Human fetal hyoid body origin revisited

Abstract

The hyoid body is traditionally believed to have a dual origin from second and third arch mesenchyme, but this theory remains controversial. We examined paraffin-embedded sections from the hyoid region of 12 embryos and fetuses at 5-7 weeks of gestation (11-22 mm cranio-rump length). We found that the second (Reichert's cartilage) and third arch mesenchymal condensations did not reach the median area at the base of the tongue. Rather, a midline mesenchymal condensation was seen, and it separated from these arches at an early stage. This condensation was triangular and plate-like, and the cranial part was narrow between the bilateral Reichert's cartilages, while the caudal part was wide along the mediolateral axis between the bilateral primitive greater horns. We considered the midline mesenchymal condensation as the hyoid body anlage. At 7 weeks, a cartilaginous mass appeared in the midline condensation. The hypoglossal nerve changed its direction at the superolateral ends of the midline condensation. We propose that: (i) the hyoid body originates from the hypobranchial eminence via the midline condensation; (ii) the lesser horn originates from the caudal end of Reichert¢s cartilage; and (iii) the greater horn of the hyoid and the superior cornu of the thyroid cartilage originate from the third arch cartilage. The second and third arches may not regulate early hyoid body morphology.

The development of the human hyoid–larynx complex revisited

“…As compared with current descriptions in literature (Fig. B), we observed a less complicated development of the hyoid–larynx complex from only the second and third pharyngeal arch cartilage, in combination with a single hyoid body anlage . The fourth and sixth pharyngeal arch cartilages that were expected to give rise to thyroid and cricoid cartilages were not observed as cartilaginous bars.…”

“…In subsequent stages, more mesenchymal‐derived cartilaginous tissue was added to this anlage until the adult shape of the hyoid bone body was reached, as shown in Figure . This anlage was described by Rodríguez‐Vázquez et al as a triangular and plate‐like condensation, but the 3D reconstruction of this anlage in stage 18 reveals a mere cylindrical appearance . In the stage 18 embryo, the auditory ossicles (i.e., malleus, incus, and stapes) could not be sufficiently separated yet, and therefore, this region of mesenchymal condensation was referred to as bone‐forming region.…”

“…Only the first three pharyngeal arch cartilages develop as pharyngeal arch cartilages, the thyroid and cricoid cartilages develop separately from each other from mesenchymal condensations. The body of the hyoid bone develops from one growth center (anlage), without the contribution from the second and third pharyngeal arch cartilages …”

The Origin of the Variations of the Hyoid Apparatus in Human

“…The first author had described development of RC from the second branchial arch in human embryos (Rodrıguez-Vazquez, 2005, 2011 (1) RC is composed of independently developed two segments those are never continuous; (2) the cranial segment is continuous with the otic capsule and gives rise to the styloid process; (3) the caudal segment gives rise to the lesser horn of the hyoid but not to a part of the hyoid body. Thus, the tympanohyal, stylohyal, ceratohyal, and hypohyal segments seem to be absent in human fetuses.…”

Development and regression of the thyroglossal duct in mice

“…The hyoid body, the lesser horn, and the greater horn and superior cornu originate from the hypobranchial eminence, Reichert's cartilage in the second branchial arch, and the third branchial cartilage, respectively (Rodríguez-Vázquez et al, 2011). The thyroglossal duct of human embryos or adult patients runs anterior to the hyoid bone and turns upward behind the hyoid body and then descends again anterior to the thyrohyoid membrane (Brintnall et al, 1954;Ellis and van Nostrand, 1977).…”