In the explanation of the coat of arms its say:  

 The F and the arrows (flechas in Spanish) represent Ferdinand II of Aragon while the Y and the yoke (yugo in Spanish) represent Isabella I of Castile. 

 Its suppose to said The F and the yoke (yugo in Spanish) not the arrows and the Y and the arrows (flechas in Spanish) not the yoke. That’s the way the picture is represented.