His shoulder had a look as though his hidden hand might be making motions. --Joe Brody confronted by private detective Philip Marlowe (The Big Sleep by Raymond Chandler, 1939, p. 77)
Body parts. 1. Paired, jointed organs which connect the arms to the torso. 2. Prominently rounded--as well as angular--parts of the external anatomy, which give the torso a squared-off silhouette. 3. Very visible body parts often singled out for display with clothing cues (see, e.g.,ARM SHOW, BUSINESS SUIT).
Usage: The flexibility and visibility of human shoulders--and the fact that they are moved by emotionally sensitive (i.e., branchiomeric or "gut reactive") muscles--renders them highly expressive as signs (see SHOULDER-SHRUG). Their size and angular silhouette when squared, e.g., bespeak dominance (see BROADSIDE DISPLAY).
Anatomy I. The bones of our shoulder girdle consist of a pair of flattened shoulder blades (or scapulas), each connected to a bracing collar bone (or clavicle). The sides of the bony girdle sit upon our rib cage, not unlike football shoulder pads. Unattached to any bones but the clavicles, the scapulas glide up and down, move back and forth, and rotate about our back and spine. Only the clavicles' attachments to the breastbone stabilize their motion.
Anatomy II. Six muscles move and connect the shoulder girdle's four bones to our main skeleton. Anterior are subclavius, pectoralis minor, and serratus anterior; posterior are levator scapulae, rhomboid, and trapezius (Rasch 1978).
Neuro-notes. Upper trapezius is emotionally sensitive because it is innervated by special visceral nerves.
Photo of clothing designed to accentuate feminine shoulders and their movements to draw male eyes (picture credit: unknown)