Difference between MVC and 3-tier architecture

Here, 3-tier design were like this:


 
The MVC pattern would be:


 
Meaning that:

1. In the 3-tier equivalent, communication between layers is bi-directional and always passes through the Middle tier

2. In the MVC equivalent the communication is in unidirectional; we could say that each "layer" is updated by the one at the left and, in turn, updates the one at the right –where "left" and "right" are merely illustrative

P.S. Client would be the View and Middle the Controller