THE VASCULAR SYSTEM 55 



terior facial runs through the parotid gland, and is super- 

 ficial to the carotid artery. The confluence of the pos- 

 terior 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. 



ARTERIES ANTERIOR 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 ahdominM aorta, 

 respectively. The aortic arch of mammals is supposed to be 

 homologous to the left fourth aortic arch of lower verte- 

 brates. 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 aortie 

 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 ven- 

 tral thoracic wall it turns medially to the side of the ster- 

 num and runs caudally, parallel to the internal mammary 



