You might thnk the humerus makes more sense from an engineering standpoint, but the radius—and ulna of course— is aesthetically and practically the right place to do it. Do what? Oh, I’ve designed a telescoping arm. Bones extend, muscles and nerves spiral like springs. Blood vessels do some frickin brilliant geometrical voodoo even if I do say so myself. Gives me up to two hundred and fifty millimeters more reach. Why? Cats, thude! That thing where they insistently meow at you to demand attention but then sit down just /barely/ out of reach. No more! Well, I guess they *could* eventually adjust their notion of what “out of reach means”; but WE’LL SEE WHO RUNS OUT OF ENGINEERING NOUS FIRST, CATTO!