the turtle, for instance, after decapitation: actions which continued to be performed for some time whilst the spinal cord remained intact, but ceased instantly on its removal. It was farther shown, that in the case of a monstrous birth, where the brain was wholly wanting, the infant, during some hours sucked and performed the other functions of complete animal life; and that in palsy, limbs which were insensible to the commands of the will, had yet their own proper movement. Hence it was very rationally inferred, that the spinal apparatus is sufficiently independent of the brain, to be capable of action without its aid, and that by its intervention many of the actions requisite to the preservation of life can be, and actually, in many instances, are performed: thus proving that besides the unconscious vegetative life of the sympathetic system, there is an unconscious animal life, whose centre is to be found in the spinal cord. For these functions, which he distinguished as reflex, Dr. Marshall Hall supposed a peculiar set of fibres to be appropriated, which he termed excito-motory. He considered that "the various muscles and sentient surfaces of the body are connected with the brain by nerve fibres which pass from one to the other. Those

changed when the body would be injured by remaining in it. The same is the case in apoplexy, in which the actions of the brain are suspended by pressure upon it: and the same will take place in an animal from which the cerebrum is removed, or in which its functions are completely suspended by a severe blow on the head. If the edge of the eyelid be touched with a straw, the lid immediately closes: if a candle be brought near the eye the pupil contracts;-if liquid be poured into the mouth it is swallowed:-if the foot be pinched, or burnt with a lighted taper, it is withdrawn, and if this experiment be made upon a frog, the animal will hop away, as if to escape from the source of irritation. Carpenter's Animal Physiology, p. 356.

fibres destined for, or proceeding from the trunk to the brain, pass along the spinal cord, so that that organ is in great part no more than a bundle of nerve fibres going to and from the brain. These

fibres are especially for sensation and voluntary motion. But in addition to these, there is another class of fibres proper to the spinal cord, and to its intercranial continuation which form a connection with the gray matter of the cord (15). Of these fibres some are afferent or incident, others efferent or reflex, and these two kinds have an immediate but unknown relation to each other, so that each afferent nerve has its proper efferent one, the former being excitor, the latter motor.-These fibres are quite independent of those of sensation and volition, and although bound up with sensitive and motor fibres, they are not affected by them, and they maintain their separate course in the nerves as well as the centres."* But this theory, however ingenious, is still but a theory; unsupported as yet by any anatomical proof, though the phenomena on which it is founded are established facts: it therefore awaits the confirmation, which perhaps we are never destined to attain, of a more accurate anatomical knowledge of parts so delicate in their structure, that they have hitherto in great measure baffled the inquirer. Before going further, however, it may be well to give what is known respecting the nature of the organ which plays so important a part in the animal economy.

15. "The spinal cord is somewhat cylindrical in shape, slightly flattened on the anterior and posterior surfaces," and is considerably thickened in those parts where the nerves supplying the limbs are

*Todd and Bowman's Phys., vol. i. p. 323.

given off or received. It is divided down the middle "by an anterior and posterior fissure into two equal and symmetrical portions, of which one may be called the right, the other the left spinal cord. A transverse bilaminate partition, extending through the entire length of the cord, separates these fissures from each other, and serves to unite the lateral portions. This partition is composed of a vesicular or gray, and a white or fibrous lamina or commissure, the gray being situated posteriorly.-On further examination of a transverse section of the cord we observe that the interior of each half of it is occupied by vesicular matter, disposed in somewhat of a crescentic form, thus:

The concavity of this crescent is directed outwards, its anterior extremity or horn is thick; but the gray matter is prolonged backwards in the form of a narrow horn, which reaches quite to the surface of the cord. The prolongation of the posterior horn of each gray crescent to the surface, divides each half of the cord into two portions. All that is anterior to the posterior horn is called the antero-lateral column, and this comprehends the white matter forming the sides and front of that half of the cord. The posterior column is situated behind the posterior horn of gray matter. The antero-lateral columns are united across the middle line by the anterior or white commissure;-the gray crescent by the pos

terior or gray commissure, while the posterior columns are not connected, except when the posterior fissure is imperfect or deficient. The roots of the spinal nerves emerge from the cord on each side along two lines; the posterior line corresponds to the margin of the posterior horn of gray matter; the anterior one is placed about midway between it and the anterior fissure. The roots of the nerves penetrate the substance of the cord, and are chiefly, if not entirely, connected with the antero-lateral column. So far as our present knowledge of the minute anatomy of the spinal cord extends, it is favorable to the supposition that the spinal nerves derive their origin, at least partly, from the gray matter. The longitudinal fibres of the cord may consist in part of fibres continuous with those of the brain or cerebellum, and in part, of commissural fibres, serving to unite various segments of the cord with each other, or to connect some part or parts of the encephalon with them. These fibres which may be regarded as strictly spinal, are probably oblique in their course, forming their connection with gray matter at a point higher up in the cord than that at which they emerge from its surface, and may readily be confounded with the longitudinal fibres when their course is long. Other oblique or transverse fibres probably do not emerge from the cord, but connect the segments of opposite sides, forming a transverse commissure. So that four classes of fibres, each different in function, may be considered to exist in the cord. 1. Spinal fibres oblique or transverse, which propagate nervous power to or from the segments of the cord itself. 2. Encephalic fibres; longitudinal; the paths of volition and sensation, which connect the spinal cord with the various segments of the encephalon. 3. Longitu

dinal commissural fibres. 4. Transverse commissural fibres.

16. Whilst the functions which, till a better term is found, we must term reflex (14), were as yet either unknown, or considered merely as isolated and strange phenomena; the controversy was warm as to the respective offices of the posterior and anterior columns of the cord, as well as of the two roots of the nerves: but nothing would now be gained by going over ground, much of which has been abandoned, and I prefer quoting the following very rational theory, which will give a notion of the question as it at present stands. "We are much disposed to think," say the authors of "the Physiological Anatomy of Man," "that the antero-lateral columns are the centres of the main actions of the cord. Both roots of the nerves are connected with these columns, and therefore fibres of sensation and motion must be found in them. These columns are always proportionate to the nerves which arise from them; they enlarge when the nerves are large, and contract when the nerves diminish in size. The posterior columns, on the other hand, are of uniform dimension throughout nearly the entire length of the cord, although the posterior roots of the nerves exhibit considerable difference in point of size in different regions. We venture to suggest, that the posterior columns may have a function different from any hitherto assigned to them. They may be in part commissural between the different segments of the cord, and in part subservient to the function of the cerebellum (17), in regulating and co-ordinating the movements necessary for perfect locomotion. The analogy of the brain, in which the various segments are connected by longitudinal commissures, suggest the probable existence of fibres similar in