At the anterior end of the embryo an opening called the stomodeum appears during the latter part of the first month of intrauterine life. The face is formed from five processes surrounding this opening: 1 frontonasal, 2 maxillary and 2 mandibular processes (Fig. 88). The mandibular processes grow medially, fuse and unite in the midline, forming the lower jaw or mandible. When a failure of fusion of these processes occurs, a fissure of the lower lip results. The fusion of the upper processes converts the single stomodeal orifice into the cheeks, the whole upper lip except the philtrum (the vertical groove in the middle of the upper lip), most of the upper jaw and the palate. The appearance of an olfactory pit divides the frontonasal process into a medial and 2 lateral nasal processes. The medial process forms the septum of the nose, the philtrum and premaxilla; the lateral processes form the side of the nose but take no part in the formation of the upper lip. By imperfect fusion various defects result, such as harelip, macrotoma, microstoma, cleft palate, etc.
KeywordsFacial Nerve Parotid Gland Masseter Muscle Lingual Nerve Facial Artery
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