( ( The heart ) ( ( is ( beginning ( to ( form ( ( the ( typical ( four-chambered structure ) ) ) ( of mammals ) ) ) ) ) ) . ) )
(ROOT (S (NP (DT The) (NN heart)) (VP (VBZ is) (VP (VBG beginning) (S (VP (TO to) (VP (VB form) (NP (NP (DT the) (JJ typical) (JJ four-chambered) (NN structure)) (PP (IN of) (NP (NNS mammals))))))))) (. .)))
The heart is beginning to form the typical four-chambered structure of mammals.
(ROOT (S (PP (IN Like) (NP (NP (DT all) (NNS tetrapods)) (PP (IN except) (NP (NNS birds) (CC and) (NNS mammals))))) (, ,) (NP (NNS frogs)) (VP (VBP possess) (NP (NP (DT a) (NN heart)) (PP (IN with) (NP (CD three) (NNS chambers))))) (. .)))