IGN PC has published a new "creature feature" for Titan Quest, in which Iron Lore art director Mike Sheidow profiles several of the game's Greek monsters. A snip about Orthus:
Orthus was the Greek mythological two headed dog that guarded the cattle of Geryon. When designing our Orthus, we wanted the design to appear slightly unearthly so we gave it glowing vents along its rib cage. We did this for two reasons. The first was to make our Orthus appear more beast like and less like a mutant dog and the second was it gave us the opportunity to apply a glow map to the fiery vents so the creature would be more visible in dark undergrounds. With many of out creature designs, we always try to take advantage of the environment the creature will be inhabiting, and use effects that will enhance that experience. When you see the glowing rib vents come out of the shadowy corners, you know you're in for a battle with the two headed dog known as the Orthus.