Extensor digitorum contracts to extend the phalanges of the fingers. To grab the glass, thenar and hypothenar muscles contract to pull the metacarpals and phalanges that flex at the carpometacarpal ellipsoidal joints, which work quite similar to a ball-and-socket joint, allowing angular motion in two planes – along or across the length of an oval. The thumb moves in opposition to grasp the glass. To bring the glass to the mouth, while the metacarpals and phalanges remained flexed to hold the glass, to flex the arm at the elbow joint, biceps brachii contract and triceps brachii relax, while
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