Well  I just recently read on net that Lions have the Largest Skull of all cats even tigers but tigers are supposed to be Largest Cats on earth isn't their Skull to be larger in physical size compared to Lions is it really true or some sort of misconception? thx

I've taken measurements off of a fair number of cat skulls and the largest one (in length) in my sample (after the American Cave Lion Panthera atrox) is the Lion Panthera leo, but only two specimens.  The rest of the Lion skulls are roughly the same size as adult Tiger skulls.  One Tiger skull actually has the largest skull width, so depending on how you determine skull size, Tigers and Lions are not that much different in overall skull size.

Using an overall skull size indicator calculated from several cranial measurements also reveal the same pattern as in using skull length: (P. atrox) > (two specimens P. leo) > (P. leo and P. tigris and Smilodon fatalis).  The extinct sabre-tooth cat S. fatalis has roughly the same size skull as the modern Lion and Tiger.  So at least in my sample, you are more or less correct to say that lions can attain larger skull sizes than tigers.

However, considering that the Tiger can attain much larger body size than the Lion, in both total body length and body mass, we could say that lions tend to have larger head sizes relative to their bodies.  Perhaps this is due to some selection pressures on Lions for larger faces; this is especially likely because of the presence of manes in the adult males, which also could make the heads look much larger.

Interestingly, Lion skulls also have an extended longer profile compared to Tiger skulls, mostly in that the former has an upturned facial region as opposed to the downturned face in the latter (see here for more on this).  This difference in morphology can in part explain the difference in skull sizes...

Manabu,

Just drifting onto S. fatalis having a skull roughly the same size as extant felids, have you any measurements for Smilodon populator ('he who brings destruction' - one of my favourite epithets!)?

I unfortunately do not.  But I know someone who personally owns a cast of one.  I remember it being pretty big.