[Illustration: FIG. 31—The arteries of the face and scalp. (Gray) FIG. 32—The external carotid and its branches. (Gray)]
The arch of the aorta now continues into the thoracic aorta, so called while it is in the thoracic cavity, and after it has passed through the diaphragm becomes the abdominal aorta. At a point opposite the umbilicus or navel the abdominal aorta divides into the two common iliac arteries. Each common iliac artery divides into an internal iliac artery, which supplies the organs of the pelvic cavity, and an external iliac artery, which passes beneath Poupart's ligament. As the artery passes down the leg it is known as the femoral artery, until it passes into the popliteal space, where it is called the popliteal artery. About one inch below the popliteal space the artery divides into the anterior tibial artery, which runs on a straight line down the front and outside of the leg to a point between the big toe and the one next to it, and the posterior tibial artery which passes down the back part of the foreleg between the inside ankle and the heel. The peroneal, a branch of the posterior tibial, passes down the foreleg between the outside ankle and the heel. The anterior tibial artery, as it passes through the instep is known as the large dorsal artery and further on is known as the small dorsal artery. In the foot is the plantar arch, formed by branches of the posterior and anterior tibial arteries, which send out branches to each toe.
[Illustration: FIG. 33—The anterior tibial artery. (Gray) FIG. 34—The popliteal, posterior tibial, and peroneal arteries. (Gray)]
Coming off the femoral are the deep femoral and the anastomotica magna arteries, which anastomose and form collateral circulation to the foreleg by means of the recurrent anterior and posterior tibial arteries.
Coming off the subclavian arteries are the superior and inferior mammary arteries, which pass down over the chest wall, anastomose and give collateral circulation to the lower extremities by means of the superior and inferior epigastric arteries, branches of the external iliac and femoral arteries.
The thoracic aorta gives off the intercostal arteries, which supply the ribs, the bronchials which supply the lungs, the esophageal which supplies the esophagus, and the pericardiac which supplies the pericardium.