Let's take a moment to look at one of the most mysterious phenomena, the creation of a living machine – the beating heart. All of these tiny molecules are cells that will eventually become the heart. They come to life one by one and start beating in unison. This basic beat is the beat of life, the precise operation of the blood pump.
The embryo is only 20 days old and about 2 millimeters long. It is a period of enormous changes to the embryo's shape. It slowly assumes human form.
The head and facial features appear. Two dark bumps emerge in the middle of the head and within days will become tiny eyes. Slowly, other organs are formed: the cartilage, muscles, and tendons.
The embryo is 34 days old and 5 millimeters long. Its development is rapid and it grows 1 millimeter a day. As the arms and legs form, the hip bone will replace the tail. The mouth and nostrils take shape and the neck shortens. Meanwhile, the brain continues to develop and is preparing for the role of "concertmaster" to the body.
The embryo is now 44 days old and 17 millimeters long. The eyes are protected by a thin, downy membrane. The back hardens and the head straightens. At this stage, the heart and most organs settle into their fixed places and begin to function.
The embryo is 60 days old and weighs almost 11 grams. At the end of the eighth week, all of the organs are present, but they still have seven more months to continue to develop.