Concerning the difference of manner, in which the subclavian and carotid arteries, upon the different sides of the body, separate themselves from the aörta, Cheselden seems to have thought, that the advantage which the left gain by going off at an angle much more acute than the right, is made up to the right by their going off together in one branch.* It is very possible that this may be the compensating contrivance; and if it be so, how curious, how hydrostatical! + II. Another perfection of the animal mass is package. I know nothing which is so surprising. Examine the contents of the trunk of any large animal. Take notice how soft, how tender, how intricate they are; how constantly in action, how necessary to life! Reflect upon the danger of any injury to their substance, any derangement of their position, any obstruction to their office. Observe the heart pumping` at the centre, at the rate of eighty strokes in a minute: one set of pipes carrying the stream away from it, another * Cheselden's Anatomy, p. 184. edit. 7. + TAB. XVII. k, the right subclavian; l, the right carotid arteries, originating from one common trunk; m, the left carotid; n, the left subclavian. TAB. XXII. Fig. 1. In this plate the parietes of the chest and abdomen, with the omentum, are removed to shew the viscera in situ; a, the heart; b, the aorta; c, the descending vena cava: d, the lungs divided by the mediastinum into two portions; three lobes belong to the right, and two to the left portion of the lungs; e, the diaphragm; f, the liver; g, the gall bladder; h, the stomach; i, the spleen; k, the large intestines; 1, the small intestines; m, the bladder. set bringing, in its course, the fluid back to it again; the lungs performing their elaborate office, viz. distending and contracting their many thousand vesicles, by a reciprocation which cannot cease for a minute; the stomach exercising its powerful chymistry; the bowels silently propelling the changed aliment; collecting from it, as it proceeds, and transmitting to the blood an incessant supply of prepared and assimilated nourishment; that blood pursuing its course; the liver, the kidneys, the pancreas, the parotid, with many other known and distinguishable glands, drawing off from it, all the while, their proper secretions. These several operations, together with others more subtile but less capable of being investigated, are going on within us, at one and the same time. Think of this; and then observe how the body itself, the case which holds this machinery, is rolled, and jolted, and tossed about, the mechanism remaining unhurt, and with very little molestation, even of its nicest motions. Observe a rope-dancer, a tumbler, or a monkey: the sudden inversions and contortions which the internal parts sustain by the postures into which their bodies are thrown; or rather observe the shocks which these parts, even in ordinary subjects, sometimes receive from falls and bruises, or by abrupt jerks and twists, without sensible, or with soon-recovered damage. Observe this, and then reflect how firmly every part must be secured, how carefully surrounded, how well tied down and packed together. This property of animal bodies has never, I think, been considered under a distinct head, or so fully as it deserves. I may be allowed, therefore, in order to verify my observation concerning it, to set forth a short anatomical detail, though it oblige me to use more technical language than I should wish to introduce into a work of this kind. 1. The heart (such care is taken of the centre of life) is placed between the soft lobes of the lungs ; tied to the mediastinum and to the pericardium: which pericardium is not only itself an exceedingly strong membrane, but adheres firmly to the duplicature of the mediastinum, and, by its point, to the middle tendon of the diaphragm. The heart is also sustained in its place by the great bloodvessels which issue from it.* 2. The lungs are tied to the sternum by the mediastinum, before; to the vertebræ by the pleura, behind. It seems indeed to be the very use of the mediastinum (which is a membrane that goes straight through the middle of the thorax, from the breast to the back) to keep the contents of the thorax in their places; in particular, to hinder one portion of the lungs from incommoding another, or the parts of the lungs from pressing upon each other when we lie on one side.t 3. The liver is fastened in the body by two * Keill's Anatomy, p. 107. edit. 3. |