( ( As ( the ( skull flexes ) ) ) ( , ( ( the cranium ) ( ( becomes ( ( ( rounder and ) ( the face ) ) ( ( shortens and ) ( retracts ( until ( it ( ( 's directly ) ( under ( the ( brain case ) ) ) ) ) ) ) ) ) ) . ) ) ) )
(ROOT (S (PP (IN As) (NP (DT the) (NN skull) (NNS flexes))) (, ,) (NP (DT the) (NN cranium)) (VP (VBZ becomes) (SBAR (S (NP (NP (NN rounder)) (CC and) (NP (DT the) (NN face))) (VP (VP (VBZ shortens)) (CC and) (VP (VBZ retracts) (SBAR (IN until) (S (NP (PRP it)) (VP (VBZ 's) (ADVP (RB directly)) (PP (IN under) (NP (DT the) (NN brain) (NN case))))))))))) (. .)))
As the skull flexes, the cranium becomes rounder and the face shortens and retracts until it's directly under the brain case.
(ROOT (S (NP (NP (NNP Cranium)) (PRN (-LRB- -LRB-) (NP (NN skull)) (-RRB- -RRB-))) (VP (VBZ is) (NP (NP (DT the) (NN term)) (PP (IN for) (NP (NP (DT the) (JJ skeletal) (NN structure)) (PP (IN of) (NP (NP (DT the) (NN head)) (SBAR (WHNP (WDT that)) (S (VP (VP (VBZ supports) (NP (DT the) (NN face))) (CC and) (VP (VBZ protects) (NP (DT the) (NN brain)))))))))))) (. .)))