( ( ( Some parts ) ( of ( the skull ) ) ) ( ( ( ( ( begin ( as cartilage ) ) and ) then ) ( ( turn ( to bone ) ) ( later ( on ( in growth ) ) ) ) ) . ) )
(ROOT (S (NP (NP (DT Some) (NNS parts)) (PP (IN of) (NP (DT the) (NN skull)))) (VP (VP (VBP begin) (PP (IN as) (NP (NN cartilage)))) (CC and) (RB then) (VP (VB turn) (PP (TO to) (NP (NN bone))) (PP (ADVP (RB later)) (IN on) (IN in) (NP (NN growth))))) (. .)))
Some parts of the skull begin as cartilage and then turn to bone later on in growth.
(ROOT (S (NP (NNS Hagfishes)) (VP (VBP have) (NP (NP (DT a) (NN skull)) (VP (VBN made) (PP (IN of) (NP (NN cartilage)))))) (. .)))