Arteries of the Upper sub clavian artery, mentioned above, after passing under the collar - bone and over the first rib, takes its course through the arm-pit to reach the arm. In the arm-pit it is called the axillary artery. When it has entered the arm it is called the brachial artery. In its passage through the arm - pit the vessel furnishes branches to the chest and shoulder. Fig. 140 indicates the general course of the vessel in the arm and its distribution. If the arm be held straight out from the side, palm up, the course of the vessel is indicated by a line right through the centre of the arm-pit and over the arm to the middle of the front of the elbow. In its course through the upper arm it is covered by little besides skin and fat ; and it gives off branches to the muscles and bone. It be comes deeper at the elbow and there divides into two (Fig. 140), one artery for the radial or thumb side of the forearm—the radial artery, and the other for the little finger or ulnar side — the ulnar artery. The former passes down to the wrist, where it winds round to the back of the wrist and then reappears in the palm be tween the thumb and first finger. The ulnar artery runs to the wrist and passes into the palm, as shown in the figure. The ends of both arteries form arches in the palm, a superficial arch formed by the ulnar, and a deep arch formed by the radial; from the arch near the surface branches proceed to each side of the fingers, and from the deep arch deep muscles and the back of the hand are supplied. It is by the radial artery at the wrist that the pulse is felt. The ulnar artery supplies a branch near the bend of the elbow, which proceeds deeply into the forearm and gives offshoots to the back of the forearm.
Arteries of the Lower has been mentioned that the aorta passes down through the chest, lying alongside of the back-bone. On its way it gives off branches to the organs of the chest—the bronchial arteries to the air tubes of the lungs, branches to the gullet, branches—intercostal—which run between the ribs, &c. In its descending course the aorta passes through the diaphragm (p. 345) and enters the cavity of the belly. Here a short thick trunk leaves it—the coeliac axis—front which arteries arise for the stomach, liver, and spleen.
A little farther on its way it gives origin to two mesenteric arteries, for the supply of the intestine. Similarly other branches pass off from the aorta in the belly for the kidneys —renal arteries. Low down on the front of the back-bone the aorta, as such, ceases by ting into two large vessels—the common iliac arteries—one of which passes to the right, the other to the left. Each one of these speedily splits into two branches, of which one, the internal iliac artery, goes deeply into the pelvis (p. 63), supplying the muscles and organs there, bladder, &c., and gives off vessels to the buttock, while the other, the external iliac artery, issues from the belly about the middle of the groin. This vessel, when it ' has appeared in the front of the thigh, is called the femoral artery. Its general course is indicated in Fig. 141. A line drawn from the middle of the groin over the front of the thigh to a little above the inner side of the knee-joint would pretty accurately map out its course. One noteworthy feature of it is that in the upper third of the thigh it is covered only by fat and skin, but after that it passes deeply into muscles. It is,
therefore, over this upper portion in front of the thigh that pressure is exerted (as shown under ACCIDENTS AND EMERGENCIES) to block the vessel and so prevent further bleeding, otherwise uncontrollable, from any part below. The artery gives off many branches in its course, for the supply of the thigh and other parts. Having reached the inner side of the lower part of the thigh, the vessel passes backwards into the ham, or popliteal space, as that part is called by anatomists, where it receives the name of liteal artery. It courses through the middle of this space over the knee-joint, giving off ous twigs to muscles and to the joint on its way. Below the knee-joint it ends by dividing into two. The course of one of the two, the posterior tibial artery, is shown in Fig. 141, as it passes down the inner side of the leg to the ankle, where it ends in branches for the sole of the foot. In Fig. 142 is represented the course of the other branch, called the anterior tibial artery. Beginning below the knee on the outer side of the leg it courses down the leg towards the middle of the front of the ankle, buried deeply under muscles till it nears the ankle. Its continuation proceeds over the back of the foot to the space between the great and second toes, through which it passes to join vessels in the sole. Fig. 142 indicates how its branches supply the back of the foot.
From this brief account of the general distribution of the arteries in the body it will be seen how all the arteries arise, directly or indirectly, from one large trunk—tile aorta—pro ceeding from the left ventricle of the heart.
Veins of the Head and general arrange ment of the surface veins is indicated in Fig. 143. They are seen convergim towards three main vessels, namely, the externs jugular vein (2 in the fig.), the internal jugular vein (3), and the anterior jugular vein (4). Of these the external jugular begins near the angle of the jaw by the union of a vein from the head and deep parts of the jaw (6) and a vein from the region behind the ear. It passes over the sterno-mastoid muscle (shown in dotted outline) to disappear behind the collar-bone at (1), where it joins another large vessel, the subclavian vein. It is a vessel very near the surface and liable to injury. The internal jugular receives blood from the cavity of the skull and descends in the neck along with the common carotid artery. It is thus placed deeply in the neck and mostly covered by the sterno-mas toid muscle. It joins the subclavian vein, as shown in Fig. 136. In Fig. 143 it is shown receiving a large branch from the face. The anterior jugular vein runs down the neck near to the middle line and joins the external jugular behind the sterno-mastoid muscle. Thus directly or indirectly the veins of the head and neck, which carry the blood from that region back to the heart, all join the subclavian vein, (see Fig. 136), which is a continuation of the large trunk carrying the venous blood from the upper limb. On each side the subclavian vein, just at its point of junction with the internal jugular, passes on to a short trunk, called the innomi nate vein, and the two in nominate veins, one from each side of the body, join to form the superior vena cava (a, Fig. 136), which passes to the right side of the heart. Thus all the blood distributed to the head, neck, and upper limbs is brought back to the heart by one large venous trunk.