The structure of the fibrous tissue on the articular surface of the temporal bone in the monkey ( Macaca mulatta)

Abstract

The articulating surface of bones which ossify in mesenchyme, like the mandible, is covered by a layer of dense, fibrous tissue. The purpose of the present study was to examine the structure of the fibrous tissue on the surface of the articular surface of the temporal bone in the monkey. Young Rhesus monkeys ( Macaca mulatta) were perfused with glutaraldehyde–paraformaldehyde. The specimens were demineralized in 0.5 M EDTA. Small pieces of fibrous tissue and underlying bone were dissected out and processed for light and electron micrscopy. The mandibular fossa is shallower and the articular eminence flatter in the monkeys as compared to humans. The articular part of the temporal bone is covered by a layer of avascular, soft tissue extending from the surface to the underlying bone. The tissue can be divided into three zones which gradually merge into one another. The zone facing the articular cavity consists of dense, fibrous tissue with layers of collagen fibers, oriented parallel to the articular surface, but at angles to each other. Fibers thought to be elastic fibers oriented parallel with the collagen fibers are also observed, particularly close to the surface, and their function is probably to impart resilience to the fibrous articular tissue. Between the fibers scattered cells with an ample rough endoplasmic reticulum are present. A thin layer of granular appearance is often observed on the surface. This layer may be of importance in joint lubrication. The second zone is more cell rich and the cells have long slender cellular processes and are surrounded by a dense collagenous matrix with an irregular orientation. These cells are probably precursor for the underlying cartilage but, not for the cells in the outer articular layer. In the third zone next to the bone the fibrous tissue gradually turns into cartilage. The cartilagenous zone is narrow, sometimes absent and is replaced by bone tissue. In some areas chondroclasts are observed, with forming osteons with osteoid seams. These observations indicate that remodeling is taking place and that cartilage is replaced by bone. The three zones observed correspond to findings in the mandibular condyle, but the zones are not as constant and distinct as in the condyle, and this reflects the adaptive role of the temporal bone in the growth of the temporomandibular joint.