258 STRUCTURE OF THE HUMAN BODY. LESSON 117. Structure of the Human Body. Car'tilage, gristle. Ad'ipose, fatty. Tendons, hard, insensible cords, by means of which muscular fibres are attached to bones. DR. HUNTER gives the following beautiful representation of the structure of the human body, with reference to all the wants and requisites of such a being as man, in answer to a supposed objector, who asks why a more simple, less delicate, and less expansive frame had not been adopted. First, says he, the mind, the thinking, immaterial agent, must be provided with a place of immediate residence, which shall have all the requisites for the union of spirit and body; accordingly, she is provided with the brain, where she dwellsas governor and superintendent of the whole fabric. In the next place, as she is to hold a correspondence with all the material beings around her, she must be supplied with organs fitted to receive the different kinds of impression which they will make. In fact, therefore, we see that she is provided with the organs of sense, as we call them; the eye is adapted to light; the ear to sound; the nose to smell; the mouth to taste; and the skin to touch. Further, she must be furnished with organs of communication between herself in the brain, and those organs of sense; to give her information of all the impressions that are made upon them; and she must have organs between herself in the brain, and every other part of the body fitted to convey her commands. and influence over the whole. For these purposes the nerves are actually given. They are soft white chords which rise from the brain, the immediate residence of the mind, and disperse themselves, in branches, through all parts of the body. They convey all the different kinds of sensations to the mind in the brain; and likewise carry out of thence all her commands to the other parts of the body. They are intended to be occasional monitors against all such impressions as might endanger the well-being of the whole, or of any particular part; which vindicates the Creator of all things, in having actually subjected us to those many disagreeable and painful sensations which we are exposed to from a thousand accidents in life. STRUCTURE OF THE HUMAN BODY. 259 The mind, in this corporeal system, must be endued with the power of moving from place to place; that she may have intercourse with a variety of objects; that she may fly from such as are disagreeable, dangerous, or hurtful; and pursue such as are pleasant and useful to her. And accordingly she is furnished with limbs, with muscles and tendons, the instruments of motion, which are found in every part of the fabric where motion is necessary. But to support, to give firmness and shape to the fabric; to keep the softer parts in their proper places; to give fixed points for, and the proper directions to, its motions, as well as to protect some of the more important and tender organs from external injuries, there must be some firm prop-work interwoven through the whole.. And, in fact, for such purposes the bones are given. The prop-work is not made with one rigid fabric, for that would prevent motion. Therefore there are a number of bones. These pieces must all be firmly bound together, to prevent their dislocation. And this end is perfectly well answered by the ligaments. The extremities of these bony pieces, where they move and rub one upon another, must have smooth and slippery surfaces for easy motion. This is most happily provided for, by the cartilages and mucus of the joints. The interstices of all these parts must be filled up with some soft and ductile matter, which shall keep them in their places, unite them, and at the same time allow them to move a little upon one another; these purposes are answered by the cellular membrane, or adipose substance. There must be an outward covering over the whole apparatus, both to give it compactness, and to defend it from a thousand injuries; which, in fact, are the very purposes of the skin and other integuments. QUESTIONS.-1. How does the soul correspond with material beings? 2. What are the nerves, and their use? 3. Of what use are the bones? 4. The ligaments, cartilages, and mucus? 5. Cellular. membrane? 6. Skin and other integuments? 260 STRUCTURE OF THE HUMAN BODY. LESSON 118. Structure of the Human Body (continued.) Secretion, the process by which various fluids are separated from the blood by means of the glands. Vas'cular, full of ves sels. THE mind being formed for society and intercourse with beings of her own kind, she must be endued with powers of expressing and communicating her thoughts by some sensible marks or signs, which shall be both easy to herself, and admit of great variety; and accordingly she is provided with the organs and the faculty of speech, by which she can throw out signs with amazing facility, and vary them without end. Thus we have built up an animal body which would seem to be pretty complete; but as it is the nature of matter to be altered and worked upon by matter, so in a little time such a living creature must be destroyed, if there is no provision for repairing the injuries which she must commit on herself, and those to which she must be exposed from without. Therefore a treasure of blood is actually provided in the heart and vascular system, full of nutritious and healing particles, fluid enough to penetrate into the minutest parts of the animal; impelled by the heart, and conveyed by the arteries, it pervades every part, builds up what was broken