The _common aorta_ is short; it originates from the left ventricle (Fig. 61_B_, No. _K_, 14), and is guarded by three _semi-lunar valves_. The aorta breaks through the pericardium just to the right of the pulmonary arteries in a ventral direction; it then turns upward dorsally and to the right of the inferior bodies of the vertebræ. It is then directed anteriorly, and dorsally to the right bronchus, between the right bronchus and the right lung. The right and the left coronaries are given off from the common aorta; they have been discussed. There is next given off the left brachio-cephalic or _brachio-cephalic sinister artery_ (Fig. 61_B_, No. _K_, 10), which is just above the border of the base of the heart. This artery passes upward and slightly forward, over the center of the inferior larynx. Just beyond this point the _subclavian artery_ is given off; this artery later becomes the axillary and the axillary the brachial artery. Then there is given off the anterior and the posterior thoracic arteries; and finally, the pectoral, which supply the pectoralis muscles and later terminate in the carotid, the vertebral, and the cervical arteries. The carotid artery gives off an esophageal artery. The other arterial trunk given off from the common aorta is the right brachio-cephalic or brachio-cephalic dexter (Fig. 61_B_, No. _K_, 18). The right brachio-cephalic artery gives off the subclavian, which continues as the axillary, and continues as the brachial artery. There is given off the anterior and the posterior thoracic, the right carotid (Fig. 61_B_, No. _K_, 11), the vertebral, and the dorsal. The last continues as the cervical. [Illustration: FIG. 61_B_. _K._ The arterial trunks. 1, The middle sacral artery. 2, The hypogastric artery. 3, The posterior mesenteric artery. 4, The ischiadic artery. 5, The femoral artery. 6, The renal artery. 7, The left pectoral artery or thoracico caudalis. 8, The left axillary artery. 9, The left carotid artery. 10, The left brachio-cephalic artery. 11, The right carotid artery. 12, The right brachial artery. 13, The right pectoral artery. 14, The common carotid artery. 15, The posterior aorta. 16, The celiac axis. 17, The anterior mesenteric artery. 18, The right brachio-cephalic artery. 19, The auricular portion of the heart. 20, The ventricular portion of same. 21, Sterno-clavicular artery. 22, Anterior thoracic.