Head Development

Introduction

Fetal head (week 12)

The head and neck is not really a "system", but structurally quite different in origin from the body. The head and neck are one of the most complicated structures that the embryo forms, with special intermediate structures (the pharyngeal arches) and contributions from all 3 embryonic layers (ectoderm, mesoderm, endoderm), and significantly, a major contribution from the neural crest. Neural crest contributes jaw skeletal elements,, connective tissues and tendons. The associated muscles derive mainly from cranial mesoderm. These components though will form different structures dependent upon which arch they are within. The cavity within the pharyngeal arches forms the pharynx.

The pharynx contributes to 2 endocrine organs, in the roof the pituitary (hypophysis) and the floor the thyroid. The thyroid gland being one of the first endocrine organs to be formed has an important role in embryonic development. The pharynx floor of all arches also contribute to the formation of the tongue.

Because the head contains many different structures also review notes on: Skull Development, Sensory (placodes, eye, ear, nose, taste), Respiratory (pharynx), Integumentary (teeth, hair) and Endocrine Development (pituitary, thyroid, parathyroid, thymus).

| 2013 Meeting Presentation

Some Recent Findings

Developmental and evolutionary origins of the pharyngeal apparatus "The vertebrate pharyngeal apparatus, serving the dual functions of feeding and respiration, has its embryonic origin in a series of bulges found on the lateral surface of the head, the pharyngeal arches. Developmental studies have been able to discern how these structures are constructed and this has opened the way for an analysis of how the pharyngeal apparatus was assembled and modified during evolution. For many years, the role of the neural crest in organizing pharyngeal development was emphasized and, as this was believed to be a uniquely vertebrate cell type, it was suggested that the development of the pharyngeal apparatus of vertebrates was distinct from that of other chordates." hand2 and Dlx genes specify dorsal, intermediate and ventral domains within zebrafish pharyngeal arches. "The ventrally expressed secreted polypeptide endothelin1 (Edn1) patterns the skeleton derived from the first two pharyngeal arches into dorsal, intermediate and ventral domains. ...Collectively, our work indicates that the expression and function of hand2 and Dlx genes specify major patterning domains along the dorsoventral axis of zebrafish pharyngeal arches."

More recent papers

This table allows an automated computer search of the external PubMed database using the listed "Search term" text link. This search now requires a manual link as the original PubMed extension has been disabled. The displayed list of references do not reflect any editorial selection of material based on content or relevance. References also appear on this list based upon the date of the actual page viewing. References listed on the rest of the content page and the associated discussion page (listed under the publication year sub-headings) do include some editorial selection based upon both relevance and availability. More? References | Discussion Page | Journal Searches | 2019 References | 2020 References Search term: Head Development <pubmed limit=5>Head Development</pubmed>

Textbooks

• The Developing Human: Clinically Oriented Embryology (8th Edition) by Keith L. Moore and T.V.N Persaud - Moore & Persaud Chapter Chapter 10 The Pharyngeal Apparatus pp201 - 240.
• Larsen’s Human Embryology by GC. Schoenwolf, SB. Bleyl, PR. Brauer and PH. Francis-West - Chapter 12 Development of the Head, the Neck, the Eyes, and the Ears pp349 - 418.

UNSW Students
	You have access the following online Embryology textbooks through the UNSW Library.
	Moore, K.L. & Persuad, T.V.N. (2008). The Developing Human: clinically oriented embryology (8th ed.). Philadelphia: Saunders. Chapter 9 - The Pharyngeal Apparatus Chapter 18 - The Eye and Ear
	Schoenwolf, G.C., Bleyl, S.B., Brauer, P.R. and Francis-West, P.H. (2009). Larsen’s Human Embryology (4th ed.). New York; Edinburgh: Churchill Livingstone. Chapter 16 - Development of the Pharyngeal Apparatus and Face Chapter 17 - Development of the Ears and Eye

Objectives

• List the main structures derived from the pharyngeal arches, pouches and clefts.
• Know the stages and structures involved in the development of the face.
• Predict the results of abnormal development of the face and palate.
• Briefly summarise the development of the tongue.

The Pharynx

The cavity within the pharyngeal arches forms the pharynx.

