548 



THE BLOOD-VASCULAR SYSTEM. 



and with the phrenic and lumbar arteries. Each intercostal artery is accompanied 

 by a vein and nerve, the former being above, and the latter below, except in the 

 upper intercostal spaces, Avhere the nerve is at first above the artery. The arteries 

 are protected from pressure during the action of the Intercostal muscles by fibrous 

 arches thrown across, and attached by each extremity to the bone. The lower 

 intercostal arteries are continued anteriorly from the intercostal spaces into the 



FIG. 307. The abdominal aorta and its branches. 



abdominal wall, except the subcostal, which lies throughout its whole course in the 

 abdominal wall, since it is placed below the last rib. They pass behind the costal 

 cartilages between the internal oblique and Transversalis muscle to the sheath of 

 the Rectus, whero they anastomose with the internal mammary and the deep 

 epigastric arteries. Behind, the subcostal artery anastomoses with the first 

 lumbar artery. 



Each intercostal artery gives off the following branches : 



Posterior or dorsal branch. Spinal. 



Collateral intercostal. 



