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The specimens measure approximately 21 to 30 mm in length.

The head region composes almost half of the embryo, its large size being due to the growth of the cerebral hemispheres. The face occupies only the lower one-half of the head. As the head continues to raise from the ventral chest wall, the cervical fold disappears and the neck region becomes well defined.

The eyes move into the frontal plane closer to the midline and nearly attain their definitive position. The eyelid folds lengthen and begin to cover the exposed surface of the eye. A short period later (35 mm) the folds will meet and fuse. They will remain fused until around the seventh month.

The auricle begins to assume its definitive shape around the external acoustic meatus.

The face exhibits smooth contours as the elevations and processes disappear. The nose becomes prominent around the external nostrils, which are adjacent to the midline and occluded by epithelial plugs. A distinct chin becomes evident in the midline at the ventral end of the mandibular area.

The upper limb bud can be called the upper limb or extremity as the shoulder, elbow and wrist areas become apparent. Likewise, the lower limb bud becomes the lower limb or extremity with the appearance of the knee and ankle areas. The limbs continue to rotate resulting in the palms and soles pointing caudally. This occurs to a greater degree in the upper limb than in the lower.

The large heart and liver bulge the ventral body wall but to a lesser degree than previously. The relative size of the umbilical cord is reduced. The infraumbilical area between the pubis and the umbilical cord begins to appear.

The surface features of the external genitalia (perineal region) are described in Section IV, F.

All evidence of a tail bud disappears.

Source: Atlas of Human Embryos.