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Hamburger and Hamilton Stage 20

HH20 (3-3.5 days).
40-43 somites; tip of tail unsegmented.
Leg buds distinctly larger than wing buds.
Wing buds approximately symmetrical, leg buds slightly asymmetrical.
L/W of wing: 3-3.9; leg: 3-3.3 (error in original?).
Tail bend extending forward into lumbo-sacral region.
Rotation completed.
Maxillary process equal or larger than mandibular process.
2nd arch projects over surface.
4th arch less prominent and smaller than 3rd.
4th cleft shorter than 3rd.
Allantois vesicular, variable in size; about the size of midbrain.
Eye pigment: faint greyish hue.


  1. TXT - Text Format
    The ABSTRACT ONTOLOGY (NOT Staged/Timed) with all pathways to child nodes materialised, in Plain Text only, as a Tree Report.

  2. OBO - OBO Format
    The ABSTRACT ONTOLOGY (NOT Staged/Timed) in OBO Flat File Format, version 1.2, available for viewing/editing using OBO-Edit.


  1. H. Eyal-Giladi and S. Kochav
    From cleavage to primitive streak formation: A complementary normal table and a new look at the first stages of the development of the chick : I. General morphology
    Developmental Biology, Volume 49, Issue 2, April 1976, Pages 321-337

  2. V. Hamburger and H.L. Hamilton
    A series of normal stages in the development of the chick embryo
    Journal of Morphology, 1951, Volume 88, Pages 49-92 (reprinted in Developmental Dynamics, December 1992, Volume 195, Issue 4, pages 231-72)

  3. R. Bellairs and M. Osmond
    The Atlas of Chick Development
    Academic Press, ISBN 0-12-084790-6, 1998

  4. C.D. Stern and P.W.H. Holland (Ed.s)
    Essential Developmental Biology: A Practical Approach
    Oxford University Press, ISBN 0-19-963423-8, 1993

  5. M.A.J. Selleck and C.D. Stern
    Fate mapping and cell lineage analysis of Hensen's node in the chick embryo
    Development, Volume 112, Pages 615-626, 1991