Hey readers! I’m in trouble, I don’t want to have to re-paint the whole lower jaw and each tooth in my model, so I was just wondering if you know how to connect the Jaw bone to the Neck bone so I can just rotate the Neck bone which will influence the whole head (including the Jaw and Tongue).
Please help! 
UPDATE: I figured it out by getting rid of the IK handles on the Tongue and Jaw and making the Jaw bone a Child of the Neck bone (which is now the Parent).
For anyone who had the same problem just use CTRL+P while the selected bones themselves are selected (not the ends of each or else you get an error) and make sure you get them selected the right way round as the first selected bones will be the Child of the last selected bone which will of course be the Parent. After doing this click the ‘Keep Offset’ option, this will ensure the bones stay in their place rather then connecting to the other bone itself.
