of both is so different, their nature, their properties, their uses, distinguishing them so remarkably, that it is absolutely impossible to describe them together, and to consider the pericardium as a single organ when we examine its anatomical details. Of these structures the exterior is fibrous and the interior is serous." Anatomie offices. The offices which the pericardium performs are twofold, Its different affording on the one hand a smooth and moistened surface, not unlike that of a bursa, in order to facilitate the constant motions of the heart upon the adjacent parts; and, on the other hand, being a very dense and strong membranous bag, it, by its connections with the mediastinum and the diapraghm, suspends the heart and prevents its being displaced during its unceasing movements, or tilting, or by changes in the form and position of the adjacent viscera. in disease. In its diseases the interior surface of the pericardium Its changes offers a strict analogy to those of other serous cavities, as the pleura, peritoneum, and membranes of the brain; its surface being covered with coagulable lymph, the fluid which its surface exhales being increased in quantity, and the membrane itself increased in thickness by an attack of inflammation; whereas its fibrous lamina, as other fibrous tissues, is in all probability affected by rheumatism. Though the membrane lining the heart and arteries bears a certain analogy to, and has been classed by the ingenious Bichat amongst, the serous membranes, yet there are peculiarities in its structure and functions, as well as in its pathological conditions, which are not found in the other membranes of that class. Like all serous membranes it has a surface intended to facilitate the motions of certain parts on one another; yet it might be expected that the same peculiar structure of its surface as the serous membranes have would not be requisite, or would not be adequate, for the movements of the intestines upon each other, or of the surface of the lungs upon the pleura, or of the brain upon the cranium. Hence we find that, as the lining, not only of the cavities of the heart, but of the whole sanguineous system, is intended for the transit of the blood with as little friction as The endocarstructure. Traité sur les dium-its Membranes. Its peculiarities. Its changes in disease. possible, the surface of this tunic is remarkable for its smoothness and polish. At the same time the lining membranes of the arterial and venous systems are somewhat different, that of the venous system being thinner, having greater powers of extension, and being less brittle and less easily torn than the inner coat of the arterial system. Neither does it appear at all improbable, from the office required of this tunic of the vascular system, that there is any fluid exhaled upon it, no moisture being requisite to render the flow of the vital stream easier along the highlypolished and slippery vascular canals; in this respect, being unlike the pericardium, pleura, or peritoneum, these surfaces are moistened in order to prevent the friction of solid substances upon one another. The most remarkable feature, and in which this membrane differs from all other serous membranes, in its diseases, is the patches or stains, of a bright scarlet colour, that are so frequently found upon it, and which cannot be traced either to an increased vascularity, as no distinct vessels can be detected in it, nor from the effect of imbibition, for it cannot be imitated by macerating an artery in blood. There is also to be observed a striking difference in the quantity of effused lymph in the interior and exterior membranes of the heart and aorta, when these have been inflamed, as we seldom or never find those large masses of coagulated lymph effused in the cavities of the heart, or upon the surface of the aorta, so constantly met with in pericarditis; and, although there may be an exudation of coagulable lymph from the inflamed endocardium, it is probable that more or less of it will be washed away by the stream of blood which is constantly passing over it. On reviewing what has been now said of the peculiarities in the structure, functions, and morbid changes of the lining membrane of the vascular system, it appears to me that it is a tissue sui generis, and ought not to be considered simply as a serous membrane. There is also upon the exterior of the heart a quantity of adipose substance, the uses of which have never been explained, and all we know is, that, unlike the rest of the body, it is usually met with in the largest quantity upon the hearts of the thinnest people, and none of it is found on the hearts of wild animals. of the heart. The coronary arteries of the heart are not only of larger The arteries dimensions than other arteries, in proportion to the bulk of the organ which they supply, but they present a striking peculiarity in their origin and in their course. These arteries arise from the root of the aorta in such a manner that, under all circumstances, the free entrance of the blood into