The medial wall of the axilla is the upper part of the serratus anterior muscle overlying the thoracic wall. The long thoracic nerve passes vertically out of the axilla and down the lateral surface of the serratus anterior muscle in a position just anterior to the posterior axillary skin fold.
The lateral boundary of the axilla is the humerus.
The floor of the axilla is the dome of skin between the posterior and anterior axillary skin folds.