Cross-section of a human tooth-germ
You can see all the layers of the developing tooth here. All the way to the right (i), you can see the tooth-sac that the developing tooth is surrounded by and nourished by. In the center (f), you can see the developing enamel (though it’s still gelatinous at this point) - h signifies the outer epithelial cells of the enamel, which will comprise the outside of the tooth when it’s fully formed. To the left, b signifies the odontoblasts (the cells that are precursors to the inner tooth structures), and a signifies the tooth-papilla, that the odontoblasts will expand into.
The tooth-germ starts like a cup, basically, and then expands both outward (to form enamel), and inward (to form the dentin and inner structures) at the same time.
Atlas and Text-Book of Dentistry, Including Diseases of the Mouth. Gustav Preiswerk, 1906.