Skull of a domestic animal 
Skull of a domestic animal (cow, sheep, goat, pig or horse), cleaned of flesh.
Characteristics
- Bone is mostly calcium phosphate (hydroxyapatite).
- In biodynamics it is the casing of preparation 505 (oak bark).
- It can be reused for several seasons.
Role in the preparation: It is filled with oak bark through the foramen magnum, sealed with clay and left in a wet place over winter.
Caution: In the EU the skull of cattle over 12 months and of sheep and goats over 12 months is specified risk material (Regulation (EC) 999/2001): check the rules and use an approved supply channel.
Sources: Biodynamic agriculture - Wikipedia · Skull - Wikipedia · Regulation (EC) 999/2001 - EUR-Lex
Documentary information: this is neither a recommendation for use nor a plant-protection or veterinary claim. Check your country's regulations before any use.