In the development

Embryogenesis

Embryogenesis is the process by which the embryo is formed and develops, until it develops into a fetus.Embryogenesis starts with the fertilization of the ovum by sperm. The fertilized ovum is referred to as a zygote...

 of vertebrate animals

Vertebrate

Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...

, pharyngeal or branchial pouches form on the endodermal side between the branchial arch

Branchial arch

In the development of vertebrate animals, the pharyngeal arches are anlage for a multitude of structures. In humans, they develop during the fourth week in utero as a series of mesodermal outpouchings on the left and right sides of the developing pharynx...

es, and pharyngeal grooves (or clefts) form the lateral ectodermal surface of the neck region to separate the arches.

The pouches line up with the clefts, and these thin segments become gills in fish

Fish

Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...

.

First pouch

The endoderm

Endoderm

Endoderm is one of the three primary germ cell layers in the very early embryo. The other two layers are the ectoderm and mesoderm , with the endoderm as the intermost layer...

 lines the future auditory tube (Pharyngotympanic " Eustachian " tube) , middle ear

Middle ear

The middle ear is the portion of the ear internal to the eardrum, and external to the oval window of the cochlea. The mammalian middle ear contains three ossicles, which couple vibration of the eardrum into waves in the fluid and membranes of the inner ear. The hollow space of the middle ear has...

, mastoid antrum

Mastoid antrum

The mastoid antrum is a cavity in the petrous portion of the temporal bone, communicating posteriorly with the mastoid cells and anteriorly with the epitympanic recess of the middle ear via the aditus to mastoid antrum .-External links: - "Illustration of the continuity of the...

, and inner layer of the tympanic membrane. & origin of Mandibular nerve & Maxillary artery.

Second pouch

• Contributes to the middle ear
  Middle ear
  The middle ear is the portion of the ear internal to the eardrum, and external to the oval window of the cochlea. The mammalian middle ear contains three ossicles, which couple vibration of the eardrum into waves in the fluid and membranes of the inner ear. The hollow space of the middle ear has...
  
  , palatine tonsils, supplied by the facial nerve
  Facial nerve
  The facial nerve is the seventh of twelve paired cranial nerves. It emerges from the brainstem between the pons and the medulla, and controls the muscles of facial expression, and functions in the conveyance of taste sensations from the anterior two-thirds of the tongue and oral cavity...
  
  .

Third pouch

• The third pouch possesses Dorsal and Ventral wings. Derivatives of the dorsal wings include the inferior parathyroid gland
  Parathyroid gland
  The parathyroid glands are small endocrine glands in the neck that produce parathyroid hormone. Humans usually have four parathyroid glands, which are usually located on the rear surface of the thyroid gland, or, in rare cases, within the thyroid gland itself or in the chest...
  
  s, while the ventral wings fuse to form the cytoreticular cells of the thymus
  Thymus
  The thymus is a specialized organ of the immune system. The thymus produces and "educates" T-lymphocytes , which are critical cells of the adaptive immune system....
  
  . The main nerve supply to the derivatives of this pouch is Cranial Nerve IX, glossopharyngeal nerve
  Glossopharyngeal nerve
  The glossopharyngeal nerve is the ninth of twelve pairs of cranial nerves . It exits the brainstem out from the sides of the upper medulla, just rostral to the vagus nerve...
  
  .

Fourth pouch

Derivatives include:

• superior parathyroid gland
  Parathyroid gland
  The parathyroid glands are small endocrine glands in the neck that produce parathyroid hormone. Humans usually have four parathyroid glands, which are usually located on the rear surface of the thyroid gland, or, in rare cases, within the thyroid gland itself or in the chest...
  
  s and ultimobranchial body which forms the parafollicular C-Cells of the thyroid gland.
• Musculature and cartilage of larynx (along with the sixth pharyngeal pouch).

Fifth pouch

• Rudimentary structure, becomes part of the fourth pouch contributing to thyroid C-cells.

Sixth pouch

• Along with the fourth pouch, contributes to the formation of the musculature and cartilage of the larynx.

External links

(Item #1 at Fig. 14)

• Outline at howard.edu (scroll down to "III. THE PHARYNGEAL POUCHES")