This section is from the book "Applied Anatomy: The Construction Of The Human Body", by Gwilym G. Davis. Also available from Amazon: Applied anatomy: The construction of the human body.
The forearm is intimately associated with the functions of the hand. It serves as a sort of pedestal or support, enabling the hand to be carried away from the body, and, by possessing certain movements of its own, - those of pronation and supination, - it increases greatly the range and character of the movements which the hand is capable of executing. The hand is the essential part of the upper extremity and the forearm is subsidiary. Hence we find that, like the neck, the forearm possesses nerves and blood-vessels much larger than its own proper functions would require and which are destined for the more important parts beyond. It is composed of two bones, the radius and the ulna, which act as the bony support of the part, of a few muscles which move these bones and many more which move the hand and fingers beyond, and of certain nerves and blood-vessels that not only supply it but also the parts beyond.