( ( Beneath ( ( the ( moist epithelium ) ) ( which lines ) ) ) ( ( each alveolus ) ( ( is ( ( an ( extensive meshwork ) ) ( of ( lung capillaries ) ) ) ) . ) ) )
(ROOT (S (PP (IN Beneath) (NP (NP (DT the) (JJ moist) (NN epithelium)) (SBAR (WHNP (WDT which)) (S (NP (NNS lines)))))) (NP (DT each) (NNS alveolus)) (VP (VBZ is) (NP (NP (DT an) (JJ extensive) (NN meshwork)) (PP (IN of) (NP (NN lung) (NNS capillaries))))) (. .)))
Beneath the moist epithelium which lines each alveolus is an extensive meshwork of lung capillaries.
(ROOT (S (NP (NP (DT The) (NNS lungs)) (PP (IN of) (NP (NNS mammals)))) (VP (VBP are) (ADJP (JJ unique) (PP (IN in) (S (VP (VBG having) (NP (NNS alveoli))))))) (. .)))