An involucrum (plural involucra) is a layer of new bone growth outside existing bone.

There are two main contexts:

• In pyogenicosteomyelitis where it is a layer of living bone that has formed around dead bone.^[1] It can be identified by radiographically (i.e., with x-rays).
• In cetaceans such as whales, it is a thick covering of bone over the middle-ear space.^[2][3]

• Sequestrum