THE RABBIT 291 



At the anterior end of the heart and between the right and left 

 precaval veins will be seen the pulmonary artery and the aorta. 

 The former springs from the right ventricle and, passing diagonally 

 forward between the auricles toward the animal's left, divides 

 almost immediately into the right and left pulmonary arteries, 

 which carry venous blood to the right and left lungs respectively. 



The aorta, which carries arterial blood to the entire body, issues 

 from the left ventricles slightly to the left of the pulmonary 

 artery ; it almost immediately makes a sharp turn to the animal's 

 left, forming an arch, and passes to the mid-dorsal line of the 

 thoracic cavity, where it runs backward just beneath the verte- 

 bral column to the hinder end of the body cavity. It is thus com- 

 posed of two divisions, the thoracic aorta and the abdominal aorta. 



Study the thoracic aorta and its branches, but do not follow 

 them out of the thoracic cavity. 



The two small coronary arteries, which supply the walls of the 

 heart with blood, leave the aorta at its base, and may be seen by 

 turning the left auricle forward. From the arch of the aorta there 

 extend three (in some rabbits only two) large arteries: the in- 

 nominate, on the animal's right; the left common carotid; and the 

 left subclavian, to the left of the latter. The innominate artery 

 almost immediately divides into two large branches, the right sub- 

 clavian and the right common carotid artery, which carry blood, 

 respectively, to the right foreleg and the head ; the left common 

 carotid (which in some rabbits branches from the innominate) and 

 left subclavian arteries carry blood to the head and the left foreleg 

 respectively. 



Note the several pairs of small intercostal arteries, which leave 

 the dorsal surface of the thoracic aorta at regular intervals and 

 pass along the hinder side of the ribs to the muscles of the body 

 wall ; also the small bronchial and oesophageal arteries, which go 

 to the lungs and the oesophagus respectively. Lying between the 

 thoracic aorta and the vertebral column is the thoracic duct, which 

 is the main vessel for the collection of the lymphatic canals in the 

 hinder part of the body ; through it the lymph is carried forward 

 to the left jugular vein, into which it is poured at its point of 

 intersection with the left subclavian vein. 



