Complex sentence: The human deltoid is of similar proportionate size as the muscles of the rotator cuff in apes like the orangutan, which engage in brachiation and possess the muscle mass needed to support the body weight by the shoulders.
Split into simpler sentences: The human deltoid is of similar proportionate size as the muscles of the rotator cuff in apes like the orangutan. These apes engage in brachiation and possess the muscle mass needed to support the body weight by the shoulders.