9. After colapsing the vertexes you may join the two parts of the model. You can make an instance of the mesh model so then you can see the proportions,and in the 3dsmax6 you can use the modifier Symetry!
10. Continue sculping the model. Try to obtain square faces, it can help the MeshSmoth.
11. Continue making the extrusions on the edges of the model, and now we'are going to work on its profile near the eyes.
12. Continue sculpting.
13. Continue sculpting. We're going to work the back side of the Skull.
14. Sometimes the extrusions don't match the vertexes, so we have to obtain a "fitting" to it. Select the two back edges in the painel Modify, go to the mode edge and click the button "Connect" so then we can colapse the vertexes.
15. Now, we can colapse.
16. Continue making estrusions on the edges front-back.