: The top of the pyramid, formed by the first rib , the scapula , and the clavicle . It connects the axilla to the posterior triangle of the neck.
The , commonly referred to as the axilla or "armpit," is a four-sided pyramidal space located at the junction of the upper limb and the thorax. It serves as a vital gateway for neurovascular and lymphatic structures traveling between the neck/torso and the upper extremity. Anatomical Boundaries axillary cavity
The cavity is filled with fat and connective tissue, which cushions several major structures: : The top of the pyramid, formed by
Anatomy, Shoulder and Upper Limb, Axilla - StatPearls - NCBI : The top of the pyramid