THE NERVOUS SYSTEM
1. IT was said that the motion which effects a sensation in our body, consists of a tremulation in the whole system, as well the nervous system as that of the bones, but it cannot be expected that reason will give its consent to this assertion before we have placed before it all the facts from which the connection of all things may be seen. And as Willis, Vieussens, and others, have enriched anatomy with the knowledge of the exact position of every part in the body, we ought now to preface the treatise itself with a short anatomical account, in order to make possible a clearer comprehension of the nature of tremulation.
It should therefore be known that beneath the cerebrum and the cerebellum there is a medullary part called the medulla oblongata, which is provided with many protuberances, glands, and other processes for the distillation of the fluid which is necessary for the membranes, nerves, and bones; of this fluid more shall be said later on. This medulla is afterwards continued all along the spinal column, down to the legs below; it runs out of the cranium through an opening called the great foramen of the occiput, entering thence the vertebra; from all along this medulla, counting from the cerebrum above, there spring forth, at certain little distances pairs of nerves which hence proceed to their own functions and uses in the body. Leaving the medulla, these nerves run hither and thither, joining and twisting about one another, again separating in order to join with other nerves, then proceeding further away, splitting up and making greater and greater ramifications, until the ramification itself produces an expanse, which is termed a membrane, or a periosteum, consisting of nothing but the most minute and extreme branches of the nerves.
Beginning from above and counting the nerves in their order as they run out of the two medullas, we find first the olfactory nerves, which run directly to the nostrils. Next come the optic nerves, which, running out of their thalami, afterwards cross each other, and then again unite, after which each one runs to its own eye. The third pair runs to three muscles behind the eyes, giving them power to move and turn. The fourth Pair proceeds also to the eyes, running obliquely across the other nerves, and making a muscle with a knot or pulley, called trochlearis. The fifth pair has an extensive ramification; it runs in four branches to the eyes, and thence to the eyebrows, the forehead, the nose, and the temples; other branches proceed to the jaws, the lips, the teeth, the palate, and the throat, afterwards sending out a few branches to join with the sixth pair, which also runs to certain motor muscles of the eye. The seventh pair is called the auditory nerves, which are double, the one soft, the other hard: the former runs to the tympanum, the cochlea, the muscle of the malleus, etc., the latter inclining towards the eighth pair, to the tongue, the pharynx, to certain muscles above the mouth, and around the eyebrows and the forehead, etc. The eighth pair, which is called par vagum , describes an extensive circuit, running to the muscles of the neck, to the hard branch of the auditory nerve, and to the intercostal nerve; it then runs down the body in a straight line, on the way sending out branches first to the cardiac plexus, whence the heart receives its nerves and ramifications; then to the heart itself and to a number of arteries and veins around which it weaves itself; also to the esophagus, to the lungs, to the stomach, as well beneath as above, terminating finally with minute branches in the liver. The ninth pair runs mostly to the tongue and the palate, and unites afterwards with the next pair. The tenth pair runs simply to the muscles of the neck, but unites on the way Keith various other nerves, as with the great intercostal nerve, and with the spinal nerve. The eleventh pair goes mostly to the muscles in the neck and to the diaphragm, uniting finally with the following pair. The twelfth pair proceeds to the arms and to the diaphragm. The thirteenth and fourteenth also to the arms; the fifteenth to the twentieth, etc., run to the muscles in the arms, the sides, and other parts of the body, uniting mostly with the intercostal nerve; the thirty-first and thirty-second to the testicles; the thirty-third sends a little branch to the penis. The thirty-fourth to the thirty seventh run only to the muscles in the legs and the loins; the thirty-fourth to the inguinal glands; the thirty-eighth unites with a nerve which runs to the thighs, but runs otherwise to the sphincter muscle of the anus, to the prostate glands, the bladder, the uterus, and the rectum; the thirty-ninth , like the others, runs into the intercostal nerve, as also to the cranial nerves, to the muscles of the penis and the anus, uniting thus with the former ones, and these again with those that run out of the intestines and the me enters and these finally with all that system which is produced by the intercostal nerve. Most of the above nerves unite to produce a great nerve, called the intercostal nerve, which runs to and from nearly all the parts of the body and effects the principal connection of all the other nerves. The intercostal nerve may therefore be called a connecting sinew and a basis and highway for all the nerves in the body, as may be seen more fully from the whole nervous system, as described and illustrated by the anatomists.
