They are the set of tubes that commence from each heart as a single trunk, from which they extend, in one case to the lungs, in the other they divide and subdivide till they reach all parts of the system. They are dense, tough, cylindrical tubes, which form they retain when emptied of blood, and even after death. From this circumstance the ancients regarded the arteries as air vessels.HBH 68.4

170. How many coats or layers of membranes compose the arteries?HBH 68.5

Three: the outer coat is of sinewy fibers; the middle is muscular, being made up of contractile fibers; the inner is like the lining of the heart and veins. It is nervous; or, in other words it is a membrane through whose substance are interspersed the nerves of organic life. The outer coat is firm and strong; the middle is thick and soft; and the internal thin and polished. The arteries maintain a cylindrical form unless forcibly compressed.HBH 68.6

171. What is the particular benefit of the muscular or elastic structure of the arteries?HBH 69.1

It allows the arteries to distend when the heart forces the blood into them, and, when its action intermits, the arteries return to their former size, which propels the blood forward, and thus the action of the arteries themselves is like that of compressed air in fire engines; so that arteries not only lead the blood to the different parts of the system, but they force it along.HBH 69.2

172. What is the number of the arteries, and what their capacity?HBH 69.3

They number about one-third as many as the veins in the system generally, and their capacity is about one-half that of the blood vessels in the lungs; but as the arteries receive the blood directly from the heart, it is forced rapidly through them.HBH 69.4

173. Where are the arteries placed?HBH 69.5

The arteries are buried deep in the flesh, and this serves two purposes: first, its warm current is less exposed to loss of heat; and secondly, they are less likely to be tapped by superficial injuries.HBH 69.6

174. How can it be known in case of a wound that an artery has been severed?HBH 69.7

When an artery is cut, and not closed by the effect of the injury, the blood flows in jets, corresponding with the pulsations of the heart. It will flow in such a case with serious rapidity, and life will be lost, unless the flow is speedily stopped by forcible compression. In case an artery is severed, if possible, a bandage, handkerchief, or cord, should be drawn tightly over the artery, between the wound and the heart. This bandage should be twisted tightly by the aid of a stick inserted beneath it while loosely tied. A knot may be made in the bandage and placed over the artery, or a smooth stone, a chip, or a few pennies may be placed under the bandage to produce pressure directly on the artery. An elastic suspender, or something of that kind, makes the best bandage, as it does not wholly check the flow of the blood. Blood is essential to the vitality of the parts immediately around the wounded part, and it would be better to lose a little blood than to have none received below the wounded part. There are cases when the flow of blood can only be stopped by taking up and tying the artery. If you find your efforts to check the blood failing, immediately secure a good surgeon to assist you.HBH 69.8

175. How do the arteries of the system arise?HBH 70.1

They arise from the left ventricle of the heart by a single trunk called aorta, or air-keeper, that turns down with a beautiful arch, from which branches sweep out into the arms and lead directly up to the head. The main subdivisions above and below are few and large, as may be seen in Fig. X. Throughout their entire length, however, they give off numerous small branches and twigs.HBH 70.2

176. How many classes of arteries are there in the greater or systemic circulation?HBH 70.3

There are twenty-three classes, and these are all used to convey the pure or arterial blood through the body.HBH 70.4

PICTURE AND TEXT
Figure X
PICTURE
THE ARTERIAL SYSTEM

177. What is noticeable in Fig. X concerning the principal branches of arteries?HBH 71.1

That those which start immediately from the aorta, or main artery, are at right angles with it, which moderates the impetus of the blood; but those branches toward the extremities of the arteries leave the main branch at an acute angle, which will aid the blood to a more rapid flow there.HBH 71.2

178. Is there more surface covered by the branches of the arteries combined, than in the main artery, and why?HBH 72.1

The combined area of the ultimate terminus of the arteries is vastly greater than that of the main trunk of the arteries. This arrangement allows a more quiet motion of the vital current in the extreme vessels, where decomposition and reforming of structure is effected.HBH 72.2

179. Is there any connection between the arterial tubes in the various parts of the body?HBH 72.3

Yes; in all parts of the body the arterial tubes communicate with each other by branches passing between them, called inosculations, and these connections increase in frequency as the vessels diminish in size, so that their final distribution is a complete circle of inosculations. This arrangement provides against obstructions, which are liable to occur in the smaller branches of the arterial tubes. When one of these branches is obliterated another branch above enlarges and makes up the loss in the circulation.HBH 72.4

180. What are the pulmonary arteries?HBH 72.5

They are the arteries which carry the impure blood into the lungs. The right pulmonary has three branches, which carry the blood to the three lobes of the right lung. The left pulmonary is the largest division; it passes to the root of the left lung. The pulmonary arteries divide and subdivide in the substance of the lungs, and finally terminate in a net-work of capillary vessels around the air cells and passages of the lungs.HBH 72.6

181. How is the substance of the lungs nourished?HBH 73.1

The pulmonary arteries which convey the blood from the heart to the lungs, and the veins which carry the blood back from the lungs to the heart, act no part in nourishing the substance of the lungs. But the bronchial arteries, and their corresponding veins, extend to every portion of the pulmonary structure; with these is connected a capillary system of muscles, and nerves of organic life, which preside over the process of building up and keeping in repair the lungs themselves.HBH 73.2

182. Do the arteries empty directly into the veins?HBH 73.3

They do not; but they empty into what is called the capillary system, which is an extremely minute net-work of vessels and nerves from which the veins arise.HBH 73.4

4 THE CIRCULATION OF THE BLOOD

CAPILLARY SYSTEM