Click on pictures for an enlarged view of the graphic. Refer to Picture 1, 2 and 3 (from: James K Avery: Essentials of Oral Histology and Embryology – A Clinical Approach, Mosby Year Book) Picture 1| Picture 2| Picture 3| The branchial (=Gr gill) apparatus comprises an early structure during embryologic development. It is associated with the formation of the head and neck. It consists of the branchial arches, the pharyngeal pouches, the branchial clefts or grooves and the branchial membranes (not pictured). A four-week-old embryo features four visible branchial arches separated by branchial grooves.
They are numbered craniocaudally. A fifth and a 6th are also present but are very small. A primitive mouth appears as a small depression referred to as stomatodeum (stomodeum). The oropharyngeal (buccopharyngeal) membrane separates the stomatodeum from the primitive pharynx (cranial part of the foregut). This membrane ruptures at 24 to 26 days and communication with the amniotic cavity is established. Identify Rathke’s pouch in Picture 3 and review your notes on the subject. BRANCHIAL ARCHES Refer to Picture 4 (from: William J. Larsen: Human Embryology, Churchill Livingstone)
Picture 4 1st branchial arch (mandibular arch) gives rise to the maxillary and the mandibular prominences. Identify the 1st branchial arch cartilage or Meckel’s cartilage. It does not form the mandible. Indicates the position of the future mandible. The mandible develops by intramembranous ossification. The malleus and the incus develop by endochondral ossification of the dorsal aspect of this cartilage. Innervation: V cranial nerve 2nd branchial arch cartilage (Reichert’s cartilage) Forms the stapes, styloid process, and superior hyoid bone. rd branchial arch forms the lower aspect of the hyoid. 4th and 6th branchial arch form the thyroid and cartilages of the larynx. PHARYNGEAL POUCHES Refer to Picture 1 (from: James K Avery: Essentials of Oral Histology and Embryology – A Clinical Approach, Mosby Year Book) 1st pharyngeal pouch forms the tubotympanic recess. 2nd pharyngeal pouch forms the palatine tonsils. Part of the pouch remains in the adult as the tonsillar fossa. 3rd pharyngeal pouch forms inferior parathyroid and thymus. 4th pharyngeal pouch forms the superior parathyroid. th pharyngeal pouch forms the ultimobranchial body that gives rise to the parafollicular cells that secrete calcitonin. BRANCHIAL CLEFTS (GROOVES) Refer to Picture 1 (from: James K Avery: Essentials of Oral Histology and Embryology – A Clinical Approach, Mosby Year Book) Four present, only one contributes to the definitive structure of the embryo. The dorsal part of the first cleft penetrates the ectomesenchyme and forms the external auditory meatus. Branchial Malformations 1st arch syndrome Insufficient migration of cranial neural crest cells into the 1st branchial arch during the 4th week.
Treacher Collins syndrome (mandibulofacial dysostosis) Pierre Robin anomalad Branchial cysts DEVELOPMENT OF THE TONGUE Refer to Picture 5 (from: AR Ten Cate: Oral Histology – Development, Structure and Function) Picture 5 The tongue begins to develop at about 4 weeks. The oral part (anterior two-thirds) develops from two distal tongue buds (lateral lingual swellings) and a median tongue bud (tuberculum impar) [1st branchial arch]. Innervation: V nerve The pharyngeal part develops from the copula and the hypobranchial eminence [2nd, 3rd and 4th branchial arches]. Innervation: IX cranial nerve
The line of fusion of the oral and pharyngeal parts of the tongue is roughly indicated in the adult by a V-shaped line called the terminal sulcus. At the apex of the terminal sulcus is the foramen cecum. Refer to Table 1 for a complete understanding of the development of the tongue. (from: William J. Larsen: Human Embryology, Churchill Livingstone Table 1 DEVELOPMENT OF THE FACE Refer to Picture 6 (from: KL Moore: Essentials of Human Embryology, BC Decker, Inc. ) Picture 6 The face develops between the 24th and 38th days of gestation. Identify the following areas and review your reading assignments.
Frontonasal prominence Maxillary prominences Mandibular prominences Nasal placodes Median and lateral nasal prominences and nasal pits Intermaxillary segment DEVELOPMENT OF THE PALATE Refer to Picture 7 (from:KL Moore: Essentials of Human Embryology, BC Decker, Inc. ) Picture 7 The primary palate develops at about 28 days of gestation. The secondary palate develops between 7th and 8th week of gestation. Identify the following areas and review your reading assignments. Primary palate Median and lateral palatine processes Secondary palate Cleft lip and palate