|These are four of the five regular solids. The tetrahedron is not mentioned here since it is a certain triangular pyramid. It’s called simply the “pyramid” in Book XIII.
The regular tetrahedron is constructed in proposition XIII.13, the cube in XIII.15, the octahedron in XIII.14, the icosahedron in XIII.16, and the dodecahedron in XIII.17. These five are shown to be the only regular solids in proposition XIII.18.