IF(TK_INTERNAL_PATH)
  VTK_GET_TCL_TK_VERSION ("TCL_TK_MAJOR_VERSION" "TCL_TK_MINOR_VERSION")
  SET (TCL_TK_VERSION "${TCL_TK_MAJOR_VERSION}.${TCL_TK_MINOR_VERSION}")
  IF("${TK_INTERNAL_PATH}" MATCHES 
     "${CMAKE_CURRENT_SOURCE_DIR}/tk${TCL_TK_VERSION}")
     ADD_SUBDIRECTORY(tk${TCL_TK_VERSION})
  ENDIF()
ENDIF()