An axillary inlet, or gateway to the upper limb, lies on each side of the superior thoracic aperture. These two axillary inlets and the superior thoracic aperture communicate superiorly with the root of the neck (Fig. 3.7).
Each axillary inlet is formed by: the superior margin of the scapula posteriorly, the clavicle anteriorly, and the lateral margin of rib I medially.