Editing Facial expression (section)

=== Facial muscles ===
[[File:Lars Jacob as Comedy & Tragedy 1972.JPG|thumb|An actor acting out ''Drama Masks'' ([[Thalia (Muse)|Thalia]] and [[Melpomene]]) in 1972]]
Facial expressions are vital to social communication between humans. They are caused by the movement of muscles that connect to the skin and [[fascia]] in the face. These muscles move the skin, creating lines and folds and causing the movement of facial features, such as the mouth and eyebrows. These muscles develop from the second [[pharyngeal arch]] in the embryo. The [[temporalis]], [[masseter]], and [[internal pterygoid muscle|internal]] and [[external pterygoid muscle]]s, which are mainly used for chewing, have a minor effect on expression as well. These muscles develop from the first pharyngeal arch.<ref name="Rinn">{{cite journal|last=Rinn|first=William E.|year=1984|title=The Neuropsychology of Facial Expression: A Review of the Neurological and Psychological Mechanisms for Producing Facial Expressions|journal=Psychological Bulletin|volume=95|issue=1|pages=52–77|doi=10.1037/0033-2909.95.1.52|pmid=6242437}}</ref>