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