THORAX. 147 



aginous circle of the false ribs, runs upwards, sending 

 intercostal collateral branches, and anastomoses with 

 the thirteenth intercostal. The mammary furnishes 

 superior brandies to the pericardium and pleura, inferi- 

 or branches to the pectoral muscles, and external rami- 

 fications to anastomose with the intercostals. 



5. The EXTERNAL THORACIC. — Tumiug over the an- 

 terior border of tlie first rib, it runs backwards inside 

 the two portions of the deep pectoral muscles in which 

 it ramifies. 



6. Tlie inferior cervical or trachelo-muscular. — 

 Passing outside the gulf of the jugulars, inside the 

 sterno-prescapularis, it terminates by an ascending and 

 descending muscular branch. 



7 and 8, — Sus and subscapular. Described in tlie 

 arteries of the anterior extremity (see page 31). 



Posterior aorta. — True continuation of the primi- 

 tive aorta. It passes upwards and backwards, forming 

 a curve called the arch of the aorta, reaches the left 

 side of the inferior face of the vertebral column, fol- 

 lows the vertebral bodies, gradually coming to the 

 median line, passes through the diaphragm, into the 

 abdomen as far as the last intervertebral articulation, 

 and terminates by the four iliac arteries. Its collaterals 

 are divided into thoracic and abdominal branches. 



Thoracic collaterals. — 1. Intercostal arteries: Sev- 