The pharynx contributes to 2 endocrine organs, in the roof the [endocrine7.htm pituitary] (hypophysis) and the floor the thyroid. The thyroid gland being one of the first endocrine organs to be formed has an important role in embryonic development. The pharynx floor of all arches also contribute to the formation of the [head6.htm tongue].

Pharyngeal Arch Components

Major features to identify for each: arch, pouch, groove and membrane. Contribute to the formation of head and neck and in the human appear at the 4th week. The first arch contributes the majority of upper and lower jaw structures.

Early Face and Pharynx

• Pharynx - begins at the buccopharyngeal membrane (oral membrane), apposition of ectoderm with endoderm (no mesoderm between)

Pharyngeal Arch Development

• branchial arch (Gk. branchia= gill)
• arch consists of all 3 trilaminar embryo layers
• ectoderm- outside
• mesoderm- core of mesenchyme
• endoderm- inside

Neural Crest

• Mesenchyme invaded by neural crest generating connective tissue components
• cartilage, bone, ligaments
• arises from midbrain and hindbrain region

Arch Features

Each arch contains: artery, cartilage, nerve, muscular component

Arches and Phanynx Form the face, tongue, lips, jaws, palate, pharynx and neck cranial nerves, sense organ components, glands

• Humans have 5 arches - 1, 2, 3, 4, 6 (Arch 5 does not form or regresses rapidly)
• from in rostro-caudal sequence, Arch 1 to 6 from week 4 onwards
• arch 1 and 2 appear at time of closure of cranial neuropore

• Face - mainly arch 1 and 2
• Neck components - arch 3 and 4 (arch 4 and 6 fuse)

Arch Features

• • arch
  • groove
    • externally separates each arch
      • also called a cleft
    • only first pair persist as external auditory meatus
  • pouch
    • internally separates each arch
    • pockets from the pharynx
  • membrane
    • ectoderm and endoderm contact regions
    • only first pair persist as tympanic membrane
• Pharyngeal Arch 1 (Mandibular Arch) has 2 prominances
  • smaller upper- maxillary forms maxilla, zygomatic bone and squamous part of temporal
  • larger lower- mandibular, forms mandible
• Pharyngeal Arch 2 (Hyoid Arch)
  • forms most of hyoid bone
• Arch 3 and 4
  • neck structures

Arch Arteries

• Arch 1 - mainly lost, form part of maxillary artery
• Arch 2 - stapedial arteries
• Arch 3 - common carotid arteries, internal carotid arteries
• Arch 4 - left forms part of aortic arch, right forms part right subclavian artery
• Arch 6 - left forms part of left pulmonary artery , right forms part of right pulmonary artery

placental vein -> liver -> heart -> truncus arteriosus -> aortic sac -> arch arteries -> dorsal aorta -> placental artery

Arch 5 Artery?
There has been ongoing controversy as to whether the fifth arch artery, that forms in fish, ever develops in birds and mammals. A recent study in mouse and human embryos identified the presence of an extra vessel presence in a single Carnegie Stage 14 human embryo.

Arch Cartilage

Meckel's cartilage, first pharyngeal arch

Pharyngeal arch cartilages

• Arch 1 - Meckel's cartilage, horseshoe shaped
  • dorsal ends form malleus and incus
  • midpart forms ligaments (ant. malleus, sphenomandibular)
  • ventral part forms mandible template

• Arch 2 - Reichert's cartilage
  • dorsal ends form stapes and Temporal bone styloid process
  • ventral part ossifies to form hyoid bone components
  • lesser cornu and superior body

• Arch 3- forms greater cornu and inferior part of hyoid

• Arch 4&6- form laryngeal cartilages, except epiglottis (from hypobranchial eminence)

Arch Muscle

• Arch 1 - muscles of mastication, mylohyoid, tensor tympanic, ant. belly digastric
• Arch 2 - muscles of facial expression, stapedius, stylohyoid, post. belly digastric
• Arch 3 - stylopharyngeus
• Arch 4&6 - crycothyroid, pharynx constrictors, larynx muscles, oesophagus (st. muscle)

