( ( In ( ( ( most tetrapod ) ( limb skeletons ) ) ( -LRB- ( ( though ( not ( in ( some amphibians ) ) ) ) -RRB- ) ) ) ) ( , ( ( the ( cartilage skeleton ) ) ( ( is ( replaced ( by ( ( bone later ) ( in development ) ) ) ) ) . ) ) ) )
(ROOT (S (PP (IN In) (NP (NP (ADJP (RBS most) (JJ tetrapod)) (NN limb) (NNS skeletons)) (PRN (-LRB- -LRB-) (FRAG (IN though) (ADVP (RB not) (PP (IN in) (NP (DT some) (NNS amphibians))))) (-RRB- -RRB-)))) (, ,) (NP (DT the) (NN cartilage) (NN skeleton)) (VP (VBZ is) (VP (VBN replaced) (PP (IN by) (NP (NP (NN bone) (RB later)) (PP (IN in) (NP (NN development))))))) (. .)))
In most tetrapod limb skeletons (though not in some amphibians), the cartilage skeleton is replaced by bone later in development.
(ROOT (S (ADVP (RB Early) (PP (IN in) (NP (NP (DT the) (NN development)) (PP (IN of) (NP (DT a) (JJ human) (NN fetus)))))) (, ,) (NP (DT the) (NN skeleton)) (VP (VBZ is) (VP (VBN made) (ADVP (RB entirely)) (PP (IN of) (NP (NN cartilage))))) (. .)))