An artery, (from air, and to keep,) because the ancients supposed that only air was contained in the arterial system; but by the word artery, Hippocrates meant what is now known by the name of aspera arteria; nor were the veins distinguished from the arteries in the oldest times: for among the ancients, was applied both to arteries and veins; and, indeed, some of our more modern writers use the term vena when speaking of the pulse.
An artery is a strong elastic ramifying tube, arising from the heart. The arteries are properly but two; they rise from the two ventricles of the heart; one of them is called aorta, which see: the other is named the pulmonary artery, for it springs from the right ventricle of the heart, and is wholly confined to the lungs. See Pulmones.
The figure of an artery somewhat resembles a tree; the smaller ramifications of the arteries frequently anastomose with each other, as may be observed in the coats of an intestine when they are injected. The largest appearance of this kind is in the vertebral arteries, which unite in the skull. The use "of the anastomosis is to keep up an equal circulation, and to prevent the bad effects of partial obstruction.
It is generally said that the arteries are of three kinds, viz. the sanguine, which circulate red blood; the serous, through which serum only is naturally conveyed; and the lymphatic, whose contents are lymph: it is also said, that if the blood is pushed into serous vessels, it is there obstructed, and produces inflammation. In reality, however, they are all the same tube continued, which gradually divides into branches, and these branches grow smaller the further they are from the heart. Near to the heart the thicker blood circulates; the force of the circulation is there stronger; and far from the heart the circulation lessens in its vigour, so the thinner fluids are only conveyed in the smaller branches. But if by exercise, or other means, the heat of our bodies is increased, the circulation is pushed forward, the red blood and other orders of thinner fluids can proceed to where still thinner fluids only circulated before; for the smaller vessels can descend to the capacity required by a more active circulation, and contract again to their former dimensions when the distending force is removed.
Arteries terminate three ways; the most common is into veins. Harvey discovered, or demonstrated, the circulation of the blood; but Malpighius first observed, that the last branches of an artery, running into minute divisions, dispose themselves on a membrane as on a firm base, and there open into one another by the mutual intercourse of small canals; he first traced out these canals, through numerous mazes and windings, through which they convey the blood; but here the small branches, disposed with great nicety, extend over equal spaces, and destitute of lateral shoots, as being no longer subdivided, constitute the origins of the veins and lymphae-ducts, with their sinuses. There are, however, many reasons to believe that the arteries and veins do not form continuous canals; but that some minute follicles are interposed. When the action of the minuter arteries is increased, as in blushing, the veins do not swell, and the pulsation of the former is lost before the vein commences; nor, in any injection, is the wax continued unbroken, from the extremity of the artery to the commencement of the vein.
The next termination of arteries is into little cavities or sinuses, as in the corpora cavernosa penis; the last is into excretory ducts.
The arteries generally lie deep, and always run on the inflected side of the limb, as in the axilla, and the inner part of the cubit: this situation prevents their being either too much stretched or compressed in the various motions of the body.
In the beginning of each of the large arteries before mentioned, there are three valves, which appear like purses, and prevent the return of the blood to the heart (see Cor); the other parts of the arteries are free from valves.
The coats of the arteries are three. 1. The external, containing a great number of blood vessels: many nerves run through it; it is elastic; and its fibres run in every direction.
The middle is composed of fibres which are disposed circularly, and nearly parallel to each other.
3. The Internal is a thin membrane, whose surface is very smooth, to give an easy passage to the blood.
Notwithstanding the disputes which have occurred among anatomists relative to the substance of these coats, it is pretty well understood that they are formed of muscular fibres and elastic ligaments, the inner being membranous and remarkably strong; and that the muscular fibres themselves are probably possessed of elasticity, as well as the ligament. The muscular fibres of the smaller arteries are in proportion more numerous than of the larger; since in Dr. Hunter's experiment of bleeding a horse to death, the aorta was contracted only one-twentieth of its natural area, and the radial one-half. The experiment is not indeed conclusive, because in the article of death, the blood is not propelled to the small ramifications. In a certain degree, however, the fact is true; and the object of this structure is, to support the circulation at a distance from the original source of motion.
The cellular membrane is improperly numbered among the coats of the arteries, for it only connects the real ones.
The nearer to the origin, the weaker are the arterial coats; whence the frequency of aneurisms in the beginning of the aorta.
Arteries are sometimes found of a serpentine form; but they are not so in a natural state of health, except during particular actions, and then they recover their original state as soon as the temporary cause is removed. This cause is the dilatation: the coats are elastic, therefore, whatever distends them must at the same time lengthen them, and thereby produce serpentine turns. This frequently happens in injecting the arteries of dead bodies: in the viper it is very apparent in an artery which runs along the outside of its lungs; every time that the heart beats, this artery is seen in a serpentine form. The arteries of the uterus are more convoluted in the last months of pregnancy than they were before conception; so far is the common observation from being true, that the uterine arteries have naturally a serpentine course to admit of the enlargement of that organ in pregnancy, without stretching the arteries.
The arteries are liable to ossification, particularly the iliac and crural; this happens where an amputation is performed: a caustic is necessary. The ossification begins in the internal membrane, which first thickens, then ossifies in distinct centres till these, enlarging, unite, and the whole becomes bone. This disorder afterwards extends to the outer coats, and a mortification is generally the consequence. See Mortificatio.
The particular arteries may be seen under their respective names, but we shall here describe their general course. From the right ventricle of the heart arises the pulmonary artery, which is wholly distributed in the lungs.
The aorta arises from the left ventricle of the heart, and immediately sends off the coronary arteries into the heart and its auricles. From the upper part of the arch of the aorta rise the carotids, which supply the head.
Near the carotids rise the subclavian arteries, which send off the internal mammary, the upper diaphragmatic, and others, which arc dispersed in the breast: when the subclavian hath passed out of the thorax, it receives the name of the axillary artery; and when in the arm the humeral, and in the fore arm the Cubital.
The upper portion of the aorta descendens sends off the Bronchiales, Oesophage.s, Intercostales, &C.
The inferior portion of the aorta sends off the inferior, Diaphragmatic, Coeliac, Mesenteric, Spermatic,
Emulgents, &c; then dividing into two, forms the iliac artery, which sends off branches about the lower part of the belly; then descending into the thighs, legs, and feet, form the crural, tibial, etc.
Wounds of the large blood vessels require amputation too frequently; the great quantity of blood which would be lost, if the usual methods to restrain haemorrhages should fail, would endanger, if not destroy, the patient. After a ligature is formed, the circulation may be duly carried on by the anastomosing vessels; if it should not, the operation will be indispensable, to prevent mortification. The intercostal artery, when wounded, is fatal. Wounds of the arteries in the hands are dangerous. The popliteal artery in the ham, if injured, absolutely demands amputation, unless the operation recommended by Mr. Hunter, in case of the popliteal aneurism, should succeed. See Aneurism. The humeral artery, if injured high up, requires the amputation of the arm. Bell's Surgery, i. 97, etc. White's Surgery, 173.
Arteria aspera. See Aspera arteria.
Arteria venosa. The pulmonary artery was so called by the ancients, from a mistaken notion that the veins came solely from the right, and the arteries from the left, ventricle.