Medical

Pharyngeal arches

The components of the pharyngeal arches are summarized in Table III-6-1.

Table III-6-1. The Neural, Arterial, Muscular, and Skeletal Elements Derived From the Pharyngeal Arches

(Neural

(Aortic Arch Mesoderm)

Muscle (Mesoderm)

Skeletal (Neural Crest)

1

V3

Tensor tympani muscle

Maxilla Mandible

Incus Malleus

2

VII

Lesser horn and upper body of hyoid bone

3

IX

Right and left common carotid arteries

Right and left internal carotid arteries

Stylo pharyngé us muscle

Greater horn and lower body of hyoid bone

4

Superior laryngeal nerve

Right subclavian artery

Arch of aorta

Cricothyroid muscle

Thyroid cartilage

6

X

Right and left

Intrinsic muscles

All other

Recurrent pulmonary of larynx (except cricothyroid muscle)

laryngeal cartilages

Recurrent pulmonary laryngeal nerve arteries

Ductus arteriosus of larynx (except cricothyroid muscle)

laryngeal cartilages

•Mote: Nerve is not derived from pharyngeal arch. It grows into the arch.

Figure 111-6-7. Tongue

Intrinsic and extrinsic muscles of the tongue are derived from myoblasts that migrate into the tongue region from occipital somites. Motor innervation is supplied by CNXII (Figure III-6-8).

Terminal

Sulcus

Foramen

Cecum

Figure 111-6-8. The Tongue

Terminal

Sulcus

Foramen

Cecum

Figure 111-6-8. The Tongue

Intermaxillary Segment 4 Incisor Teeth

palate)

Figure 111-6-9. Palate and Face Development palate)

Figure 111-6-9. Palate and Face Development

Clinical Considerations

First arch syndrome results from abnormal formation of pharyngeal arch 1 because of faulty migration of neural crest cells, causing facial anomalies. Two well-described syndromes are Treacher Collins syndrome and Pierre Robin sequence. Both defects involve neural crest cells.

Pharyngeal fistula occurs when pouch 2 and groove 2 persist, thereby forming a fistula generally found along the anterior border of the sternocleidomastoid muscle.

Pharyngeal cyst occurs when pharyngeal grooves that are normally obliterated persist, forming a cyst usually located at the angle of the mandible.

Ectopic thyroid, parathyroid, or thymus results from abnormal migration of these glands from their embryonic position to their adult anatomic position. Ectopic thyroid tissue is found along the midline of the neck. Ectopic parathyroid or thymus tissue is generally found along the lateral aspect of the neck. May be an important issue during neck surgery.

Thyrogl ossal duct cyst or fistula occurs when parts of the thyroglossal duct persist, generally in the midline near the hyoid bone. The cyst may also be found at the base of the tongue (lingual cyst).

DiGeorge sequence occurs when pharyngeal pouches 3 and 4 fail to differentiate into the parathyroid glands and thymus. Neural crest cells are involved.

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