痩せてあばらが浮き出ている。
He's so thin his ribs are showing.
Standard kanji spelling for 'rib' or 'rib cage', though the full form 肋骨 is more common in formal contexts.
Kana spelling is common in everyday writing, especially when the kanji is considered difficult or when used in compounds like あばら骨.
An old native Japanese word for the ribs or rib cage, attested independently of the Sino-Japanese compound 肋骨. The character 肋 is used to write the native word あばら.