Yeah, you've defined the muscles very strangely. I'd recommend you try smoothing it all out, and then using a smaller harder brush to define the masses. At the moment the muscles look like blobs, very soft and uneven. Think about tendons, where the bellies of the muscles are (thickest points), insertions etc. It looks like youve just masked off the area where a muscle should be and inflated it at the moment.
Theres a book called an Anatomy of Animal Anatomy by W Ellnberger, H Dittrich and H Baum thats got some great lion muscle references. A long time ago someone posted a link in 2d and 3d discussion with a bunch of scanned anatomy books which included this one. I had a bit of a look for it but couldn't see it there. If you want to go trolling through the archives you might be able to dig it out. Its a good book. Well worth picking up if you ever come across it.
On another note, Animal anatomy (mostly mammal based?) has a similar muscle structure to human anatomy, just that the proportions of the arms, forearms, hands, fingers etc are stretched or shortened.
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Some more work, mainly the forelegs.
I used some horse anatomy ref to change the muscles, unfortunately i cant find any good cat muscles ref.
EDIT: I found one page of it with a lion face which may help you to some degree.
http://www.dogwise.com/Item_Inside.cfm?ID=DAN122&curImage=4&Zoom=yes
I couldnt find it here but i purchased it.