Of the Arteries. 



THE Arteries are cylindrical tubular vessels, which serve to convey blood 

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

 named arteries (a^p, air] tqpttv, to contain), from the belief entertained by 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 

 circulation. 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 situations, 

 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 intoseveral 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 isclichotomous, as, for instance, the 

 aorta dividing into the 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 lum- 

 bar 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 combined 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 greatly 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, 

 forming what is called an anastomosis (ivd, between ; atopa, mouth], or inoscula- 

 tion : and this communication is very free between the large, as well as between 

 the smaller branches. The anastomoses between trunks of equal size are 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 very free anastomoses between 

 their larger branches. In the limbs, the anastomoses are most frequent and of 

 largest size around the joints; the branches of an artery above freely inoscu- 



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