Bone · Hand

2nd metacarpal

The longest of the metacarpals, and the most firmly fixed. Its base is deeply grooved and slots into the trapezoid, with further facets for the trapezium and the capitate, so it articulates with three carpal bones where the others manage one or two. Extensor carpi radialis longus attaches to the back of that base and flexor carpi radialis to the front, so both of the wrist muscles that steer the hand toward the thumb pull on this ray. Its head forms the prominent knuckle of the index finger.