26. Select the faces and extrude them, use the value 20 in "Extrusion Height" (Shift + e).
27. Edit the new vertexes. The red edges are the edited points. Cut, drag and move the vertexes to obtain this result.
28. Extrude the shown faces and move the vertexes as image 079 shows.
29. Here it will be a good moment to analyze the references, try to understand it like the model is. It's very important your understanding about the references and model, so then you will obtain a better result.
30. Continue the work as image 080 shows.
31. Create a cut in the mesh.
32. Work the model... Make extrusions, cuts and move the new vertexes if necessary.
33. Now select the faces as image 083, delete it. Select the suitable vertex in the same image, use Weld (Weld + w - Weld function: the value in the dialog box, inform the 3dsmax at distance it can collapse the vertexes, if you use the value 2, 3, 4 or other, 3dsmax will understand that collapse should weld at this value).
34. After the join, organize the vertexes, you maybe think that it's necessary to add an edges line into the bone structure, for example: select an edge and use Ring (Shift + r). That's ok.
35. Analyze the references and you will note a certain sinking on the skull, well the edges shown are edited.
36. You can use Meshsmooth to see the smooth in the object.
37. We're going to the superior teeth, hide the selected faces (Shift + h).
38. Adjust the vertexes to be at least similar to the example, study the anatomical references! It's useful.