The First Intermediate Period, Middle Kingdom, and Second Intermediate Period (2181–1570 BCE)
Further developments in mummification were made during this period. In a mass burial of Dynasty 11 (2160-2040 BCE) princesses, we see the first use of large amounts of dry natron packed around the bodies to remove all the water. The viscera of these princesses were also removed to slow the process of decay, but not through a normal incision. They were removed by injecting an enema of oleo-resin (a substance like turpentine) to dissolve the organs, which then could flow out of the body.
Because they could fall off and become lost during the natron drying process, fingernails and toenails were now tied on with thread. It was essential that all parts of the body be taken into the tomb so that the whole person could exist in the afterlife.
More internal organs were being removed from the body than in the previous period. The heart was not removed, though, for it was believed that the deceased would need it later. Once emptied, the body cavity was stuffed with linen or linen and sawdust soaked in resin. This helped the mummy keep its shape.
During the Middle Kingdom, close-fitting masks made of cartonnage were created to cover the mummy's head and shoulders. The mummy's face and wig were represented on the mask to make it easily recognizable.
"I am purified with natron, I chew natron, incense... I am pure, and pure are the recitations which come from my mouth." Spell 172 - The Book of the Dead