dulla spinalis, a vast number of small medullary white fibres are sent out, which, at their first egress, seem easily to separate, but as they pass forward are somewhat more, but still loosely connected, by the coat which they obtain from the pia mater, and at last piercing the dura mater, are closely embraced by that membrane, which covers them in their progress. Hence they become white, firm, strong cords, and are well known to anatomists by the name of nerves. To these coats an infinite number of vessels, both arteries and veins, are distributed. The nerves, which if all joined together, would hardly make a cord of an inch diameter, would seem, from their existing in almost every part, to be distributed with the utmost degree of minuteness. In their course to the places for which they are destined, they generally run as straight as the part over which they are to pass, and their own security from external injuries will allow, sending off their branches at very acute angles; and, consequently, running more parallel than the blood-vesels.

Nor less contrivance, nor less curious art,
Surprise and please in every other part.
See how the nerves, with equal wisdom made,
Arising from the brain our frame pervade:
Form'd of the finest complicated thread,

These numerous cords are through the body spread.
A thousand branches from each trunk they send,
Some to the limbs, some to the bowels tend.
In straight, in transverse lines, they may be found;
One forms a crooked figure, one a round;
The entrails these embrace in spiral strings;
Those clasp th' arterial tubes in tender rings;
The tendons, some, compacted close, produce,
And some thin fibres for the skin diffuse;
These subtile channels (such is every nerve)
For vital functions, sense, and motion serve.

BLACKMORE.

By elevating gently the brain from the basis of the cranium, the first nine pair are found arising in the following order:

1. Nervi olfactorii, distributed through the pituitary membrane, which constitute the organ of smell.

2. The optici, which go to the eyes, where they receive impressions of visible objects.

3. Oculorum motores, distributed to the muscles of the eye.

4. The pathetici, going to the superior oblique muscles of the eyes, the motion of which is expressive of certain passions of the soul.

5. Divide into three branches: 1. Opthalmicus, which goes to the eyes, eye-lids, forehead, nose, and integuments of the face. 2. and 3. to the superior and inferior maxilla.

6. Abductor muscle of the eye, receives those which draw the globe of the eye from the nose.

7. Auditorii, distributed to the organs of hearing.

8. Par vagum, which has its name from the great number of parts to which it gives branches, both in the thorax and abdomen. 9. The linguales or hypo-glossi, which go to the tongue, and appear to contribute both to the organ of taste, and to the motions of the tongue.

;

On viewing nature's noble plan of things,
We find five senses mov'd by double strings;
While every fibre aids the lively sense,
Ordain'd by wisest laws of Providence.
The first in rank directs our fragrant smell
The second gives us power of seeing well;
The third commands the motion of our sight,
To contemplate with ease the sacred light;
The fourth to secret lovers gives the law;
The fifth keeps time in moving either jaw ;
The sixth, by turns, pourtrays our pride or sight;
The seventh asserts to melody a right:

To wake the soul with feelings fit for kings,

The eighth strong nerve employs a hundred springs;

The ninth excites the call for daily bread;

The tenth sustains with grace the neck and head.

The spinal marrow sends off thirty-one pair of nerves; chiefly distributed to the exterior parts of the trunk, and to the extremities. These are divided into cervical, dorsal, lumbar, and sacral nerves. The cervical from the neck are eight pair; the dorsal

twelve; the lumbar five; the sacral five or six, depending on the holes in the sacrum. The knots or ganglions of nerves are met with at their exit from the spine, and in various other parts. Some have considered these as so many little brains. Lancisi fancied he had discovered muscular fibres in them; but they are certainly not of an irritable nature. Dr. Johnstone imagines they are intended to deprive us of the power of the will over certain parts; the heart, for instance. If this were true, we should meet with them only leading to involuntary muscles; whereas it is certain, that the vo luntary muscles receive their nerves through ganglions. Dr. Monro, from their structure, supposed them new sources of nervous energy. The nerves, like blood-vessels, communicate with each other, and these communications form what is called a plexus, from whence branches again issue. The most considerable of these are the semilunar plexus, the pulmonary plexus, the hepatic, cardiạc, &c. A late author (Dr. Wallis) observes, that the nerves may be traced to their origin, either in the brain or spinal marrow, except where they form a bundle of fibres, or ganglions; then you can trace it no farther. These ganglia are never found in the nerves of sense, very rarely, or in a very inconsiderable degree, in nerves going 10 voluntary muscles; but in such as supply the involuntary muscles they always occur. Thus their office is supposed to be that of intercepting the influence of the will. Assuming this to be the fact, then it furnishes an additional instance of the wonderful wisdom and contrivance of our Maker, in thus preventing the will from arresting the vital functions, and destroying the machine.