For the further elucidation of tremulation let us consider the most minute parts of the body, and we will see that there is a connection and harmony between all these parts, no matter where they be situated. Take, for instance, any little nerve or point of membrane in the stomach: it will be noticed, first, that both the upper and the lower parts of such a nerve or point are joined to transverse sinews and afterwards are incorporated in the par vagum nerve, which runs to the esophagus, the lungs, the heart, the pericardium, the throat, on the way weaving itself about arteries and veins; it finally flows into the intercostal nerve and now describes another great arch in the body, running to the kidneys, the spleen, the liver, the gallbladder, and round about the intestines and the mesenteries; it is thus connected with the branches of all the other nerves which join the intercostal, anti is therefore connected also with the legs and the loins, the head, the face, and all the organs of sense, etc.; finally, by a circuit, it becomes again connected with the par vagum, which terminates in the stomach. Or take any other part of the body, such as the least cuticle on a finger, or on the sole of the foot, and it will be observed similarly that this cuticle, which is nothing but a ramification of nerves, is collected into a greater nerve, and afterwards, by means of other nerves, becomes connected with all other cuticles and membranes in the whole body.
This is, therefore, another clear proof that every sensation is a tremulation in the whole nervous system, (neural transmission) and that a sensation is not confined to any particular place beneath the cerebellum or within any certain protuberance or ventricle here or there, but that it exists as in one, so in all places simultaneously; before it can properly be called a sensation it must have been felt in every part of the body which is reached by a nerve. As soon as the least impression is made on the ramification of any nerve, it is at once communicated to all the nerves and membranes of the whole body, so that one and all must necessarily be touched and impressed. The most direct highway of sensation is the medulla spinalis, which, as to its tunics, is contiguous with the brain; the sensation or tremulation is therefore at once communicated to the medullary tunics and to the cerebellum. As now all the sinews, threads, or nerves, which are found in any part of the body, originally come from this medulla, it may be understood how the tremulation as soon as it reaches the fountain or origin of all the nerves must run like s a lightning over them all, in whatever corner of the body they may be. That is, the tremulatory motion is received especially by the medulla spinalis, whence it is Communicated to everything contiguous with this medulla, namely, the brain, and all the nerves, membranes, and cuticles in the whole body, all this showing that a living sensation is not confined to any particular body of matter or little protuberance in the brain, but free from any bridle or constraint, it runs like a lightning over the whole body, and then first presents the sensation. (irradiation->sensation)
2. Having now exhibited the connection of all the nerves, and the harmony of our whole body in respect to its sinews, it will next be necessary to deal with the system of the membranes, inasmuch as the tremulation flows over these up to the cerebrum, using the membranes as a bridge over which it is carried to its termini above and below.
In general it is to be known that a membrane is nothing but a contexture of nerves, which by countless ramifications have been woven into a tissue or coat, to clothe and distinguish the various parts of the body. By the microscope one may distinguish innumerable filaments of nerves, entangled and crossing one another; the lymph flows in some of these filaments, the arterial or venous blood flows in the others. According to the latest discoveries, the membranes consist mostly of nervous lymphatic ducts, the blood vessels constituting the lesser part: all these, infinitely ramified, produce an expanse like a retina. Every least part of the body is thus clothed with a membrane, thick or thin according to the use and nature of the part, and often with two or three membranes in which the nerves terminate and thereby compose the chief structure of these membranes. Such is the composition of the stomach, the mesentery and everything else, as is held for certain by some perspicacious scientists.
Chief among all the membranes are those which are called matres or meninges: the upper one, which differs from the other as to thickness, is called dura or crassa mater; the lower one which is thin and fine, is called gangs or pia mater. It is in these that the principal motions of tremulation take place; in these reside most sensibly the most subtle sensations, and in these, as in little mirrors, may be seen the real nature of tremulation.
The dura my be said to produce an expanse over the whole body, for it communicates membranes and tunics to all parts, making a continuous system just as the nerves do. It is expanded over the whole brain, extends itself into all fissures, as between the cerebrum and the cerebellum, and surrounds the medulla spinalis throughout; all the nerves which flow forth from the medulla similarly cover themselves with a tunic from the dura mater and carry it with themselves to all parts of the body. As now the nerves to send out ramifications to all the periostea, to all the muscles, and to all the blood vessels, it follows that the dura mater provides clothing for all these parts, forming all cuticles, periostea, and integuments in the body, so that the whole contiguous stem of membranes is nothing but a continuous extension of the dura mater. Beneath this latter lies the pia mater which still more encloses all parts which are distinct from one another. It surrounds especially the cerebellum and enters into every sinus there; it covers all the protuberances and glands of the brain with little membranes, gives a tunic to the ventricles, runs along all the nerves which flow forth from their roots to their foramina in the cranium, accompanies the medulla along the spine as an inner coat and divides it into two parts. In a word, it encloses inwardly everything that is of a lymphatic or soft nature.
