var chapter_list = new Array(
  ["Vol.01 Ch.001: Access:1","v01/c001"],
  ["Vol.01 Ch.002: Access:2","v01/c002"],
  ["Vol.01 Ch.003: Access:3","v01/c003"],
  ["Vol.01 Ch.004: Access:4","v01/c004"],
  ["Vol.01 Ch.005: Access:5","v01/c005"],
  ["Vol.01 Ch.006: Access:6","v01/c006"],
  ["Vol.01 Ch.007.5: Access:7.5","v01/c007.5"],
  ["Vol.02 Ch.007: Access:7","v02/c007"]
);

var total_chapters = 8;

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;