Coming off the subclavian arteries are the superior and inferior mammary arteries, which pass down over the chest wall, anastomose and give collateral circulation to the lower extremities by means of the superior and inferior epigastric arteries, branches of the external iliac and femoral arteries. The thoracic aorta gives off the intercostal arteries, which supply the ribs, the bronchials which supply the lungs, the esophageal which supplies the esophagus, and the pericardiac which supplies the pericardium. The abdominal aorta gives off in rotation the coeliac axis, which as a hub in a wheel gives off three spokes, the gastric artery to the stomach, the hepatic to the liver, and the splenic artery to the spleen. The next branch is the phrenic, which supplies the diaphragm, then the suprarenal artery, two or more in number coming off of both the aorta and the renal arteries. The suprarenal arteries supply the suprarenal capsules. The next branch is the superior mesenteric artery, which supplies the small intestines; the next branch is the renal arteries, which supply the kidneys; the next branch is the spermatic or the ovarian arteries, which supply the testes in the male or the ovaries in the female; the inferior mesenteric artery, which supplies the large intestines. Also coming off the aorta at regular intervals are the lumbar arteries, which supply the side walls. =The Capillary Circulation.=—The capillaries are very minute blood vessels, forming a network between the terminating arteries and the commencing veins. They derive their name from the word capillus (hair). They vary in size from 1-3500 to 1-3000 of an inch, the largest capillaries being those of the skin. These little vessels are so thickly distributed throughout most of the tissues of the body as to make it impossible to insert a cambric needle in the flesh without pricking scores of them. When we embalm a body the object should be to introduce a sufficient amount of fluid through the arterial system so that these tiny capillaries will be filled. These little vessels are so minute and the walls are so thin that the fluid is immediately taken up into the tissues. If every tissue of the body can be supplied with fluid by means of the capillaries, we would have the ideal, the body would be perfectly embalmed. Let us then not only be arterial embalmers, but, better still, let us be capillary and tissue embalmers. [Illustration: FIG. 35—Capillaries a, cells; b, nuclei. (Gray)] Capillaries have one wall, which is the continuation of the inner wall of the artery, thus making the capillary so thin that fluid finds its way easily through it into the surrounding tissues. Some parts of the body are more vascular than others and some tissues of the body, such as the cornea of the eye, the epidermis, cartilage, the substance of the brain, etc., are entirely destitute of capillaries.