CIRCULATION. The arterial supply of the brain comes from two sources, the internal carotids and the vertebrals. At the base of the brain these fora• vessels form a remarkable anasto mosis of large arterial trunks which is known as the circle of Willis. The arrangement of these vessels can be best appreciated by refer ence to the accompanying diagram. From this circle there pass off to the brain three main sets of branches: (1) The anterior cerebral,which pass fo•wa•d in the great longitudinal fissure. curve around the anterior border of the cor pus callosum, and, running backward on its upper surface, terminate by anastornosing with the posterior cerebral arteries. They supply the under surfaces of the anterior lobes, part of the internal surfaces of the liemispheres, the corpus callosum, the third ventricle, and the anterior perforated space, Near their origin from the internal carotids, the two anterior ce rebrals are milted by a short thick trunk, the anterior communicating. (2) The middle cerebral or Sylvian arteries, which pass outward along the Sylviall fissures, within which each divides three branches—an anterior to the anterior lobe, a posterior to the posterior lobe, and a median to the small lobe near the end of the fissure of Sylvins. (3) The posterior cerebral arteries, which, arising from the basilar, pass backward and outward on the under surfaces of the occipital lobes, each terminating in three branches, which pass respectively to the uncinate gyrus, to the temporo-sphenoidal lobe, and to the lingual lobule, cunens, and occipital lobe.
All these arteries ramify in the pia, where they anastomose freely. From this anastomosis are given off small brandies which enter the substance of the brain, the shorter ones breaking up into a capillary network in the gray matter, the longer ones passing to the more deeply situ ated white matter. After entering the brain substance, there is no further anastomosis. the arterial capillaries passing directly into ye nons capillaries without communicating With the capillaries of neighboring. arteries.
Besides these cortical branches, branches, from the circle of Willis supply the basal ganglia. Like those in the cortex, these arteries do not anastomose after entering the hrain substance.
The blood supply of the spinal cord is derived from three main arteries, the anterior spinal posterior spinal. The anterior spinals arise from the vertebral s. and. passing downward on the anterior surface of the medulla, unite to form a single trunk, which passes down the cord along the anterior median fissure. The posterior Spinal arteries also arise from the vertebral arteries and pass down the posterior aspect of the cord along the line of the posterior nerve roots. Branehes from the spinal arteries form an extensive anastomosis in the pia miter.
From this network branches pass into the sub stance of the curd. These arteries, like those in the brain, do not anastomose after entering the nervous tissue proper.
01' THE CEtumauxt. The brain, and more especially the cerebral hemispheres, must Ire considered as the organ of the mind. It is here that those material activities take place which underlie those mental attributes which we recognize as consciousness, intellect, emotions, and will. In the ease of the higher animals removal of the cerebrum results so promptly in death of the animal that few conclusions can be drawn. In one of the lower animals, e.g. the frog, the result is the destruction of all volition and apparently of all conseions»ess. Stimula tion, such as pinching the toes or applying the electric current to nerves or muscles, causes muscular contraction and consequent movement. but if left entirely alone the frog shows no sign of movement, with the exception of the automatic movements connected With the heart boat and with breathing. In some cases where after a time slight voluntary movements seemed to occur. it was found that small portions of the brain had not been removed. Professor Dalton's de script', of a pigeon from which the cerebrum been removed is as follows: "The effect of this mutilation is simply to plunge the animal into a state of profound stupor in which it is almost entirely inattentive to surrounding ob jects. The bird remains silting motionless upon his perch or standing upon the ground with eyes closed and head sunk between the shoulders. plumage is smooth and glossy, but is oni formly expanded by a kind of erection of the feathers, so that the body appears somewhat purred out and larger than natural. Occasionally the bird opens its eyes with a vacant stare. stretches its neck, perhaps shakes its bill once or twice, or smooths down the feathers upon its shoulders, and then relapses into its former apathetic The brain would thus seem to he essential to any :1011'14. Whatever functions are carried on by the rest of the nervous system enter into consciousness only through the brain. Thus stimolalioW of a sensory nerve may be conceived as causing a motion (as in the ease of the frog without a cerebrum) entirely independent of the brain. lint in such a case there is neither any consciousness of the stimulation (sensation), nor any knowl edge or control of the resulting motion. It is a purely reflex :let. By 111(.11111.-; of the brain. then. stimulation of sensory nerves result, in an ac tivity in consciousness which We call sensation. and by the same means both knowledge of and control over motion are accomplished. The so. called higher mental net ivities. intellect or thought. and feeling or emotion, are also entirely dependent upon 1 III. cerebrum.