ANAT2341 Lab 6 - Early Embryo

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

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

Week 5

Stage 13

Human face development (Week 5)

Sensory Placodes

Stage 14

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, lens placode and nasal placode.  ‎‎Placode 1 Page | Play

Stage 13

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

Pharyngeal Arches

Stage 13 Pharyngeal Arches

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.

Structures derived from Arches

Arch	Nerve	Muscles	Skeletal	Artery
1 (maxillary/mandibular)	trigeminal (V)	mastication (temporalis, masseter, medial pterygoid, lateral pterygoid)	Meckel's cartilage mandible modelmalleus, incus	maxillary(terminal branches)
2 (hyoid)	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)
3	glossopharyngeal (IX)	stylopharyngeus	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

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

Additional Information

Neural Crest

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

See also this 2014 Review:

Epigenetic regulation in neural crest development.

"The neural crest is a migratory and multipotent cell population that plays a crucial role in many aspects of embryonic development. In all vertebrate embryos, these cells emerge from the dorsal neural tube then migrate long distances to different regions of the body, where they contribute to formation of many cell types and structures. These include much of the peripheral nervous system, craniofacial skeleton, smooth muscle, and pigmentation of the skin. The best-studied regulatory events guiding neural crest development are mediated by transcription factors and signaling molecules. In recent years, however, growing evidence supports an important role for epigenetic regulation as an additional mechanism for controlling the timing and level of gene expression at different stages of neural crest development. Here, we summarize the process of neural crest formation, with focus on the role of epigenetic regulation in neural crest specification, migration, and differentiation as well as in neural crest related birth defects and diseases."

Epigenetics

Human cranial compartments different embryonic origins

Our data suggest that in the second trimester of human foetal development, a gene expression signature of neural crest origin still exists in frontal and metopic compartments while gene expression of parietal and sagittal compartments is more similar to mesoderm."

Placodes

The links below are to additional information providing background about each of the sensory systems.

Taste Links: Introduction

Glossary Links

Glossary: A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z | Numbers | Symbols | Term Link

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Cite this page: Hill, M.A. (2026, September 12) Embryology ANAT2341 Lab 6 - Early Embryo. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/ANAT2341_Lab_6_-_Early_Embryo

What Links Here?

© Dr Mark Hill 2026, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G