Arch Nerve

• Arch 1 - CN V trigeminal, caudal 2/3 maxillary and mandibular, cranial 1/3 sensory nerve of heaad and neck, mastication motor
• Arch 2 - CN VII facial
• Arch 3 - CN IX glossopharyngeal
• Arch 4&6 - CN X vagus, arch 4- superior laryngeal, arch 6- recurrent laryngeal

Arch Pouches

• Arch 1 - elongates to form tubotympanic recess, tympanic cavity, mastoid antrum, eustachian tube
• Arch 2 - forms tonsillar sinus, mostly oblierated by palatine tonsil
• Arch 3 - forms inferior parathyroid and thymus
• Arch 4 - forms superior parathyroid, parafollicular cells of Thyroid

Thyroid Gland

• not a pouch structure
• first endocrine organ to develop day 24
• from floor of pharynx
• descends thyroglossal duct (which closes)
• upper end at foramen cecum

Anterior Pituitary

Pituitary

• not a pouch structure
• boundary epitheilal ectoderm in the roof of the pharynx
• forms a pocket (Rathke's pouch) that comes into contact with the ectoderm of developing brain.
  • Rathke's pouch is named after German embryologist and anatomist Martin Heinrich Rathke (1793 — 1860).

Face Development

Begins week 4 centered around stomodeum, external depression at oral membrane

5 initial primordia from neural crest mesenchyme

• single frontonasal prominence (FNP) - forms forehead, nose dorsum and apex
• nasal placodes develop later bilateral, pushed medially
• paired maxillary prominences - form upper cheek and upper lip
• paired mandibular prominences - lower cheek, chin and lower lip

Frontonasal Process

The frontonasal process (FNP) forms the majority of the superior part of the early face primordia. It later fuses with the maxillary component of the first pharyngeal arch to form the upper jaw. Failure of this fusion event during the embryonic period leads to cleft lip. Under the surface ectoderm the process mesenchyme consists of two cell populations; neural crest cells, forming the connective tissues; and the mesoderm forming the endothelium of the vascular network.

A chicken developmental model study has identified a specific surface region, the Frontonasal Ectodermal Zone (FEZ), initially induced by bone morphogenetic proteins that appears to regulate the future growth and patterning of the frontonasal process. The specific frontonasal ectodermal zone was located in the frontonasal process ectoderm flanking a boundary between Sonic hedgehog (Shh) and Fibroblast growth factor 8 (Fgf8) expression domains.

Head/Skull

• chondrocranium forms base of skull
• in lower vertebrates encases brain
• cranial vault
• calveria
• facial skeleton
• pharyngeal arches

Sensory Placodes

Sensory placodes (week 5)

• During week 4 a series of thickened surface ectodermal patches form in pairs rostro-caudally in the head region.
• Recent research suggests that all sensory placodes may arise from common panplacodal primordium origin around the neural plate, and then differentiate to eventually have different developmental fates.
• These sensory placodes will later contribute key components of each of our special senses (vision, hearing and smell). Other species have a number of additional placodes which form other sensory structures (fish, lateral line receptor). Note that their initial postion on the developing head is significantly different to their final position in the future sensory system

Otic placode

in the stage 13/14 embryo (shown below) the otic placode has sunk from the surface ectoderm to form a hollow epithelial ball, the otocyst, which now lies beneath the surface surrounded by mesenchyme (mesoderm). The epithelia of this ball varies in thickness and has begun to distort, it will eventually form the inner ear membranous labyrinth.

Lens placode

lies on the surface, adjacent to the outpocketing of the nervous system (which will for the retina) and will form the lens.

Nasal placode

has 2 components (medial and lateral) and will form the nose olefactory epithelium.

Links: Placodes

Head Growth

Developing skull Computed Tomography (CT) image showing normal sutures.

• continues postnatally - fontanelle allow head distortion on birth and early growth
• bone plates remain unfused to allow growth, puberty growth of face

Fetal head growth (circumference)

• 

  Second and third trimesters

• 

  Second trimester

Skull Overview

Chondrocranium - formed from paraxial mesoderm

• cranial end of vertebral column
• modified vertebral elements
• occipital and cervical sclerotome
• bone preformed in cartilage (endochondrial ossification)

Cranial Vault and Facial Skeleton - formed from neural crest

• muscle is paraxial mesoderm
• somitomeres and occipital somites

Calveria - bone has no cartilage (direct ossification of mesenchyme)

• bones do not fuse, fibrous sutures 1. allow distortion to pass through birth canal 2. allow growth of the brain
• 6 fontanelles, posterior closes at 3 months, anterior closes at 18 months

Links: Skull Development

Palate

The palate has two key stages of development during embryonic and an early fetal involving the fusion of structures (epithelia to mesenchymal).

