In this chapter, the authors discuss the macro- and microanatomy of the brachial plexus cords below the clavicle. The area below the clavicle is defined, for the purposes of this discussion, as the area from just below the clavicle - the proximal infraclavicular area, to the lateral border of the major pectoral muscle and the deltopectoral groove – the distal infraclavicular area. In the proximal infraclavicular area, the three cords are situated lateral to the axillary artery and vein and all three cords are in a communal circumneural (paraneural) sheath. As the cords track more distally, they spread out around the artery so that the three cords are apart and each is in its own circumneural sheath. The lateral cord is now anterolateral, the medial cord is anteromedial, and the posterior cord is posterior to the axillary artery.
Keywords: Ansa pectoralis, Axillary artery, Axillary vein, Brachial plexus, Brachial plexus sheath, Circumneural sheath, Deltopectoral groove, Epineurium, Infraclavicular block, Lateral cord, Lateral pectoral nerve, Macroanatomy, Major pectoral muscle, Marti-Gruber, Medial cord, Medial pectoral nerve, Microanatomy, Minor pectoral muscle, Paraneural sheath, Posterior cord, Secondary block.