What is the "keystone" bone of facial bones?

The maxilla is the keystone of facial bones.

It is the keystone because it anchors all facial bones except the mandible.

It consists of two bones (maxillae) fused together at the midline.

Each maxilla forms joints with seven other facial bones plus two of the cranium.

These bones are the

• nasal
• zygomatic
• lacrimal
• inferior nasal concha
• palatine
• vomer
• the adjacent fused maxilla
• frontal
• ethmoid

(From slideplayer.com)