Final answer:
The metacarpals, numbered 1-5 starting from the thumb side, make up the palm of the hand and are connected to the phalanges at the metacarpophalangeal joints, which form the knuckles.
Step-by-step explanation:
The metacarpals form the hand. Specifically, there are five metacarpal bones that make up the palm of the hand. These bones are elongated and lie between the carpal bones of the wrist and the bones of the fingers and thumb. The metacarpals are numbered 1 through 5, starting with the thumb side of the hand. The first metacarpal bone is distinct in that it is freely mobile while the others are more fixed. Each metacarpal articulates at the proximal end with the carpal bones, and at the distal end with the phalanges to form the articulations known as the metacarpophalangeal joints, which are essentially the knuckles we see on the back of the hand. The phalanges themselves are the bones of the fingers, each finger housing three phalanges except for the thumb, which has two. Therefore, the correct answer to the question 'The _____ form the hand' would be a. metacarpals.