Exactly in the middle of mortuary (4,6)
I believe the answer is:
dead centre
'exactly in the middle' is the definition.
I don't understand the rest of the clue.
(Other definitions for dead centre that I've seen before include "Right in the middle" , "heart" , "Smack in the middle" , "bullseye" , "Position when engine crank and connecting-rod are in line" .)