In the fourth intercostal space, detach the internal intercostal muscle from the fifth rib and reflect it superiorly . Within the costal groove of the fourth rib, identify the intercostal nerve, artery, and vein [nerve is identified by the probe]. These three structures are located within the costal grooves of all of the ribs in a consistent pattern, from superior to inferior: vein, artery, and nerve (Figure 18.4). This arrangement can be easily remembered with the aid of the mnemonic "VAN" (Vein, Artery, and Nerve).
Deep to these vessels and nerves identify the innermost intercostal muscle [beneath and lateral to the probe] [cross-section]. This muscular layer is the deepest of the three intercostal muscles and extends from the angles of the ribs posteriorly to the costochondral junctions anteriorly.
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