In chemistry signifies gold; sometimes an intense fire. In botany, it is the heart of vegetables, or their pith. See Meditullium and Corculum.

Co'r, (from contr. hebrew, koaeb, the middle,) called also by the ancients cardia. The heart. This viscus is double, consisting of two cavities on each side, serving for two circulations of the blood, one through every part of the body, and the other through the lungs. The right side of the heart is similar to the left, excepting that both its auricle and ventricle have fewer muscular fibres. The auricle receives blood from the venae cavae, and the ventricle throws it into the pulmonary artery.

The situation of the heart is in the middle of and across the cavity of the thorax, but rather inclining to the left; on each side of it lie the lungs, playing on the ribs and diaphragm, and following closely all their motions; attached at their roots to the heart by the pulmonary vessels. The heart is close, on its lower side, to the diaphragm, covered by the pericardium, which is a membranous bag, enclosing this organ and all the parts belonging to it, with a small proportion of fluid or halitus interposed. The figure of the heart is conoid, its base is irregular, because all the large vessels are fixed there. The human heart differs from those of quadrupeds, which are more round: the human rather represents half a cone, because the under part which lies upon the diaphragm is flat.

The apex of the heart is to the left and forwards: its situation varies but little with the motion of the diaphragm, as it lies upon the tendinous part.

The body of the heart is composed of two large muscular cavities, called ventricles; one to the right and forwards, the other to the left and backwards. Wins-low calls them anterior and posterior.

At the basis of the heart are two muscular bags, called auricles, adjoining to the ventricles. They lie contiguous to one another below; but above they are distant, as the aorta and pulmonary artery pass between them. The right is larger than the left, and it is very thin. The left is thicker, unequally square: into which the four pulmonary veins empty themselves. The heart hath a septum divided into two, called ventricula-rum, et auricularum septum.

The right auricle receives the two venae cavae, one at the upper part, the other at the lower. At their union, these vessels are dilated, forming a sinus, styled sinus venosus. The blood, brought there by the contraction of the auricle, passes into the right ventricle, from thence into the pulmonary artery, and through its minutest branches; then through the pulmonary veins, into the left auricle, which propels it into the left ventricle, from whence it is sent into the aorta, to be dispersed all over the body, and at last is returned by the two cavae to the right auricle.

The two cavae go into the middle part of the auricle, each a little inclined inwards; the angle between them is partly filled up by the left auricle; there is a transverse ridge upon the septum auricularum, called tuber-culum Loweri, which is placed there to hinder the current of the blood from each cava rushing directly against each other. The existence of any such tubercle is, however, denied by later authors; and, indeed, it could be of little utility, since the opposing currents of blood would supply its office.

The right auricle hath an appendage, which serves to fill up the part between that and the aorta; for the same reason the left hath a similar appendage upwards, and to the left side, to fill up the space between the pulmonary artery and the left ventricle. The whole of the cavity of the auricles internally is not smooth, but composed of fasciculi, running from one side to the other. This fasciculated texture is less in the left than in the right auricle, and is most observable in the appendages of the auricles; supposed to be with a view to hinder the blood from concreting, as there it is most out of the way of the circulation; but with little reason, as solid bodies assist concretion. It is probably designed to assist the weaker action of the auricle at a distance from the centre of its greatest power.

Under the reputed tuberculum Loweri, we see the foramen ovale, which runs upwards from the right to the left auricle, and goes through the auricularum septum, directly opposed to the vena cava inferior. Soon after the child is born this hole closes, though in some instances it remains a little open, even in old age. In the foetus there is a valve which is loose, but this valve in adults is connected to the septum.

The coronary vein opens into the right auricle, between the orifice of the cava inferior and the passage into the ventricle. The fibres of the auricle are so irregularly disposed as to act as sphincters, and hinder the regurgitation of the blood.

At the insertion of the cava inferior, is a valve called valvula nobilis: it is larger in the foetus than in the adult; and its office is to hinder the blood from flowing back into the vein.

