Each downstream stage has {HEAD ~ its input circuit} coupled to {TAIL ~ the output circuit} of an upstream stage 
coupled to
Each downstream stage has { HEAD ~ its input circuit } coupled to { TAIL ~ the output circuit } of an upstream stage
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH