( ( ( ( ( This ( cartilage opening ) ) ( ( closes up ) ( as ( ( the baby ) grows ) ) ) ) and ) ( ( the skull ) ( closes ( over it ) ) ) ) . )
(ROOT (S (S (NP (DT This) (NN cartilage) (NN opening)) (VP (VBZ closes) (PRT (RP up)) (SBAR (IN as) (S (NP (DT the) (NN baby)) (VP (VBZ grows)))))) (CC and) (S (NP (DT the) (NN skull)) (VP (VBZ closes) (PP (IN over) (NP (PRP it))))) (. .)))
This cartilage opening closes up as the baby grows and the skull closes over it.
(ROOT (S (NP (NNS Hagfishes)) (VP (VBP have) (NP (NP (DT a) (NN skull)) (VP (VBN made) (PP (IN of) (NP (NN cartilage)))))) (. .)))