Brain
2 of the 7 encyclopedias on this shelf carry an entry for Brain. Both are reproduced below, so you can see where they agree and where they differ.
Collier's New Encyclopedia (1921)
the encephalon, or center of the nervous system and the seat of consciousness and volition in man and the higher animals. It is a soft white and gray matter contained the skull of vertebrated animals. The invertebrata have, instead of a true brain, nervous ganglia, situated near the end of the body. The external gray matter is softer than the white matter and consists of variously shaped nerve cells communicating with nerve fibers, and thereby receiving and discharging impressions. The internal white matter is compose almost entirely of medullated nerve fibers which transmit nerve impulses from one point to another. The brain is enveloped by three membranes called the Dura mater, which is dense and elastic; the Arachnoid, thin and double; and the Pia mater, which covers the whole surface of the brain and supplies the nervous tissues. These support the blood vessels which nourish the cranium and the brain, and also contain a clear fluid, the cerebro-spinal fluid, which removes the product of the brain waste and serves like a water cushion to diminish the effect of external shocks. The brain consists of two principal parts, the cerebrum and cerebellum, connected by bands of fibers. The cerebrumgreat brain or cerebral hemisphere-occupies in man the upper part of the head and is seven or eight times larger than the cerebellum, which lies behind it and below it in a peculiar cavity of the skull. The cerebrum is divided into two portions, the right and left hemispheres, by the longitudinal fissure, the hemispheres being at the same time transversely connected by a band or bridge of nervous matter called the corpus callosum. The cerebellum, like the cerebrum, is also divided into right and left hemispheres, connected by a bridge of nervous matter called the pons Varolii, under which is the medulla oblongata, or continuation of the spinal marrow. At the base of the brain are several masses of nervous matter or ganglia known as the corpora striata (two), and optic thalami (two) and corpora quadrigemina (four); and there are in it certain cavities or ventricles. Cerebrum. The cerebrum underlies the whole vault of the cranium and covers all the rest of the brain. The hemispheres, which are divided by a deep median fissure, are covered by a thin layer of matter, or nerve cells, and thrown into ridges or furrows called convolutions or gyri and fissures. These ridges are the result of the folding of rid the cerebral surface during the growth of the brain. On the outer surface of these hemispheres is the fissure of Sylvius, which is a deep incision at the base of the brain and runs in several directions. The fissure of Rolando runs almost vertically from the fissure of Sylvius nearly to the border of the hemispheres. On the inner surface, half way between the central fissure and the rear end of the brain, is the parietooccipital incision. These fissures form the boundaries of the various lobes of the cerebrum. (1) The frontal lobe is that part of the outer and corresponding median surfaces which lies anterior to the fissure of Rolando, and is probably associated with the exercise of the higher mental faculties. (2) The temporo. sphenoidal lobe lies below the fissure of Sylvius. (3) The occipital lobe lies behind the parieto-occipital fissure and includes the corresponding parts on the outer surface. (4) The parietal lobe is bounded by the fissures of Rolando and Sylvius, and by the occipital lobe. (5) The central lobe or island of Reil lies at the bottom of the fissure of Sylvius and is hidden in the adult by overreaching adjacent lobes. Secondary fissures on these lobes divide them into convolutions. On the under surface of the cerebrum are two olfactory nerves and two optic nerves. The olfactory nerves cross like the letter X, wind around the two cerebral peduncles and terminate in the olfactory thalami and the olfactory lobe. These peduncles pass from under the surface of the hemispheres and approach each other as they enter the Varolii. If we press apart the two cerebral hemispheres, we come upon the corpus callosum, which is a band of white fibers connecting the convolutions of both hemispheres. On dividing these and removing some white fibers and a layer of connected tissue called velum interpositum, with its vascular margin, we expose the two lateral and the third ventricles of the cerebrum, the former occupying the hemispheres, the latter lying between them and continued backward through a narrow channel (the aqueduct of of Sylvius) into the fourth ventricle, which lies behind the pons Varolii and the medulla. Projecting into the third and lateral ventricles are rounded masses of gray matter, the corpus striatum and optic thalamus, called the basal ganglia. The whole cerebrum is surrounded by a thin, convoluted envelope of gray matter about a quarter of an inch thick. Within this lies the centrum ovale, composed of white nerve fibers passing in all directions and difficult to unravel. Connecting the two hemispheres is the corpus callosum. Underneath are the septa lucida and the fornix. Into the ventricles project the ovoid optic thalamus and the caudate nucleus of the corpus striatum. A wedge-shaped mass of gray matter, the lenticular nucleus of the corpus striatum, is separated from the first two nuclei by a band of white fibers. The internal capsule is composed of two