Developmental Anatomy

Stage 13: Summary

External view Internal view

External: All four limb buds are usually visible; the optic vesicle is closed; the lens disc is generally not yet indented.

Internal: Septum primum and foramen primum appear in the heart; right and left lung buds are recognizable, and the trachea begins its development; retinal and lens discs appear; the endolymphatic appendage becomes distinguishable by the end of the stage.

Lab Manual - Horizon 13 (8066)

First view Second view

  • Length: 4 - 6 mm.
  • Pore of optic invagination closed.
  • Lens vesicle not yet indented.
  • Definite arm buds and beginning leg bud.
  • Heart chambers distended.
  • Ovulation age: 28 - 32 days.

Stage 13: Animation

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Developmental Stages in Human Embryos by Ronan O'Rahilly and Fabiola Müller.
Published by Carnegie Institution of Washington, Publication 637. 1987.

Stage 13 (PDF 1 MB)


QUESTION: What are some characteristics of the heart chambers?