BRAIN, that portion of the nervous system contained, for the most part, within the skull. It is usually divided into two parts. The larger mass is termed the cerebrum, the smaller the cerebellum; from the lower end of the cerebrum the medulla oblongata tapers down into the spinal cord. The brain is, as it were, the _great central station of the nervous system. From the surface of the entire body nerve fibres pass into the spinal cord, up the cord and into the brain; these carry impressions of all kinds — touch, taste, sight, hearing, pain, temperature, etc.— from the surface of the body, external as well as internal, to the brain. Starting in the brain mass itself, there is a corresponding series of fibres that run down into the medulla and spinal cord, out into the nerves and end in some muscle or organ of special character. There are literally millions of incoming fibres, millions of outgoing fibres and millions of minute cells in direct association with these fibres. Thus it may be seen that the brain is merely a collection of nerve ganglion cells and their associated fibres, both of which have a characteristic appearance as seen by the naked eye; that portion of the brain that preponder ates in cells is the "gray matter° and that por tion richer in fibres is the "white matter.° It thus represents a central switchboard, which binds all parts of the body together and puts the entire body in touch with its surroundings, that it may act as a distributor or transmitter of the vast sources of cosmic energy which is constantly beating upon the human body from the environment.
The larger brain mass, the cerebrum, consists of two symmetrical halves, the hemispheres, separated above by the great longitudinal fissure and held together at the bot ton of the fissure by a firm band of fibres, the callosum, and at the base by the cerebral peduncles, which unite below to form part of the pons, and the medulla. All of the fibres passing to and fro go up and down in the peduncles, separating into each hemisphere. The surface of the hemispheres is divided by fissures into several larger areas and a number of smaller ones. Thus in the lower side there is a large fissure, the fissure of Sylvius, below it there are three lobes, the first, second and third temporal lobes. Running from the great longi
tudinal fissure, making an angle of about with the Sylvian fissure, the second most marked fissure, that of Rolando, is found. This divides off an anterior region in which the first, second and third frontal convolutions are to be found. Immediately around the fissure of Rolando are grouped the anterior and posterior parietal lobes, and at the back end of the hemispheres the occipital lobes are All of these lobes are divided into smaller areas by the fissures, the chief end subserved by these fis sures being to increase the amount of outside surface of the hemispheres and thus make room for the enormous number of cells that are lo cated in this outermost gray layer, the cortex. A further function seems to be expressed by this division into lobes and convolutions, namely, a localization of function, a concen tration of energy as it were, certain types of brain activity being relegated to certain brain areas. Thus it is assumed that the main func tion of the frontal lobes is largely that of the reasoning faculties and higher intellectual proc esses. It is very well established that the cells in the cortex that are grouped up and down both sides of the fissure of Rolando are the cells that govern the motor acts of the body ; irri tate these, and muscular convulsions in certain groups will occur ; destroy them by accident or disease, and paralysis, or loss of muscular func tion, will result. The localization for certain muscle groups, such as those for the head, arm, eyes, leg, etc., are very well known. In the oc cipital lobes, particularly in certain areas about the angular gyrus, are the centres for sight memories. Their destruction may result in mind blindness (see APHASIA). In much the same manner the memories of sound are lo cated in the temporal convolutions, and there are a large number of areas thus localized. These different areas are all brought into con nection, the one with the other, by hosts of fibres, and as already indicated the two hemi spheres of the cerebrum are connected by millions of fibres that are in the callosum.