Branchial (Pharyngeal) apparatus
System Based Embryology
Dr.Luma Al-Allaf
After gastrulation, neural crest cells are specified at the border of the neural plate(opposite to primitive streak) and the non-neural ectoderm. During neurulation, the borders of the neural plate, also known as the neural folds, converge at the dorsal midline to form the neural tube
They are numbered in craniocaudal sequences
Masseter.
Pterygoideus externus.
Temporalis.
Pterygoideus internus.
The thyroid originates from two main structures: the primitive pharynx and the neural crest.
The rudimentary lateral thyroid develops from neural crest cells, while the median thyroid, which forms the bulk of the gland, arises from the primitive pharynx.
The thyroid gland forms as a proliferation of endodermal epithelial cells on the median surface of the developing pharyngeal floor.
The site of this development lies between 2 key structures, the tuberculum impar and the copula, and is known as the foramen cecum.
The thyroid initially arises caudal to the tuberculum impar, which is also known as the median tongue bud. This embryonic swelling develops from the first pharyngeal arch and occurs midline on the floor of the developing pharynx.
The foramen cecum begins rostral to the copula, also known as the hypobranchial eminence.
This median embryologic swelling consists of mesoderm that arises from the second pharyngeal pouch (although the third and fourth pouches are also involved). The thyroid gland, therefore, originates from between the first and second pouches.
BRANCHIAL ANOMALIES
Anomalies
Branchial cleft cysts are congenital epithelial cysts, which arise on the lateral part of the neck from a failure of obliteration of the second branchial cleft in embryonic development.
