On the presence of a secondary cartilage in the mental symphyseal region of human embryos and fetuses.

The presence of a secondary cartilage in the mental symphyseal region was examined in this study. A double-staining method with alcian blue and alizarin red S was performed on both whole human embryos and fetuses (developmental age between 8 and 17 weeks, crown-rump length, CRL, between 37 and 124 mm) and their disjointed mandibles. Histological and histochemical techniques were applied to transverse serial sections of whole disjointed fetal heads. The ossification process observed in the mental symphysis is quite different from that of the mandibular body, whose membranous ossification is induced by the contiguous Meckel's cartilage. No evidence of any fusion of Meckel's cartilage with the symphyseal cartilage, that lies within the symphyseal space, was detected. On the basis of these findings, we suggested that the mental secondary cartilage is able to change into bone according to an endochondral ossification process. Moreover, the role of mechanical causes in the development of the mental symphysis was hypothesized.