The thyroid gland begins at around the 3rd and 4th weeks of embryonic development as a proliferation of endodermal cells at the foramen cecum of the developing tongue. The gland descends to its final location anterior and inferior to the larynx but is still connected to the foramen cecum via the thyroglossal duct until that is broken down in the 5th week of development. CLINICAL … Continue reading Thyroid gland development

The pharyngeal clefts and pouches are grooves on the ectoderm and endoderm respectively that seperate the pharyngeal arches. Some of them develop into structures of the head and neck including glands and tubes. Derivatives of pharyngeal clefts On the outside, the 1st cleft forms the external auditory meatus. Since the 2nd overgrows the 3rd and 4th arches, the 2nd, 3rd and 4th clefts become buried … Continue reading Pharyngeal clefts & pouches

The pharyngeal arches appear around the 4th to 5th week of development and develop into structures of the head and neck. They are bars of mesoderm tissue forming around the pharynx and demarcated internally by the pharyngeal pouches (grooves on the endoderm) and externally by the corresponding pharyngeal clefts (grooves on the ectoderm). There are six arches, but only five are considered as the 5th … Continue reading Pharyngeal arches

During development, bones of the skull base ossify in cartilage (i.e. endochondral ossification). They include the basioccipital, basisphenoid, petrous temporal and ethmoid bones. The skeletal capsules that house and protect the special sense organs also contribute to the skull base: the olfactory capsule contributes to the ethmoid bone, the optic capsule to the sphenoid bone and the otic capsule to the petrous temporal bone. The … Continue reading Skull development

Face The external face forms between the 4th and 6th weeks of embryonic development. It initially involves degeneration of the oropharyngeal membrane that divides the primitive mouth and pharynx. The face is then completed by fusion of five neural crest-filled swellings of ectoderm: the unpaired medial frontonasal process which is divided into lateral and medial nasal processes on each side by the future nostrils. The … Continue reading Face & palate development