"Fetal development in pregnancy week 4: embryo in first month By the end of this week the round and pointy ends of your little pear-shaped baby will be slightly more exaggerated and their body will look more like that of a miniature manatee. Despite your baby not looking particularly human without any eyes, ears or mouth, the earliest developments of what will become the larynx, internal ear, and eye lens are already forming, although you’d have to be a trained expert to recognize them for what they’re going to be in the future. Likewise, tiny bumps are forming on your little embryo which will eventually be their cute little arms, elbows, fingers, legs, knees and toes. What’s more your little swimmer will have a teeny tiny tail by the end of this week-- but don’t worry, it’s just the end of their developing spinal cord! A microscopic photo would reveal what seems to be their vertebrae filling out the spine and tail. Although they aren’t bones yet, but rather, the “bone seeds” that will give rise to your baby's tiny vertebrae, ribs and sternum."
That's a lot of crazy stuff that's happening already!