- Arteries enter intercostal spaces at the back and front
- Posterior
- Upper 2 spaces: Supplied by the Superior intercostal artery, i.e. the descending branch of the Costocervical Trunk (from the 2nd part of the Subclavian Artery behind Scalenus Anterior)
- Enters thorax by passing across the front of the neck of 1st rib
- Relations here: Medial side: Sympathetic Trunk; Lateral side: 1st Thoracic nerve passes across 1st rib to join Brachial plexus
- Small 1st Posterior Intercostal Vein lies between artery and Sympathetic Trunk
- Here: 1st Thoracic Sympathetic Ganglion frequently fused with Inferior Cervical Ganglion to form the Cervicothoracic (Stellate) Ganglion
- Remaining 9 spaces: Supplied by separate branch of Descending Thoracic Aorta
- Branches cross the front of the vertebrae and Anterior Longitudinal Ligaments, behind the Hemiazygous Veins and Thoracic Duct
- All 11 arteries = Posterior Intercostal Arteries
- Each artery gives off small collateral branch – passes around neurovascular plane at a lower level than the main trunk
- 12th subcostal artery
- Anterior
- At the front: Internal Thoracic Artery in the upper 6 spaces and the Musculophrenic Artery in the 7-9th spaces give off 2 Anterior Intercostal Arteries ⇒ Pass backwards and anastomose with Posterior vessels
- No anterior intercostal spaces in the last 2 spaces
