Page:The New International Encyclopædia 1st ed. v. 01.djvu/743

ANZIO. lation, in IflOl, 35G1. Consult Sofvcdini, Sforia di Anzio (Rome, 1879). AOMORI, ii'6-mo'r^, or AWOMORI, ii'woiiu.'ie. A town of Japan, capital of the prefecture of the same name, situated at the northern end of Honshiu. on the Aomori Bay (Map: Japan, G 3). It is a station on the Northern Railway and carries on a considerable trade with Hakodate. In appearance it differs from most Japanese towns, its streets being wide and straight. Pop. 1898, 28,000. AO'NIA (Gk. 'Aovia). A part of Boeotia, so called frniii the Annes, an old barbaric tribe who settled in this region. The Muses, as dwelling on Mount Helicon, in Aonia, were called Aonides. A'ORIST (Gk. dipio-Tos, aoristos, -nnthout boundaries, indefinite, from d, a, priv. 4. 6pifeii», hori:€in, to divide, to bound). A form of the Greek verb by which an action is expressed as taking place in an indefinite past time. In dis- tinction from the imperfect, the aorist expresses only the occurrence of an action or the entrance into a state or condition, while the imperfect represents an action or state as going on or re- peated in past time.

AORTA .4, ascending arch of aorta; s.s. coronary arteries: b', Imiiiininata artery: b, right wubclavian : c, right carotid; d, left carotid ; e, left subclavian ; /, thoracic aorta ; gg, diaphragm ; ii, phrenic arteries; i, coeliac axis; k. coron- ary or gastric; f. splenic; m, hepatic: d, superior mesen- teric; 00, renal arteries; p, spermatic; q, common iliac; r, middle sacral. AOR'TA (Gk. dopTij, aorte, from aeip^iv, aeirein, to lift, raise I. The great arterial trunk which, rising from the left ventricle of the heart, sends its branches ramifying through the whole body. The aorta in man is subdivided by anatomists into the arch, the thoracic aorta, and the abdominal aorta. The arch is a loop with the convexity directed upward, forward, and to the right side, reaching at its highest part to a level with the second piece of the breast-bone, and then descending to the left side of the fourth dorsal vei-tebra. Five arteries arise from the arch — viz., two coronaries, for the supjily of the muscular tissue of the heart itself: the innominate, and the left carotid and left suix-lavian arteries. At the commencement of the arch are three small swellings or pouches, the aortic si- nuses, below which are the three semilunar valves or folds of the lining membrane, which prevent regurgitation of the blood into the heart. The thoracic aorta extends from the fourth dorsal ver- tebra to the diaphragm, gradually occupying the mid line of the spine. The thoracic aorta gives off the bronchial arteries (two or three) to sup- ply the tissue of the lungs : and some small branches (three or four) to the oesophagus, and intercostal arteries, to supply the walls of the chest (ten on left, and nine on right side). The ahdominal aorta passes from the diaphragm to the fourth lumbar vertebra, opposite the lower margin of which it divides into the two common iliac trunks. The abdominal aorta gives ofi' the two phrenic arteries to the diaphragm; the cceliac a.xis, which divides into three large branches for the stomach, liver, and spleen; the superior mesenteric for the small, and part of the large intestine; the renals (two) ; the supra- renals (two), one for each kidney; the sper- matic; the inferior mesenteric, for the part of the large intestine not supplied by the superior mesenteric; and four or five lumbar arteries, which supply the lower part of the abdominal walls (the loins). Where the aorta bifurcates, a small artery, the sacramedia, or caudal artery, arises, and passes along in the mid line; in fish and in animals with large tails, this branch is a continuation of the aorta.

The above is the usual arrangement; but occasionally it varies, especially in the number of arteries springing from the arch. The aorta has the same coats as one of the large arteries — consisting of an inner coat, the intima, a middle coat, the media, and an outer coat, the adven- titia. The aorta differs from an ordinary artery in the absence of a distinct elastic membrane limiting the intima, and in the very large amount of elastic tissue intermingled with the smooth muscle of the media. ( See Abteey ; ClBCU- LATION. ) During fcetal life, there is a communi- cation between the arch of the aorta and the pulmonary artery called the ductus arteriosus, the canal of which becomes obliterated after birth. The velocity of the blood current in the carotid artery has been estimated at 300 to 500 milli- metres per second. In the aorta the velocity must be considerably greater. The pressure of the blood in the aorta of a dog has been found to be 121 millimetres of mercury. In man the pressure must be at least as great. For diseases to which the aorta is subject, see Abtery and Abterio-sclebosis. AOSTA. a-os'ta (anciently Lat. .it/ (/usfa) . A town in northern Italy, on the left bank of the Dora Baltea, 49 miles northwest of Turin ( Jlap: Italy, B 2). Originally the capital of the ancient Salassi, it was converted. into a Roman colony by Augustus, as a punishment for the depredations of its former inhabitants. Monuments of the ancient city are a well-preserved arch, two gateways, the ruins of an amphitheatre, and a bridge. The cathedral was built in the Sixth Century,