Bone · Hand

Metacarpal bones

Ossa metacarpi

The metacarpals are the five bones of the palm, one running out to the base of each digit; their heads are the knuckles you make a fist with. Four of them are held in a fairly tight row, but the thumb's metacarpal is set at an angle and meets the wrist at a saddle joint, and that one difference is what lets the thumb swing across the palm to meet the fingers. The small interossei muscles fill the spaces between the shafts.