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: -The earliest vertebrates resembled hagfish and lived more than 500 million years ago. As other classes of fish appeared, they evolved traits such as a complete vertebral column, jaws, and a bony endoskeleton. Amphibians were the first tetrapod vertebrates as well as the first vertebrates to live on land.

Detailed explanation-4: -Homologous structures are similar structures that evolved from a common ancestor.