AP BIOLOGY

Detailed explanation-1: -The resulting pouches give rise to the middle ear cavity, Eustachian tube, mastoid air cells, palatine tonsils, thymus, parathyroid, and parafollicular cells of the thyroid. [7] Each of these tissues develops from their respective pharyngeal pouch, or pouches, in the case of the parathyroid gland.

Detailed explanation-2: -Pharyngeal pouches develop in the early embryos of all vertebrates, including the air-breathing terrestrial reptiles, birds, and mammals. The number of pouches has been reduced in the course of evolution from six or more to four in tetrapods, and the posterior pouches may not actually break through.

Detailed explanation-3: -In the embryonic development of vertebrates, pharyngeal pouches form on the endodermal side between the pharyngeal arches. The pharyngeal grooves (or clefts) form the lateral ectodermal surface of the neck region to separate the arches.

Detailed explanation-4: -Each of the four pouches develops from the endoderm whereas each cleft derives from ectoderm. The pharyngeal membranes exist between the clefts and pouches and are composed of external ectoderm, mesoderm, cells of the neural crest in the core and internal endoderm as a lining.