chela vs pterygium

chela

noun
  • A pincer-like claw of a crustacean or arachnid. 

  • A pupil or disciple, especially in Hinduism. 

pterygium

noun
  • A generalized limb of a vertebrate 

  • An abnormal mass of tissue in the corner of the eye that obstructs vision 

How often have the words chela and pterygium occurred in a corpus of books? (source: Google Ngram Viewer )