Comparative histological contributions to the development of the ear-ossicular joints and the temporomandibular joint in the mouse.

The genesis, differentiation, development and growth of the ear-ossicular joints and temporomandibular joint (TMJ) in the Slc-ICR mouse were studied by means of light and transmission electron microscopy. The differentiation of the ossicular joints and TMJ anlagen was initiated during the fetal stages. Although morphogenesis, development and growth of the TMJ were already evident in the prenatal stages, the joint-cleaving associated with the occurrence of interzones in the cartilaginous ossicular chain was observed during the neonatal stages. However, the simple diarthrodial ossicular joints were completed and became mature earlier than the double synovial TMJ having an articular disc in early postnatal life. TEM examinations revealed that the articulating epiphyseal cartilage of the ossicular joints consisted of hyaline cartilage, while the intracapsular structures in the TMJ were composed of fibrocartilage. The synovium of the diarthroidal joints was supplied by blood vessels, nerve fibers, collagen and elastic fibers. No distinct aging in the cellular and fibrous components of the synovial tissue of the completed TMJ and ossicular joints was evident in the present study.