ABSTRACT
The bony labyrinth develops from the otic capsule. Its matrix is trilamellar, consisting of the internal periosteal (or endosteal) layer, the middle mixed layer of intrachondrial and enchondral bone, and the external periosteal layer. The internal and external periosteal layers are derived, respectively, from the embryonic internal and external perichondrium (see the section on ossification, chap. 9, p. 287). Scattered within the middle layer is intrachondrial bone (globuli interossei) (Figs. 1 and 2) which consists of islands of cartilage, the lacunae of which develop a thin layer of bone from invading osteoblasts. The amount of intrachondrial bone decreases with the age of the individual (102). Following fracture, this middle layer of bone fails to heal by osteoid or callus formation. The endosteal (inner periosteal) layer also demonstrates poor reparative capability. Fractures of the temporal bone heal predominantly with fibrous tissue and some bone from the external periosteal layer.
