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.

The mandibular body of the human fetus. Histologic analysis of the basilar part

Histologic and microradiographic analyses of 47 human mandibles from 42 fetuses and 5 neonates have been carried out to study the development of the mandibular body. This not only entails woven bone formation along Meckel's cartilage but also endochondral ossification in the condylar cartilage, the pillars of which are included in the posterior part of the mandibular body. Progressively, woven bone is replaced by lamellar bone, and typical Haversian systems are already present at the fifth month of fetal life. This early occurrence of bone remodelling is related to the fact that the mandible is subjected to intense activity from sucking and swallowing.

The mineralized ring, a single structure peculiar to long bone growth

Mineralized ring, an elongated tubular structure ensheathing bone metaphysis, is described at successive stages of long bone growth. It is shown that the mineralized ring is characterized by different morphological aspects during its development, corresponding to successive growth stages of one and the same anatomical formation. Its origin is different from periosteal bone and its development is parallel to that of the metaphysis.