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From Embryology
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Embryo at Day 0Day 1Day 2Day 3Day 4Day 4.5Day 5Day 6Day 6.5Day 7Day 7.5Day 8Day 8.5Day 9Day 9.5Day 10.5Day 11Day 11.5Day 12Day 13Day 14Day 15Day 16day 17Day 18Day 19

The above illustrations highlight what can be observed in the mouse embyro throughout its development. They progress from Day 0 (top left) to Day 19 (bottom right).

  • Day 0 One Cell Egg
  • Day 1 Dividing cells. Cleavage of cells has begun. Day ends with 4 cells present
  • Day 2 Formation of Morula
  • Day 3 Advanced Segmentation. 16-25 cells within same sized morula.
  • Day 4 Blastocyst formation
  • Day 4 ½ Implantation and invasion into the uterine epithelium
  • Day 5 Formation of the egg cylinder occurs.
  • Day 6 Differentiation of Egg Cylinder
  • Days 6 ½ Advanced Endodermal Reaction
  • Day 7 Amnion formation
  • Day 7 ½ Neural Plate, Presomite Stage
  • Day 8 First somite formation. Day ends with 1 - 7 somites present
  • Day 8 ½ Rotation of the Embryo. 8 - 12 somites present
  • Day 9 Formation and Closure of the anterior neuropore. 13 - 20 somites present in the embryo
  • Day 9 ½ Formation of the posterior neuropore and forelimb bud. There are 21 - 29 somites present. The embryo is 1.8 - 3.3 mm.
  • Day 10 Closure of the posterior neuropore and hind limb bud and tail bud formation occurs. 30-34 somites present and the embryo is 3.1-3.9mm.
  • Day 10 ½ Deep lens indentation occurs. There are 35-30 somites present and the embryo is now 3.5-4.9mm.
  • Day 11 The lens vesicle closes. There are 40-44 somites present and the embryo has reached 5-6mm in length.
  • Day 11 ½ The lens vesicle is now completely spearated from the surface of the embryo. There are currently 45 - 47 somites and the embryo reaches a length of 6 - 7mm
  • Day 12 Features the earliest signs of fingers forming. The embryo is 7 - 9mm in length from crown to rump and there are 48 - 51 somites.
  • Day 13 The footplate becomes indented with the early toe structures. The pinna (external ear) development occurs rapidly. The embryo is now 9 - 11mm in length and has 52 - 55 somites.
  • Day 14 The fingers begin to separate distally. The embryo has 56 - 66 somites and is 11-12mm in length.
  • Day 15 The toes separate. at this stage, the embryo is 12 - 144m from crown to rump.
  • Day 16 The umbilical hernia is repositioned. The fetus now measures between 14 and 17 mm.
  • Day 17 The Fingers and Toes align and join together. The skin is wrinkled and thickened and the umbilical hernia has disappeared. The fetus measures 16.5 - 20mm depending on the degree of curvature.
  • Day 18 The whiskers have increased in length dramatically. The length of the embryo varies between 18 and 23 mm due to the degree of curvature of the fetus.
  • Day 19 The Newborn mouse is between 23 and 27 mm due to varying degrees of flexure of the body axis.
Average Length of the Mouse Embryo