Thyroid continues to develop and the lymphatic system, which filters out bacteria, starts to form. Thorax Heart chambers are filled with plasma and blood cells making the heart seem distended and prominent. The heart and liver combined are equal in volume to the head by this stage. The villous network is in place to accommodate the exchange of blood between the woman and the embryo. Aortic arches 4 and 6 develop and 5 may appear.
Lung buds continue to form.
Abdomen and Pelvic Regions Gall bladder, stomach, intestines, pancreas continue to form and the metanephric bud appears in the chest cavity. The stomach is in the shape of a spindle and the pancreas may be detected at the intestinal tube. The developing liver receives blood from the placenta via the umbilical cord. Limbs Upper limb buds are visible as ridges and the lower limb buds begin to develop. Folding is complete and the embryo is now three-dimensional and is completely enclosed in the amniotic sac.