The first appearance of Meckel's cartilage in the fetus

Meckel's cartilage plays an important role in the topographical organisation and in the differentiation of the facial structure during the embryonal and even much later during the foetal period. Our observations on serial sections carried out in two human foetuses aged 12 and 16 weeks indicate that the two dorsal (tympanic) and ventral (mandibular) branches of Meckel's cartilage are perfectly defined at 16 weeks. In the dorsal branch, the primordia of the incus and of head of the malleus are still composed on non-ossified cartilage. In the ventral branch, it is also possible to describe at 16 weeks three posterior, medial and anterior parts which are composed of cartilage. The initiating role played by the ventral part of Meckel's cartilage on the ossification of the mandible leads during the embryonal period to the formation of the mandibular primary growth center, which is therefore clearly defined in our first stage at 12 weeks. The partial fibrous evolution and the regression of the major part of the ventral branch of Meckel's cartilage only start after 16 weeks of intrauterine life.