ABSTRACT
To elucidate the histological findings of the anlage of the mandibular condyle during very early developmental stages, we analyzed sagittal and frontal plane serial sections of mouse fetuses for which the gestational period was precisely determined. An aggregate of mesenchymal cells around the buccal nerve (peripheral cell aggregate) could be seen at 12.0 days post-conception (dpc). Another cell aggregate (core cell aggregate), which almost coincided with the outline of the condylar head, was detected on the inside of the dome-shaped peripheral cell aggregate at 12.75 dpc. The cells of the peripheral cell aggregate were gradually flattened in accordance with cell differentiation, and formed a fibrous sheath covering the condylar head by 15.0 dpc. The cells of the central region of the core cell aggregate differentiated into hypertrophic chondrocytes by 14.5 dpc, whereas the cells of the fringe of the core cell aggregate differentiated into osteogenic cells to form the bone collar by 15.0 dpc. The continuity of the anlage of the condyle with that of the mandibular ramus was first recognized at 13.0 dpc. As the anlage of the mandibular condyle was observed histologically during very early developmental stages, further research is necessary to characterize the development of this anlage in greater detail.