Embryonic

Primary palate, fusion in the human embryo between stage 17 and 18, from an epithelial seam to the mesenchymal bridge.

Fetal

Secondary palate, fusion in the human embryo in week 9. This requires the early palatal shelves growth, elevation and fusion during the early embryonic period. The fusion event is to both each other and the primary palate. palatal shelf elevation | secondary palate

Links: Palate Development

Ear Auricles

• form from 6 hillocks (week 5)
• 3 on each of arch 1 and 2

Tongue Development

] ]

• Ectoderm of the first arch surrounding the stomodeum forms the epithelium lining the buccal cavity.
• Also the salivary glands, enamel of the teeth, epithelium of the body of the tongue.
  • As the tongue develops "inside" the floor of the oral cavity, it is not readily visible in the external views of the embryonic (Carnegie) stages of development.

• Contributions from all arches, which changes with time
• begins as swelling rostral to foramen cecum, median tongue bud

• • Arch 1 - oral part of tongue (ant 3/2)
  • Arch 2 - initial contribution to surface is lost
  • Arch 3 - pharyngeal part of tongue (post 1/3)
  • Arch 4 - epiglottis and adjacent regions

Tongue muscle

tongue muscle

• Tongue muscles originate from the somites.
  • Tongue muscles develop before masticatory muscles and is completed by birth.
• Masticatory muscles originate from the somitomeres.
  • These muscles develop late and are not complete even at birth.

Salivary Glands

• epithelial buds in oral cavity (week 6 to 7) extend into mesenchyme
• parotid, submandibular, sublingual

Links: Tongue Development | Development Animation - Tongue

Pharyngeal Arch Tables

Structures derived from Arches

Arch	Nerve	Skeletal Structures	Muscles	Ligaments
1 (maxillary/mandibular)	trigeminal (V)	mandible, maxilla, malleus, incus		ant lig of malleus, sphenomandibular ligament
2 (hyoid)	facial (VII)	stapes, styloid process, lesser cornu of hyoid, upper part of body of hyoid bone		stylohyoid ligament
3	glossopharyngeal (IX)	greater cornu of hyoid, lower part of body of hyoid bone
4 & 6	superior laryngeal and recurrent laryngeal branch of vagus (X)	thyroid, cricoid, arytenoid, corniculate and cuneform cartilages

	mandible
	hyoid
File:Larynx cartilage sm.jpg

Structures derived from Pouches

Each pouch is lined with endoderm and generates specific structures.

Pouch	Overall Structure	Specific Structures
1	tubotympanic recess	tympanic membrane, tympanic cavity, mastoid antrum, auditory tube
2	intratonsillar cleft	crypts of palatine tonsil, lymphatic nodules of palatine tonsil
3	inferior parathyroid gland, thymus gland
4	superior parathyroid gland, ultimobranchial body
5	becomes part of 4th pouch

Structures derived from Grooves

Only the first groove differentiates into an adult structure and forms part of the external acoustic meatus.

Structures derived from Membranes

At the bottom of each groove lies the membrane which is formed from the contact region of ectodermal groove and endodermal pouch. Only the first membrane differentiates into an adult structure and forms the tympanic membrane.

Movies

‎‎Face Development Page | Play

‎‎Palate (oral view) Page | Play

‎‎Palate (front view) Page | Play

‎‎Tongue Page | Play

‎‎Mandible Growth Page | Play

Links: Quicktime Movies | Flash Movies

References

Reviews

<pubmed>20607135</pubmed>| PMC2895339 | Integr Comp Biol.

Search PubMed

Search term: Head Development | Pharyngeal Arch Development | | Face Development

Additional Images

• 

  Adult axial skeleton

• 

  Adult skull (lateral simplified)

• 

  Fetal head lateral (12 weeks)

• 

  Fetal head medial (12 weeks)

• 

  Fetal head section (12 weeks)

• 

  adult mandible

• 

  adult hyoid

Historic

Development or the Face

• 

  Fig. 1. Showing the formation of the face by the Nasal, Maxillary, and Mandibular processes in an embryo of the 4th week.

