Below the 12th rib, there is no intercostal space or intercostal artery, so we call the segmental neurovascular structures subcostal. Completely review the blood supply to an intercostal space. Intercostal spaces in general are supplied by posterior and anterior intercostal arteries. Posterior intercostal arteries 3 through 11 are branches of the descending thoracic aorta. The first two posterior intercostal arteries are branches of the highest intercostal artery, which is a branch of the costocervical trunk from subclavian artery.
Anterior intercostals are branches of the internal thoracic or the musculophrenic arteries.
The posterior branches of posterior intercostal arteries supply the deep and superficial back muscles, skin of the back, and the vertebral column. They have radicular branches that reach the spinal cord along the dorsal and ventral rootlets. Observe the azygos venous system. There are also connections between the various left-sided venous channels. Both first posterior intercostal veins drain directly into their respective brachiocephalic veins.