handspan vs manus

handspan

noun
  • The distance between the outstretched tips of the little finger and thumb when used as a unit of measurement 

manus

noun
  • A hand, as the part of the fore limb below the forearm in a human, or the corresponding part in other vertebrates. 

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