Lectures of Human Embryology By Dr. Noura El Tahawy Faculty of Medicine; El Minia University; Egypt

1. Development of the tongue
By
Dr. Noura El Tahawy

4. Development of tongue
 Time:
 Origin:
 The tongue appears in embryo of approximately 4 weeks.
 Mucous membrane:
 Muscles:
 Nerve supply:

5. Development of tongue
 Mucous membrane:
 1st pgaryngeal arch: gives 2 lateral buds called lingual swellings and a median bud called tuberculum impar.
 3rd & 4th arches: give the hypobranchial eminence (copula)
 4th arch: gives epiglottal swelling.

6. Development of tongue
 Muscles:
 Develops from 3-4 occipital myotomes.
 Nerve supply of the tongue:
 Motor: Hypoglossal N. (C XII)
 Sensory: general and special.
 Freeing of the tongue: by forming the alveo-lingual groove& frenulum

10. Formation of alveolo-lingual groove
Frenulum of tongue
To Free the Anterior 2/3 of tongue

11. Innervation of the tongue

12. Development of the Tongue Epithelium (Mucus membrane)(endodermal)
1- The anterior two thirds:
Origin: from The 1st Pharyngeal arch (mandibular processes)  two lateral lingual processes+ one tuberculum impar meet  fuse  anterior 2/3 of the tongue The site of fusion between the two lateral lingual swellings in the ant. 2/3 is indicated by the median sulcus.
2- The pharyngeal part (posterior third):
Origin: 3rd & 4 th pharyngeal arches hypobranchial eminence  four swellings  meet  fuse copula of Hypobranchial eminince  posterior third of the tongue.
3. Fusion of ant. 2/3 with post. 1/3 : The site of fusion between anterior 2/3 & posterior 1/is indicated by V- shaped sulcus terminalis.
4. Free ant . 2/3 by forming Alveolo-lingual groove: U shaped sulcus mobile tongue leaving frenulum linguae.
Tongue Musculature:
is derived from 3-4 occipital myotomes, supplied by hypoglossal nerve.
SUMMARY OF TONGUE DEVELOPMENT

13. Embryological background that explains tongue innervation
This unusual development of the tongue explains its innervation
Since the mucosa of the anterior two thirds of the tongue is derived from the first arch, it is supplied by the fifth cranial nerve (trigeminal nerve), whereas the mucosa of the posterior third of the tongue, derived from the third arch, is supplied by the ninth cranial nerve (glossopharyngeal nerve)
The epiglottis is formed from 4th arch, so it is supplied by superior laryngeal nerve of vagus (4th arch nerve).
- Musculature is derived from occipital myotomes which migrate to the tongue carrying with them its nerve supply: The hypoglossal nerve.

14. Congenital Anomalies of the Tongue
Cause: incomplete degeneration of the cells which connect the undersurface of the tongue to the floor of the mouth. (Incomplete formation of alveolo-lingual groove). Features: the frenulum may be thick and short or it may extend to the tip of the tongue leading to limitation of tongue protrusion. It is treated by freneotomy.
Tongue-tie (Ankyloglossia)
- Cyst within the tongue: remenant of thyroglossal cyst
- Persistant thyroglossal duct that remain opened
- lingual thyroid
Congenital Cyst
& fistula
Complete or partial absence of the tongue
Aglossia
Abnormal small tongue
Microglossia
Abnormal large tongue
Macroglossia
Due to failure of complete fusion of lingual swellings
Bifid tongue

15. Anomalies of the tongue
 Ankyloglossia (Tongue-tie) :
Normal

16. Development of tongue
 Freneotomy:
Normal

18. Development of thyroid gland
In the 4th week (at 24 days of gestation), the thyroid gland develops as a depression and epithelial thickening in the floor of the pharynx. (endodermal)
This appears at a point between the body and base of the tongue called the foramen caecum.
From this point, the thyroid primordium descends in the neck as a bilobed diverticulum to reach apiont in front of the trachea in the 7th week.
During this migration, the gland remains connected to the floor of the oral cavity by an epithelial cord or duct, the thyroglossal duct which later becomes a cord of cells.
The foramen caecum remains at the site of origin.
The thyroid gland begins to function at the beginning of the 3rd month when colloid containing follicles appear.

19. Adult Thyroid gland

23. Summary

24. Developmental defects of thyroid
1.Aplasia of thyroid: Failure of development of Thyroid gland (Cretinism)
2.Ectopic Thyroid gland: Incomplete descend of thyroid gland to become in the substance of tongue (Lingual thyroid)
3.Aberrant thyroid: in the superior mediastinum
4.Accessory Thyroid Tissue
5.Thyroglossal Cyst : See Below
6.Thyroglossal Fistula: See below

25. •Thyroglossal cyst and Fistula: The cyst is due to persistence of part of the duct with cyst formation. Fistula means the presence of connection between the cyst & the surface of the neck . Cysts and fistulae found in the midline of the neck along the course of the thyroglossal duct. But it is usually found at the level of the hyoid bone and the thyroid cartilage. Infection of the cyst or fistula may occur
Developmental defects of thyroid

26. Sites of ectopic thyroid

27. Thyroglossal duct Cyst
Developmental defects of thyroid

28. Development of Parathyroid Glands
The inferior parathyroid glands develop from endoderm of third pharyngeal pouch, they travel downwards during the foetal life.
In contrast, the superior parathyroid glands develop from endoderm of fourth pharyngeal pouch. They remain superior to the thyroid lobes.
The parathyroid hormone is produced from the 12th week of development onwards.

29. Development of Parathyroid Glands

30. Salivary glands

31. Appear as epithelial buds from oral cavity.
Parotid gland: The first to appear, early in 6th week, from oral ectoderm, near angle of stomodeum. It forms a tube, extends into cheek’s mesoderm. (Between the mandibular&Maxillary processes)
Its Proximal part forming the parotid duct;
Its distal end breaks to form the glandular alveoli.
Capsule & connective septae develop from surrounding mesoderm.
 The duct opening is carried to open inside the cheek.
Submandibular gland: Appear late in 6th week, from an endodermal bud in floor of stomodeum (alveolo- lingual groove).
Develops in same way as parotid gland.
Sublingual gland: appear in 8th week, from multiple endodermal buds in the alveolo-lingual groove.
Summary of Salivary glands development

32. • Paranasal sinuses develop during late fetal life.
• They form as outgrowths or diverticula of the walls of the nasal cavities and become air filled extensions of the nasal cavities in the adjacent bone.
- Frontal – 3 to 4 months of I.U
- Ethmoidal – 4 months of I.U
- Maxillary – Develops at 10 weeks of I.U
- Sphenoidal – 4 months of I.U
DEVELOPMENT OF PARANASAL SINUSES

33. Thanks