Volume 3, Chapter 6:
Names Associated with the Interior of the Ch’in
The
string eyes go through (the body) beyond the edge of the bridge. The inside begins to be hollow around eight
to nine tenths of an inch inside the bridge border. Some wood is left around the
edges on the left and right. The na-yin
(納音) are slightly raised at the positions at the pool
and the pond.[1] Wood must also be left where the wild geese
feet (雁足) are placed.
(These places) on the outside are half moon (in shape) and square on the
inside. These are called foot pools (tz’u-ch’ih
足池). In the center of the extreme end area, wood is
left on both sides. This is called the
sound container (ch’eng yin 承音). The sides
here should be substantial. In the
center of the interior, one has two pillars.
Heaven is round and the earth is square.
The pillar of heaven (天柱) goes in between the third to fourth hui. The earth pillar (地柱) is placed between the eighth and ninth hui.