Between the dura and the pia mater the anatomists have also found a thin membrane, called the arachnoid. This one encloses the whole medulla spinalis, and, I believe, also the cerebellum; it lies so close to the pia mater that many may suppose it to be the uppermost tunic of this mater, but it may be seen most distinctly at the punctures whence the nerves come forth from the medulla spinalis. This arachnoid. membrane also accompanies the nerves as a second coating, continuing perhaps, to the smaller ramifications as covering lamina and producing a great number of tunics and periostea. The meninges of the brain, therefore, produce a continuous system of membranes over the whole body, and as this whole system covers a structure of continuous vessels lymphatic as well as sanguineous and all filled with their own fluids, it follows that these membranes are hereby kept expanded and distended for the requirements of the tremulation, being more or less attuned, as it were, according to the influx of these fluids. But of this more will be said in another chapter, in which we shall demonstrate the theory of the circulation of the lymph and the blood.
3. It must also be shown how the bones are connected and articulated one with the other, inasmuch as on this connection depends to a very great extent the instantaneous communication of the tremulatory notion. A skeleton clearly demonstrates this connection. It should also be remembered that every bone as to its least part is enveloped by a periosteum, that is, by a membrane extended from the dura mater (although the temporal bone has been excepted by some, yet not by ball the anatomists). The dura mater, therefore, applies itself closely to the bones, seeking as it were to incorporate itself with them in order to give them nutriment by its fluid. It also extends little tendons or threads far into the substance of the bones, thus joining the membrane so closely that it can hardly be separated from the bone. In the cranium itself the dura mater applies itself so firmly to the rough surface of the bones, that it is difficult to separate it without causing some injury. By little tubules and points it is also joined to the pericranium so firmly, that nothing is felt in the one which is not also felt in the other membrane. Moreover, in the great foramen, through which the medulla spinalis enters from the head into the vertebrae the dura mater is so swollen that it seems fibrous and fleshy; the reason for this is that all the tremulations must flow through this opening, as through a bridge on a violin, before entering the concave part of the cerebrum.
4. From the above we may now have a better comprehension of the communication of tremulation. For it is known that the tremulation flows with the rapidity of lightning over membranes and nerves, from one end to the other, in an instant making the most subtle waves over the whole expanse, like the oscillation in water or in the atmospheres. As now all the membranes are expanses, and are continuous with the aura mater, and as the meninges surround the medulla spinalis, divide it into two, and enclose the whole cerebrum and cerebellum, it may be seen, in regard to the nature of tremulation, how quickly this will vibrate from one terminus to the other. It is so swift, in fact, that we cannot form a conception of its celerity by any comparison with our divisions of time. It has been shown further, that all membranes are joined with what is hard, that is, with bones, from which it follows that every tremulation in the membranes is at once communicated to the bones; the same motion that begins in the nervous system is instantly communicated to the osseous system, thereby assisting the tremulation as well in respect to the swiftness of its distribution as in respect to its continuation in the same degree throughout. For if there were no contact with something hard, the expansion of the membranes would not be sufficient to effect the communication of the tremulation so swiftly, inasmuch as this motion always loses somewhat of its force when it meets anger thing that is soft. When we examine the periostea, which surround vertebral foramina, it will be seen that these are, indeed, separate tunics, yet derived finally from the dura mater, so that there can be no tremulation in the one which is not ultimated in the other. The tremulation is therefore at once communicated from the spine, with all its membranes and vertebrae, to the cranium; the latter, which is the exit and entrance or the very bridge of all tremulations, is so completely joined and fixed to the matres, that any motion in one part must necessarily be felt at once in all the parts of the head. Moreover, there are concave cartilage's on all sides, anal the cranium itself is so porous, that it is especially fitted for the reception of what is tremulatory. For porosity contributes more than anything else to the communication of the finer contremiscences; the more porous a thing is, the better does it play with the tremulation of a chord; porous wood, such as cedar or Spruce, is far more Suitable to conduct the sound of a chord than any harder' of wood. The all wise God of nature has therefore created in man a great cavity, surrounded by a very porous cranium, so that it is like the body of an instrument, from which the membranes receive a higher tone or pitch, for the effecting of sensation in the body. And as each one must form his own opinion according to his own brain, we may be allowed to express our belief that the tremulation first runs as far up as to the great foramen of the occiput or the interstice of the medullas, and thence into the cranium to the coronal suture. For the matres are here joined to the cranium, and in the foramen they seek as it were to attune the Sound, like a bridge on a musical instrument, whence it flows up and down, and effects in us the quality of the tremulation. Quod erat demonstrandum.