THE VASCULAR SYSTEM. 



ARTERIES. 



THE arteries are vessels which convey blood from the 

 heart to the tissues and organs. The largest arteries are 

 the aorta and pulmonary. The aorta springs from the 

 left ventricle and transmits oxygenated blood to every 



part of the body. The pulmo- 

 nary artery comes from the right 

 ventricle and conveys the blood 

 charged with carbonic oxide to 

 the lungs, there to be oxygen- 

 ated. An artery, as it follows 

 its course, branches repeatedly, 

 often dichotomously, and forms 

 frequent anastomosis among its 

 branches. Each time an artery 

 gives off a branch its diameter 

 decreases ; where an artery such 

 as the abdominal aorta divides 

 into the two large trunks each 

 trunk has an area larger than 

 one-half the area of the main vessel, and the combined 

 area of the two vessels is larger than the area of the 

 main trunk. The combined area of all the ultimate 

 branches of the arterial tree is many times more than 

 the area of the aorta. The arteries are highly elastic, 

 both in diameter and length, and under the impulse of 

 the blood-wave stretch in length and swell in diameter. 

 They are composed of three coats, external or fibrous, 

 middle or muscular, and internal or serous. The inner 

 and middle coats are closely adherent. The external 

 (23:2) 



FIG. 104. DIAGRAM OF THE 

 CIRCULATION. 



A, heart: B, vena cava; C, right 

 auricle ; D, right ventricle : E, pulmo- 

 nary artery ; F, pnlmonic capillaries ; G, 

 left auricle ; H, left ventricle ; J, aorta ; 

 1, systemic capillaries. 





