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The specimens measure approximately 8 to 14 mm in length.

The head region greatly increases in size. The second branchial arch grows caudally forming the opercular fold that partially covers the third and fourth branchial arches in the floor of the cervical sinus. The optic cup and lens vesicle, as well as various areas of the brain, can be located on the surface. The olfactory placode sinks below the surface in the floor of the nasal pit. The surface features of the face are described in Section III, A.

The limb buds become finlike with a constriction around the middle portion, which separates off a distal segment called the primitive hand or foot plate.

The heart and liver form prominences in the ventral wall between the branchial arches and umbilical cord.

The amnion fuses with the surface of the large umbilical cord. Its attachment moves to the distal part of the cord and is no longer evident on the ventral body wall. The yolk stalk becomes incorporated into the cord and usually disappears.

The surface features of the external genitalia (perineal region) between the lower limb and tail buds are described in Section IV, E.

The tail bud becomes more pointed and begins to disappear.

Source: Atlas of Human Embryos.