Pharynx, Face, Nasal Cavity and Mouth Embryology

Question 1

1) What does the head consist of?
2) What is the cranium formed by?
3) What does it contain?
4) What is the face formed by?
5) What does it contain?
6) What can the face undergo development-wise?

Answer 1

1) face and cranium
2) the head process
3) brain, eyes and pharynx
4) later by outgrowth
5) mouth and nasal cavity
6) wide variation in shape and size (dogs)

Question 2

1) Where is the embryonic pharynx?
2) When does it arise?
3) What is the pharynx bounded by?
4) Initially the pharynx is what? by what?
5) What is the oropharyngeal membrane composed of? following growth of what? What must happe to the membrane?
6) How many pharyngeal arches develop?
7) What does each arch contain?
8) What do the arches contribute to the formation of?

Answer 2

1) the anterior end of foregut
2) during head process and lateral body fold formation –> embryo becoming cylindrical
3) externally by pharyngeal arches –> demarcated externally by pharyngeal clefts and internally by pharyngeal pouches
4) closed anteriorly by an oropharyngeal membrane
5) pharyngeal endoderm and surface ectoderm; stomadeum (mouth); it must degenerate to permit communication
6) six pairs (3 are evident, 5 atrophies, 4 & 6 combine)
7) aortic arch vessel, ectomesenchyme (neural crest), myotomes (somite/somitomere), innervation from one cranial nerve
8) jaws, larynx, hyoid bones and head muscles

Question 3

1) What is the mesenchyme within the pharyngeal arches and frontonasal prominence?
2) What does ectomesenchyme form?
3) How do bones along base of skull develop?
4) What is skeletal muscle derived from?
5) Name the arches, what they develop into and innervations

Answer 3

1) ectomesenchyme derived from neural crest’
2) fascia and intramembranous bone of he face and calvaria
3) endochondrally from occipital somite sclerotomes
4) somite or somitomere myotomes that migrate into pharyngeal arches (or frontonasal prominence)
5) Arch I - mastication muscle - V nerve

Arch I - facial muscles - VII nerve

Arch III - pharyngeal muscle - IX nerve

Arch IV and VI - muscles of pharynx, larynx and esophagus

Question 4

1) In fish, what are pharyngeal arches called?
2) How are they formed?
3) Where do somitomeres originate?
4) How many pairs?
5) What do they give rise to?

Answer 4

1) branchial arches (gills)
2) tissue spreading external clefts and internal pharyngeal pouches degenerates –> gill slits
3) from paraxial mesoderm –> rsotral to notochord.and are less developed somites
4) 7 pairs
5) extraocular, masticatory, facial and some pharngeal mucles

Question 5

1) Describe what each pouch forms?

Answer 5

1) 1st pouch - tympanic (middle ear) cavity and auditory tube
2) 2nd pouch - fossa for palatine tonsil and fold covering it
3) 3rd pouch - external parathyroid gland and thymus
4) 4th pouch - internal parathyroid gland
5) 5th pouch - parafollicular cells of thyroid gland (

Question 6

1) What does the thyroid gland originate as?

2) What is species dependent?
3) What normally degenerates?

Answer 6

1) a single endoderm outgrowth from floor of pharynx
2) thyroid may remain single (pig)

split into bilateral lobes connected by isthmus (horse)

separate paired lobes (dog)

3) thyroid connection to pharynx; remnant persists as a cyst that can enlarge and interfere with breathing by compressing pharynx

Question 7

1) What does the face develop from?
2) What does growth of the 1st pharyngeal arch form?
3) What is the frontonasal prominence?
4) What does it form?
5) What’s the first step of development involving the 1st pharyngeal arch?
6) What do they form?

Answer 7

1) outward growth of the cranium
2) lower jaw and most of upper jaw
3) ectomesenchyme from neural crest, located rostral to neural tube
4) upper incisor region and the nose and forehead
5) It divides into two processes: ventral mandibular process and a dorsal maxillary process
6) mandibular process –> mandible and soft tissue of lower jaw

maxillary process –> most of upper jaw, caudal to incisor teeth

Question 8

7) What is the mandibular symphysis?
8) What happens to the frontonasal prominence?
9) What do they form?

Answer 8

7) fusion of right and left sides of mandible/lower jaw

8) dorsal to 1st arch, it expands and divides into a frontal prominence and medial and lateral nasal processes
9) frontal prominence –> frontal bone of forehead

medial and lateral nasal processes –> nose, nasal cavity and primary palate

Question 9

1) What is the first step in nasal cavity formation?
2) What is the 2nd step?
3) What is the next step?
4) Fusion of what? forms what?
5) What does the primary plate become?

