The fossa between the lateral part of thorax upper part of humerus and lower part of the shoulder. axilla is the passageway for the vessels and nerves from trunk to reach to the upper limb. It is roughly pyramidal in shape, having an apex a floor and four walls. Anterior - Clavicle Posterior - superior margin of the scapula Medial - first rib Walls of the axilla Lateral: interubercular groove of the humerus Medial: 1st-4th ribs land associated intercostal muscles) and serratus anterior muscle Axillary artery and its branches Carry oxygenic blood from heart to the structures Axillary vein and its branches Carry deoxygenated blood toward heart Axillary artery Axillary artery, axillary vein and the infraclavicular part of the brachial plexus is enclosed within a fascia called the axillary sheath. Axillary sheath Axillary sheath is the continuation of the prevertebral layer of the deep cervical fascia.