387. CHAPTER VI. THE PECULIAR ARTERIES AND VEINS OF THE HEART, AND THE CORONARY VESSELS.
LANCISI. "It is to be observed in the first place, that the coronary artery, which arises from the aorta within the pericardium, most generally by two branches, very rarely by three, or by one (if by one, it immediately afterwards divides into two), is so placed as to form an acute angle with the section of the aorta that lies between it and the heart; and therefore it may perhaps be thought, -as the direction of the motion of the blood propelled by the systole of the heart, is not in the same line with the direction of the coronary arteries, but on the contrary forms so acute an angle with them, that only a very small quantity of the stream can flow at that time, and in that direction, into the coronary arteries. But on the contrary, and company, and company.... It should by no means be overlooked, that of the branches of the coronary arteries (with the exception of those that nature dispenses to the adipose follicles of the heart, and to the trunks of the great arteries and veins), the first are distributed to the auricles, and the subsequent branches to the ventricles: consequently the passage of the blood running through the coronary twigs from the aorta to the auricles, is a little shorter than that of the blood running to the ventricles.... It is to be observed that the coronary arteries, by their larger branches, which form wonderful anastomoses with each other, creep over the external surface of the heart, running partly like a crown about its base, and partly in straight furrows as it were from the base to the apex; but that they do not penetrate to the inner muscular substance of the heart except by the minutest twigs. It seems also worthy of remark, that the larger branches, which occupy the external surface of the heart, are covered throughout their course with adipose follicles and little bands; and thus are extremely lax and soft, and if slit up longitudinally with the scissors, they are found to be marked on the inside by minute irregular rugae; and on this account admit of being easily distended and enlarged both in length and breadth ... again it is to be observed, that the coronary arteries have no valves at their immissaries; 1
although Thomas Bartholin, because he happened to meet with valves once or twice (as I myself likewise have done), presumes that they are to be found always. And indeed arteries of this kind require no valvular barriers to prevent the blood from regurgitating into the aorta; since the constant pressure and struggle of the blood in the aorta, is powerful enough on every side effectually to counteract the return of the blood from the mouths of the coronary arteries. But this does not bold in the lesser branches of the coronaries, which dip deeply into the muscular substance of the heart and auricles; for here we find little sphincters and valves beautifully and abundantly distributed. (De Motu Cordis, and company, lib. i., prop. 39.) After attempting in vain by the introduction of a probe, and by other means, to find any valves either in the orifices, or the larger branches, of the coronary arteries, it occurred to us to examine some of the twigs proceeding from them, after having previously opened them with a lancet. Into these then we inserted a bristle, and on pushing it in the direction of the larger branches, we met with an obstruction. In order to prove to ocular demonstration what it was that impeded the further progress of the bristle, and prevented its entrance along the cavity of the branches, and to ascertain whether it was a valve, or anything else, we proceeded with extreme care ... to separate the coronary arteries from the substance of the heart, together with the segment of the aorta from which they issued. These we detached with their large, lesser, and least and most delicate branches, to as great an extent as we could; and we then placed the whole tree of vessels in a basin of water. Having done this, we observed all the extreme vessels, both by reason of their minuteness and of the air they enclosed, spread about in every direction, and floating on the water, so as to present a beautiful appearance, like portions of windweed, anise, or fennel; and we remarked both in the larger and lesser series of tubes a variety of phenomena. We observed first, that the great stems of the coronary arteries, which surround the base of the heart, and reach to its apex, floated in a spiral order and with a spiral motion, and after they were taken out of the water, they could be extended to a much greater length than when they adhered to the heart. On injecting mercury into the coronary artery, it was curious to see the larger branches become corrugated, and the smaller strangulated, as if by nervous threads....When we slit up the trunks of the coronary arteries, and the larger branches proceeding from them, we found the interior membrane much whiter and thicker than in the other arteries (in which the arachnoid membrane is plainly seen); and so much softer, than when we attempted to pull it off, it followed the fingers with more facility than in the case of any other artery. It appeared that this was the case, because nowhere in the body are the arteries placed in greater and more violent motion than in the heart; for which reason the external membrane, as well as the intermediate muscular