Answer 9

1) bilateral nasal placodes (ectoderm thickenings) appear at the rostral end of the frontonasal prominence
2) growth of surruonding medial and lateral nasal processes establishes bilateral nasal pits
3) continued growth of nasal processes produces –> primitive nasal cavity and subsequence oronasal erosion during growth establishes communication btw nasal and oral cavity
4) Fusion of R and L medial nasal processes –> primary palate rostrally and the nasal septum caudally
5) incisive bone, upper incisor teeth and rostral upper lip

Question 10

6) What is the nasal septum?
7) What are the external nares?
8) How are they formed along with the cartilage of the nose?
9) What do each lateral nasal process form?
10) How is the nasolacrimal duct formed?

Answer 10

6) separates R and L halves of the nasal cavity

7) nostrils
8) bilateral rostral openings of nasal cavity –> external nares and ectomesenchyme surrounding them –> cartilage of nose
9) alar cartilage of nose, nasal bone and lacrimal bone
10) by ectoderm along seam where lateral nasal process meets maxillary process of 1st pharyngeal arch

Question 11

1) Nasal and oral cavities communicate with each other after what?
2) How are nasal and oral cavities separated again?
3) What is the primary palate formed by? What does it become?
4) How is the secondary palate(hard palate) formed?
5) What are the palatine processes?
6) What happens to them?
7) What do the caudal extensions form?

Answer 11

1) the erosion of an oronasal membrane that initially separated them
2) by formation of primary and secondary palates that shift the nasal-oral communication caudally into pharynx
3) medial nasal processes; becomes incisive bone
4) bilaterally by maxillary processes extensions
5) the maxillary processes extensions
6) they meet at the midline, merge dorsally with nasal septume and rostrally with primary palate
7) caudal extensions of secondary palate into pharynx –> soft palate which separates dorsal nasopharynx from ventral oropharynx

Question 12

1) What does cleft palate result from?
2) Which palate is affected more commonly?
3) What is it caused by?
4) True or False: Cleft palate is often fatal in animals
5) Explain #4
6) What does failure of medial nasal process fusion (primary cleft palate) produce?
7) What species is this defect alone normal for?

Answer 12

1) failure of the palate to close along midline, leaving a gap or cleft
2) secondary palate
3) may be inherited or the result of exposure to a teratogen (an agent that causes birth defects)
4) True
5) due to inability to suckle or because of aspiration of milk into lungs (aspiration pneumonia)
6) hare lip and related defects
7) haires, sheep, etc

Question 13

1) What are conchae?
2) What do they originate as?
3) How are paranasal sinuses formed?
4) When does most sinus development occur?
5) What is the vomeronasal organ?
6) How is it formed?

Answer 13

1) turbinates –> thin bone scrolls covered by mucosa within the nasal cavity
2) originate bilaterally as cartilaginous ridges of bones that formt he nasal cavity wall
3) arise as epithelial lined diverticula of the lining of the nasal cavity; extent of development varies in species
4) postnatally, newborn animals have cute rounded heads that become angular with age as sinuses develop
5) specialized olfactory sense organ located rostrally in the floor of each nasal cavity
6) produced by outgrowth of nasal epithelium that forms a caudally-closed tube

Question 14

1) What does the mouth (oral cavity) develop as a consequence of?
2) What is the first evidence of an oral cavity?
3) What does it contain?
4) What is the oropharyngeal membrane?
5) What is it composed of?
6) What happens to the oropharyngeal membrane?
7) The stomadeal cavity and nasal pits are initially separated by what?
8) What happens to it?
9) What eventually develops?

Answer 14

1) upper and lower jaw formation
2) stomadeum
3) stomadeal cavity
4) deep boundary of the stomadeum
5) a layer of stomadeal ectoderm apposed to a layer of pharyngeal endoderm
6) becomes fenestrated and disintegrates ( palatoglossal fold marks its location in adults)
7) an oronasal membrane
8) subsequently degenerates so the cavities communicate freely
9) palates develop –> shifts oral-nasal communication caudally into pharynx

Question 15

1) What is the labiogingival lamina?
2) Where does it form?
3) What does the lamina form and how does it do it?
4) What does the groove form?
5) How are cheeks formed?

Answer 15

1) outer arc of thickened ectoderm
2) in ectoderm lining the stomadeal cavity on upper and lower jaws
3) lamina invaginates into underlying ectomesenchyme –> labiogingival groove
4) future oral vestibule;

tissue external to groove –> lips;

medial tissue –> gingivae

5) caudal fusion of upper and lower lips

Question 16

1) What is the dental lamina?
2) What are dental buds?
3) What do they give rise to?
4) If a deciduous tooth is destind to form, what happens?
5) What is the first step in tooth development?
6) How is a dental papilla formed?
7) How are odontoblasts formed?
8) What do they do?

