THE AETERIES. 



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 (d^p, air ; rypslv, 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 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 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 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 with one another, forming 

 what is called an anastomosis (civa, 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 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 communicating trunk ; it is also found in the abdo- 

 men, the intestinal arteries having very ample anastomoses between their larger 

 branches. In the limbs the anastomoses are most numerous and of largest 

 size around the joints, the branches of an artery above inosculating with branches 

 from the vessels 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 twigs these inosculations become so numerous as to constitute 

 a close network that pervades nearly every tissue of the body. 



Throughout the body generally the larger arterial branches pursue a perfectly 

 straight course, but in certain situations they are tortuous ; thus, the facial artery 

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

 their course, to accommodate themselves to the movements of the parts. The 



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