Prenatal development of the mandibular joint in mice

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Abstract
The prenatal development of the mandibular joint in mice was studied in fetuses at 15 to 20 days insemination age. The ramus of the mandible can be delineated as early as the fifteenth day by distinct differences in the degree of condensation of mesenchyme at the site of the future joint. The future condylar process of the mandible can be recognized in its relationship to the external pterygoid muscle, inferior alveolar nerve, Meckel's cartilage, pre‐cartilaginous alisphenoid process of the future basisphenoid bone, and the anlage of the squamosal bone with its zygomatic process.Differentiation is rapid through the twentieth day of gestation at which time the following major elements of the joint can be recognized: a fibrous intra‐articular disc continuous with the tendon of the external pterygoid muscle; a vascular synovial mesenchyme with upper and lower synovial spaces; an ossified squamosal bone with a fibrous joint lining; and a well developed condylar process with good representation of differentiating cells in the zones of chondrification and ossification.Among the elements not yet evident, however, are (1) hemopoietic marrow in the condyle, (2) a constricted neck at the base of the condyle, and (3) a fibrous capsule or capsular ligament.