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; is 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 The mediastinum is a membrane which divides the chest into two parts. in its place by the great blood-vessels 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.* 3. The liver is fastened in the body by two ligaments: the first, which is large and strong, comes from the covering of the diaphragm, and penetrates the substance of the liver; the second is the umbilical vein, which, after birth, degenerates into a ligament. The first, which is the principal, fixes the liver in its situation, whilst the body holds an erect posture; the second prevents it from pressing upon the diaphragm when we lie down; and both together sling or suspend the liver when we lie upon our backs, so that it may not compress or obstruct the ascending vena cava, to which belongs the important office of returning the blood from the body to the heart. 4. The bladder is tied to the navel by the urachus, transformed into a ligament: thus, what was a passage for urine to the fœtus, becomes, after birth, a support or stay to the bladder. The peritonæum† also keeps the * A membrane, called the pleura, lines the chest and covers its contents: on each side it forms a distinct bag for the lungs, and the lungs of opposite sides being independent, breathing may be continued in one lung, though the other has been destroyed. + The peritoneum is a smooth shining membrane enveloping the liver, stomach, spleen, and intestines; the kidneys and bladder are partially covered by it. The lower surface of the diaphragm, and the parietes or viscera from confounding themselves with, or pressing irregularly upon the bladder: for the kidneys and bladder are contained in a distinct duplicature of that membrane, being thereby partitioned off from the other contents of the abdomen. 5. The kidneys are lodged in a bed of fat. 6. The pancreas, or sweetbread, is strongly tied to the peritoneum, which is the great wrapping sheet that encloses all the viscera contained in the lower belly. 7. The spleen also is confined to its place by an adhesion to the peritoneum and diaphragm, and by a connexion with the omentum. It is possible, in my opinion, that the spleen may be merely a stuffing, a soft cushion to fill up a vacancy or hollow, which, unless occupied, would leave the package loose and unsteady: for, supposing that it answers no other purpose than this, it must be vascular, and admit of a circulation through it, in order to be kept alive, or be a part of a living body." 8. The omentum,t epiploon, or cawl, is an apron tucked up, or doubling upon itself, at its lowest part. The upper edge is tied to the bottom of the stomach, sides of the abdomen, receive their exterior covering from it. The inner surface habitually exhales a moisture which bedews the surface of the several organs, permits motion, and prevents adhesion. The mesentery, the broad ligament of the liver, and the omentum, are productions or folds of the same membrane. * The several viscera are correctly described, and sufficient is said for the purposes for which they are introduced. To the supposed use of the spleen only an objection must be taken: various hypotheses have been entertained as to its office, but none are perfectly conclusive; the most probable is, that it is a source of supply of blood for furnishing the gastric secretion, or that the blood undergoes some important change in it. See note, p. 48. + The omentum is spread over the intestines, and is formed of a duplicature of the peritonæum with more or less of fat interposed; indeed it receives the superfluous depositions of fat. Like other parts of the peritonæum it is an exhaling organ for producing the fluid necessary for the due action and condition of the intestines. |