You can display and then select two isoparms beside each other near the nose, then choose Edit Nurbs>Insert Isoparms. This will create more flexibility to that area. It does have its drawbacks, however. When you do this, the isoparm will go all the way around the head. If you want to later sculpt a section of the head that lies in the path of this newly created isoparm, it may be difficult to adjust the vertices exactly how you want it.

Truely, I think the best way to model a head is through patches. This site explains in great detail how to do so. https://coldfusion.art.msstate.edu/ca...ngtheory3.html
The navigation is in the upper left-hand corner.