HEART and CIRCULATION. Aorta: During foetal life, there is a communication between a, ascending arch of aorta; Rs, the arch of the A. and the pulmonary artery called the coronary n ductus arteriosus, the canal of which becomes obliterated c, right earOtid; left carotid; after birth. It has been calculated that the velocity of e, lefa subclavian; f, thoracic the blood in the ascending part of the arch is 21 in. in , , a second. The pressure of theblood in the A. of a horse coronary or' gastric; I, splenic; has been estimated to be 11 lbs.; and in man's, 4 lbs. m, hepatic; n, superior mesen 6 ozs. teric; oo, renal arteries: p, hi ferior mesenteric • p', sperrnat The coats of the A. are very subject to fatty disease ic; q, common iliac; r, middle termed atheronia (q.v.), and in advanced life, to calcare- sacral.
ous degeneration or deposit of earthy particles, which destroys their elasticity. This change renders them very liable to aneurism (q.v.), which, as may be expected, is gen erally situated at the curves of the A., especially at the arch. Sufferers from this disease
in the arch or thoracic A., suffer from palpitation within the chest, difficulty of breath ing, occurring in paroxysms and during sleep, and shoots of pain through the chest. If the aneurism is on the arch, it generally presses forward, and may completely destroy the breast-bone, forming a pulsating tumor, covered only by the skin, or it may press up into the neck. If low in the chest, the aneurism may compress the thoracic duct, and cause emaciation. In the abdomen, the symptoms are pulsation and pain; but in both situations aneurism may exist for a length of time without attracting attention.
In some cases the A. has been found obliterated, showino. that the lower extremities can be supplied with blood by the anastomosing branches. showing Astley Cooper and other surgeons have tied the A. for aneurism, but without success.