mastoid            
adjective  medical specialized uk/ˈmæs.tɔɪd/ us/ˈmæs.tɔɪd/
 乳突骨
relating to the mastoid process (= part of the skull just behind the ear)
  Mastoidectomy is performed to remove infected air cells within the mastoid bone. 乳突切除术是指移除乳突骨内被感染的气房。 
  乳房状的;乳头状的
shaped like a breast or a nipple (= one of the two small darker parts that stick out from the breasts or chest)