Ah, so that is what the arms were for!
Myelin sheathing or not (are you claiming someone found intact T-Rex nerves? I’m dubious too), T. Rex was smart enough to completely dominate us mammals until the end of the world (well, the Mesozoic world, anyway).
Regarding the plural of T. Rex – no one is expected to survive encountering a single T. Rex, so the language for describing multiples has never evolved. 
Wouldn’t surprise me; scientists have found other T. Rex soft tissues, like blood vessels, collagen and hemoglobin.
http://www.smithsonianmag.com/science-nature/dinosaur.html?c=y&story=fullstory