Heraldic terminology and fossilised language

Last week ladymoonray and I went to the Royal Academy to see the 'Turks' exhibition. (Interesting, but full of people: I'd have enjoyed it more if I hadn't had to queue at every exhibit to see it explained.)

One item -- a mirror, I think, was decorated with 'two sphinxes, addorsed'. I hadn't come across the term before, but deduced that it meant 'back to back' (from dorse, as in 'dorsal'). Turns out to be a heraldic term -- and an introduction to a vast new subset of jargon, loosely based (it seems to me, a non-expert) on medieval French, Latin and English.

Some examples (from An Illustrated Dictionary of Heraldry:
ravissant - a beast in the act of springing on its prey
regardant - looking back over shoulder (of beasts)
reremouse - a bat
retorted - twined together (of snakes)

I've been poking around on the interweb for a site that deals with the origins of the terms: if you like, a discussion of when they fossilised out of common language to become specific to heraldry. Any ideas?