Intercostal vein is a term that is used to describe the numerous veins that function to drain the rib cage's intercostal spaces. The intercostal spaces, often abbreviated as ICS, are located between two ribs. Rib cages consist of 11 of these spaces in total. Another common word for the intercostal spaces is 'costae.' A handful of different divisions of these veins exist. These divisions are posterior veins, anterior veins, superior veins, supreme veins, and subcostal veins. The posterior veins drain the spaces from the back. The anterior veins drain out the anterior regions. The superior veins drain blood from the second, third, and fourth intercostal spaces. The supreme veins drain from the first costae. Lastly, the subcostal veins are situated directly under the lowermost rib and are similar to the posterior veins.