membrane, falling as they do, so often and so strongly, into contraction and distraction, are in a manner disjoined and separated from the internal membrane; while the innermost membrane runs into numerous rugae, which in some measure perform the office of valves, and pre vent the return of the blood into the aorta, as well as its reaction or resistance a tergo. We observed branches proceeding from the trunks of the coronary arteries, and twigs from the branches, proportionally more numerous and abundant than in the arteries of any other muscle; and not without reason, for since the muscular planes and fascise are far more abundant is the heart than in any other muscle, it is necessary that each line and curve thereof, each bundle, and each fibre, should be tracked by little arteries of its own. We carefully noted the skill of nature in placing at the mouths of each of the larger coronary arteries, where they divided into the smaller, a kind of circular margin or border, and as it were a delicate sphincter.... But at the little mouths of the lesser and least arteries that are distributed through, and buried within, one or other of the muscular planes, we saw valves opposed, which in fact prevented the regress of the blood from the lesser arteries into the larger. This arrangement seems to me to conduce in a remarkable way to the systole of the heart. For when its fleshy fibres begin to be stretched, they are at the same time increased in bulk;... and hence we find that water injected into the coronary arteries, and diffused through the substance of the heart, never runs back even when the heart is compressed; the contrary being the case in the veins, through the mouths of which any liquid that is thrown in, soon regurgitates. But in order to see these valves clearly, we must select the small arteries, and introduce into them a fine probe, or a bristle, gently driving it the wrong way of the vessels, that is, towards the larger branches; for near each of the little mouths that open towards the trunks, we shall observe even with the naked eye, that the membranes of the valves are raised, and the point of the probe or bristle impeded and entangled. But if we still push on the probe, we shall find it clothed and covered with the membrane of the valve, which is thus expanded by force. All these appearances are best seen in the heart of the horse;... for here the valves that hinder the passage of the probe, are raised in every one of the sections or origins of the smaller trunks, until they are either ruptured by force, or else opening out in a contrary direction, give way and sheathe the probe. In like manner small sphincters are here and there clearly observed in the twigs of the little arteries, like little knots, which are seen even in the last ramifications, so far as the microscope will enable us to follow them. (Ibid., prop. 40.) Nature is so variable and inconstant in locating the mouths of the coronary arteries, that a few dissections only, especially if made in the human subject, are sufficient to present us with many varieties.... In those persons who during life had a strong pulse, we generally found the orifices above the margins of the valves: in those who had a moderate pulse, we observed them in the confines of the valves, or one orifice placed above [the valves], and the other below, as Morgagni also has noticed: while in those who had had a small pulse, and particularly in women, we found them for the most part opening behind the margins of the valves. We have observed something similar, but much more evidently, in brutes;... for instance, in horses, in which we have seen the orifices situated more frequently above than below the margins.... In dogs also these orifices open a little above the margins, and in our numerous experiments upon these animals, we have only once or twice found the same immissaries on a level with the borders of the valves; the animals in these cases being gentle of temper and domestic. In slow footed, languid animals, such as oxen and sheep, we saw the orifices buried below the margins of the valves. But whether any, and what, variety, in the motion and how of the blood through the coronary arteries, is produced by the variety of situation in the orifices, is a question of no very easy solution....The membranes of these valves are tendineo-muscular, movable, and in great part free, but nevertheless attached to, and continuous with, the base of the heart, and in three places continuous with the parietes of the great artery. Thus when the heart falls into systole, these membranes, as parts of it, are necessarily s little contracted, and become shorter, as far as they can, both in length and breadth, and company.... In the vivisection of mastiffs (which have the orifices of the coronaries above the margins of the valves), when the thorax is opened and the pericardium divided, we have seen the coronary artery pulsating at the same time with the sorts, both being expanded and constricted simultaneously; and in like manner when punctured, the jet of blood from both, and the interval between the jets, was synchronous. But in sheep, which have the immissaries of the coronary arteries pieced under the valves, we saw the sorts begin its diastole somewhat before the coronary artery, but both completed the diastole at the same time. (Ibid., prop. 41.)
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