function toggleThumb(img) {
  if ( img.src.match(/-over\.jpg$/) ) {
    img.src = img.src.replace(/-over\.jpg$/, '.jpg');
  }
  else {
    img.src = img.src.replace(/\.jpg$/, '-over.jpg');
  }
}

function nextThumb() {
  showThumbs('next');
}

function prevThumb() {
  showThumbs('prev');
}

function showThumbs(dir) {
  var thumbsToShow = 8;
  var thumbs = $('#thumbs img.thumb');
  var lastVisible = 0;
  for ( i = 0; i < thumbs.length; i++ ) {
    if ( thumbs[i].style.display != 'none' ) {
      lastVisible = i;
    }
  }
  // move one to the right
  if ( dir == 'next' ) {
    var last = lastVisible+1;
    var first = last - (thumbsToShow-1);
    if ( last >= thumbs.length ) {
      last = thumbs.length;
      first = last - thumbsToShow;
    }
  }
  // move one to the left
  else {
    var last = lastVisible-1;
    var first = last - (thumbsToShow-1);
    if ( first <= 0 ) {
      first = 0;
      last = first + (thumbsToShow-1);
    } 
  }
  for ( i = 0; i < thumbs.length; i++ ) {
    if ( i >= first && i <= last ) {
      thumbs[i].style.display = 'inline';
    }
    else {
      thumbs[i].style.display = 'none';
    }
  }
}