The development of the mandible was traced on serial sections of 20 human
embryos aged 5-8 weeks (developmental stages 13-23). Special consideration
was given to the differentiation of skeletal units proposed by Sperber. The first
skeletal units, namely the mandibular body, the alveolar unit and the condylar
unit, may be distinguished in the 7th week. The primordia of all units are identified
by the end of the embryonic period (8 weeks)