Purpose: In this study, the development of human embryonic temporomandibular joint (TMJ) and masticatory muscles were investigated by using computed 3-dimensional reconstructions. Materials and Methods: Sixteen human embryos and fetuses, ranging from 6.5 to 107 mm crown-rump length, were examined. Results: At 10 weeks, a band of mesenchyme extending from the attachment of the lateral pterygoid muscle to the condylar process was observed to pass through the medial side of the condylar process to attach to the malleus. The temporal, masseter, and pterygoid muscles develop from the so called 'temporal muscle' primordium, and the temporal muscle was in continuity with the masseter muscle until 14 weeks of fetal life. Conclusions: The study shows that the muscles of mastication arise from a single primordium. It also confirms the presence of a ligamentous attachment between the lateral pterygoid muscle and the malleus. (C) 2000 American Association of Oral and Maxillofacial Surgeons.