parts, an interior and posterior limb, which meet each other at an obtuse angle (the knee). Directly outside the lenticular nucleus is the white external capsule, separated by the claustrum, a thin band of gray matter, from the island of Reil. Some of the fibers of the claustrum ovale connect the frontal and occipital lobes, others connect the basal ganglia with the cortical gray matter. An important group, the corona cortex, passes from the internal capsule to the whole of the cortex. That part of the corona radiata entering the occipital lobes is called the optic radiation of Gratiolet, who considered it to be the central expansion of the optic nerve. The optic lobes consist of anterior and posterior pairs of rounded eminences of gray matter situated close to the optic thalami and underlying the pineal gland, a cone-shaped organ thought by Descartes to be the seat of the soul. Research justifies the belief that this is the remains of the pineal eye; the third organ of sight, formerly found in the lower animals. The optic lobes are closely connected with the optic nerves, part of these ending in the anterior pair, and to the third and fourth nerves, whose nuclei of origin lie just underneath them in front of the aqueduct of Sylvius. The crura cerebri are formed of fibers passing up from the medulla cord and from the cerebellum to the cerebrum. Removing the cerebral lobe from an animal deprives it of volition and intelligence and a similar experiment on man, or an imperfect development of the cerebrum, results in imbecility and idiocy, and the races that have the heaviest cerebra and the most fully developed convolutions have the most intelligence. Among animals the degree of intelligence increases with the increase in size of the cerebrum relatively to the other parts of the brain. The cerebellum possesses a median and two lateral hemispheres which have been subdivided into lobes. Its parts are arranged in thin laminæ or folia with deep intervening fissures. These laminæ have a central core of white matter with a thin covering of gray matter. The cerebellum has three pairs of peduncles: (a) Superior, which pass upward and across the middle line toward the opposite cerebral hemisphere but ending under the optic lobe; (b) middle, which is that part of the pons Varolii which enters indirectly into connection with fibers from the opposite cerebral hemisphere; (c) inferior (the restiform body), which are connected with the medulla and spinal cord. There is also a close connection with the auditory nerve and semicircular canals of the ear. Medulla Oblongata. This is the lowest and most dependent division of the brain. It is conical in form, with the base toward the pons Varolii, the narrow end toward the spinal each side of the middle line of the ancord, with terior pyramids crossing the other where the medulla passes into the spinal cord. External to them is the ovoid projection. The olivary body of the dorsal surface is the lozenge-shaped fourth ventricle, which is bounded below with the two ferior and above by the two superior peduncles of the cerebellum. Destrucpedu tion of the anterior part of the medulla causes a tendency to fall forward. Loss of its posterior part causes a tendency to fall backward; and of one lateral lobe to rotate toward the side injured. Stimulation of any of the parts causes movements of the head, eyes, and limbs such as would counteract the disturbance of the equilibrium by the destruction of the parts. The medulla is the great seat or center for the functions of organic life, as it gives origin to all the cranial nerves except the first four numbers. These centers are the center for respiratory movements, under the extremity of the fourth ventricle; (2) for the restraint and acceleration of the heart; (3) for the control of the blood pressure including the diabetic center, which is simply a vasomotor center for the liver; (4) the center for swallowing; (5) center for the movements of the gullet and stomach; (6) movements of articulate speech; (7) for the suppression of the saliva. Every part of the brain is exactly symmetrical with the part opposite. Twelve pairs of nerves proceed from the base of the brain, including the nerves for the organs of sight, hearing, taste, and of smell and of touch, also those for the muscles of the face, those for the cavity of the mouth and for the larynx. Sight. Destruction of one lobe causes permanent blindness in one side of both eyes. In man, disease of the left angular gyrus produces what is called "wordblindness." In this condition, one loses the power of reading words, although one sees the characters distinctly and may be even able to spell the word, and write it, and yet be unable to read what has been written. Hearing. The center of hearing seems to lie in the first temporal sphenoidal convolution in both sides. Partial destruction of this convolution on the left side causes the condition of "word deafness," that is, to hear sounds but have no sense of their meaning. Taste and Smell.-Ferrier locates the sense of taste and of smell in the unciate gyrus on the inner surface of the temporo-sphenoidal lobe. Touch.