( ( Some ( of ( your joints ) ) ) ( , ( ( like ( those ( in ( your skull ) ) ) ) ( , ( ( ( ( are fixed ) and ) ( ( do n't ) ( allow ( any movement ) ) ) ) . ) ) ) ) )
(ROOT (S (NP (NP (DT Some)) (PP (IN of) (NP (PRP$ your) (NNS joints)))) (, ,) (PP (IN like) (NP (NP (DT those)) (PP (IN in) (NP (PRP$ your) (NN skull))))) (, ,) (VP (VP (VBP are) (VP (VBN fixed))) (CC and) (VP (VBP do) (RB n't) (VP (VB allow) (NP (DT any) (NN movement))))) (. .)))
Some of your joints, like those in your skull, are fixed and don't allow any movement.
(ROOT (S (NP (JJ Fixed) (NNS joints)) (VP (VBP do) (RB not) (VP (VB allow) (NP (NP (DT any) (NN movement)) (PP (IN of) (NP (DT the) (NNS bones)))))) (. .)))