jected in different directions, and belong to distinct filaments*, they must be finally conjoined and in union. The anatomy conforms to this idea; the cords of communication between the seat of volition and the organs of the body proceed from a centre, run parallel, undergo similar changes, and are blended in their ultimate distribution, as in their central or cerebral relations.

It is pleasing to see that through the labours of members of this Society the principles which have directed the author in the investigation of the human anatomy are likely to be extended in their application, by a correspondence being observed in the arrangement of the nervous tracts through every class of animals possessing volition. It has long appeared to the author that the system does not differ, even in the different classes of animals, although there is much apparent variety in the distribution of the nerves.

When it became a question whether or not Crustacea possessed the organ of hearing, the celebrated SCARPA undertook the investigation. With this purpose he did not pry about to discover the external organ of the sense. He looked to the brain, or cerebral ganglion,-recognised the part from which the acoustic nerve should come, according to the analogy of other animals. He found the nerve, and traced it to its destination; that simple rather than imperfect organ, which, but for the circumstance of the auditory nerve in its cavity, might have been supposed too defective in its organization to be capable of receiving the impulse of sounds.

course.

In this manner is the nervous system to be studied; for there is an internal change, in accordance with outward organization, whilst the system or great plan does not vary. There is an endowment in each particular column; it is one through its whole An animal, or a class of animals, may have a particular organ developed, and with the external apparatus there is a corresponding or an adjusted condition of the appropriated nerve. Another class may be deficient in the external organization, when we shall in vain look for the accompanying nerve; it is contracted, or hardly visible; but with all this the system is unchanged.

From a more cursory view of the comparative anatomy than others may have taken, this is my conclusion; but my time for such investigations has been given almost exclusively to the human anatomy; and in it I hope it will be granted that the system, as it regards sensation and motion, has been displayed so as to increase the interest of these pursuits, and to direct the studies of the pathologist to beneficial results; much advantage could hardly have been expected by dissection of the brain, even from the utmost ingenuity of research, whilst the very elements of the subject, as regards the natural anatomy, were unknown.

* See the paper on the Nervous Circle.

Explanation of the PLATE.

PLATE III.

Fig. 1. A transverse section of the spinal marrow, showing the distinctions of the medullary and cineritious substance.

Fig. 2. Shows the section with the medullary columns parted at their natural divisions, viz. by insinuating the curette into the cineritious substance, and opening the sulci.

A. The posterior column.

B, B. The lateral columns.

c. The anterior columns.

Fig. 3. The same parts still further separated, so as to exhibit the connexion between the posterior columns of the spinal marrow and the motor columns. The letters refer to the same parts as in the last figure.

D. The connexion between the posterior and anterior columns.

Fig. 4. In this view the posterior part of the spinal marrow, that which belongs to the cerebellum, is taken away, leaving those columns only which belong to the cerebrum. As the posterior portions (figg. 2. & 3. A.) enter deeply into the spinal marrow, when they are taken away the remaining columns fall flat on the board, and permit an easy separation.

A, A. The cineritious matter which intervenes between the columns belonging to the cerebrum, and those belonging to the cerebellum.

B. Projecting lines where the posterior columns of the spinal marrow were connected with the anterior. (See fig. 3. D.)

c, c. The lateral columns, or sensitive columns, after raising the cineritious substance. Into these the sensitive roots of the spinal nerves are traced. D, D. A deeper dissection of the cineritious substance exposes here the posterior surface of the anterior or motor columns.

Fig. 5. This figure represents a posterior view of the upper part of the spinal marrow, and the medulla oblongata.

A. The two posterior columns of the spinal marrow being dissected up, they are here represented diverging towards the cerebellum at G.

B. The cineritious matter left on the remaining part of the spinal marrow, after raising the column (a.). The separation of the columns having been made at the intervening cineritious matter, both surfaces have that matter attached to them-both A and B.

c, c. The lateral columns of the spinal marrow (figg. 2. & 3. B, B.), displayed on

their posterior surface. They are discovered on raising the cineritious matter B. Into these columns the posterior root of the spinal nerves are traced: they are the columns of sensation.

D. The short column formed by the union of the columns c, c. On dissecting this portion, the decussation of the columns will be seen.

E, E. The same columns which were lateral in the spinal marrow, now continued upwards, and visible in the fourth ventricle without dissection. They ascend under the valvula cerebri and under the corpora quadrigemina, and fall into the crura cerebri. So that, tracing them from above, each of these columns descends from that part of the crus cerebri which is posterior to the corpus nigrum.

F. The origin of the sensitive root of the fifth nerve of the encephalon.
G. The processus cerebelli ad medullam oblongatam.

Fig. 6. This figure represents the further dissection of the parts seen in fig. 5.
^, ^. The columns marked E in the former plate. They are divided transversely,
and the lower portion folded down, being separated from the parts below
by a delicate dissection.

B. These columns folded down.

c, c. The lateral columns of the spinal marrow continued up into B.

D. The union of the anterior columns seen in their posterior aspect. The lateral or sensitive columns, and the anterior or motor columns, are held together at this point. But it appears more for security than reunion. A fine dissection exhibits them quite distinct; and the parts above continuous into the columns of the spinal marrow; each separately.

E, E. The sensitive roots of the fifth pair of nerves.