Thats not a 3-link.. Thats a version of a Watts link.
This is a 3 link:
See how there are (2) lower control arms and (1) upper control arm. That's a 3-link. A 4-link would have 2 uppers and 2 lowers.
A Watts link or Pan Hard Bar keeps the rear end centered under the the car from left to right where the 4-link, 3-link, ladder bar, torque arm ect keeps the rear from moving forward or backwards.