The Circulatory System 



167 



the left shoulder and arm. This is the condition that occurs in the 

 human being and in many other mammals, including the rat. In other 

 mammals, the cat for example, only two vessels leave the arch. These 

 are the right and left innominates, each of which gives rise to a com- 

 mon carotid and a subclavian. 



mCHT COMMON CAROTia 



RIGHT SUBCLAVIAN 



LEFT COMMON CAROTID 



AORTIC ARCH 

 PULMONARY 



INTERCOSTAL 



DIAPHRAGM 



LEFT GASTRIC 



SPLENIC 



SPLEEN 



PANCREAS 



INFERIOR MESENTERIC 



LEFT COMMON ILIAC 



Fig. 48. — Diagram of the arterial circulation of a mammal. 



Once the aorta has bent to the left, it follows a straight pathway 

 along the dorsal midline of the body. It penetrates the dorsal portion 

 of the diaphragm muscle and enters the abdominal cavity. At its pos- 

 terior end it breaks into two vessels, the common iliacs, one of which 

 goes to each leg. In animals with tails, the prominent caudal arises in 

 the region of the common iliacs. Its exact position varies. 



Along the length of the dorsal aorta, subbranches are given off 

 to the various organs. In the thoracic cavity, intercostal arteries arise 

 to supply the segmental muscles between the ribs. Esophageal arteries 



