THORAX. 145 



divides into two brandies, one horizontal and one ver- 

 tical, disposed like the ri2;ht cardiac. These tv7o arteries 

 anastomose with those of the opposite side, and from 

 their division send collateral branches to the muscular 

 tissue of the heart. 



Anterior aorta. — Tiie shortest of the terminal 

 branches, runs obliquely upwards and forwards above 

 the right auricle, under the trachea on the left side of 

 the anterior vena cava, and terminates by the two 

 branches : 



1. Brachial OR axillary artery. — Running a course 

 forward, between the layers of the mediastinum under 

 the trachea, it reaches the entrance of the thorax, twists 

 round the first rib, into the axillary space and becomes 

 humeral (see page 31). 



It gives off eight collateral branches : 



1 The DORSAL. — Synonyms. Dorso-muscular, run- 

 ning towards the second intercostal space, through 

 it outside the thorax, bends slightly backwards and 

 ramifies into the muscles of the anterior part of the 

 dorsal region, having a larger branch passing for- 

 ward and upwards near the superior border of the neck 

 to anastomose with the superior cervical. It gives oif 

 one collateral branch, the subcostal, which passes into 

 the costo- vertebral groove backwards, giving off the 

 second, third and fourth intercostal arteries, and tcrmi- 