-Some physiologists place these in the motor area. Fibers from the various sense organs lead to the cortical areas through the posterior third of the internal capsule. If this is injured, loss of all forms of sensibility, hearing, sight, taste, etc. of the opposite side follows. In man the brain weighs from two to four pounds; the average weight in male European adults being 49 to 50 ounces or about 1-35th of the weight of the body; in the dog the average weight is about 1-120th of the animal; in the horse 1-450th. The brain of females weigh five ounces less on the average than that of males. The ratio of the brain-weight to that of the body is the same in both sexes; consequently the difference of weight in the brain of males and females is due to the lesser body weight in the woman and not to inferior cerebral development. At birth, the p proportionate weight of the brain to the body is greatest. It diminishes slowly to the 10th year, when 1:14 is the ratio. About the 40th year the brain is heaviest. After that it diminishes at the rate of an ounce every 10 years. The theory that the size and weight of a man's brain is in direct proportion to his intellect is discredited. The brain attains its highest degree of development earlier than any other part of the body. The parts lying in front have functions connected with the intellectual part of man's nature; while the parts lying nearer the back belong to the merely animal or organic nature. As the central organ of the nervous system the brain is sympathetically affected in nearly all cases of acute diseases. Diseases of the Brain. -Diseases of the brain fall into two classes, according as they exhibit mental characteristics alone, or also anatomical disturbances. To the former class belong hypochondria, mania, etc. Among the latter may be mentioned meningitis, or inflammation of the membranes of the brain, which seldom occurs without affecting the substance of the brain also, and thus giving rise to phrenitis, hydrocephalus, or water in the head, caused by pressure of water in the cavities of the brain. Consult "Diseases of the Nervous System," Jeliffe and White (1917).
Aiton's Encyclopedia (1910)
that part of the nervous system inclosed in the skull. It is continued downward as the spinal cord through an opening at the base of the skull, called the foramen magnum. The cell substance of which the brain is built is exceedingly soft and easily injured by pressure or friction. It is well protected, however, not only by its thick, bony covering, the skull, but by three membranes which entirely cover it. The outermost of these membranes is thick and tough, and fits closely by its outer roughened surface to the inner surface of the bones. Its inner surface, next to the brain, is smooth. This outer membrane is still called by its early Latin name, dura mater, which means hard mother, because in early times it was thought that all membranes of the body originated from this. The second membrane is like a delicate transparent sac, its sides flattened close against each other. It fits against the smooth inner surface of the dura mater, and is called the arachnoid, or spider's web, because it is so soft and thin. Beneath the arachnoid is a third thin membrane known as the pia mater, which is Latin for kind or tender mother. This membrane is composed of a network of blood vessels held together by tissues and it is these blood vessels that supply the nourishment and remove the wastes of the entire brain. It is almost impossible to remove the pia mater from the brain, because it dips into every fissure and surrounds all parts. On examining the brain as a whole we find that it consists of three parts: a large anterior part, known as the fore-brain or cerebrum; a narrow middle portion, the mid-brain; and a posterior part, the hind-brain. The fore-brain occupies the greater part of the skull-cavity, and is nine-tenths of the bulk of the entire brain. A deep fissure partially divides the fore-brain into right and left hemispheres. These two hemispheres are united near their under surface by a narrow band of fibers known as the corpus callosum, or callous body. The mid-brain is very small and narrow, and carries the optic lobes, two swellings, into which the sensory nerves from the eyes enter. The hind-brain consists of two parts. One of these is just posterior to and beneath the fore-brain, and is known as the cerebellum; the other is united at its narrowest part with the spinal cord. This is known as the medulla oblongata. The structure of the brain is very complex, and only the main features can be considered here. In lower animals, such as the frog, the fore-brain, mid-, and hind-brain, lie in a horizontal plane; but in the human being, they are doubled on one another, so that they form a figure something like a question mark (?). The fore-brain occupies all of the upper curved portion of the question mark; the cerebellum is below in the upper part of the stem; and the medulla oblongata occupies the lowest part of the stem. If the brain is viewed from the top, only the two hemispheres of the fore-brain are seen. Each of these is seen to be made up of folds of pale gray matter. These folds are numerous, and are arranged so as to form more or less definite divisions of the hemispheres, called lobes. The folds are known as convolutions; the indentations separating the lobes are known as fissures. Each convolution and each lobe bears a definite name, and it is found very useful in the study of normal, as well as diseased brain-activity, to know both the name and the location of these parts. When the brain is viewed from below, we can see a large part of the underside of the fore-brain, as well as the mid- and hind-brain. Projecting from the fore-brain, on each side of the mid-brain, are the olfactory lobes. Nerves run through these lobes from the nose to the cerebrum, and are the means by which