ARTERY (bat. arteria, Gk, apntpin arteria, witul-pilw, artery). An anatomical term desig nating any one of the vessels through which the blood passes from the left side of the heart to the tissues, named from the old idea that these tubes were air-earricrs because they are empty after death. The structure of an arterial tube is very complex, and a section of it may be roughly subdivided into three layers, called the coats of the artery: an external, which is elastic and distensible, the tunica adrentitia; a middle, which is muscular, contractile, and brit tle, the tunica media; an internal, also brittle, smooth, and transparent, being lined within by endothelium, the tunica intima. The tube is also enveloped in cellular tissue, termed the sheath of the artery. When an artery is wounded by a sharp instrument, the effect varies with the direction of the cut. Thus, if longitudinal, the edges may not separate, and the wound may heal without much bleeding; if oblique or transverse the edges gape. and a nearly circular orifice al lows of a profuse hemorrhage. If the artery be completely divided. its walls do not collapse like those of a vein. lint pass through certain changes provided by nature to limit hemorrhage. The cut orifice contracts, and also retracts into its cellular sheath ; this checks the flow of blood, a clot of which shortly forms on the outer side; then another forms inside the vessel, and to gether they stein the flow till the cut edges of the artery have time to throw out lymph (see ADHESION), and heal as wounds of other tissues.
When an artery is compressed by a ligature, the brittle inner and middle coats crack, curl in wards, and unite. See BLEEDING.
The arteries of the human body are all offsets, more or less direct, of the aorta. As each main trunk passes into a portion of the body, it divides into two principal divisions: one, which breaks up into brandies for the supply of the tissues in the vicinity—the artery of supply; and another. which passes almost branchless to sup ply the parts beyond—the artery of na )11 iSSiOn. These, however, anastomose freely, so that the distant tissues are not solely dependent for their supply on only one arterial trunk. Thus, the femoral artery divides in the groin into the profunda, or deep femoral. to supply the thigh. and the superficial femoral, to supply the leg be low the knee. Again, the carotid divides into external carotid. to supply the neck and head, and the internal carotid to supply the brain. Although arteries have generally the same distribution or arrangement of branches. they occasionally vary. and may in this way be misleading to the student or the surgeon. Com parative anatomy goes far to explain these ap parent diserepancies in arterial distribution.