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 rr^uv, to contain air), 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, contained blood in 

 the living body. 



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

 venous blood directly into the lungs, from whence it is returned by the pulmonary 

 veins into the left auricle. This constitutes the lesser or pulmonic circulation. 

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

 blood to the body generally ; from whence it is brought back to the right side of 

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

 culation. 



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

 mon 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 

 animal body, with the exception of the hairs, nails, epidermis, cartilages, and 

 cornea ; and the larger trunks usually occupy the most protected situations, run- 

 ning, 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 cceliac 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 the two common iliacs ; and the common carotid, into the external and internal 

 carotids. 



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

 intercostal arteries, arise from the aorta 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 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 (ava, between ; oro^a, moutli), or inosculation ; and this 

 communication is very free between the large, as well as between the smaller 

 branches. The anastomoses between trunks of equal size is found where great 

 freedom and activity of the circulation is 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 inter-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 inosculating with branches from 

 the vessel below. These anastomoses are of considerable interest to the surgeon, 

 as it is by their enlargement that a collateral circulation is established after the 

 application of a ligature to an artery for the cure of aneurism. The smaller branches 

 of arteries anastomose more frequently than the larger ; and between the smallest 

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