ARTERY (Lat. aer and tern) named from the old idea that these tubes were air-car riers. Arteries are the vessels through which the blood passes from the left side of the heart to the tissues. The structure of an arterial tube is very complex, and a section of it may be roughly subdivided into three lavers, called the coats of the artery: an exter nal, which is elastic and distensible; a middle, which is muscular, contractile, and brit tle; an internal, also brittle, smooth, and transparent, being lined with epithelium on the side washed by the Mood. The tube is also enveloped in cellular tissue, termed the sheath of the A. When an A. is Wounded by a sharp instrumerit, 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 allows of a pro fuse hemorrhage. If the A. be completely divided, its walls do not collapse like --:------ .1.
.'..-•”" .t.A10,-te of a vein, but pass through certain changes i, ,,•;\ , provided by nature to prevent fatal bleed- ,, '"r • iug. The cut orifice contracts, and also re- ''.';''';, r tracts into its cellular sheath; this checks :4', ' T - the flow of blood, a clot of which shortly If.T Li.. .; ? ,, i.)4, , .,' .
forms on the outer side; then another forms . tli ik,,-, • , -.,,,,<.-. v,,, inside the vessel; and together, they stem .., ,,, 4.,, the flow, till the cut edges of the A. have ,.,,. , time to throw out lymph (see AmiEstoN), .---- ••• -.., ..*,, , „ ' :. • and heal as wounds of other tissues. When , ' „"4::,,w5.4...-4- 4 . 1/ - an A. is compressed by a ligature, the brittle ,, -‘-zitrz-E_:''--7.::- inner and middle coats crack, curl inwards, and heal. See BLEEDING. I a 3 4 9 a
The arteries of the human body are all offsets, more or less direct, of the aorta. As Subdivisions of arterial wall.
each main trunk passes into a portion of the 1. Epithelial, 'internal. 3. Muscular, t middle. ' 2• Fenestrated, 4. Elastic, I body, it divides into two principal divisions: one, which breaks up into branches for the 6. t external, supply of the tissues in the vicinity—the A.
of supply; and another, which passes almost branchless to supply the parts beyond— the A. of transmission. These, however, anastomose (q.v.) freely, so that the distant tissues are not solely dependent for their supply on only one arterial trunk. Thus, the femoral A. divides in the groin, into the profunda, or deep femoral, to supply the thigh, and the superficial femoral, to supply the leg below the knee. Again, the common carotid divides into external carotid, to supply the neck and head, and the internal car otid to supply the brain. Although arteries have generally the same distribution or ar rangement of branches, they occasionally vary, and thereby are apt to puzzle a super ficial anatomist. Mr. Thomas Nunn of London, an excellent human anatomist, has clearly shown that these anomalies in arterial distribution are all governed by the law of arterial distribution just mentioned, a fact which not only simplifies the study of arte rial anatomy, but assists the operative surgeon out of perplexing positions, The prin cipal arteries will be considered under their distinctive names. The best authority on arteries is the splendid work of R. Quoin. See ARTERIES, DISEASES OF.