Django forms for related objects

Question

#models.py
class Legs:
  left = TextField(default='-')
  right = TextField(default='-')

class Animal:
  #possibly, more fields
  description = TextField()
  front_legs = OneToOneField(Legs, related_name='front_animal')
  back_legs = OneToOneField(Leg,s related_name='back_animal')

#forms.py
class LegsForm(ModelForm):
  """"
  Not needed, but declared to have the LegsForm name to use next.
  """"
  class Meta:
    model = Legs
# form for Animal

How to create a ModelForm for Animal that incorporates all its fields and also handles the creation of the related objects using the two forms for the legs, i.e., LegsForm(prefix='front') and LegsForm(prefix='back') ?