On both sides of the thoracic wall, remove the intercostal muscles from the first to the seventh intercostal spaces, as far laterally as the mid-axillary line. Take care not to damage the underlying costal pleura or internal thoracic vessels .
Identify the internal thoracic (mammary) artery and vein [cross-section] located approximately one cm lateral to the sternum. Deep to the internal thoracic vessels, also identify the transversus thoracis muscle.
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