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Functional anatomy

The brachial plexus cords enter the axillary fossa through the costoclavicular space, lateral to the axillary artery (Fig-1).

Fig-1. Anatomy of the brachial plexus above and below the clavicle.

The cords assume a circumferential disposition around the axillary artery on their course deep to the pectoralis major and minor muscles (Fig-2).

The three cords of the brachial plexus surround the axillary artery. Their names are derived from their relationship to it: lateral, posterior, and medial cord.

Fig-2. Brachial plexus cords and their relationship with the axillary artery.

The position of the cords around the axillary artery substantially varies (Fig-3).

Fig-3. Anatomic variations of the brachial plexus cords around the subclavian/axillary artery.

The fascia of the pectoralis minor muscle is one of the crucial anatomical landmarks. To facilitate visualization of the pectoralis minor fascia, the arm should be abducted 90 degrees to stretch the muscle and its fascia.