rately to the left, both in fize and shape; but the arterial branches, which fupply the two arms, do not go off from their trunk, in a pair, in the fame manner, at the fame place, or at the fame angle. Under which want of fimilitude, it is very difficult to conceive how the fame quantity of blood should be pushed through each artery: yet the refult is right; the two limbs, which are nourished by them, perceive no difference of fupply, no effects of excefs or deficiency. Concerning the difference of manner, in which the fubclavian and carotid arteries, upon the different fides of the body, feparate themselves from the aorta, Chefelden feems to have thought, that the advantage which the left gain by going off at a much acuter angle than the right, is made up to the right by their going off together in one branch*. It is very poffible that this may be the compenfating contrivance: and, if it be fo, how curious, how hydrostatical! II. ANOTHER perfection of the animal mafs is the package. I know nothing which is fo furprising. Examine the contents of the * Chef. Anat. p. 184. ed. 7. trunk trunk of any large animal. Take notice how foft, how tender, how intricate they are; Reflect how conftantly in action, how neceffary 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 ftrokes in a miuute: one fet of pipes carrying the ftream away from it, another fet, bringing, in its course, the fluid back to it again: the lungs performing their elaborate office, viz. diftending and contracting their many thousand veficles, by a reciprocation which cannot ceafe for a minute: the stomach exercifing its powerful chymistry: the bowels filently propelling the changed aliment; collecting from it, as it proceeds, and tranfmitting to the blood an inceffant fupply of prepared and affimilated nourishment: that blood pursuing its course; the liver, the kidneys, the pancreas, the parotid, with many other known and diftinguishable glands, drawing off from it, all the while, their proper fecretions. These several operations, together with others more fubtile but lefs capable of being inveftigated, are going on within us, at one and the fame time. Think of this; and then obferve how the body itfelf, the cafe which holds this machinery, is rolled, and jolted, and toffed about, the mechanifm remaining unhurt, and with very little moleftation even of its niceft motions. Obferve a rope dancer, a tumbler, or a monkey; the fudden inverfions and contortions which the internal parts fuftain by the poftures into which their bodies are thrown ; or rather obferve the fhocks, which thefe parts, even in ordinary fubjects, fometimes receive from falls and bruifes, or by abrupt jerks and twifts, without fenfible, or with foon recovered damage. Obferve this, and then reflect how firmly every part must be fecured, how carefully furrounded, how well tied down and packed together. This property of animal bodies has never, I think, been confidered under a diftinct head, or fo fully as it deferves. I may be allowed therefore, in order to verify my obfervation concerning it, to fet forth a fhort anatomical detail, though it oblige me to ufe more technical language, than I should wish to introduce into a work of this kind. 1. The heart (fuch care is taken of the centre centre of life) is placed between two soft lobes of the lungs; is tied to the mediastinum and to the pericardium, which pericardium is not only itfelf an exceedingly ftrong membrane, but adheres firmly to the duplicature of the mediaftinum, and, by its point, to the middle tendon of the diaphragm. The heart is alfo fuftained in its place by the great blood, veffels which iffue from it*. 2. The lungs are tied to the fternum by the mediaftinum, before; to the vertebræ by the pleura, behind. It feems indeed to be the very ufe of the mediaftinum (which is a membrane that goes ftraight 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 lobe of the lungs from incommoding another, or the parts of the lungs from preffing upon each other when we lie on one fide †. 3. The liver is faftened in the body by two ligaments; the firft, which is large and strong, comes from the covering of the diaphragm, and penetrates the fubftance of the liver; the fecond is the umbilical vein, which, after *Keill's Anat. p. 107. ed. 3. ↑ Ib. 119. birth, degenerates into a ligament. The firft, which is the principal, fixes the liver in its fituation, whilft the body holds an erect posture; the second prevents it from preffing upon the diaphragm when we lie down; and both together fling or fufpend the liver when we lie upon our backs, fo that it may not comprefs or obftruct 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 paffage for urine to the foetus becomes, after birth, a support or stay to the bladder. The peritoneum alfo keeps the vifcera from confounding themselves with, or preffing 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 fweetbread is ftrongly tied to the peritonæum, which is the great Chef. Anat. p. 162. wrapping |