Lips are muscular folds covered by skin outside and mucous membrane inside, forming the movable opening of the mouth.
The reddish color of the lips is caused by the quantity of blood vessels surrounding that area. That also explains why they tend to bleed easily.
Aesthetics
Wide full lips are generally considered ideal.
Leonardo da Vinci thinks the oral commissures should be as wide as the IPD (interpupilary distance).
Symmetry of the lips is also as important as the width and volume. The upper lip should be slightly smaller as the lower lip.
Here is a great example of good lips. The lips are wide, proportional and have decent volume.
The primary muscle of the lips is the orbicularis oris.
It controls all the movements you can make with your lips.
Palate width
There is the big misconception that a wide palate correlates with wider lips, but this simply isn't true.
Palate width also doesn't even correlate that heavily with facial width as you can see with the individual Jordan Barrett.
That doesn't look like a wide palate to me.
His oral commissures are also wider than his palate.
So how the fuck do we ascend our lips? More about that on the next pages.