be complex and intricate, and such as can be learned only in time and by practice under the direction of an intelligent volition. The movements of the hands and fingers in playing musical instruments, and the various dextrous movements necessary to the plying of many of the industrial arts, are examples of these, and may be justly styled skilled movements. Again, some of our movements are simple in character, such as may be brought under the control of the "will" without much practice. They are the first movements learned by the child; they are common to all, and may be illustrated by the movements of the face and the eyes, by simple movements of the limbs, as walking, etc. These may be termed fundamental movements in opposition to acquired movements, or those which are not common to all, and which are accomplished only by much practice. All of our movements, which are not properly reflex or automatic in character, come under the head of voluntary movements. Sometime in the life of the individual these movements must be learned. The disposition to acquire some, such as NO. 12. walking, may be inherited; nevertheless the child must learn to walk. In more difficult movements, such as playing a musical instrument, there is no element of inheritance that is common to all. Here the movements must be learned without the help of heredity. For the sake of distinction, then, voluntary movements may be divided into two classes: 1. Primary- those for which we have an inherited predisposition. 2. Secondary- those which are wholly acquired. All the different parts concerned in the development of voluntary movements taken together, make up what we may term the voluntary motor mechanism. In this mechanism the muscle is but a link in the chain, of which there are many parts. This mechanism, as related to its center, the motor area of the brain, may be said to have two general divisions: one concerned in carrying impulses inward, and hence afferent in its functions; the other concerned in originating nervous impulses, and carrying them outward, and hence efferent in its functions. In the present paper we shall deal principally with the efferent side of the motor mechanism, and shall leave for consideration elsewhere those parts of the nervous system which have to do with carrying nervous impulses from muscles, joints, skin, etc., inward to the brain, by means of which the motor cortex of the brain, which has to do with sending nervous impulses outward to the muscles, may be kept informed of the positions of the various parts of the body, the relation of distant parts to each other, and of the body as a whole to its environments. The afferent part of our motor mechanism, then, really has nothing to do with originating those nervous impulses which give rise to muscular contraction. The effer ent part, on the other hand, is concerned in originating nervous impulses, conducting them along certain paths to the muscles, where they bring about those changes in the muscles which result in motion. A destructive lesion in any of its parts always produces a partial or complete loss of motion, which we term paresis, or paralysis. Leaving the efferent side out of the question for the purpose of this paper, we may regard the motor mechanism as made up of the following elements : 1. A cortical motor cell. 2. The axis cylinder process of the cortical motor cell. 3. A spinal motor cell. 4. The axis cylinder process of the spinal motor cell. 5. The muscle. That part of the cortex of the brain where the cortical motor cells are grouped together, we call the motor area. The cortical motor cell, with its axis cylinder process, which becomes a nerve fiber, forms the upper segment of the motor path. The spinal motor cell and its axis cylinder process, which also becomes a nerve fiber with a myelin sheath and neurilemma, form the lower segment of the motor path. The motor path, then, in its entirety, includes these two segments, and is the complete line over which an efferent, or outgoing, nervous impulse travels from the cortex of the brain to the muscle. (See frontispiece, 1, 2, 2, 2, 2, and 2 form the upper segment of the motor path; 5, 6, and 7 the lower.) THE MOTOR AREA. In 1870, Fritz and Hitzig, two German investigators, produced coördinated movements in the limbs, face, and neck of dogs, when certain parts of the cortex of the brain were stimulated with weak currents of electricity; and, curious as it then seemed, these movements were al ways on the side of the body opposite to the part of the brain stimulated. These investigators found that while stimulating certain parts of the cerebral cortex with an electrical current produced muscular contractions, stimulating other parts gave negative results. They went still further, and demonstrated that within that part of the cortical area which responded to electrical stimulation, there were certain centers, the stimulation of which was always followed by definite coördinated movements in certain parts of the body, which seemed to be related to the cortical area stimulated. The experiments of Fritz and Hitzig marked the beginning of a new epoch in the field of experimental physiology, and opened the way for our present knowledge of localization of brain function. We cannot here enter into a discussion of the various steps and methods which have led up to our present knowledge of this subject, but, without going into detail, the main facts of our knowledge of the motor area at the present date, are as follows: 1. The motor area is that part of the cerebral cortex in which originate those efferent nervous impulses which give rise to voluntary movements. (We must not conclude that this part of the brain subserves no other function than that of motion. There is reason for believing that it has sensory as well as motor functions, and hence is sometimes called the sensori-motor area.) 2. It occupies a part of both the external and the internal surfaces of each hemisphere. On the external surface it is made up of the ascending frontal and ascending parietal convolutions, which are separated by the fissure of Rolando, the greater part of the superior parietal, and possibly the base of the superior frontal convolution. On the internal surface, it occupies the paracentral lobule, which is a continuation of the ascending frontal and ascending parietal convolutions on the median surface of each hemisphere, lying in front of the upturned end of the collosso-marginal fissure. It has been demonstrated by Shäfer, Horsley, and Beevor, that the motor area in the monkey, besides including the above, also takes in the base of the three frontal convolutions, and all of the superior parietal lobule. superior parietal lobule. And it is very probable that the motor area of man extends over quite as wide an area; but there are some centers, particularly those for the conjugate movements of the head and eyes, which are located at the base of the three frontal convolutions in the monkey, that have not yet been positively proven to be present in the brain of man, by actual demonstration. The centers for the various movements of different parts of the body have been carefully located in the monkey's brain by Shäfer, Horsley, and others. Corre sponding centers have for the most part been demonstrated in the brain of man by surgical operations and post-mortem examinations. Those centers adjacent to the longitudinal fissure extend over on the paracentral lobule on the median surface of the hemisphere, and here occupy the same relative position as they do on the external surface. The relative position of the face, arm, and leg centers, with the pyramidal fibers arising from them, is shown in the frontispiece. 