In Judges 9:53 and 2 Kings 9:35, this signifies, as a bone, little or no spiritual life in understanding or will. People who serve the uses of the bones are slow, stupid, heavy, and sluggish in everything. (Arcana Coelestia 5562-5563)

In John 19:17, this signifies the state of temptations in lowest or outermost things. (Divine Love and Wisdom 12)

People who have lived in deadly hatred, by the revenge of such hatred, and in the falsities derived from them, have totally hardened skulls, and some have skulls like ebony, which light or truths cannot penetrate, but are completely reflected.

(Odkazy: Arcana Coelestia 5563)