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