The right ventricle, on its lower part, lies on the diaphragm; and on its upper, makes the larger part of the heart. It is thicker than the auricle, and the whole internal surface of it is fasciculated. Its lower orifice receives the blood, and the upper yields it a passage: the auricular orifice is surrounded by a loose membrane, which hangs into the ventricle, connected with it by loose tendinous chords. When, therefore, the blood flows into the ventricle, this membrane hangs loose; but, on the blood regurgitating, the fluid behind presses it backward, and produces the effect of a valve. These tendinous chords are divided into three sets, and hence called valvulae tricuspidales.

The other orifice, which leads into the pulmonary artery just at its beginning, is furnished with three semilunar valves, whose loose floating edges lie towards the artery, whilst the others are fixed to the ventricle. In order to make these valves close more accurately, each hath a little mamilla in its middle, (to fill up the triangular space which is left,) called the corpus sesa-moideum: these valves hinder the blood from regurgitating into the heart.

The left auricle lies rather on the back part, behind the basis of the heart, and towards the left. It is situated below the bifurcation of the trachea and pulmonary artery. It is stronger than the other, and is smooth internally, except at the little appendicle. There are no valves on the orifices of the pulmonary veins. This auricle is stronger than the right, because the left ventricle is stronger than the right, and therefore requires more force to overcome the resistance.

The left ventricle is fasciculated. At the orifice, between the auricle and the ventricle, is a valve, called the valvula mitralis vel episcopalis, so called from resembling a mitre, which runs from the one to the other; it is fissured into two points, which are fixed to the auricles, and hang down loose into the ventricles, resembling in structure the valvulae tricuspidales. The chordae tendineae, and columnae carneae, are the same as in the other, but much stronger. The orifice, by which it expels the blood, is situated in the middle of the ventricle; so the aorta rises from the middle of the basis of the heart. The larger flap of the valvula mitralis hangs down between the auricle and ventricle: and it has been supposed to serve as a valve to both the auricular and arterial orifices; but for this purpose neither its structure nor its situation is adapted.

The coronary arteries are two. See Coronarae arteriae.

The foramina the besii are venal orifices, said to open into all the cavities of the heart.

The fibres of the heart are muscular; at each of the orifices is a tendinous ring, where the fibres of the ventricles begin, which go downwards to the apex, where they turn in, and run up on the inside, representing in perspective a figure of 8. There are some fibres common to both ventricles, which, as they compress them both, Dr. Hunter thinks is a proof of their acting at the same time.

According to Lancisi, the nerves of the heart are both numerous and large. In each side there are inserted five pair; viz. from the par vagum, the superior intercostal pair, the vertebral pair, the inferior intercostal pair, and the phrenic pair. The heart hath two motions, systole and diastole. Harvey and others say, that the systoles of the two auricles of the heart, the two ventricles, and the aorta and pulmonary artery, are respectively synchronous with each other: but Dr. Nichols thinks that the motion of the auricles is synchronous, and that the ventricles and arteries are likewise dilated and contracted at different periods of time. As the auricles throw blood into their respective ventricles, so do the ventricles perform the same duty; viz. the right throws blood into the pulmonary artery, the left into the aorta.

The real course of the circulation, and the alternate action of the different parts of the heart, we shall describe. The blood passing from the left ventricle into the aorta, is returned by the venae cavae. It then passes into the right auricle. This sac is excited to contraction by the dilatation, and propels the blood into the right ventricle. Their action is consequently successive. For a similar reason, the action of the left auricle and ventricles is successive; but as the times required for emptying and filling are nearly equal, the action of the auricles and ventricles are respectively synchronous. This succession is proved by actual observation of the action of the heart in the mammalia, and from the situation of the different valves. Animals without lungs, and which do not breathe, have only a single heart; but a considerable artery from the aorta passes to the organs which supply the place of lungs, as the gills of fish, and bring back the blood meliorated by the action of air.

See Winslow's Anatomy. Haller's Physiology. Se-nac on the Heart.