The axilla, or armpit, is a localized region of the body between the upper humerus and thorax. It provides a passageway for the large, important arteries, nerves, veins and lymphatics which insure that the upper limb functions properly.  The axilla can be visualized as having a floor, an apex, and four walls (medial, lateral, anterior and posterior). See the figure.  The apex is pointing toward the root of the neck. It is formed by the convergence of the clavicle (anterior), the scapula (posterior) and the first rib (medially). All the nerves and vessels of the upper limb pass through this interval.  The anterior axillary fold A is made up of the pectoralis major and minor muscles.  The posterior axillary fold P is made up of the latissimus dorsi and teres major muscles  The base faces inferiorly and is formed by the skin and fascia of the concave axilla (armpit). Check out a transverse section of the axilla for its boundaries.  The other boundaries are as listed in the following tables:  Clinical Notes:  Keep in mind that many of the structures found in the axilla can be palpated (felt) or observed visually. In all general physical examinations, the axilla should be carefully examined.