File:Stage18 em11.jpg

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Human Embryo Carnegie Stage 18

Scanning election micrograph (SEM). Carnegie Stage 18, Week 7, 44 - 48 days, 13 - 17 mm.

Labeled View: Ventral view head. Amniotic membrane removed. (see unlabeled image)

Note at this embryonic stage of development the simple appearance of the lower lip and lower jaw (mandible) compared to the complex structure of the upper lip and upper jaw (maxilla).

Upper lip

  • Two lateral components formed by maxillary prominences of the first pharyngeal arch.
  • One midline component formed by the frontonasal prominence in the midline central portion between the medial nasal elements.
  • Clefts lying between these components will fuse by epithelial to mesenchymal transition.
    • Failure of this fusion event represent the common sites of cleft lip, either unilateral or bilateral clefting.
  • Clefts lying above each of the the maxillary prominences is the nasolacrimal groove (lacrimal groove, lacrimal sulcus).
    • Fusion of the groove leads to internalisation of the space forming the nasolacrimal canal (duct).
    • Nasolacrimal duct (tear duct) connects the eye (puncta lacrimal) to the nasal cavity (inferior nasal meatus)


EM Links: Image - stage 16 | Labeled Image - stage 16 | Image - stage 17 | labeled Image - stage 17 | Image - stage 18 | Labeled Image - stage 18 | Image - stage 19 | Labeled Image - stage 19 | Palate Development


SEM Image Source: Prof Virginia Diewert


Carnegie Stages: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | About Stages | Timeline



Cite this page: Hill, M.A. (2019, August 21) Embryology Stage18 em11.jpg. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/File:Stage18_em11.jpg

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© Dr Mark Hill 2019, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G

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