Involucrum

 ( Bones ) 

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

There are two main contexts:

• In pyogenic osteomyelitis where it is a layer of living bone that has formed around dead bone. It can be identified by radiography (i.e., with ).
• In cetaceans such as whales, it is a thick covering of bone over the middle-ear space.

• Sequestrum