3. In the lower animals, as the rabbit, dog, and monkey, the limits of these different centers are not bounded by sharp and well-defined lines, but the different centers blend one into another. The dividing line is more sharply drawn in the dog than in the rabbit, still more in the monkey; and although the opportunities for stimulating these different centers in the brain of man have been comparatively few, the results obtained lead us to conclude that the differentiation is even greater than in the monkey. 4. Movements, and not parts of the body, are represented in the motor area. Any part of the body which is capable of performing a great variety of movements, occupies a comparatively larger part of the motor area than some other part of the body which can perform but few movements. 5. These different centers are capable of electrical stimulation, either by an interrupted constant current, or by the induced current. Stimulations of the different centers are followed by movements on the opposite side of the body, which are represented in the center stimulated. 6. Those muscles which usually or always act together, as the muscles of the eyes, face, and larynx, the muscles of mastication, the respiratory muscles, and some of the muscles of the trunk, have a bilateral representation in the brain; i. e., they have a center in each hemisphere. In cases of hemiplegia, in which the influence of the motor centers of one hemisphere are cut off from the muscles on the opposite side of the body, by a lesion in some part of the pyramidal tract, these muscles are slightly or not at all affected; for when they are separated from one center by disease, the center in the other hemisphere of the brain is left in charge of their movements. centers cause spasm or convulsions in those parts on the opposite side of the body that are related to the centers irritated. The irritation may be communicated to adjacent centers, and general convulsions follow. Destructive lesions cause paralysis in corresponding parts. 8. The evidences of the above facts have been obtained principally by experimentation on the cortex of the brain of the lower animals, and by clinical observation of disease, followed by postmortem examination, or surgical procedure, in man. The pathological evidence is the most demonstrative. Prominent among the many investigators of this subject may be mentioned Fritz, Hitzig, Ferrier, Munk, Shäfer, Horsley, Exner, Nothnagle, Beevor, Golotz, Luciani, and many others. THE CORTICAL MOTOR CELLS. Our conception of the nerve cell, and the anatomical relations existing between it and nerve processes, has been very much modified and broadened during the past two or three years, by the examination of the minute anatomy of the central nervous system by the staining method of Golgi, of Pavia, whose work has been confirmed and extended by S. Raymon y Cajal, of Barcelona, and by Kölliker; by the embryological investigations of His; by the comparative and histological histological observations of Retzius, Nansen, and Biederman; by the method of studying degenerated nerve fiber as introduced by Marchi; by the method of staining intravitam by methyl-blue, originated by Erlich; and by the course taken by "action currents, as demonstrated by Gotch and Horsley with the electrometer, and by the labors of many others. In the present paper we can only refer to the results obtained along these various lines of investigation in so far as they are related to the motor cells and their processes. In the cortex, or grey matter, of the brain, are found nerve cells with their various processes. These cells are grouped together in layers from the surface downward, each of the different layers being characterized by cells which are different in shape and size from all the others. There can usually be demonstrated five distinct layers of cells. The 7. Irritating lesions in any of these shape and size of the cells in the first In the light of modern research, the cortical motor cell, with all its parts, as well as every other nerve cell, is a distinct and isolated anatomical nerve unit. To this nerve unit Waldeyer has given the name of neuron. Shäfer prefers to regard this nerve unit as simply the nerve cell (which seems to us to be the most natural), and applies the term neuron to the axis cylinder process of the cell. The motor cell of the cortex, then, may be considered as made up of two parts, the cell body and the cell processes. The processes are of two kinds: 1. The protoplasmic processes of Deiters, or dendrites (His), or dendrons (Shäfer); 2. The axis cylinder process, or neuron, of Shäfer. (See Fig. 1; also frontispiece, 1 and 2.) The body of the cell is large, irregular, triangular, or pyramidal in shape, with the apex pointing upward. It has a large nucleus and a large nucleolus. There is a reticulum in the protoplasm of the cell, and an intranuclear network. From the apex of the cell passes upward for some distance a protoplasmic process, or dendron, which divides and subdivides near its terminus into smaller branches. There are also protoplasmic processes arising from the base of the cell, which extend out laterally. The axis cylinder process, or neuron of Shäfer, starts from the base of the cell, takes on a medullary sheath, and extends for a long distance downward. It is the efferent or projection fiber of the cortical motor cell. In its course downward it sends out various branches, to which Cajal has given the name of collaterals. One of these (3, in frontispiece) passes through the corpus callosum to the other hemisphere of the brain, where it divides into fine branches, which end around the motor cells on the opposite side of the brain. By this branch an association is formed between corresponding centers in the two cerebral hemispheres. Mott and Mott and Shäfer have shown experimentally in the monkey that when the corpus callosum was stimulated with weak currents of electricity, bilateral movements of the head, trunk, and limbs were obtained. When one hemisphere of |