Table 111

Adult Derivatives of the Pharyngeal Arches

Arch Nerve

Adult Derivatives

CN V

CN VII

CN IX

CN X (superior laryngeal branch)

CN X recurrent laryngeal branch)

Mesoderm: Muscles of mastication, mylohyoid, anterior belly of digastric, tensor veli palatini, tensor tympani

Neural crest cells: Maxilla, zygomatic bone, squamous portion of the temporal bene, palatine bone, vomer, mandible, incus, malleus, sphenomandibular ligament

Mesoderm: Muscles of facial expression, posterior belly of the digastric, stylohyoid, stapedius

Neural crest cells: Stapes, styloid process, stylohyoid ligament, lesser horn and upper body of hyoid bone

Mesoderm: Stylopharyngeus, common carotid arteries, internal carotid arteries

Neural crest cells: Greater horn and lower body of the hyoid bone

Mesoderm: Muscles of the soft palate (except tensor veli palatini), muscles of the pharynx (except stylopharyngeus), cricothyroid, cricopharyngeus, laryngeal cartilages, right subclavian artery, arch of the aorta

Neural crest cells: None

Mesoderm: Intrinsic muscles of larynx (except the cricothyroid), upper muscles of the esophagus, laryngeal cartilages, pulmonary arteries, ductus arteriosus

Neural crest cells: None

2. The posterior third of the tongue is characterized by the lingual tonsil; the lingual tonsil, palatine tonsil, and pharyngeal tonsil (adenoids) are collectively called Waldeyer's ring, which protects the oral port of entry.

Table 11-2

Adult Derivatives of the Pharyngeal Pouches, Grooves, and Membranes

Table 11-2

Adult Derivatives of the Pharyngeal Pouches, Grooves, and Membranes

Pouch

Adult Derivatives

1

Epithelial lining of the auditory tube and middle ear cavity

2

Epithelial lining of the palatine tonsil crypts

3

Inferior parathyroid gland and thymus

4

Superior parathyroid gland and ultimobranchial body*

Groove

1

Epithelial lining of the external auditory meatus

2, 3,4

Obliterated

Membrane

1

Tympanic membrane

2, 3, 4

Obliterated

'♦Neural crest cells migrate into the ultimobranchial body to form parafollicular cells (C cells) of the thyroid, which secrete calcitonin.

'♦Neural crest cells migrate into the ultimobranchial body to form parafollicular cells (C cells) of the thyroid, which secrete calcitonin.

In the newborn

Median sulcus

Oral part

(anterior two thirds)

Terminal Sulcus Tongue

Foramen cecum

(posterior one third)

Foramen Cecum Tongue

Foramen cecum

Copula

Hypobranchial eminence

Laryngeal orifice

At week 5

Median tongue Distal tongue bud bud v

In the newborn

Median sulcus

Oral part

(anterior two thirds)

Terminal sulcus

Foramen cecum

(posterior one third)

Figure 11-2. Development of the tongue. (A) At week 5. (B) In the newborn. (Adapted from Dudek RW, Fix JD: BRS Embryology, 2"d ed. Baltimore, Williams & Wilkins, 1998, p 153.)

3. General sensation from the mucosa is carried primarily by the glossopharyngeal nerve (CN IX).

4. Taste sensation from the mucosa is carried predominantly by the glossopharyngeal nerve (CN IX).

C. Muscles of the tongue

1. The intrinsic muscles and extrinsic muscles (styloglossus, hyoglossus, genioglos-sus, and palatoglossus) are derived from myoblasts that migrate into the tongue region from occipital somites.

2. Motor innervation for all muscles of the tongue is supplied by the hypoglossal nerve (CN XII), except for the palatoglossus muscle, which is innervated by the vague nerve (CN X).

A. The face is formed by three swellings: the frontonasal prominence, maxillary prominence (pharyngeal arch 1), and mandibular prominence (pharyngeal arch 1).

B. Bilateral ectodermal thickenings called nasal placodes develop on the ventrolateral aspects of the frontonasal prominence.

C. The nasal placodes invaginate into the underlying mesoderm to form the nasal pits, thus producing a ridge of tissue that forms the medial and lateral nasal prominences.

D. The nasolacrimal groove forms between the maxillary prominence and the lateral nasal prominence and eventually forms the nasolacrimal duct and lacrimal sac.

A. Intermaxillary segment

1. The intermaxillary segment forms when the medial growth of the maxillary prominences causes the two medial nasal prominences to fuse together at the midline.

Week 6

Lateral nasal prominence

Medial nasal prominence

Week 6

Lateral nasal prominence

Medial nasal prominence

Frontonasal Prominence

Frontonasal prominence

Nasal pit

Maxillary prominence { Pharyngeal Mandibular prominence ( arch 1

Frontonasal prominence

Nasal pit

Maxillary prominence { Pharyngeal Mandibular prominence ( arch 1

Intermaxillary Segment
Figure 11-3. Development of the face. Note that pharyngeal arch 1 plays a major role. (Adapted from Dudek RW, Fix JD: BRS Embryology, 2nd ed. Baltimore, Williams & Wilkins, 1998, p 154.)

2. The philtrum of the lip, four incisor teeth, and primary palate in the adult are formed from this segment.

B. Secondary palate

1. The secondary palate forms from outgrowths of the maxillary prominences called the palatine shelves.

2. Initially, the palatine shelves project downward on either side of the tongue but later attain a horizontal position and fuse along the midline palatine raphe to form the secondary palate.

3. The primary and secondary palate fuse at the incisive foramen to form the definitive adult palate.

4. Bone develops in both the primary palate and the anterior part of the secondary palate.

5. Bone does not develop in the posterior part of the secondary palate, which eventually forms the soft palate and uvula.

6- The nasal septum develops from the medial nasal prominences and fuses with the definitive palate.

Intermaxillary Segment

A B Nasal septum

Anterior Placenta And SectionAnterior Placenta And Section

Figure 11-4. Development of the palate. (A) This horizontal section shows the intermaxillary segment and maxillary prominence with palatine shelves growing toward the midline (arrows). (B, C) Coronal sections showing the movements of the palatine shelves (single arrows) and fusion with the nasal septum (double airows). (D) A horizontal section (as indicated) of the adult palate. (Level of sections in A-D is noted ir. top drawing.) (Adapted from Dudck RW, Fix JD: BRS Embryology, 2"J ed. Baltimore, Williams & Wilkins, 1998, p 155-156.)

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