Adplantation (stage 4)

The blastocyst attaches to the uterine wall by means of its polar trophoblast, which lies next to the embryoblast (adplantation, stage 4). It secretes enzymes that erode the uterine mucosa, and then it penetrates the endometrial stroma. Currently there are no reliable pictures for this stage of human development and so we have to refer to examples from the development of Rhesus monkey.