Answer:
endometrium
Step-by-step explanation:
The endometrium is the uterus lining to which the egg attaches. It is the same lining that sheds during menstruation when the matured endometrium do not receive fetus.
After fertilization when the egg reaches the uterus, it remains within the uterine cavity for nearly 24 hours in a free state. This layer thickens itself and the level of estrogen and progesterone increases to nourish the fetus.
When the fetus attaches to the endometrium , the outer cells of the egg starts growing and make a contact with the uterine wall. After this contact is established, the cells of the egg get embedded into the endometrium