Also to cover the headstone in its head to open it!
还能把盖在它头上大石头顶开呢！
2
The stone which the builders refused is become the headstone of the corner.
匠人所弃的石头、 已成了房角的头块石头。
3
The excess water delivered through the buttresses emerges at the apex or headstone and overflows down their outer surfaces to create a contrasting movement or feature.