The organization of a typical intercostal space, the nerves and blood vessels
In addition to the three layers of muscle, a bundle of nerve + artery + vein runs at the inferior border of the ribs. The nerve is the intercostal nerve, which is the ventral ramus of the thoracic spinal nerve, and it runs around the interior of the rib cage sending off cutaneous branches. The arteries are the anterior and posterior intercostal arteries (branches of the thoracic aorta and anterior thoracic arteries respectively) which anastamose laterally. The veins are anterior and posterior intercostal veins which dump into the interior thoracic veins and the azygous/hemiazygous/accessory hemiazygous veins respectively.