pinna vs rachis

pinna

noun
  • A feather, wing, fin, or other similar appendage. 

  • The visible part of the ear that resides outside of the head, the auricle; outer ear excluding the ear canal. 

  • A leaflet or primary segment of a pinnate compound leaf. 

rachis

noun
  • The central shaft of a feather. 

  • The main shaft of either a compound leaf, head of grain, or fern frond. 

  • An anatomical shaft or axis in a marine invertebrate. 

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