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Developmental Anatomy

Stage 15: Summary

First view Second view

External: Lens vesicles are closed; nasal pits are appearing; hand plates are forming.

Internal: Foramen secundum begins to develop in the heart; a definite intestinal loop and caecum are present; lobar buds appear in the bronchial tree; the pelvis of the ureter develops, and the primary urogenital sinus forms; the future cerebral hemispheres are better delineated, the future paleostriatum and neostriatum become distinguishable, and the primordium of the epiphysis cerebri becomes recognizable; retinal pigment appears.

Lab Manual - Horizon 15 (CC#3512)

First view Second view

  • Length: 7 - 9 mm.
  • The lens vesicle is no longer open and closure pores have disappeared.
  • Olfactory placodes are beginning to submerge.
  • Ventral segment of the hyoid bar shows the first indication of the primordium of the antitragus.
  • Arm buds are regionally subdivided into distal hand segment and proximal segment that will form arm and shoulders.
  • Leg buds show beginning evidences of regional differentiation.
  • Ovulation age: 35 - 38 days.

Stage 15: 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 15 (PDF 935 KB)

 

QUESTION: The arm buds are divided into what segments?