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