Triceps

Biceps

Brachialis

Erector Spinae

These last few muscles discussed (Erector Spinae, rectus abdominus, and the obliques) are the muscles that move the trunk.  We have so few muscles moving the trunk in comparison to the upper arm because the trunk has a much smaller range of motion.  It can basically bend forward, backward, side to side, and twist.  We sacrifice range of motion for stability.