and

We observe a variety of opinions on this subject; one considering a trunk of nerves as a solid chord, capable of being divided into an infinite number of filaments, by means of which the impressions of feeling are conveyed to the sensorium commune; another supposes it to be a canal, which separates into more minute channels; or as being an assemblage of very small distinct tubes, connected and forming a cylindrical cord. They who contend for their being solid bodies, are of opinion that feeling is occasioned by vibration; so that, by pricking a finger, a vibration would be occasioned in the nerve, which being extended to the sensorium, would be an excital

of pain. But the inelasticity, softness, connexion, and situation of the nerves, are proofs against the system of vibration.

But an hypothesis more probable is, that in the brain and spinal marrow a very subtile fluid is secreted, and from thence conveyed through the imperceptible tubes, which they consider as existing in the nerves: to this fluid the name of animal spirits has been given. Mr. Cheselden says, “I think the nerves may be tubes, and that a fluid, whose cohesion is very little, and whose parts, perhaps, are finer than light, may move freely in them."

The Brain.

From the preceding observations it most evidently appears, that the nerves are all connected with the brain, which will naturally lead us in the next place to consider that gland.

Sensorium of the soul, that dost dispense

Each nerve that vibrates to the feeling heart;

Organ of life, of reason, and of sense,

Bright form that wisdom did from love impart.
Oh! may each thought that fills my teeming brain
The bias take that virtue can approve,

Each cause of reason and of right maintain,

And crown each action with benignant love.

The brain is a large round viscus, divided superiorly into a right and left hemisphere, and inferiorly into six lobes, two anterior, two middle, and two posterior; situated within the cranium, and surrounded by the dura and pia mater, and tunica arachnoides. It is composed of a cortical substance, which is external; and a medullary, which is internal. It has three cavities, called ventricles; two anterior, or lateral, which are divided from each other by the septum lucidum, and in each of which is the choroid plexus, formed of blood-vessels; the third ventricle is a space between the thalami nervorum opticorum. The principal prominences of the brain are, the corpus callosum, a medullary eminence, conspicuous upon laying aside the hemispheres of the brain; the corpora striata, two striated protuberances, one in the anterior part of each lateral ventricle; the thalami nervorum opticorum, two whitish eminences behind the

former, which terminate in the optic nerves; the corpora quadrigemina, four medullary projections called by the ancients nates and testes; a little cerebrine tubercle lying upon the nates, called the pineal gland; and, lastly, the cura cerebri, two medullary columns which proceed from the basis of the brain to the medulla oblongata. The cerebral arteries are branches of the carotid and vertebral arteries. The veins terminate in sinuses, which return their blood into the internal jugulars. The use of the brain is to give off nine pairs of nerves, and the spinal marrow, from which thirty-one more pairs proceed, through whose means the various senses are performed, and muscular motion excited.

In all those curious parts which compose the human fabric, there does not appear to be any fit organ, instrument, or receptacle for the mind, or rational soul; in the brain, which is generally considered as the seat of reason, not any thing of moment can be discovered more than in the cranium of a brute. The same observation applies to the pineal gland, wherein the Cartesians placed the seat of intelligence: this is found to be precisely the same in beasts and in men. An argument this, which affords no inconsiderable proof as to the inorganity of the soul, at least in the sense we usually conceive the term. Thus we are men we know not howa compound of matter and intelligence: yet there is something implanted within us, that can subsist without us, and will exist after the body is turned to corruption.*

Before we conclude this part of our history, I cannot refrain from again expressing my admiration of this complicated piece of machinery. Pause, reader! and consider its wonderful contrivance, and delicate mechanism! what plans of geometry have been laid! what operations of chemistry are performed! in a word, what miracles of art and elegance are wrought, in order to furnish us with necessary supplies and even the delights of life!

the

*The foregoing quotations on Anatomy are taken principally from the works of the