canal vs epithelial duct

canal

noun
  • A tubular channel within the body. 

  • An artificial waterway or artificially improved river used for travel, shipping, or irrigation. 

  • One of the faint, hazy markings resembling straight lines on early telescopic images of the surface of Mars. 

verb
  • To dig an artificial waterway in or to (a place), especially for drainage 

  • To travel along a canal by boat 

epithelial duct

noun
  • Any duct lined with epithelium 

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