instep vs tarsus

instep

noun
  • The arched part of the top of the foot between the toes and the ankle. 

  • In horses, the hind leg from the ham to the pastern joint. 

  • A section of any footwear covering that part of the foot. 

tarsus

noun
  • The true foot or the fifth joint of the leg of an insect or other arthropod, typically consisting of several small segments and ending in a claw. 

  • A plate of dense connective tissue found in each eyelid, attached to either the superior tarsal muscle (in the upper eyelid) or inferior tarsal muscle (lower eyelid), which aid with sympathetic control. 

  • The shank or tarsometatarsus of the leg of a bird or reptile. 

  • A group of small bones in this part of the foot. The seven bones of the human tarsus form the ankle and upper part of the foot. 

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