• 

  Fig. 2. Showing the parts of the face formed from the Nasal, Maxillary and Mandibular processes.

• 

  Fig. 3. Showing the structures formed in the Mesial Nasal Processes.

• 

  Fig. 4. Showing the trough-shaped Vomer of the newly born.

• 

  Fig. 5. Showing the suture on the face between the premaxilla and maxilla in the skull of a young orang.

• 

  Fig. 6. Showing the structures formed in the Lateral Nasal Processes.

• 

  Fig. 7. Coronal section of the skull of a 7th month human foetus to show the cartilages of the Lateral and Mesial Nasal Processes and the bones formed round them.

• 

  Fig. 8. Showing the ingrowth of the palatal plates of the two maxillary processes early in the 2nd month. (After Kollmann.) .

• 

  Fig. 9. Showing the Hard Palate at birth. The premaxillary part is formed from the Mesial Nasal Processes ; the remainder by the Palatal Plates of the Maxillary Processes.

• 

  Fig. 10, a, b, c. Showing what become of the skeletons of the Mandibular Arch (Meckel's Cartilage) and Maxillary Process (Palato-quadrate Cartilage).

• 

  Fig. 10 D. Illustrating Gadow's view of the origin of the Auditory Ossicles and Tympanic Plate.

• 

  Fig. 11. Showing the manner in which the development of the Maxillary Antrum affects the size of the palate and position of the molar teeth.

• 

  Fig. 12. Showing the Centres of Ossification and age changes in the Lower Jaw.

• 

  Fig. 13. The chief types of the Temporo-Maxillary Articulation. A. Carnivorous Type. B. Omnivorous Type. C. Herbivorous Type.

• 

  Fig. 14. Showing the Chief Changes after birth in the form of the TemporoMaxillary Articulation.

• 

  Fig. 15 A. Sagittal Section showing the Stomodaeum and position of the Oral Plate in the 3rd week.

• 

  Fig. 15 B. Showing the parts of the Buccal and Nasal Cavities formed from the Stomodaeum. The relative position of the Oral Plate is indicated.

Development of the Pharynx and Neck

• 

  Fig. 21a. Showing the Visceral Arches and Cleft-depressions in the Pharyngeal Wall of a 4th week human Embryo. Each Visceral Arch contains an Aortic Arch. (After His.)

• 

  Fig. 21b. Showing the position of the Heart, Visceral and Aortic Arches in a fish. (Diagrammatic — after Gegenbaur.)

• 

  Fig. 22. Showing the Primitive Pharynx of a 3rd week embryo in sagittal section, bounded by the Visceral Arches. (After His.) .

• 

  Fig. 23. Showing the Floor of the Pharynx of a 4th week human embryo. (After His.)

• 

  Fig. 24. Schematic Section of a Visceral Arch.

• 

  Fig. 25. Showing the position of the External Cleft Depressions in the Adult.

• 

  Fig. 26. Showing what become of the Cartilages of the Visceral Arches.

• 

  Fig. 27. Showing what become of the Nerves of the Visceral Arches, hyoid arch) is represented by the chorda tympani and great superficial petrosal.

• 

  Fig. 28. Showing what become of the Aortic Arches in the adult. Only the shaded parts persist.

• 

  Fig. 29. The condition of the Eight and Left Doral Aortae in a 6th week human foetus.

• 

  Fig. 30. Showing the Buccal and Pharyngeal parts of the Tongue.

• 

  Fig. 31. Showing the origin of the tongue in the floor of the primitive pharynx. (After His.)

• 

  Fig. 32. Showing the origin of the Submaxillary and Sublingual Glands from furrows between the gum and tongue during the flth week. (After His.) .

• 

  Fig. 33. Showing the position of the Visceral Clefts in the Adult.

• 

  Fig. 34. Showing the origin of the Tonsil, Thymus, and Thyroid from the Internal Cleft Recesses during the 4th week. (After His.).

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Cite this page: Hill, M.A. (2024, May 1) Embryology Head Development. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Head_Development

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