Embryology

Question 1

Thyroglossal duct

Answer 1

• Distal end usually forms the thyroid gland
• Proximal part normally degenerates
• Failure to degenerate may lead to a thyroglossal duct cyst or median cervical cyst

Question 2

First pharyngeal pouch

Answer 2

• Forms the middle-ear cavity and auditory tube

- Normally remains patent

Question 3

First pharyngeal cleft

Answer 3

• Forms the external ear canal

- Normally remains patent

Question 4

Second pharyngeal cleft

Answer 4

• Normally does not remain patent
• Typically covered by the overgrowth of the second pharyngeal arch.
• If part of this pouch remains patent, it may form a lateral cervical cyst, which is seen on the lateral side of the neck along the anterior border of the sternocleidomastoid muscle.

Question 5

Second pharyngeal pouch

Answer 5

• Forms the tonsillar fossa of the pharynx
• The pharyngeal mucosa in this area arises from the endoderm of the pouch.
• Ingrowth of mesoderm cells results in the formation of the palatine tonsil