I'm guessing that the second depiction is actually St. Demetrius who is often paired together with Saint George in compositions like triptycs, he and Saint George were both early martyrs who served in the Roman army. The man on the other end of the spear is a gladiator named Lyaios who played a part in St Demetrius' story

Why he is headless and holding an antenna, I dont know, I've never seen one like that before (assuming it is what i think it is)
I'd love to see a picture of it if you'd like to email me zoemark@earthlink.net

Mark K