This hole itself has the pronunciation of "ほら". In the word "bone hole", the bone hole (ほら) promotes sound+semi-voiced sound, so it becomes "こっぽら"

All pronunciations of the hole

voice

ズヅヅヅ (off-balance sheet)

Chinese pronunciation: トウ (トウ) (off-balance sheet)

Idiomatic sound: ドウ (ドウ)

cultivate

List of commonly used Chinese characters

ほら

Off-balance sheet of commonly used Chinese characters

とう