LOST. 10 tonight, Channel 6.

BE CAREFUL what you ask for.

With Monday's announcement that ABC's "Lost" would continue for just three more years - totaling 48 episodes - after its May 23 season finale, there's every reason to be happy, right?

Not only do we know that the show's going to continue for a while longer, but we also know that it's not going to drag on forever, that sometime in May 2010 we may actually understand the Dharma Initiative and the Others and perhaps even what Kate (Evangeline Lilly) sees in Jack (Matthew Fox).

I wouldn't mind a little of that certainty for CBS' "Jericho" (8 p.m., Channel 3), which goes into its season finale tonight in far more precarious shape, having suffered the same kind of post-hiatus loss of viewers as "Lost" but without knowing for sure that there'll be time to tie up loose ends and perhaps lift it out of the depressing place it's been mired lately.

(I know, I know. Shows about the aftermath of nuclear detonations aren't always going to be light and bright.

But if you take away too many characters' reasons to live, you're bound to take away a lot of people's reasons to watch. Who needs "24"-in-Kansas?)

But as the writers of "The Sopranos" could probably attest, there's more to an exit strategy than negotiating a particular number of episodes.

With three years to go, the "Lost"-ies are suddenly looking like lame ducks.

Forty-eight episodes offer plenty of time for the writers to spin new conspiracies, and I'm sure they will.

But spin too many and it begins too look like throat-clearing, or even avoidance.

That's how "The Sopranos" felt to a lot of people last year, and with just four episodes to go, I'm not sure it doesn't still feel that way.

It's entirely possible that on the night of June 10 I'll look up from the set satisfied that all this scene-setting has been worth it.

I certainly hope so.

I don't have specific requirements for how any show "should" end - I've seen some of the lists compiled by "Gilmore Girls" fans, and all I can say is that they might as well write their own finales and skip the actual episode - but I do think more is expected from writers who've had an opportunity to plan their escapes.

The longer the time, the higher the bar.

Starting now, the clock's ticking for "Lost."

Keeping your head

"This one has got one very, very short clean cut through the third cervical vertebrae," a scientist with piercings in her nose and lower lip informs a colleague in "Secrets of the Dead" (8 p.m., Channel 12).

"Absolutely wonderful cut, isn't it?" asks her more conservative-looking colleague in the tone of voice one might use at the supermarket meat counter.

"It is. It's very nice, yeah," agrees the first.

Gotta love those British osteoarchaeologists.

The PBS series for those who watch Fox's "Bones" for something other than the sexual banter tonight serves up "Headless Romans," an unsettling blend of science, history and educated guesses that left me with nightmares.

Still, anyone who waded through some of the bloodbaths of HBO's "Rome" will probably appreciate the tale behind the discovery of dozens of decapitated skeletons in an ancient burial ground in York, England.

Don't be surprised, though, if you end up with your own head buried deep under the covers afterward. *

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