Some great drawings here, I think overall, you have a pretty good grasp on 3D forms.

Some feedback:

It seems that you are going over some of your lines many times, giving your line work a very sketchy and scratchy feeling. Try to plan your lines more carefully, and execute using one confident line as opposed to many lines laid over the top of each other.

Try construct actual tufts of hair instead of just using single line strokes, it adds character far more effectively. Also try to vary the lengths and spacing between tufts of hair to avoid excessive uniformity.

Overall great work!