Lefthanded pitcher Martin Perez will throw off of a full mound tomorrow, Thursday and Sunday, per Stefan Stevenson on Twitter.
Perez underwent Tommy John surgery in late May of 2014, and is working his way back from that. Throwing off of a full mound is a significant step forward in his recovery, and by all accounts, he's making good progress thusfar.
The Rangers have said that Perez is expected to be ready to return at some point after the All Star Break, about 14 months after he went under the knife, although with pitchers coming back from Tommy John surgery, there is never an exact timeline -- some make it back in a year, while in other cases (such as Neftali Feliz), it can be a couple of years before a pitcher makes it all the way back.
Perez will likely start the season on the 60 day d.l. and stay back in extended spring training before going out on a rehab assignment at some point during the season. Perez should be expected to spend a full 30 days out on assignment, so his expected return will likely be a month after his first rehab start. Perez has options remaining, of course, so the Rangers could opt to send him down if he needs more than 30 days to shake off the rust.