BLOOD-VESSELS. ARTERIES AND VEINS. 377 



2. BLOOD-VESSELS. ARTERIES AND VEINS. 



The descriptive anatomy of the blood-vessels includes an account of their origin, 

 extent, form, position, mode of division, distribution, anastomoses with each other, 

 and relations to other parts. Seeing, however, that the blood-vessels are subject to 

 numerous variations, while the most frequent forms and modes of distribution are 

 described as the normal, it will be necessary to refer also to the more important 

 varieties which have been observed among them. 



The varieties of blood-vessels may consist of a deviation either from the usual 

 size of the channels or from their usual position and their connection with other 

 vessels. In the latter case they may be described as consisting in differences of origin 

 from the main stem, or from a branch, or from quite another source than that which 

 is the most common or usual. But some varieties are so common that it becomes 

 doubtful which form is to be described as normal. 



Fig. 328. GENERAL VIEW OP THE HEART AND BLOOD-VESSELS OF THE TRUNK, FROM BEFORE, 

 IN A MALE ADULT. (Allen Thomson.) 1 



A, Right auricle ; B, left auricular appendix ; C, right ventricle ; D, part of left ventricle ; I, I, 

 aorta ; II, trunk of pulmonary artery dividing into its right and left branches, and connected to the 

 aorta by the cord of the ductus arteriosus ; III, superior vena cava ; IV, IV, inferior vena cava. 



1, innominate artery and right carotid ; 1', left carotid ; 2, 2, right and left subclavian arteries ; 3. 

 intercostal vessels ; 4, inferior phrenic arteries ; below 4, the cceliac axis and superior mesenteric 

 artery ; 5, renal arteries ; 6, 6', spermatic arteries ; below 6, the inferior mesenteric ; 7, 7', right and 

 left common iliac arteries ; 8, 8', external iliac arteries ; 9, left epigastric and circumflex iliac arteries ; 

 10 ; 10', internal iliac arteries ; and between these two figures, the middle sacral artery ; 11, 11, femoral 

 arteries ; 12, deep femoral artery of the left side. 



a, right innominate vein ; a', the left ; b, b', right and left subclavian veins ; 6", the cephalic vein 

 of the right arm ; c, c', internal jugular veins ; c", right facial vein ; d, d, external jugular veins 

 formed by the posterior auricular and part of the temporo-maxillary ; d', anterior jugular veins with the 

 transverse branch joining them ; e, azygos vein arching over the root of the right lung ; /, hepatic veins ; 

 ff, renal veins ; to the sides are seen the kidneys and the suprarenal bodies ; g', right, g", left ureter ; 

 /i, k', spermatic veins ; i, i, common iliac veins ; i' t i', external iliac veins ; h, k t femoral veins ; I, in- 

 ternal saphenous vein of the right side. 



Many of these varieties are not only compatible with life, but cause no disturb- 

 ance whatever in the performance of the ordinary functions of the body. Others 

 are of such a nature as to be compatible only with the conditions of the circulation 

 subsisting during intrauterine life, and therefore prove fatal at birth. Some are of 

 considerable interest from their frequency, and others from their existing in situa- 

 tions where they are liable to affect the progress or results of surgical operations. 



Many vascular varieties repeat forms which are natural in different species among 

 the lower animals ; others are obviously due to the persistence of early foetal forms 

 of distribution ; and not a few are, explicable on the supposition of abnormal 

 enlargement or diminution of naturally existing vessels. 



For fuller information on the natural and abnormal distribution of the blood-vessels, the 

 reader may consult the works of Haller, Tiedemann, and Barkow, and more especially the 

 "Anatomy of the Arteries," by Richard Quain, 1844, and Henle's "Handbuch," vol. iii, part 1, 

 2nd ed., 1876, in which a connected view of the varieties by W. Krause is given. 



The dimensions of the arteries vary to some extent in different individuals and 

 in the two sexes, as well as at different periods of life ; for it is found that, as in the 

 case of the heart, both the capacity and the thickness of the walls of the large 

 arteries increase gradually with advancing years. At the same time they gain in 

 length, and as a result of this and of a diminution in elasticity of their coats they 

 often become markedly tortuous in old persons. The primary branches of the aortic 

 trunk, and their secondary and tertiary ramifications are divided by Henle, accord- 



