TY - CHAP M1 - Book, Section TI - Chapter 372. The Head, Face, and Neck A1 - Derkay, Craig S. A1 - Cunningham, Michael J. A2 - Rudolph, Colin D. A2 - Rudolph, Abraham M. A2 - Lister, George E. A2 - First, Lewis R. A2 - Gershon, Anne A. PY - 2011 T2 - Rudolph's Pediatrics, 22e AB - The critical period of cervicofacial growth and differentiation occurs between weeks 4 through 8 of embryologic development.1 The beginning of this stage is characterized by the appearance of the frontonasal process—the precursor of the forebrain and upper face—with development soon thereafter of the optic and otic vesicles; the nasal placodes; the primitive mouth, or stomodeum; and five ridges on the ventrolateral surface of the embryonic head, which is known as the branchial system. Many of the symmetrically paired skeletal and neuromuscular structures of the head and neck arise from the first (mandibular), second (hyoid), third (pharyngeal), and fourth (laryngeal) arches of this fetal branchial system (Table 372-1). The skull, facial, and neck bones have begun to ossify by the end of the eighth fetal week, which coincides with a recognizable human embryonic face with easily discernible ears, eyelids, cheeks, nose, and upper and lower lips. SN - PB - The McGraw-Hill Companies CY - New York, NY Y2 - 2024/03/29 UR - accesspediatrics.mhmedical.com/content.aspx?aid=7034330 ER -