system
Given the following post, respond as if you're commenting on Reddit:
human
[biology] How is the jaw pulled down?
gpt
Well, long story short: 

- if upright, passively by releasing the masseter muscle (excentric contraction)

- for wider opening or a different position, there are muscles in the front of your neck that will open the mouth 

Note that muscles can only pull, but sometimes gravity + contraction can still work as if the agonist muscle is 'pushing'