FACIAL MECHANICS. “Internal facial morphology consists of the mimetic musculature and its motor supply, branches of the facial nerve. Mimetic musculature is responsible for generating facial displays or facial expressions. These displays assist in regulating and maintaining social bonds and the social group by cueing conspecifics to the emotional and behavioral intentions of the sender.”
http://onlinelibrary.wiley.com/doi/10.1111/joa.12440/full