Answer the following question given this paragraph: 

Some animals deposit chemicals to mark the boundary of their territory. This is why dogs urinate on fire hydrants and other objects. Cats may also mark their territory by depositing chemicals. They have scent glands in their face. They deposit chemicals by rubbing their face against objects.


Q: When cats mark their territory by rubbing their face against an object, they deposit chemicals released by what structures?


A:
scent glands