My merpeople have ink sacs in their heads, as they can spray ink from tentacles (like Medusa's snakes) on their head. The problem is, I don't know where said ink sac for each tentacle would go without the brain getting in the way.
Where in their head does the ink sac go so that it doesn't interfere with the brain and so that the brain doesn't interfere with it? I want them to look fairly human, so they can't stick out somewhere outside the head.