down, and sweeps away the old and useless materials. Hence we see the necessity or advantage of the heart and arterial system. The heart consists of four cavities, from one of which, the blood is driven into the arteries through the body, by another, it is received back again by the veins it then passes into the third, whence it is forced into the lungs. Having there been revivified by coming in contact with the air, it is carried back by a set of veins into the fourth cavity, and thence into that in which it began its course: it is then again forced into the arteries, brought back by the veins, and thus circulates till the end of life. Each cavity of the heart is generally called into action four thousand times every hour. The arteries, into which the blood is forced, branch in every direction through the body, like the roots, branches, and leaves of a tree, running through the substance of the bones, and every part of the animal, till they are lost in such fine tubes as to be wholly invisible. In this man STRUCTURE OF THE HUMAN BODY. 261 ner, they distribute nourishment, supply perspiration, and renew all the waste of the system; and by passing through glands in every part of the body, all the various animal secretions are elaborated. In the parts where the arteries are lost to the sight, the veins take their rise, and in their commencement are also imperceptible. The blood is then of a dark colour. In this discoloured state it has lost some of its vital power; but on being driven through the lungs its colour is restored. All this provision, however, would not be sufficient, for the store of blood would soon be consumed, and the fabric would break down, if there was not a provision for fresh supplies. And we actually find that on its passage from the lungs to the heart the blood receives a supply of a new fluid extracted from the food by myriads of fine tubes which carry it to a larger one, that empties itself into a large vein, and being mixed with the blood is conveyed to the heart. We see, therefore, by the very imperfect survey which we have been able to take of this subject, that the animal man must necessarily be complex in his corporeal system, and in its operations. He must have one great and general system, the vascular, branching through the whole circulation; another, the nervous, with its appendages the organs of sense, for every kind of feeling; and a third for the connexion and union of all these parts. Besides these primary and general systems, he requires others which may be more local or confined. One for strength, support, and protection; another for the requisite motion of the parts among themselves, as well as for moving from place to place, the muscular system; another to prepare nourishment for the daily recruit of the body, the digestive organs; and others for the various purposes of existence. QUESTIONS.-1. What are the uses of the blood? 2. Describe the circulation of the blood. 3. Describe the arteries. 4. What changes does the blood undergo in the course of its circulation? 5. How is provision made for a fresh supply of blood? [NOTE. That cavity of the heart from which the blood is driven into the arteries is called the left ventricle; the next is called the right auricie; the third the right ventricle; and the fourth the left auricle.] 262 THE HUMAN VOICE. LESSON 119. The Human Voice. Epiglottis, a small and thin piece of cartilage, placed at the back of the tongue, and having the office of closing the glottis, when the food is passing. THE parts employed in the production of the voice are three in number, the trachea, or wind-pipe, by which the air passes to and from the lungs; the larynx, which is a short cylindrical canal at the head of the trachea; and the glottis, which is a small oval opening between two semicircular membranes. The glottis being very narrow compared with the size of the trachea, the air can never pass through it without acquiring a considerable degree of velocity; so that the air thus compressed and forced on communicates, as it passes, a vibratory motion to the particles of the two lips of the glottis, which produces the sound. The sound thus produced is reverberated through the different parts of the mouth; and it is the mixture of different reverberations, well proportioned to one another, which produces in the human voice a harmony, which no instrument can equal. The most wonderful part of the mechanism of the voice is the contraction and dilatation of the glottis. It is these changes which produce all the variety of tone. The diameter of the glottis never exceeds one tenth of an inch: now suppose a person capable of sounding twelve notes-to which the voice easily reaches, there must be the difference of the hundred and twentieth part of an inch for each note. But if we consider the subdivision of notes of which the voice is capable, the motion of the sides of the glottis appears still more minute. Suppose that a voice can divide a note into one hundred parts; it will follow that the different openings of the glottis will be twelve hundred in one tenth of an inch, and it is known that each of these will produce sounds perceptibly different to a good ear. But the movement of each side of the glottis being equal, it is necessary to double this number, and the side of the glottis, therefore, actually divides the tenth of an inch into twenty-four hundred equal parts. Speech is articulated voice, that is, voice modified by the action of the palate, teeth, tongue, and lips. All animals |