In the full ration Master Cleanse one is consuming 1200 calories so there is no chance the body consuming muscle. One does go into ketosis on the MC. It's highly unlikely that the system will use up muscle tissue. When fasting and the body goes into Ketosis the sytem will scour itself for dead or damaged tissue and will use that for fuel way before it goes into any muscle tissue. That is basically how fasting heals.
After more that a dozen 40 day MCs and at least 10 years of sharing experiences on this forum I can tell you that the tongue thing is not a reliable indicator as to when to stop the fast. Some folks never get it at all and some will have it one day and gone the next The spot on the liver side of the tongue I would say is actually a good sign that your liver is detoxing. The wisdom is to continue fasting to allow the liver complete it's detox cycle.
If you are doing the MC by the book is highly unlikely that you are experiencing "real" hunger and it more a psychological issue . If you've been cheating even with the samllest tidbits all bets are off because you will have activated the digestive system and that will definitely make you hungry and or have cravings