When we extrude the quad on the top to create the head, we get a two-headed monster! What's wrong?

Using a control mesh makes us feel as though we are performing a kind of NURBS modeling process with control vertices. But this is only an illusion. The control mesh is actually a polygonal mesh of it own that is being smoothed to create the subdivision surface. By changing from wire to a shaded view, it's clear that the extrusion of the head created a quad right on the vertical centerline.

We need to delete this quad so that the model is hollow from the crotch to the top of the head – the centerline passing through the body. Once deleted, the head mirrors continuously with the torso.

Take a look at Starfishman.

This simple structure forms the basis for modeling the human form in whatever detail you may desire. From here, it's all a matter of adding new rows and columns of edges, a few more extrusions for the extremities, and a lot of tedious moving and scaling of vertices. We'll finish up the next time.