366 ARTERIES. 



the pulmonary artery and the appendix of the right auricle. It passes forwards 

 to the right side in the groove between the right auricle and ventricle, and, curving 

 around the right border of the heart, runs along its posterior surface as far as the 

 posterior interventricular groove, where it divides into two branches, one of which 

 continues onward in the groove between the left auricle and ventricle, and anas- 

 tomoses with the left coronary; the other descends along the posterior inter- 

 ventricular furrow, supplying branches to both ventricles, and to the septum, 

 anastomosing at the apex of the heart with the descending branch of the left 

 coronary. 



This vessel sends a large branch along the thin margin of the right ventricle to 

 the apex, and numerous small branches to the right auricle and ventricle, and 

 commencement of the pulmonary artery. 



The Left Coronary, smaller than the former, arises immediately above the free 

 edge of the left semilunar valve, a little higher than the right ; it passes forwards 

 between the pulmonary artery and the left appendix auricula?, and descends 

 obliquely towards the anterior interventricular groove, where it divides into two 

 branches. Of these, one passes transversely outwards in the left auriculo-ventri- 

 cular groove, and winds around the left border of the heart to its posterior surface, 

 where it anastomoses with the superior branch of the right coronary ; the other 

 descends along the anterior interventricular groove to the apex of the heart, 

 where it anastomoses with the descending branch of the right coronary. The left 

 coronary supplies the left auricle and its appendix, both ventricles, and numerous 

 small brancfies to the pulmonary artery, and commencement of the aorta. 



Peculiarities. These vessels occasionally arise by a common trunk, or their number may be 

 increased to three ; the additional branch being of small size. More rarely, there are two addi- 

 tional branches. 



AETEEIA INNOMINATA. 



The innominate artery is the largest branch given off from the arch of the aorta. 

 It arises from the commencement of the transverse portion in front of the left 

 carotid, and, ascending obliquely to the upper border of the right sterno-clavicular 

 articulation, divides into the right carotid and subclavian arteries. This vessel 

 varies from an inch and a half to two inches in length. 



Relations. In front, it is separated from the first bone of the sternum by the 

 Sterno-hyoid and Sterno-thyroid muscles, the remains of the thymus gland, and 

 by the left innominate and right inferior thyroid veins which cross its root. Behind, 

 it lies upon the trachea which it crosses obliquely. On the right side are the right 

 vena innominata, right pneumogastric nerve, and the pleura ; and on the left side, 

 the remains of the thymus gland, and origin of the left carotid artery. 



PLAN OF THE KELATIONS OF THE INNOMINATE ARTERY. 



In front. 

 Sternum. 



Sterno-hyoid and Sterno-thyroid muscles. 

 Remains of thymus gland. 

 Left innominate and right inferior thyroid veins. 



Right side. ^^_^^ Left side. 



Right vena innominata. /^ ^\ Remains of thymus. 



Right pneumogastric nerve. ( T \ Left carotid. 

 Pleura. 



Behind. 

 Trachea. 



Peculiarities in point of division. "When the bifurcation of the innominate artery varies 

 from the point above mentioned, it sometimes ascends a considerable distance above the sternal 



