Why do characters in some art styles have a broken line for mouths?


Kaname Madoka from _Puella Magi Madoka Magica_ and Nakano Azusa from _K-On!_
have a broken line for mouths.

![Kaname Madoka](https://i.stack.imgur.com/JG3aWm.jpg)

![Nakano Azusa](https://i.stack.imgur.com/W4kcMm.jpg)

Why do characters in some art styles have a broken line for mouths? The lines
are broken unless it defines lips but I don't know otherwise.




I think the explanation given in [moegamisama's
answer](https://anime.stackexchange.com/a/23013/) is a step in the right
direction; however, an argument purely from high-level principles about
moe/cuteness lacks sufficient explanatory power to explain why _this_
particular style ("broken line" mouths) is often seen. I think a more
mechanistic explanation for why mouths are drawn this way is also necessary.

Taking for granted that the minimization of some facial features (a small
nose, compensated by large eyes, say) is a common feature in "moe" character
design today, and observing that the mouth is an oft-minimized feature, the
mechanistic explanation, then, is as follows.

Take a close look at the way Madoka's mouth is drawn in the picture you
posted. You will notice that the thickness of the line that represents her
mouth is not constant. Rather, it is thickest near the edges and becomes
thinner as we approach the center of her face. The line "breaking" at the
center of her face strikes me as an artistic convenience: rather than drawing
a super-thin line there, the artist simply omits the line altogether, and the
viewer's mind merely fills it in (this is the so-called ["principle of
closure"](https://en.wikipedia.org/wiki/Principles_of_grouping#Closure) of
gestalt psychology). You see the same thing (albeit less delicately) in the
picture of Azusa.

