AD5933 : Measure small impedance add circuits?

I would like to design measuring human skin conduction(like GSR; It is small impedace as i know).

So, Add circuits for measure small impedance like AD5933 Datasheet.

But I confused about Figure 35 (additional external amp circuit)  and  Figure 39(EVAL-AD5933EBZ USB Schematic) on AD5933 Data Sheet.

Which is add circuits? Figure 35? Figure 39?

Please, let me guide some ways, ASAP.