them cannot be interrupted. In consequence of their mouths opening into the "lesser sinuses" or pouches of the aorta, the current of the blood ejected from the left ventricle is not able to press the semilunar valves against the sides of the aorta, so that the flow of blood is not impeded into the coronary vessels; and, likewise, as the semilunar valves are kept in the middle of the current of the retrograde blood, the orifices of the coronary arteries are constantly open, and thus the supply of blood to the heart is never interrupted. In their course, the coronary arteries exhibit a great peculiarity, described by Professor Jeffrey, and to which I shall afterwards have occasion to refer, when pointing out the influence of muscular contractions upon the circulation in arteries. These vessels, in place of being encircled by, or intermingled with, muscles, pass along the tendinous and deep grooves which separate the auricles from the ventricles; and by which simple contrivance neither the arteries nor the See Appendix (B). The coronary veins. Their structure. the ventricles are drawn, by which it is evident that neither their contraction nor relaxation can have any influence on the transit of the blood. (a, a, a), the muscular parietes of the right and (b,b,b), the parietes of the left ventricle. (c, c) and (d, d) are the mouths of the right and left coronary arteries and veins. The two coronary arteries supply with blood not only the muscular structure of both auricles and ventricles, and the coats of those portions of the large arterial trunks which are within the pericardium, but some of their branches are reflected on the aorta and pericardium itself. These branches also inosculate with branches of the internal mammary and bronchial vessels, thus establishing a vascular connection amongst the different structures of the heart-a connection which is exemplified in many diseases. The coronary arteries inosculate very freely with one another, and the surface of the heart is covered with a prodigious number of minute branches injected and beautifully delineated by Ruysch. In the accompanying diagram some of the most important Fig. 2. branches of the coronary arteries and their principal anastomoses are represented. Having shown the contrivances by which the coronary arteries provide the structure of the heart with a constant supply of blood, we are next led to inquire by what mechanism the coronary veins carry on the venous circulation, Although there is a regurgitation of the venous blood into the two vena cava, caused by the contractions of the right auricle, any reflux of the venous blood into the great coronary vein is completely guarded against, that vessel having a semilunar valve placed at its mouth. By this mechanism no venous blood can pass from the auricle into the vein during the auricular contractions ; and at the same time a provision is made by the sinus venosus for receiving whatever blood may flow into the great venous trunk during the closure of its mouth. This sinus, or enlargement of the coronary vein, seems to me to perform here the office of a receptaculum, being so placed in relation to the ventricle and auricle that their systole and diastole cannot influence its circulation, and receiving the blood coming from all the venous branches into the great trunk, until its mouth is again opened by the auricular diastole ; and thus any over-distention of the veins in the substance of the heart is carefully guarded against-a circumstance which would inevitably take place was there no sinus. From the arrangement of the coronary vessels it may be readily understood how disturbances in their functions should be materially affected when the cavities of the heart become congested, or when morbid changes are going on in its different structures: subjects which have hitherto excited but little attention from pathological inquirers. The sinus venosus use of. Jeffery's Obthe Heart. servations on See Appendix In general, throughout the system, it may be observed, that the blood in the veins flows in an opposite direction to that in the arteries, so that the two streams of blood are, as it were, opposed to each other. But, in the heart, the current of the blood in the large branches of the coronary veins, which vessels are placed alongside the coronary arteries, runs in the same direction with the blood in the arteries. The heart has a smaller proportion of nerves than some The nerves of other organs; and these, being derived both from the great sympathetic and par vagum, explains the influence which the mind exercises on the heart, as well as its sympathies with the respiratory and digestive apparatus. (C). the heart. Independently of such diseases as are confined either to Its diseases. the pulmonic or systemic heart, each of the heart's structures is liable, as similar tissues in other organs into the composition of which they enter, to be affected separately, or they may be all involved in one disease; and, whenever any part of the structure of the heart is changed, some of its D |