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