Fig. 4.

Acromial deltoid segment structure. (A–D) Lateral deltoid (anterior = left). (A,B) (specimen S0) Deltoid after removal of subdermal fat. (B) Interdigitating muscle fiber triangles eased apart. White dotted lines: ET blades towards which muscle fibers bipennately converge. White striped lines: OT lamellae, from which muscle fibers bipennately diverge. (C,D) (specimen S5) OT lamellae in situ after gradual removal of muscle fibers. (E–G) (specimen S1) Dissection of a single acromial segment. (E) Superficial aspect. (F) Superficial muscle fibers removed from OT lamella. (G) Muscle fiber segment removed from ET blades and retracted. OT lamella and ET blades have approximately the same length and have considerable overlap (double white arrow). (H) (specimen S2) OT lamella and its ET blades, all muscle fibers removed. Shoulder in adduction to minimize OT and ET overlap for photograph. The left ET blade has the same length (white arrows) and width (black arrows) as the OT lamella. The same width relationship is not visually evident in the right ET blade, which is spread wider than in the anatomical position.