Developmental Anatomy

Stage 19: Summary

First view Second view

External: The trunk has begun to elongate and straighten slightly, with the result that the head no longer forms a right angle with the line of the back of the embryo. The limbs extend nearly directly forward; The toe rays are more prominent, but interdigital notches have not yet appeared in the rim of the foot plate. 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 19 (CC#4501)

First view

  • Length 17 - 20 mm.
  • Trunk beginning to straighten out and cervical angle less acute.
  • Coalescence of parts of branch region has altered appearances of external ear, and the hillocks are less conspicuous.
  • Axes of arm are almost at right angles to the dorsal line of the body of the embryo.
  • Various parts in leg and arm can be identified.
  • Toe rays are more prominent.
  • Ovulation age: 48 - 51 days.

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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 19 (PDF 1.5 MB)


QUESTION: What has altered the appearance of the external ear?