Lots of straight dope about turtles. (With a side note on other tushie-breathers)

Is it true turtles breathe through their butts?

Actually, a group of questions about turtles –

I have read that turtles can breathe through their bums. Is this true, and if so, why did they evolve such a talent and what are the mechanics of this trick?

My understanding of physiology is that animals (including humans) draw in air by expanding the volume of the chest cavity. How does a turtle, with a fixed chest cavity determined by its shell, draw in air?

When turtles put their heads in their shells, what happens to their spines? Do they buckle or contract?
Here’s the Answers

tangential – a word that sounds more naughty than it is, also urbane

tangential – what you have, after going to a nude beach.

seriously –

tangential tan-JEN-shuhl adjective

1. Only slightly relevant to the matter in hand; digressive; divergent.

2. Merely touching.

3. Mathematics: Of or pertaining to the nature of a tangent.

From Latin tangent-, tangens, present participle of tangere (to touch).

urbane ur-BAIN, adjective:
Polished and smooth in manner; polite, refined, and elegant.

From Latin urbanus, “of a city,” hence “refined, polished,” from urbs, “city.” The noun form is urbanity (pronounced ur-BAN-ih-tee).