enroll vs split off

enroll

verb
  • To enlist oneself (in something) or become a member (of something) 

  • To enter (a name, etc.) in a register, roll or list 

  • To enlist (someone) or make (someone) a member of 

split off

verb
  • To break away from a group or mass. 

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