BGDB Face and Ear - Early Embryo

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Practical 6: Trilaminar Embryo | Early Embryo | Late Embryo | Fetal | Postnatal | Abnormalities

Week 4

During week 4 a number of features appear visible on the embryo surface:

  • At the level of the body heart, liver, somite bulges and limb buds appear.
  • At the level of the head sensory placodes and pharyngeal arches appear.

Carnegie Stage 12 to 14

Week 4

Stage 11

Stage11 sem13c.jpg Stage11 sem20c.jpg

This is a scanning EM of the embryo superior dorsal view showing the paired otic placodes sinking into the surface at the level of the hindbrain between day 24 and day 25

Stage 12

Stage12 sem1c.jpg Stage12 bf2c.jpgStage12 bf1c.jpg

Stage12 sem4.jpg Stage12 sem5.jpg

Week 5

Stage 13

Stage13 sem1c.jpg Stage13 bf1c.jpg Stage13 sem2c.jpg

Sensory Placodes

Sensory placodes develop as small patches of ectodermal thickenings.

The placodes are laterally paired and contribute key components to sensory structures of the ear, eye and nose.

Named by the sensory system and components they will form: otic placode, optic (lens) placode and nasal placode.

Stage 13

Otic placode forms the otocyst

Stage 13 image 051.jpg

Stage 13 image 052.jpg

Stage 13 image 053.jpg

Stage 13 image 054.jpg

Stage 13 image 055.jpg

Identify the structure and position of the otic vesicle (otocyst) relative to other head structures.

Stage 13 Movie - Overview of Head, Pharyngeal Arches and Pharynx

Pharyngeal Arches

Head arches cartoon.jpg Pharyngeal arch structure cartoon.gif

Stage 13 Pharyngeal Arches

Stage13 pharyngeal arch excerpts.gif

Section Images: A6L  A7L  B1L  B2L  B3L  B4L  B5L  B6L

Look through the above cross-sections of the stage 13 embryo observing and identifying structures of the face and ear visible at this stage.

Pharyngeal arch cartilages.jpg

Structures derived from Arches






trigeminal (V)

(temporalis, masseter, medial pterygoid, lateral pterygoid)

Meckel's cartilage
mandible modelmalleus, incus

maxillary(terminal branches)

facial (VII)

facial expression
(buccinator, platysma, stapedius, stylohyoid, digastric posterior belly)

Reichert's cartilage
stapes, styloid process, lesser cornu of hyoid, upper part of body of hyoid bone

stapedial (embryonic)
corticotympanic (adult)

glossopharyngeal (IX)


greater cornu of hyoid, lower part of body of hyoid bone

common carotid, internal carotid (root)

4 and 6
superior laryngeal and recurrent laryngeal branch of vagus (X)

intrinsic muscles of larynx, pharynx; levator palati

thyroid, cricoid, arytenoid, corniculate and cuneform cartilages

4 - aortic arch, right subclavian
6 - ductus arteriosus, pulmonary (roots)

Structures derived from Pouches


Overall Structure

Specific Structures


tubotympanic recess

tympanic membrane, tympanic cavity, mastoid antrum, auditory tube


intratonsillar cleft

crypts of palatine tonsil, lymphatic nodules of palatine tonsil


inferior parathyroid gland, thymus gland


superior parathyroid gland, ultimobranchial body


becomes part of 4th pouch

Additional Information

Content shown under this heading is not part of the material covered in this class. It is provided for those students who would like to know about some concepts or current research in topics related to the current class page.

Other Sensory Systems

The links below are to additional information providing background about each of the sensory systems. Only hearing is covered in today's class.

Hearing Links: Introduction | Science Lecture | Medicine Lecture | Inner Ear | Middle Ear | Outer Ear | Balance | Hearing - Neural Pathway | Stage 22 | Abnormalities | Neonatal Diagnosis - Hearing | Hearing test | Sensory Introduction | Placodes | Student project | Category:Hearing
Historic Embryology
Historic Embryology: 1902 Development of Hearing | 1918 Human Embryo Otic Capsule | 1918 Cochlea | 1918 Grays Anatomy | 1922 Human Auricle | Historic Disclaimer

Vision Links: Introduction | Lens | Retina | Placodes | Extraocular Muscle | Cornea | Eyelid | Abnormalities | Student project 1 | Student project 2 | Category:Vision
Historic Embryology
1906 Eye Embryology | 1907 Development Atlas | 1912 Eye Development | 1918 Grays Anatomy | 1921 Eye Development | Historic Disclaimer
Smell Links: Introduction | Placodes | Rhinencephalon | Head Development | Student project | Taste | Sensory Systems | Category:Smell
Historic Embryology: 1902 Olfactory Structures
Taste Links: Introduction

Neural Crest

During this period neural crest cells migrate into the pharyngeal arches and other head locations, and have an important contribution to many different head structures. Neural crest cells at other levels contribute to body many structures. There are also many developmental abnormalities associated with abnormal neural crest development and/or migration. This topic is beyond the scope of the current class.

Links: Neural Crest Development
Cranial neural crest skeletal fate 01.jpg Cranial neural crest contribution to skeletal structures

The embryo figure shows colonization of the head and pharyngeal arches by diencephalic, anterior and posterior mesencephalic, and rhombencephalic neural crest cells (NCCs), as indicated by the colour code. The diagram is representative human embryos, although the NCC migratory pathways might differ slightly in different species. The skull drawings show contributions of NCC populations to cranial skeletal elements of humans, based on NCC fate-mapping studies and on extrapolation of avian and mouse data to known homologues in the human.

Some bones, including the squamosal (SQ), alisphenoid (AS), and pterygoid (PT), are shown with mixed contribution from different NCC populations. Note that in mammals the frontal (FR) and parietal (PA) bones have been reported to be of neural crest and mesodermal origin, respectively.

(text modified from original figure legend)

  • BA1-BA3 - pharyngeal arches 1 - 3
  • di - diencephalon
  • FNP - frontonasal process
  • HY - hyoid bone
  • IN - incus
  • MA - malleus
  • mes - mesencephalon
  • MX - maxillary bone
  • NA - nasal bone
  • R1–R7 - rhombomeres 1 – 7
  • ST - stapes
  • ZY - zygomatic bone

Reference: Fabio Santagati, Filippo M Rijli Cranial neural crest and the building of the vertebrate head. Nat. Rev. Neurosci.: 2003, 4(10);806-18 PMID: 14523380 | Nat Rev Neurosci.

Practical 6: Trilaminar Embryo | Early Embryo | Late Embryo | Fetal | Postnatal | Abnormalities

BGDB 2015: Lecture - Gastrointestinal System | Practical - Gastrointestinal System | Lecture - Face and Ear | Practical - Face and Ear | Lecture - Endocrine | Lecture - Sexual Differentiation | Practical - Sexual Differentiation | Tutorial

Glossary Links

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Cite this page: Hill, M.A. (2015) Embryology BGDB Face and Ear - Early Embryo. Retrieved March 28, 2015, from

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© Dr Mark Hill 2015, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G