The tarsier's eyes are so large that each bony eye orbit is larger than its brain pan and larger than its stomach (you know the old addage...).
Their eyes are fixed in place, but they've got incredible flexibility in their neck (upwards of 300 degree range) which allows them to see in most directions.
Unlike most nocturnal animals, the tarsier doesn't have any reflective quality to its retinas Enter those massive eyes again. Huge eyes equals huge pupil dilation equals lots o' light coming in.
Curious to see just how large the eye orbits are? Look below.