is gained a knowledge of the smell of substances. Just back of the olfactory lobes are the crossed optic or eye-nerves, which enter the mid-brain. Back of the mid-brain is a band of white matter called the pons, or bridge, because it connects the two lobes of the cerebellum. The cerebellum has a wrinkled appearance; but the wrinkles are regularly arranged and really appear like very small convolutions. The surface of the medulla oblongata is smooth. Twelve pairs of cranial nerves can be seen on the under side of the brain. Some of these nerves carry impulses from the brain to the various parts of the head or body, and are called motor nerves, or nerves that cause motion. The nerve which governs the movement of the eyeball is a motor nerve. Others carry impulses from the various parts of the body to the brain, and are called sensory nerves. The optic nerve is sensory. Still other nerves are both motor and sensory, as in the case of the fifth pair of cranial nerves, which carry impulses from the brain to the muscles of the jaws and eyelids, and impulses from the face and teeth to the brain. The tenth pair of cranial nerves is very important. It largely governs the action of the lungs, the heart, and the stomach. It is called the vagus, or wanderer. The above are some of the features that can be noted by observation of the exterior of the human brain. When the brain is cut into halves, in the direction of the median fissure, one finds that it is a hollow organ, with its cavity surrounded by outgrowths or walls. All regions of the brain are connected with its cavity, which, in turn, is connected with the cavity of the spinal cord. During life this continuous cavity is filled with a fluid known as the cerebro-spinal fluid. Its walls are supplied with blood from a network of blood vessels, and it is the rupture of some of these which is one cause of apoplexy. If we cut into the brain from the top downward we find that its solid parts consist of two kinds of matter, white and gray. In the cerebrum and the cerebellum, the gray matter, about one-eighth inch in thickness, is on the outside; the white forms the central core of the mass. In the medulla oblongata the gray matter is broken up into masses which serve as centers of origin for various nerves. In the lower animals, as in the frog, the brain is essentially like that of the human; but the various parts are not developed to the same extent as in the human brain. Thus, in the frog, the cerebrum is comparatively small and not at all convoluted, but smooth; the mid-brain and the hind-brain are large. The higher the animal in the scale of life, the more complex is the structure of the brain, shown by wrinkling and folding of its surface into convolutions and lobes. Thus, the brain of the chimpanzee, of the horse, cow, and sheep, is more like the human brain than is that of the fish, frog, or bird. It is thought that these differences in structure are somehow related to the amount and kind of work that can be done by the brain. In all animals the brain controls all the higher work or activities of the animal, such as voluntary movement and sensations. The brain also controls such important operations within the body as the beating of the heart, breathing, and digestion. An animal may have the stomach removed and continue to live; but it cannot survive the loss of the brain. The results of experimentation indicate that the seat of intelligence, memory, will, and the emotions in man is in the gray matter or cortex of the cerebrum. The cortex is also the seat of conscious sensation. By this, we mean that if the gray matter of the cerebrum were removed, a human being would be unable to see, hear, taste, smell, or to exercise the sense of touch. A piece of ice might be placed in the hand and no feeling of cold would result. If the sun shone ever so gloriously upon one without a cerebral cortex, everything would seem to such an one in total darkness. Though breathing and other life processes might continue, though movement would be possible, there would be no consciousness of movement. Such a being would show no signs of fear or pleasure; there would be no feeling of hunger nor any desire to move or to work, to sleep, or to talk. Patient, careful study of the brain has revealed many wonderful things; but much remains still unknown. We know that the brain is made up largely of nerve cells and nerve fibers. The fibers connect the brain with all parts of the brain with every other part. The power to think is connected in some way with the activity of the nerve cells; but in just what way, we do not know. Nerve cells seem to generate and receive impulses and sensations; how they do it, we do not know. The changes which take place in nerve cells are essentially like those which take place in muscle cells. Nerve cells require air, food, rest, and exercise for their continued well-being, as do other cells and tissues in the body. But they can perform a work in the body that no other cells seem able to do. In the same way we know that nerve fibers conduct impulses and sensations. How they do it, we do not know.-ELLEN TORELLE. 2026 Editor's Note: The organ this entry describes anatomically is now known to hold roughly 86 billion neurons, and — contrary to a century of teaching — to keep changing throughout life, rewiring itself after injury and learning. That capacity, neuroplasticity , underlies modern rehabilitation. Scanners can now watch a living brain at work, something no dissection could ever show. (Ed: BR 2026-06-06)