Transistor 168 has its emitter coupled to low voltage source A via {HEAD ~ resistor} 170, the combination of which forms {TAIL ~ a current source} 
Transistor 168 has its emitter coupled to low voltage source A via { HEAD ~ resistor } 170 , the combination of which forms { TAIL ~ a current source }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL