function changeImage4()
            {
            var list = document.getElementById('optionlist4');
            document.mainimage4.src = list.options[list.selectedIndex].value;
            }
        function prevImage4()
            {
            var list = document.getElementById('optionlist4');
            if(list.selectedIndex == 0)
                {
                list.selectedIndex = list.options.length-1;
                }
            else
                {
                list.selectedIndex--;
                }
            changeImage4();
            }
        function nextImage4()
            {
            var list = document.getElementById('optionlist4');
            if(list.selectedIndex == list.options.length-1)
                {
                list.selectedIndex = 0;
                }
            else
                {
                list.selectedIndex++;
                }
            changeImage4();
            }