The forearm consists of the:

radius and ulna

radius and humerus

ulna and humerus

humerus and carpus

Radius and Ulna.

Those are the long bones that together form the forearm.

The external bone is the radius, and the inside bone is the ulna, they are joint by its extremes.

The humerus is the bone that forms the arm.

Carpus is a conjunction of bones that form the wrist.