Page:Laboratory Manual of the Anatomy of the Rat (Hunt 1924).djvu/69

Rh terior facial runs through the parotid gland, and is superficial to the carotid artery. The confluence of the posterior auricular vein and the posterior facial forms the external jugular. The posterior auricular arises behind the external ear.

The internal maxillary will be found superficially on the median surface of the angle of the jaw. Here it curves laterally to join the superficial temporal, thus forming the posterior facial vein.

Exercise XIV. Make a labeled sketch of the veins anterior to the heart. This will be combined later (Exercise XXV) with a similar sketch of the veins posterior to the heart.

The arterial blood leaves the left ventricle of the heart through the aorta. This turns dorsally and to the left, as the aortic arch, and runs caudally through the thoracic and abdominal cavities near the ventral surface of the spinal column. The thoracic and abdominal sections of the aorta are called the thoracic and abdominal aorta, respectively. The aortic arch of mammals is supposed to be homologous to the left fourth aortic arch of lower vertebrates. The branches of the aortic arch in the rat carry blood to the head, neck, fore limbs, and thoracic wall. Named in order from right to left, these branches are the innominate, left common carotid and left subclavian arteries.

The left subclavian artery runs cephalad from the aortic arch, carrying blood to the vessels described below.

Left internal mammary artery. Its origin is the left subclavian artery. It sends branches to the thymus gland, pericardium, and lung. On the inner surface of the ventral thoracic wall it turns medially to the side of the sternum and runs caudally, parallel to the internal mammary