The rotator cuff keeps the humerus in a position biased toward external rotation and seats the head of the hurmerus in the glenoid fossa.

• 当手接触到书时，手会贴附着书脊，而伸手模式的功能会神奇地反转而将书送到身侧。当人将书从书架上移开，抓握的骨骼肌会依照书的重量做力量的调整。