function prev_pic() {

   pics_index--;
   if (pics_index < 0) pics_index = pics.length-1;
   document.getElementById('pal_pic').style.backgroundImage = "url("+pics_path + pics[pics_index]+")";
}

function next_pic() {

   pics_index++;
   if (pics_index > pics.length-1) pics_index = 0;
   document.getElementById('pal_pic').style.backgroundImage = "url("+pics_path + pics[pics_index]+")";
   
}