Answer 16

1) an arc of thickened ectoderm situated inside of the labiogingival lamina
2) periodic thickenings of lamina
3) individual teeth
4) an additional bud for its permanent replacement develops superficial and medial to the deciduous bud
5) bud assumes a cup-shaped configuration –> enamel organ
6) condensation of extomesenchyme within the concavity of the cup
7) concave epithelial layer of enamel organ induces ectomesenchyme of dental papilla –> epithelial layer of odontoblasts
8) deposit dentin of tooth

Question 17

9) What do the odontoblasts induce?
10) What do ameloblasts do?
11) How is a dental sac formed?
12) What does it give rise to?
13) Describe general pathway of tooth development?

Answer 17

9) concave epithelium of enamel organ to differentiate into ameloblasts

10) form enamel of crown of tooth
11) ectomesenchyme surrounding enamel organ condenses
12) 3 layers:

outer cells –> osteoblasts –> deposit alveolar (tooth socket) bone (osteoclasts re-absorb bone prior to eruption)

middle layer –> periodontal ligament (anchors tooth within alveolus

inner cells –> cementoblasts –> cementum (modified bone) –> adheres to surface of tooth, particulary dentin surface of root of tooth

13) dental lamina –> dental buds –> enamel organ –> dental papilla –> odontoblasts –> ameloblasts –> dental sac –> outer cells, middle layer, inner cells

Question 18

1) What does the tongue develop from?
2) body and apex formed by what?
3) What happens?
4) the body and apex arise from what?
5) general sensation comes from which nerve?
6) Which arch also contributes?

Answer 18

1) four swellings situated on floor of pharynx
2) distal (lateral) swellings in floor of pharynx
3) swellings fuse along midline and grow forward into oral cavity (thereby acquiring an ectodermal covering)
4) predominantly from 1st pharyngeal arch
5) 5th cranial nerve, trigeminal nerve
6) 2nd pharyngeal arch

Question 19

7) Where does taste sensation come from?

8) Root is formed by what?
9) It arises from what?
10) sensation comes from what?
11) In what species does the median swelling contribute?
12) Where do the muscles of tongue originate?
13) What are they innervated by?

Answer 19

7) 7th cranial nerve, facial nerve

8) proximal swellings and covered by endoderm
9) 3rd pharyngeal arch
10) 9th cranial nerve, glossopharyngeal nerve
11) significantly to tongue only in ungulates (esp in cattle –> prominent bulge)
12) from occipital somites
13) 12th nerve, hypoglossal nerve

Question 20

1) What are salivary glands derived from?
2) What is the process of salivary gland formation typical of?
3) Describe steps
4) What does grwoth of jaw cause?
5) What is a polystomatic duct?

Answer 20

1) ectoderm = parotid, zygomatic, labial and buccal accessory salivary glands

endoderm = madibular and mono- and poly-stomatic sublingual salivary glands

2) exocrine gland development in general
3) surface epithelial cells undergo localized proliferation –> cellular cords –> invade underlying ectomesenchyme
- inital site of penetration –> duct openings at surface
- invading cord of cells begins to branch –> main duct and branched ducts of gland
- masses of epithelial cells accumulate at ends of each branch –> secretory acini of gland
- epithelial cords and masses canalize (become hollow) and the gland becomes functional
4) elongation of main ducts
5) one that has many duct openings to surface; arise as a series of independent epithelial cords; although independent glands embryologically –> form single mass and in gross anatomy they are collectively identified as single gland

Question 21

1) What is the hypophysis?
2) What does it consist of?
3) What are they controlled by?
4) How is the 2nd controlled?
5) How is the 1st connected to hypothalamus?
6) How does adenohypophysis develop?
7) What happens to placode?
8) What happens to pouch?
9) Depending on species, what can happen to cavity of pouch?

Answer 21

1) pituitary gland
2) neurohypophysis and adenohypophysis
3) both controlled by hypothalamus of brain
4) hypothalamic neurons must release hormones into blood stream to control adenohypophysis
5) neurohypophysis connected by means of an infundibulum; axons run through infundibulum and terminate in neurohypophysis
6) from an ectodermal thickening (placode) in roof of stomadeal cavity
7) placode evaginates to forma n hypophyseal pouch (Rathke’s pouch)
8) separates from stomadeal ectoderm and wraps around neurohypophysis (outgrowth of hypothalamus)
9) may persist as a cleft