( ( As ( ( this fold ) ( ( grows up ) ( around ( the embryo ) ) ) ) ) ( it ( ( ( ( meets above ) and ) ( incloses ( ( ( ( ( a sac ) , ) ( known ( as ( the ( amniotic sac ) ) ) ) ) , ) ( which ( surrounds ( ( ( the embryo ) and ) ( which ( becomes ( filled ( with ( ( a ( watery liquid ) ) ( known ( as ( ( the ( amniotic fluid ) ) ( -LRB- ( ( Fig. ( 256 D ) ) -RRB- ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) . ) ) )
(ROOT (S (SBAR (IN As) (S (NP (DT this) (NN fold)) (VP (VBZ grows) (PRT (RP up)) (PP (IN around) (NP (DT the) (NN embryo)))))) (NP (PRP it)) (VP (VP (VBZ meets) (ADVP (RB above))) (CC and) (VP (VBZ incloses) (NP (NP (DT a) (NN sac)) (, ,) (VP (VBN known) (PP (IN as) (NP (DT the) (JJ amniotic) (NN sac)))) (, ,) (SBAR (WHNP (WDT which)) (S (VP (VBZ surrounds) (NP (NP (DT the) (NN embryo)) (CC and) (SBAR (WHNP (WDT which)) (S (VP (VBZ becomes) (VP (VBN filled) (PP (IN with) (NP (NP (DT a) (JJ watery) (NN liquid)) (VP (VBN known) (PP (IN as) (NP (NP (DT the) (JJ amniotic) (NN fluid)) (PRN (-LRB- -LRB-) (NP (NNP Fig.) (NNP 256) (NNP D)) (-RRB- -RRB-)))))))))))))))))) (. .)))
As this fold grows up around the  embryo it meets above and incloses a sac, known as the amniotic sac,  which surrounds the embryo and which becomes filled with a watery  liquid known as the amniotic fluid (Fig. 256 D).
(ROOT (S (NP (NP (DT The) (JJ amniotic) (NN sac)) (, ,) (SBAR (WHNP (WDT which)) (S (VP (VBD was) (VP (VBG sitting) (PP (IN on) (NP (NP (NN top)) (PP (IN of) (NP (DT the) (JJ flat) (NN embryo))))))))) (, ,)) (VP (VBZ envelops) (NP (DT the) (NN embryo)) (SBAR (IN as) (S (NP (PRP it)) (VP (VBZ folds))))) (. .)))