Classes: wxSplitterWindow
The following screenshot shows the appearance of a splitter window with a horizontal split.

The style wxSP_3D has been used to show a 3D border and 3D sash.
The following fragment shows how to create a splitter window, creating two subwindows and hiding one of them.
  splitter = new wxSplitterWindow(this, -1, wxPoint(0, 0), wxSize(400, 400), wxSP_3D);
  leftWindow = new MyWindow(splitter);
  leftWindow->SetScrollbars(20, 20, 50, 50);
  rightWindow = new MyWindow(splitter);
  rightWindow->SetScrollbars(20, 20, 50, 50);
  rightWindow->Show(false);
  splitter->Initialize(leftWindow);
  // Set this to prevent unsplitting
//    splitter->SetMinimumPaneSize(20);
The next fragment shows how the splitter window can be manipulated after creation.
  void MyFrame::OnSplitVertical(wxCommandEvent& event)
  {
        if ( splitter->IsSplit() )
            splitter->Unsplit();
        leftWindow->Show(true);
        rightWindow->Show(true);
        splitter->SplitVertically( leftWindow, rightWindow );
  }
  void MyFrame::OnSplitHorizontal(wxCommandEvent& event)
  {
        if ( splitter->IsSplit() )
            splitter->Unsplit();
        leftWindow->Show(true);
        rightWindow->Show(true);
        splitter->SplitHorizontally( leftWindow, rightWindow );
  }
  void MyFrame::OnUnsplit(wxCommandEvent& event)
  {
        if ( splitter->IsSplit() )
            splitter->Unsplit();
  }