"I visit the graves and sacrifice."
Translation:Sepulchra visito et sacrifico.
Fat and burnt bones actually. Prometheus tricked the gods at a feast by hiding the bones under the fats and the meats under the animal skins. Zeus chose the lovely looking fats as his (the gods) meal leaving the gross looking skins to the humans.
So the Greeks sacrificed fats and bones (among non-animal sacrifices) by burning then on alters.
BAH!!! Sorry, it was sometime around midnight when I wrote that. Same myth, just substitute Zeus with Jupiter and Greeks with Romans. The Romans weren't shy about adopting interesting aspects from other pantheons... they didn't even always change the gods' names (See Apollo).
No, the singular form is sepulchrum.
Declension of sepulchrum (second declension, neuter):