Talk:K12 Week 5 to 8
Then have a look at living embryos in the ultrasound movies below. The first 2 movies are at 7 weeks (the first a single embryo, the second twins).
The next movie is one week later (week 8) where the limb buds and spine can now be clearly seen. At this early stage ultrasound shows the beating heart is the most obvious feature within the embryo. Ther is also another page covering this period looking at development of the arms and legs.