And a good thing, too. That heritage has helped sustain Jaguar over some tough times. It's not much of an exaggeration to say that during the years preceding Ford's 1989 buyout, Jaguar was a severely endangered species. Antiquated factory tooling and poor quality control created big durability and reliability image problems. Limited capital held back new product development. Without some outside help, Jaguar would certainly have joined the long, long list of companies that were - but are no more.

We're happy to report that Jaguar's dark ages seem to be coming to an end. Ford cash, quality control techniques and electronic know-how have produced steady improvements in existing Jaguars, something that proved to be a much bigger undertaking than anticipated.

And now, at last, the renaissance has advanced to a new car, the XJ Series sedan. It's not quite all-new, as with the Oldsmobile Aurora, but it's attractively restyled and sweepingly re-engineered.

The XJ Series sedans have been expanded to four models for 1995: the basic XJ6, the Vanden Plas, the 12-cylinder XJ12 and our test car, the formidable XJR.

Chassis and overall dimensions remain the same, but most of the mechanical particulars have been thoroughly revised: a completely redesigned aluminum in-line 6-cylinder engine, which includes a new supercharged variant; power and efficiency improvements to the super-smooth V12; a stronger chassis; and more powerful brakes.

An in-line 6-cylinder engine design is inherently smoother than a V6, and the latest Jaguar six is a honey. It produces more power and more torque than the previous generation - enough to give the basic sedan, heavy as it is, acceleration that we'd call lively.

However, if really brisk acceleration is what you're after, the new supercharged version of the engine makes this Jaguar into one very fast cat indeed, producing more power than even the V12.

The list of comfort/convenience features is certainly what you'd expect from a car in this class, but there are several less-than-terrific details.

Some examples: Adding a passenger's airbag has eliminated the glove box. At night, the instrument panel is bathed in a subdued greenish glow that doesn't compare at all favorably with, say, the excellent display in the Lexus LS 400. And the U-shaped shift pattern on the automatic transmission - standard on all XJ sedans - is an awkward device to use, at least as we found so in our test drive.

Also, rear-seat legroom, a weak point with the previous car, hasn't improved at all, even though competing manufacturers' models have. And the trunk volume of XJ sedans continues to be the smallest in this class.

On the other hand, assembly quality in our test car seemed to be excellent, and the materials were first-rate. And with the addition of the aforementioned passenger airbag, the new Jaguar's safety features - including standard anti-lock brakes (ABS) and side-impact protection - certainly measure up as current.

The XJR's power had something to do with our prompt seduction. Throttle response is instantaneous, and it takes less than 7 seconds for the speedometer needle to zip up to 60 mph. Passing acceleration is, if anything, even more impressive. Press down on the pedal and the XJR absolutely hurls itself forward, emitting a determined growl in the process.

That's the beauty of supercharging versus turbocharging for extracting extra power from a given engine size. With a turbocharged engine, there's always a little waiting for boost pressure to build up, a phenomenon known as turbo-lag. With a supercharger, the response is immediate. And the effect, in this car, is very heady indeed.

However, power is only part of the story. The new XJ's improved chassis and rugged suspension provide a level of handling that's certainly as agile and aggressive as any car in this class. It's interesting to note that the XJ sedans achieve their handling superiority without resorting to electronic suspension trickery - self-adjusting shock absorbers and the like.

Although the basic XJ6 is impressive in the handling department, the XJR does add some extra capability, primarily because of its 17-in. wheels and fatter performance tires with a lower profile. The level of cornering power that goes with this setup is eye-widening. Our XJR gobbled up winding back roads at a pace that would certainly leave many competitors - particularly its front-wheel- drive competitors - far behind.

The steering is direct, precise and sports-car quick, just 2.8 turns from absolute left to absolute right, which enhances the XJR's sporty feel.

Superb braking performance rounded out our XJR experience. With big vented discs at all four corners, powerful calipers plus ABS, this system does an exceptional job of dealing with the car's substantial mass. Try as we might, we were unable to provoke any brake fade in hard stops.

You might expect that limited body roll and high cornering capabilities would produce a firm ride - and you'd be correct. The XJR, along with the other members of the series, is indeed firm in the ride department. But like other European road cars, firm shouldn't be confused with harsh. Shock absorber valving in all the XJ sedans is supple enough to damp out small bumps without drama, although really nasty potholes can produce jolts.

From interstates to boulevards, though, the XJ sedans will provide the kind of ride you'd associate with a luxury car.

We do have a couple of footnotes to our generally positive XJR test. The first involves interior noise: There's more of it, mostly from the engine, than in other luxury-sedan leaders.

Second, a day in extremely icy conditions reacquainted us with something we already knew: The combination of high horsepower, rear-wheel drive and tires designed for maximum adhesion on dry pavement can be a handful when the going gets wet and slippery.

Even with traction control, our test car had real difficulty scrambling up some icy slopes. In fact, on one steep slope we had better luck when we switched off the traction control system. The rear wheels were able to dig down through the slush to get a bite on the pavement beneath, and we crabbed our way cautiously up the hill.

But we don't think any of this will matter to drivers who value outstanding road manners. In this respect, the XJ Series is the equal of its rivals from Munich and better than just about anything else.

And the XJ Series cars manage to retain the Jaguar mystique and the Jaguar class. Thanks to the quality improvements that have come along under Ford's stewardship, we expect these cars to defy the ravages of time.