The two sub regions of center region 34, in an embodiment, are connected together {HEAD ~ external} of {TAIL ~ the sub regions} 
The two sub regions of center region 34 , in an embodiment , are connected together { HEAD ~ external } of { TAIL ~ the sub regions }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL