Area of anatomic deltoid muscle segments. On T2 weighted transverse MR images the area of seven anatomic defined segments of the deltoid muscle were measured exactly at the mid-glenoid level. These segments were identified following the visible tendons from their origin-points of the clavicle (A1), the anterior surface of the acromion (A2), the lateral aspect of the acromion (A3, M1 and P1) and the scapular spine (P2 and P3) respectively.