In this view of the nerves the internal and radical distinctions are more insisted upon, than that enumeration of their origin and description of their devious course through the body which have hitherto served

* I have represented above, in a general way, the columnar appearance of the spinal marrow at its upper part; that superior extremity, which, being traced out of the base of the brain, is called medulla oblongata.

only to confound the enquirer. We must, therefore, begin the description of the system with that of the spinal marrow. It is by a right arrangement of matters which are familiar, and by attention to a few remarkable and prominent facts, that the groundwork of this system will be best understood.

The spinal marrow is peculiar to the vertebral animals. It will suffice for superficial observers to say, that it must be so, because the spine is necessary to conceal and protect the marrow: but there is much more than this in the established relationship; the spine formed by vertebræ is necessary to such a constitution of the thorax as shall be capable of the motion of respiration; and the spinal marrow is equally necessary to that form and distribution of the nervous system which is required for associating and combining the

muscles of respiration.

Without the ma

chinery of the spine and ribs the thorax and abdomen could not rise and fall in respiration; and without the spinal marrow that arrangement of nerves would be wanting which is necessary to regulate the motions of the trunk in respiration. Thus the spinal marrow, the spine and ribs, and the muscles of respiration, are essential to each other; as constituting the several parts of a grand design subservient to respiration.

Different columns of nervous matter combine to form the spinal marrow. Each lateral portion of the spinal marrow consists of three tracks or columns; one for voluntary motion, one for sensation, and one for the act of respiration. So that the spinal marrow comprehends in all six rods, intimately bound together, but distinct in office; and the capital of this compound column is the medulla oblongata.

These six columns of the spinal marrow are discoverable on looking to the fore part of that body; but no doubt these grander columns contain within them subdivisions. Thus, if we lift up the medulla spinalis from the cerebellum, and look to it on the back part, we shall see more numerous cords, the offices of which will one day be discovered.

The medulla oblongata, raised by a thread, so as to expose the posterior

surface.

This view of the constitution of the spinal marrow led me to institute experiments, which were followed by the discovery of the distinct functions performed by the several roots of the spinal nerves; without stating these experiments or their results, we shall proceed with the general view.

but

The anterior column of each lateral division of the spinal marrow is for motion ; the posterior column is for sensation; and the middle one is for respiration. The two former extend up into the brain, and are dispersed or lost in it; for their functions stand related to the sensorium: but the latter stops short in the medulla oblongata, being in function independent of reason, and capable of its office independent of the brain, or when separated from it.