ARTERIA INNOMINATA. 299 



divides into two branches ; one of which winds around the base of the 

 left ventricle in the auriculo-ventricular groove, and inosculates with 

 the right coronary, forming an arterial circle around the base of the 

 heart ; while the other passes along the line ef union of the two ven- 

 tricles, upon the anterior aspect of the heart, to its apex, where it 

 anastomoses with the descending branch of the right coronary. It 

 supplies the left auricle and the adjoining sides of both ventricles. 



The right, or posterior coronary, passes forwards, between the root 

 of the pulmonary artery and the right auricle, and winds along the 

 auriculo-ventricular groove, to the posterior median furrow, where it 

 descends upon the posterior aspect of the heart to its apex, and 

 inosculates with the left coronary. It is distributed to the right 

 auricle, and to the posterior surface of both ventricles, and sends a 

 large branch along the sharp margin of the right ventricle to the apex 

 of the heart. 



ARTERIA INNOMINATA. 



The Arteria innominata (fig. 116, No. 4) is the first artery given off 

 by the arch of the aorta. It is an inch and a half in length, and 

 ascends obliquely towards the right sterno-clavicular articulation, where 

 it divides into the right carotid and right subclavian artery. 



Relations. It is in relation, in front with the left vena innomi- 

 nata, the thymus gland, and the origins of the sterno-thyroid and 

 sterno-hyoid muscles, which separate it from the sternum. Behind 

 with the trachea, pneumogastric nerve and cardiac nerves ; externally 

 with the right vena innominata and pleura ; and internally with the 

 origin of the left carotid. 



Plan of the Relations of the Arteria Innominata. 

 In Front. 



Left vena innominata, 

 Thymus gland, 

 Sterno-thyroid, 

 Sterno-hyoid. 



Right Side. 



Right vena inno- 

 minata, 

 Pleura. 



Behind. 

 Trachea, 



Pneumogastric nerve, 

 Cardiac nerves. 



The arteria innominata occasionally gives off a small branch, which 

 ascends along the middle of the trachea to the thyroid gland. This 

 branch was described by Neubauer, and Dr. Harrison names it the 

 middle thyroid artery. A knowledge of its existence is important in 

 performing the operation of tracheotomy. 



