Introduction: an intercostal space is a space between two ribs, there are eleven pairs of intercostal  space. They are deeper anteriorly than posteriorly and deeper between the superior than inferior ribs.
The 3rd to 6th intercostal  space are typical, the others are atypical
Content: a typical intercostal space contains
– intercostal muscle
– vessels
– nerves
Intercostal muscles: there are three of them
A. External intercostal muscle
B. Internal intercostal muscle
C. Innermost intercostal muscle.
Action: the intercostal muscles are inspiratory muscles. They raise the ribs during inspiration and keep the intercostal space rigid thereby preventing them from bulging out during inspiration.
Arteries: the arterial supply to a typical intercostal space is by three arteries; a large posterior intercostal artery and a small pair of anterior intercostal artery.
Veins: they accompany the intercostal arteries and nerves and lie deepest in the in the costal groove.
Nerves: derived from the ventral rami of the corresponding spinal segment. The neurovascular bundle is arranged: vein, artery and nerve; V.A.N supero-inferioly.
Clinical correlates: A needle or trocar for pleural drainage is inserted just above the rib that forms the lower margin of the space in order to avoid the main nerve and vessel that are at its upper boundaries.