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pressure, which there would be no valves to resist.— Their number and free communication are remarkable. For an admirable description of those of the spinal column, I must refer to the article " Venous System," in "Todd's Cyclopedia," by Dr. M'Dowel, Professor of Anatomy and Physiology in the University of Dublin.
The Spinal Cord is the first portion of the cerebrospinal axis we shall examine, as it is the primary element in lower animals, and the higher nervous action will be more readily comprehended when its functions are understood. In form it is a tapering mass, differing from a cylinder in being flattened on its anterior and posterior surfaces. It extends from the first vertebra—where the decussating fibres of the pyramid mark it from the medulla oblongata—to the second lumbar vertebra in adults, or to the sacrum in the foetus.
By this ascent the sacral nerves are dragged within the spinal canal, and form the cauda equina. The brachiorachidian and lumbo-rachidian bulbs are two swellings where the nerves to the upper and lower extremities are given off, and their respective size in various animals corresponds to the development of these members. In man, the lumbar swelling has most grey matter. The medulla oblongata, being very similar in appearance, is often termed the superior rachidian bulb, but we shall see its functions are of a higher order. The cord, on an average, weighs about 1£ oz., being much less in proportion to the brain than in other animals. A transverse section is figured on following page, after Lockhart Clarke, who steeps it in a solution of chromic acid, to render it transparent. It shows the division of the cord into two symmetrical halves by anterior and posterior fissures. The former is wide, dips in for one-third the antero-posterior diameter, and a white commissure unites the opposite halves, as the corpus callosum does the cerebral hemispheres. The posterior fissure is very narrow and indistinct, divides one-half the cord, and is closed by a grey band uniting the vesicular masses in a way compared to the intercrural lamina between the loci nigri of the crura cerebri. The section shows two grey masses of a semilunar shape, with the concavity outwards, and" the convexities joined by the grey commissure. Each mass terminates anteriorly in a rounded end, from which some
Tramcerse Section of Cord, at the lumbar enlargement, showing on the right the grey mass,and on the left, the course of the root fibres. The ventricle is seen in the middle of the grey commissure.
fibres of the anterior root of the spinal nerves arise, and posteriorly it comes quite to the surface, when it seems to form directly the posterior roots. About midway between the grey commissure and the posterior roots, there is found "the gelatinous substance" described by Rolando, which consists of much vesicular neurine and longitudinal fibres. The relative amount of grey matter increases from above downwards. The groove where the posterior roots emerge marks the cord into an antero-lateral column, extending from thence to the anterior fissure, and a posterior column reaching to the posterior fissure. The anterior and posterior roots of the nerves are connected with antero-lateral columns, which are also joined by a commissure, according to most anatomists, save Clarke, who states the commissure is composed entirely of grey matter; whereas the posterior columns are quite severed—except in the dorsal region, where the posterior fissure can be scarcely distinguished. In the centre of the grey commissure is seen a canal, lined by cylindrical ciliated epithelium, and extending even to the filum terminale. It is continuous with the fourth ventricle, about T^c in diameter, and in birds dilates at the lumbar swelling into the sinus rhomboidalis.
The fibres of the spinal cord are thus arranged by Todd and Bowman:—1. Spinal oblique or transverse. 2. Encephalic, longitudinal. 8. Longitudinally commissural. 8. Transversely commissural. The view still held by some anatomists, that all the fibres proceed from the brain, is disproved by the fact that the cord does not uniformly taper from above downwards, which should be the case if, like a great nerve, it gave off these fibres as it passed along. The size of the cord really corresponds to the number of nerve-tubes given off at any point, as proved by the following calculations of Volkmann, who gives the weight of 4 segments, each 7 centimetres long, from the cord of a horse, and the respective extent of the grey matter in square lines:
r n'n« Area of Grey. Area of White trains. Matter. Matter.
From below 2nd nerve 219 13 109
8th „ 293 28 142
19th „ 168 11 89
80th „ 281 25 121
It was Grainger who first stated that some of the fibres had their origin in the cord itself.
The Functions of the Cord will be best understood by arranging them into—1, those which it possesses as an independent centre, and 2, those it performs for the brain. Division of the cord deprives all parts below of the endowments of sensation or voluntary motion. The section has been made on living animals; and disease or injury too often perform the same experiment on man, whose body is then " like a living head and a dead trunk—dead to its own sensations and to all voluntary control over its movements" (Todd and Bowman). The amphioxus or lancelot fish, however, seems to prove that sensation and voluntary motion may exist in animals from whom the brain is absent, for this creature's cord tapers as finely at one extremity as at the other; and the cephalic ganglion which exists seems merely to minister to special senses. As we stated before of an ordinary nerve, if the cord be divided, irritation of the upper segment will produce pain and movement of all muscles which derive their nerves from above the section; irritation of the lower will excite only movements. Division of one half will produce these effects on the corresponding side only. A stimulus applied to the skin or other sensitive parts will also excite involuntary movements. Hunter relates that irritation was applied to the lower extremities of a man whose spinal cord had been severed by injury; they jerked vigorously. Being asked if he felt the irritation, he replied: "No, sir; but you see my legs do," and in that answer is embodied most of the views now entertained on the independent endowments of the spinal cord. That such movements are truly spinal, having no dependence on the brain, is still further shown by their occurring in brainless foetuses and pithed or even decapitated animals; but if the cord be removed from the latter, all capability of motion ceases. This excito-motory function of the cord, alluded to by Whytt and Prochaska, was so named and admirably investigated by Marshall Hall, who considered the " true spinal cord" as extending as far as the crura cerebri, and consisting of excito-motor fibres, grey matter, and reflecto-motor fibres, quite distinct from ordinary sensitive and motor fibres, and as being the seat of all physical nervous action. Disease most strikingly illustrates this reflex function, the discovery of which has thrown a flood of light on the pathology of innervation. Many examples will be hereafter adduced, but in this place two instances will make the principles more easily understood. In children, a morbid condition of the gastric mucous membrane transmits an irritation along the excito-motor fibres of the pneumogastric nerve to the medulla oblongata, whence it is sent along the reflectomotor fibres which branch into the recurrent nerve to the laryngeal muscles, producing that disease which Sir H. Marsh so well described as "spasm of the glottis." In a recent case which I saw in consultation with a former pupil, the irritant was malarious air, and the reflex disease disappeared a few days after the child's arrival in this country. A wound in the sole of the foot will so excite the polarity of the cord as to produce tetanic spasm of nearly all the muscles—those about orifices being most affected, which is usually the cause of death, and which supports'M. Hall's view—that the excito-motory system chiefly presided over the muscles of ingestion and egestion. Strychnine is a special excitant of the reflex function, and does not act directly on the cord, for if the posterior nerves be divided it will produce no tetanoid spasms, although the animal will die. Gold, as when applied along the spine in tetanus, conium, belladonna, and tobacco, are the most powerful means we have for reducing the polarity of the cord. The physiologically antidotal power to strychnia of the latter substance, was discovered by Prof. Haughton of Trinity College, Dublin, and has already saved human life. Wourara appears to be a destroyer of all nervous force. The nearer to periphery the stimula to reflex action is applied, the more powerful the result—a principle which suggests that the endermic application of strychnia is preferable to its internal administration; and I have tested practically the value of the suggestion.