The output of the NAND gate is used as {HEAD ~ a first control signal} to set the flip flop and to cause {TAIL ~ another circuit} to activate data transfer 
to cause
The output of the NAND gate is used as { HEAD ~ a first control signal } to set the flip flop and to cause { TAIL ~ another circuit } to activate data transfer
OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH