Regarding the formation of the infraclavicular part of the brachial plexus, the three cords are arranged around the second part of the axillary artery. The POSTERIOR cord receives its contributions from which segments?

• A Posterior divisions of all three trunks ✓
• B Anterior divisions of all three trunks
• C Posterior divisions of the middle and inferior trunks only
• D Posterior divisions of the superior and middle trunks only

Explanation

Each trunk splits into anterior and posterior divisions behind the clavicle. The three posterior divisions, one from each of the superior, middle and inferior trunks, unite to form the posterior cord, so its constituent fibres span C5 to T1. Its major branches are the axillary and radial nerves plus the three subscapular branches including the thoracodorsal nerve. Options listing only two divisions ignore that every trunk contributes a posterior division.

Reference: Gray's Anatomy for Students, 4th ed.

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