Table 2.
Observed function of facial muscles during intramuscular stimulation in the rhesus macaque (current study) compared to humans and chimpanzees [14].
| Muscle | Rhesus | Human | Chimpanzee |
|---|---|---|---|
| Frontalis (inner) | Elevates the medial portion of the brow (AU1: inner brow raiser) | Elevates the medial portion of the brow (AU1: inner brow raiser) | Elevates the medial portion of the brow (AU1: inner brow raiser) |
| Frontalis (outer) | Elevates the lateral portion of the brow (AU2: outer brow raiser) | Elevates the lateral portion of the brow (AU2: outer brow raiser) | Elevates the lateral portion of the brow (AU2: outer brow raiser) |
| Corrugator supercilli | Lowers the brow inferiorly with slight medial contraction (corrugation) (part of AU4: brow lowerer) | Draws the brow medially and superiorly (AU1+AU4: inner brow raiser + brow lowerer) | Not stimulated (but likely present) |
| Depressor supercilli | Not present | Depresses the medial portion of the brow (part of AU4: brow lowerer) | Not stimulated (but may be present) |
| Procerus | Depresses the medial portion of the brow (part of AU4: brow lowerer) | Depresses the medial portion of the brow (part of AU4: brow lowerer) | Depresses the medial portion of the brow (part of AU4: brow lowerer) |
| Orbicularis oculi | Inferior portion elevates infraorbital triangle (or equivalent area) superiorly and medialwards | Elevates the infraorbital triangle (cheek) superiorly and medialwards (AU6: cheek raiser) | Inferior portion elevates infraorbital triangle (or equivalent area) superiorly and medialwards |
| Nasalis | Wrinkles skin on bridge of nose (part of AU9) | Wrinkles skin on bridge of nose (part of AU9) | Not stimulated |
| Levator labii superioris alaeque nasi | Wrinkles the skin alongside the nose (AU9: nose wrinkler) | Wrinkles the skin alongside the nose (AU9: nose wrinkler) | Wrinkles the skin alongside the nose (AU9: nose wrinkler) |
| Levator labii superioris | Elevates upper lip (AU10: upper lip raiser) | Not stimulated (but present). | Elevates upper lip (AU10: upper lip raiser) |
| Zygomatic minor | Not stimulated (but may be present) | AU11 (nasolabial furrow deepener) | Not stimulated (but may be present) |
| Zygomatic major | Elevates lip corners superiorly and draws lip corners laterally, increasing angle of the mouth (AU12: lip corner puller) | Elevates lip corners superiorly and draws lip corners laterally, increasing angle of the mouth (AU12: lip corner puller) | Elevates lip corners superiorly and draws lip corners laterally, increasing angle of the mouth (AU12: lip corner puller) |
| Buccinator | Not stimulated (but present) | Not stimulated (but present) | Not stimulated (but present) |
| Depressor anguli oris | Depresses lip corners (AU15: lipcorner depressor) | Depresses lip corners (AU15: lip corner depressor) | Depresses lip corners (AU15: lip corner depressor) |
| Depressor labii inferioris | Depresses medial portion of lower lip (AU16: lower lip depressor) | Depresses medial portion of lower lip (AU16: lower lip depressor) | Depresses medial portion of lower lip (AU16: lower lip depressor) |
| Mentalis | Pushes skin of the chin boss superiorly (AU17: chin raiser) | Pushes skin of the chin boss superiorly (AU17: chin raiser) | Pushes skin of the chin boss superiorly (AU17: chin raiser) |
| Orbicularis oris | Reduces lip aperture and protrudes lips causing pursing (AU18: lip pucker) | Tightens lip margins (AU23: lip tightener). Other FACS movements not stimulated (AU18:lip pucker, AU22: lip funneler,AU24: lip presser; AU28: lip suck) | Reduces lip aperture and funnels/protrudes lips (AU22: lip funneller) |