Page:Every Woman's Encyclopedia Volume 1.djvu/646

 MEDICAL 620 the organs of the body to ensure that they do their special work. This is supphed in the form of the deUcate apparatus called the Nervous System, which regulates every organ, every rnuscle, every part of the body. Because we are supplied with a nervous system we are sensitive, active, reasoning beings. Because our brain is a highly developed organ, we possess, or ought to possess, reason, intelligence, reverence, and under- standing. For the sake of description we shall divide the nervous system into four parts : (i)The brain, (2) the spinal cord, (3) the nerves, (4) the sympa- thetic system ; and wc shall consider them in turn. The brain is a complicated mass of nervous matter, contained in the skull, which is a bony box less than a quarter of an inch thick. The brain is made-up of nerve-cells and nerve-fibres. These nerve-cells are microscopic in size, very complex in structure, and he over the surface of the brain, forming what is called the grey matter. In this grey matter, which is the most wonderful substance in the whole of creation, all ideas are formed, " will " is originated, and sensations are perceived. It is the organ of consciousness — in a word, the mind. It is by reason of our minds that we are think- ing beings, that we are able, however imper- fectly as yet, to get into conscious relationship with the visible universe. Nerve-fibres of the brain pass from the nerve-cells downwards to the spinal cord, and are in connection with all parts of the body by means of the nerves, which pass out from the spinal cord. The brain weighs about three pounds. A woman's brain weighs a few ounces less than a man's. This fact was formerly regarded as a positive proof that woman was intellectually inferior to man. Greater knowledge, however, has demonstrated that quahty of brain, not quantity, is all-important. The Brain and Spinal Cord If the skull could be opened, the living brain w'ould be found to be enclosed in three protective membranes, between which lies a quantity of fluid. This furnishes a sort of water-bed to protect the soft semi-sohd organ. The surface of the brain is raised into a series of folds called " convolutions." These convolutions increase the surface area of the brain, and the different convolutions have their different functions. For example, if one could stimulate a convolution lying about the middle of the right side of the skull we should cause the leg or arm on the opposite side of the body to move, because the muscles are controlled by that particular area of the brain. The brain consists of two halves, or hemi- spheres, which are separated from one another by a deep cleft. The right side of the brain controls the left side of the body, and vice versa, and the two sides of the brain communicate and act with each other. It is impossible in this space to give any idea of the wonderful functions of the different areas of the brain, but it m.ay be said speaking broadly, that the front part of the brain behind the brow has to do with the intel- Icctual functions. The middle area of the brain rules and regulates locomotion, or movement Ihe posterior area lying at the back of the head has to do with sensation. From the lower part of the brain a tail-like projection tapers downwards measuring about eighteen inches in length. This is the spinal cord which hes inside the bony spinal column just as the brain lies inside the skull. The spinal cord is about the thickness of the little finger above, and becomes smaller as it passes down the spinal canal. By means of the spinal cord the brain can communicate with the nerves going to the rest of the body. These nerves pass off in pairs from the spinal cord, and make their exit from the spinal column, or vertebral column, through little openings down each side. There are thirty - one pairs of spinal nerves and twelve pairs of brain nerves, or cranial nerves, which come off the brain itself. The cranial nerves supply the face and head. The first pair, for example, are called the optic nerves, and they pass to the back of the eyes and carry messages from the eye-structures to the brain, which thus perceive light and various objects. The second pair of cranial nerves have to do with the sense of smell, and therefore pass to the nose. Another pair are called the auditory Area which controls Motion Intellectual Area of the Brain Sensory Area V Spinal Cord lying '* in Spinal Canal The Vertebral Column Diagram of brain and spinal cord. The convolutions of the brain are shown, and the taiUlike spinal cord lying in the spinal canal. nerves, or nerves of hearing. The rest of the cranial nerves are distributed to the face, head, and neck. One pair of cranial nerves called the " facial nerves " supply the mucles of expression. If one facial nerve is cut off from its communica- tion with the brain, as happens in certain cases of paralysis, for example, we have one side of thej face a blank, because the muscles supplied by the facial nerve are no longer controlled by the brain. The Nerves In appearance the nerves are white cords con- sisting of nerve-fibres, and vary a great deal in size. The smallest is only just visible to the naked eye, whilst the sciatic nerve in the thigh is nearly as large as the little finger. The function of these nerves is extremely interesting. In the first place they convey sensation to the brain. If you laid the tip of your finger on a hot range, the sensation of heat would be carried up the