The buses of one layer are connected to {HEAD ~ the appropriate bus} of {TAIL ~ the other layer} using through holes located in the array 
The buses of one layer are connected to { HEAD ~ the appropriate bus } of { TAIL ~ the other layer } using through holes located in the array
OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH