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 <   >  search results: facial muscle Search   Atlas 8-10
All of the definitive skeletal muscles and their innervation can be identified by the end of the eighth week. Stimulation studies have shown that some of the skeletal muscles are reflexly active at this time. Motor nerve fibers are in the vicinity of the premuscle cells at the time the premuscle cells begin to differentiate. Most contractions of premuscle cells are probably neurogenic in origin.

The muscles of mastication (masseter, temporalis, medial pterygoid and lateral pterygoid) differentiate from the premuscle mass in branchial arch 1. The premuscle cell laminae and facial nerve branches from branchial arch 2 spread into the face from the lateral aspect of the head. Facial muscles begin to differentiate laterally in the lower face, gradually proceeding to the midline and to the upper face. Around the end of the third month all of the definitive facial muscles can be identified in their definitive position.

Source: Atlas of Human Embryos.