"The manubrium is the superior part of the sternum lying at the level of T3-T4 vertebrae. It forms the superior wall of the anterior mediastinum and its superior border also contributes to the superior thoracic aperture (thoracic inlet). The upper border of the manubrium also serves as the apex for the anterior triangle of the neck."
"The manubrium articulates with the body of the sternum at the sternomanubrial joint through a secondary cartilaginous joint (symphysis). As the two components lie in slightly different planes, the palpable sternal angle or angle of Louis is projected. This occurs at the T4-T5 vertebral level, at the transthoracic plane of Louis."
"There are two angles on the superolateral corners, the clavicular notches, bilaterally beside the jugular notch. Clavicular notches form the sternoclavicular joints. Immediately inferior to the sternoclavicular joints lie the site for the attachment of the costal cartilages for the first ribs. Along the inferorlateral borders lie demifacets for the second ribs. These demifacets are shared with the body of the sternum."