THE ARTERIES. 



Arteries are cylindrical tubular vessels which serve to convey blood from 

 _L both ventricles of the heart to every part of the body. These vessels were 

 named arteries (dr /t o. air : -r^titv, to contain) from the belief entertained bv the 

 ancients that they contained air. To Galen is due the honor of refuting this 

 opinion : he showed that these vessels, though for the most part empty after death, 

 contain blood in the living body. 



The pulmonary artery, which arises from the right ventricle of the heart, 

 carries venous blood directly into the lungs, whence it is returned by the pul- 

 monary veins into the left auricle. This constitutes the lesser or pulmonic circu- 

 lation. The great artery which arises from the left ventricle, the aorta, conveys 

 arterial blood to the body generally, whence it is brought back to the right 

 side of the heart by means of the veins. This constitutes the greater or systemic 

 circulation. 



The distribution of the systemic arteries is like a highly ramified tree, the 

 common trunk of which, formed by the aorta, commences at the left ventricle of 

 the heart, the smallest ramifications corresponding to the circumference of 

 the body and the contained organs. The arteries are found in nearly every 

 part of the body, with the exception of the hairs, nails, epidermis, cartilages, 

 and cornea : and the larger trunks usually occupy the most protected situa- 

 tions, running, in the limbs, along the flexor side, where they are less exposed 

 to injury. 



There is considerable variation in the mode of division of the arteries : occa- 

 sionally a short trunk subdivides into several branches at the same point, as we 

 observe in the coeliac and thyroid axes ; or the vessel may give off several branches 

 in succession, and still continue as the main trunk, as is seen in the arteries of 

 the limbs; but the usual division is dichotomous; as, for instance, the aorta 

 dividing into tne two common iliacs. and the common carotid into the external 

 and internal. 



The branches of arteries arise at very variable angles : some, as the superior 

 intercostal arteries from the aorta, arise at an obtuse angle : others, as the lumbar 

 arteries, at a right angle : or. as the spermatic, at an acute angle. An artery from 

 which a branch is given off is smaller in size, but retains a uniform diameter until 

 a second branch is derived from it. A branch of an artery is smaller than the 

 trunk from which it arises ; but if an artery divides into two branches, the com- 

 bined area of the two vessels is, in nearly every instance, somewhat greater than 

 that of the trunk : and the combined area of all the arterial branches greatlv 

 exceeds the area of the aorta; so that the arteries collectively may be regarded 

 as a cone, the apex of which corresponds to the aorta, the base to* the capillary 

 system. 



The arteries, in their distribution, communicate freely with one another, form- 

 ing what is called an i.'fn-'tst'.'/iiosis (d^d. between; <rro ( a, mouth), or inosculation ; 

 and this communication is very free between the large as well as between the 

 smaller branches. The anastomosis between trunks of equal size is found where 

 great freedom and activity of the circulation are requisite, as in the brain; here 

 the two vertebral arteries unite to form the basilar. and the two internal carotid 

 arteries are connected by a short communicating trunk ; it is also found in the 

 abdomen, the intestinal arteries having verv free anastomoses between their larger 



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