In the limbs and arms the anastomoses are more numerous and of larger size around the joints. The branches of the artery above, unite with branches, from the vessels below. These anastomoses are called collateral circulations. The principal ones of interest to the embalmer are those of the deep brachial uniting with the recurrent radial and ulnar arteries, forming the collateral circulation in the arm; the deep femoral uniting with the recurrent posterior and anterior tibials, forming the collateral circulation in the leg; the superficial and deep mammary arteries, branches of the subclavian artery uniting with the superficial and deep epigastric arteries, branches of the external iliac, forming the collateral circulation over the abdomen and chest, and may be considered the longest collateral circulation in the body. A terminal artery is one which forms no anastomoses; such vessels are found in the heart, brain, spleen, kidneys, lungs and mesentery. _Structure._—An artery consists of an internal, a middle and an external coat. The inner coat consists of endothelial cells and elastic fibrous tissue, sometimes arranged longitudinally, but usually they form a distinct fenestrated membrane (similar to a doorscreen). The middle coat consists mostly of elastic tissue and white fibrous tissue. The external coat is called the fibrous coat. It contains fibrous connective tissue and elastic tissues. _Vasa-Vasorum._—Running in the outer wall of the artery, we find small capillary vessels, and their function is that of nourishing the outer wall, for the blood which passes through the artery does not nourish the artery from within, but depends on these small capillaries, called vasa-vasorum, for their nutrition. The individual sheath, or arterial sheath, the covering for the artery, is composed of connective tissue, and at places may adhere very tightly to the artery. [Illustration: FIG. 9—Valves of the veins. FIG. 10—Cross section through a small artery and vein. (Klein and Noble Smith)] =Veins.=—The veins are the vessels which carry the blood from the capillaries back to the right auricle of the heart, and are found in nearly every tissue of the body. They commence as venous capillaries, uniting together into larger and larger veins, until we have the great ascending and descending venae cavae. In form the veins are perfectly cylindrical, like the arteries, but with this difference, that their walls collapse when empty and that they contain valves. _Structure._—The vein has about the same structure as the artery, only that the middle coat is much thinner and less elastic than the artery, and for this reason it easily collapses. Veins are divided into superficial, deep and sinuses. Superficial veins are found between the layers of the superficial fascia, just underneath the skin. Deep veins accompany the arteries, and are usually enclosed in the same common sheath with the artery.