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 (oyp, air; Tr^oslb, to contain) from the belief entertained by the ancients 

 that they contained air. Galen is believed to have been the first to show that 

 during life they contain blood. 



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 periphery 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 a limb, along the 

 flexor side, where they are less exposed to injury. 



There is considerable variation in the mode of division of the arteries; occasion- 

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

 in the celiac and thyroid axes; or the 



vessel may give off several branches in A. B 



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 exter- 

 nal and internal carotids. 



A branch of an artery is smaller than 

 the trunk from which it arises; but if 

 an artery divides into two branches, the 

 combined cross-section area of the two 

 vessels is, in nearly every instance, 

 somewhat greater than that of the 

 trunk; and the combined cross-section 

 area of all the arterial branches greatly 

 exceeds that 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 are called anastomoses or inosculations (Fig. 427); and these communications 

 are very free between the large as well as between the smaller branches. An anasto- 

 mosis between trunks of equal size is found where great activity of the circulation 

 is requisite, as at the base of 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 ample anastomoses between their larger branches. In the limbs the anasto- 

 moses are most numerous and of largest size around the joints, the branches of an 



(575) 



FIG. 427. Diagram showing the anastomosis of 

 arteries. (Poirier and Charpy.) 



