File:Patten041.jpg

Fig. 41. Drawing to show the external appearance of the structures in the ora region of a four-day chick

Ventral aspect.

The cervical flexure presses the pharyngeal region and the ventral surface of the head so closely together that it is difficult to make out the topography of the oral region by study of entire embryos. If the head and pharyngeal region are cut from the trunk and viewed from the ventral aspect the relations of the structures about the mouth are well shown (Fig. 41). The mandibular arch forms the caudal boundary of the oral depression. Arising on either side in connection with the mandibular arch are paired elevations, the maxillary processes, which grow mesiad and form the cephalolateral boundaries of the mouth opening. The nasal pits appear as shallow depressions in the ectoderm of the anterior part of the head which overhangs the mouth region. Surrounding each nasal pit is a U-shaped elevation with its limbs directed toward the oral cavity. The lateral limb of the elevation is the naso-lateral process, and the median limb is the naso-medial process. As development proceeds the two naso-medial processes grow toward the mouth and meet the maxillary processes which are growing in from either side. The fusion of the two naso-medial processes with each other in the mid-line, and the fusion of each of them laterally with the maxillary process of its own side gives rise to the upper jaw (maxilla). The fusion in the mid-line of the right and left components of the mandibular arch gives rise to the lower jaw (mandible).

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Reference

Patten BM. The Early Embryology of the Chick. (1920) Philadelphia: P. Blakiston's Son and Co.

Cite this page: Hill, M.A. (2024, April 23) Embryology Patten041.jpg. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/File:Patten041.jpg

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