Spinal cord

“ The spinal nerves are those nerves which arise from the sides of the spinal cord. They differ from the cranial nerves not only in their origin outside the cranium, but also in that each spinal nerve arises by two roots which spring from the spinal cord near the dorsal and ventral surfaces. Each root passes through a foramen in the cartilaginous wall of the neural canal, the ventral a little anterior to the dorsal, after which they unite to form the spinal nerve. ”

“ In an embryo but slightly more advanced than the one last described, important steps have been made in the development of the nerve-rudiment. The spinal cord itself now possesses a covering of white matter; this is thickest at the ventral portion of the cord, and extends to the region of the posterior root of the spinal nerve.
The junction of the posterior root with the spinal cord is easier to observe than in the last stage. ”

“ The spinal cord, as we have seen, is a mass of nervous substance continuous with the brain; from the spinal cord nearly all the nerves of the body are given off; those nerves whose branches go to the biceps muscle in the arm leave the spinal cord somewhere in the neck. ”

“ As near as I can make out, the effusion of blood within the spinal canal has been safely absorbed, or nearly so. There seems to be no displacement or injury to the spinal bones; there is no wasting away of the muscles as would be the case if the spinal cord were injured. There is, I believe, good reason to hope that the loss of power in his legs is a sequel of organic conditions which have now passed away. ”

“ SPINAL CORD, in anatomy, that part of the central nervous system in man which lies in the spinal canal formed by the vertebrae, and reaches from the foramen magnum to the lower margin of the first lumbar vertebra. It is about 18 in. long, and only occupies the upper two-thirds of the spinal canal. The cord is protected by the same three membranes which surround the brain. Outside is the dura mater, which differs from that of the brain in not forming a periosteum not to the bones, in sending no processes inward, and in having no blood sinuses enclosed within its walls. ”

“ Now, when we come to man, and observe the experiments which are constantly being made for us, both in health and disease, we can not avoid placing the spinal cord much higher as a nerve-center than it is usually placed by physiologists.
In human anencephalic monsters, or those born without a brain, we have interesting examples of the fact that the spinal cord is possessed of perception and volitional power. ”

“ In many cases, as has been remarked before, the pathological process descends into the spinal cord. Here, as in the medulla oblongata, the degeneration is principally confined to the motor centres located in the anterior horns, while the posterior horns, together with the lateral and posterior white columns, remain free from disease. The degree of degeneration taking place in the fibres of the respectively paralyzed muscles also corresponds to that of the elements of the nerve-centres from which they are supplied. ”

“ A spinal tube is formed in the external skin of the back, and from this first comes a simple spinal cord without brain, such as we find to be the permanent psychic organ in the lowest type of vertebrate, the amphioxus. ”

“ Along the extreme dorsal summit of the spinal cord there arises on each side a continuous outgrowth.
From each outgrowth processes corresponding in number to the muscle-plates grow downwards. These are the posterior nerve-rudiments. ”

“ The Spinal Cord.—The spinal cord proceeds from the base of the brain downward about eighteen inches through a canal provided for it in the vertebræ of the spinal column. It is composed of white matter on the outside, and gray matter within. ”

“ Since the trophic centres for the muscles are situated in the spinal cord, cerebral hemiplegia, which does not cut off their connection, does not produce the rapid wasting seen in some cases of spinal paralysis, unless descending degeneration involves the anterior gray columns. The limbs preserve their fulness for a time, although the muscular masses become flabby and slowly atrophy for want of use. ”

“ This cord connects the brain with the various parts of the body. There is a soft cushion of cartilage between each spine, which adds much to the elasticity of the back-bone, protecting the brain from shocks. This protection is further accomplished by the curvature of the spine. These bones are not placed directly over each other, but are so arranged as to give three curves to the spinal column. Along the column there are openings, at each joint, through which the nerves come to supply fibers to the different organs of the body. ”

“ The Reflex Action of the Cord.—We have already considered the cord as the great motor and sensory nerve of the body, but it has another and extremely important use. By virtue of the gray matter, which occupies its central portion, it plays the part of an independent nerve centre. The spinal cord not only conducts some impressions to the brain, but it also arrests others ”