title: Tongue Growth during Prenatal Development in Korean Fetuses and Embryos.
abstract: BACKGROUND
  Prenatal tongue development may affect oral-craniofacial structures, but this muscular organ has rarely been investigated.
  
  
  METHODS
  In order to document the physiology of prenatal tongue growth, we histologically examined the facial and cranial base structures of 56 embryos and 106 fetuses.
  
  
  RESULTS
  In Streeter's stages 13-14 (fertilization age [FA], 28 to 32 days), the tongue protruded into the stomodeal cavity from the retrohyoid space to the cartilaginous mesenchyme of the primitive cranial base, and in Streeter's stage 15 (FA, 33 to 36 days), the tongue rapidly swelled and compressed the cranial base to initiate spheno-occipital synchondrosis and continued to swell laterally to occupy most of the stomodeal cavity in Streeter's stage 16-17 (FA, 37 to 43 days). In Streeter's stage 18-20 (FA, 44 to 51 days), the tongue was vertically positioned and filled the posterior nasopharyngeal space. As the growth of the mandible and maxilla advanced, the tongue was pulled down and protruded anteriorly to form the linguomandibular complex. Angulation between the anterior cranial base (ACB) and the posterior cranial base (PCB) was formed by the emerging tongue at FA 4 weeks and became constant at approximately 124°-126° from FA 6 weeks until birth, which was consistent with angulations measured on adult cephalograms.
  
  
  CONCLUSIONS
  The early clockwise growth of the ACB to the maxillary plane became harmonious with the counter-clockwise growth of the PCB to the tongue axis during the early prenatal period. These observations suggest that human embryonic tongue growth affects ACB and PCB angulation, stimulates maxillary growth, and induces mandibular movement to achieve the essential functions of oral and maxillofacial structures.
authors.affiliation: Department of Oral Pathology, College of Dentistry, Gangnueng-Wonju National University, Gangneung, Korea.
authors.forename: Soo Jeong
authors.initials: SJ
authors.lastname: Hong
authors.affiliation: Department of Orthodontics, College of Dentistry, Gangnueng-Wonju National University, Gangneung, Korea.
authors.forename: Bong Geun
authors.initials: BG
authors.lastname: Cha
authors.affiliation: Department of Dental Hygiene, College of Health Sciences, Cheongju University, Cheongju, Korea.
authors.forename: Yeon Sook
authors.initials: YS
authors.lastname: Kim
authors.affiliation: Department of Oral Pathology, College of Dentistry, Gangnueng-Wonju National University, Gangneung, Korea.
authors.forename: Suk Keun
authors.initials: SK
authors.lastname: Lee
authors.affiliation: Department of Pathology, Seoul National University College of Medicine, Seoul, Korea.
authors.forename: Je Geun
authors.initials: JG
authors.lastname: Chi
keywords: Development; Human embryos and fetuses; Tongue