var chapter_list = new Array(
  ["Vol.001 Ch.001","v001/c001"],
  ["Vol.001 Ch.002","v001/c002"],
  ["Vol.001 Ch.003","v001/c003"],
  ["Vol.002 Ch.004","v002/c004"],
  ["Vol.002 Ch.005","v002/c005"],
  ["Vol.002 Ch.006","v002/c006"],
  ["Vol.003 Ch.007","v003/c007"],
  ["Vol.003 Ch.008","v003/c008"],
  ["Vol.003 Ch.009","v003/c009"],
  ["Vol.004 Ch.010","v004/c010"],
  ["Vol.004 Ch.011","v004/c011"],
  ["Vol.04 Ch.012.1","v04/c012.1"],
  ["Vol.04 Ch.012.2","v04/c012.2"],
  ["Vol.05 Ch.013.1","v05/c013.1"],
  ["Vol.05 Ch.013.2","v05/c013.2"],
  ["Vol.05 Ch.014","v05/c014"],
  ["Vol.05 Ch.015.2","v05/c015.2"],
  ["Vol.06 Ch.015.1: Part A","v06/c015.1"],
  ["Vol.06 Ch.016.1","v06/c016.1"],
  ["Vol.06 Ch.016.2","v06/c016.2"]
);

var total_chapters = 20;

for (var i = 0; i < chapter_list.length; i++) {
  document.getElementById('top_chapter_list').options[i] = new Option(chapter_list[i][0], chapter_list[i][1]);
  document.getElementById('bottom_chapter_list').options[i] = new Option(chapter_list[i][0], chapter_list[i][1]);
}
document.getElementById('top_chapter_list').value=current_chapter;
document.getElementById('bottom_chapter_list').value=current_chapter;
var current_chapter_index = document.getElementById('top_chapter_list').selectedIndex;