The radius connects to many muscles, such as the biceps, supinator, flexor digitorum superficialis, flexor pollicis longus muscles, extensor ossis metacarpi pollicis, extensor primi internodii pollicis and the pronator teres muscles Furthermore, the radius is found on each arm thus contributing a total of two bones to the human body skeleton. http://www.learnbones.com/arm-bones-anatomy/
This arm bones diagram shows all the important bones that make up the arms of the human body. They include such bones as the clavicle, scapula, humerus, radius, ulna, carpus, metacarpus, phalanges and more
In archery, it is important to keep your shoulders in line. In picture A, the individual would have a difficult time aiming because they are using their muscles to hold the bow. I realize that you use muscles to hold the bow, but in picture B, the individual is using the bones in their arm to hold the pressure of the bow, allowing for a steadier aim.