116 ANATOMY FOR NURSES. [CHAP. X. 



The arteries unite at frequent intervals when they are said 

 to anastomose or inosculate. Such inosculations admit of free 

 communication between the currents of the blood, tend to pro- 

 mote equality of distribution and of pressure, and to obviate 

 the effects of local interruption. 



Arteries commonly pursue a tolerably straight course, bat in 

 some parts of the body they are tortuous. The facial artery 

 in its course over the face, and the arteries of the lips, are 

 extremely tortuous, so that they may accommodate themselves 

 to the movements of the parts. The uterine arteries are also 

 tortuous, to accommodate themselves to the increase in size of 

 the uterus during pregnancy. 



In describing the distribution of the arteries we shall first 

 consider the artery arising from the left ventricle of the heart, 

 the aorta, and its branches. 



The aorta. The aorta is the main trunk of the arterial sys- 

 tem. Springing from the left ventricle of the heart, it arches 

 over the root of the left lung, descends along the vertebral col- 

 umn, and after passing through the diaphragm into the abdomi- 

 nal cavity, ends opposite the fourth lumbar vertebra by dividing 

 into the right and left common iliac arteries. In this course 

 the aorta forms a continuous single trunk\ \\ttdch gradually 

 diminishes in size from its commencement to its termination 

 -(from 28 to 17 mm.), and gives off larger or smaller branches 

 at various points. It may be divided into the ascending aorta, 

 the short part which is contained within the pericardium ; the 

 arch, the part extending from the ascending aorta, and forming 

 a well-marked curve in front of the trachea, and around the root 

 of the left lung to the border of the fourth dorsal vertebra ; the 

 descending thoracic aorta, the comparatively straight part extend- 

 ing to the diaphragm ; the abdominal aorta, below the diaphragm. 

 The ascending aorta gives off two small branches, the right and 

 left coronary arteries, which supply the substance of the heart 

 with blood. The arch gives off three large trunks, the innomi- 

 nate, the left common carotid, and the left subclavian artery. 



The innominate artery arises from the right upper surface of 

 the arch, ascends obliquely towards the right, until, arriving on 

 a level with the upper margin of the clavicle, it divides into 

 the right common carotid and right subclavian arteries. Its usual 

 length is from one to two inches. 



