Fig 1.
Identification of facial musculature in the common marmoset.
A—Lateral view of the inverted facial mask dissection technique (from Burrows [51]). B—Lateral and dorsal view from dissection diagram (adapted from Huber [52] and Lightoller [57]) illustrating additional muscles not identified in A. Labels: AA: Anterior auricularis, PA: Posterior auricularis, DAO: Depressor anguli oris, DLI: Depressor labii inferioris, ZM: Zygomaticus major, Zm: Zygomaticus minor, SAL: Superior auriculolabialis, LLS: Levator labii superioris, OO: Orbicularis oculi, OOM: Orbicularis oris, DS: Depressor supercilii, P: Procerus, DH: Depressor helicis, SA: Superior Auricularis, O: Occipitalis.
Fig 2.
Direction of muscle contraction.
Labels represent approximate points of muscle origin (except for the Or muscle, which has no clear insertion). Labels: AA—anterior auricularis; DH—depressor helicis; DL—depressor labii inferioris; F—frontalis; L—levator labii superioris; Oc—orbicularis occuli; Or—orbicularis oris; P—procerus and/or depressor supercilii; SA—Superioris auricularis; SAL—Superior auriculolabialis; ZM—zygomaticus major. The occipitalis (O) and the posterior auricularis (PA) are not represented here as they are not visible from a frontal view. The O inserts in the galea aponeurotica, originates in the occipital region, and contracts ventrocaudally, while the PA inserts in the ear cartilage, originates in the occipital region, and contract caudally.
Table 1.
Comparison between FACS Action Units (AU) for humans [3] and common marmosets [51, 52, 57] according to underlying musculature.
✓- present, x—absent.
Fig 3.
Spatial representation of directional terminology for a quadruped animal.
Cranial: towards the cranium, along the long axis of the trunk (craniocaudal axis). Rostral: towards the apex of the nose, along the long axis of the head (rostrocaudal axis). Caudal: towards the tail or back of the head, along the long axis of the trunk or head, respectively. Dorsal: towards the spinal column or the top of the head, along the short axis of the trunk or the short axis of the head, respectively (dorsoventral axis). Ventral: towards the abdomen or the underside of the head, along the short axis of the trunk or the short axis of the head, respectively. Medial: towards the medial plane (represented by the midline) of the body or head. Lateral: from the medial plane, towards the left or right side of the body or head. These terms can be combined to describe a movement in additional directions, as for example: dorsocaudal, ventrocaudal, dorsocranial, ventrocranial.
Table 2.
Comparison between FACS movements for ears and related movements of the tufts and scalp for humans [3] and common marmosets [51, 52, 57], according to underlying musculature, including Ear Action Descriptors (EAD) and Action Descriptors (AD).
✓- present, x—absent.
Table 3.
Comparison between other FACS Action Descriptors (AD) for humans [3] and common marmosets.
✓- present, x—absent.
Fig 4.
Variation of facial coloration in wild and captive marmosets.
Fig 5.
Facial landmarks in common marmosets.
Fig 6.
Variation in teeth visibility.
One of the upper tooth tips is visibly protruding from the lips, indicated by the yellow arrow.
Table 4.
Mean Wexler’s index [67] (1) and independent coding agreement for each AU, AD and EAD in the three coding rounds.
NA denotes instances where all coders agreed that a particular Action was not present in any of the clips.
Fig 7.
Left: Neutral; Right: AU41—Glabella Lowerer. Still frames from S3 Video.
Fig 8.
Left: Neutral; Centre: AU6—Cheek Raiser at its apex; Right: AU6—Cheek Raiser returning to neutral. Still frames from S8 Video.
Fig 9.
AU43—eye closure/AU45—blink at the apex with appearance change 3.
Fig 10.
Examples of eyelid position at the apex of AU43/45 or AU47.
a) eyelids do not cover eyeball, and thus AU43/45 and AU47 are not present. b), c) and d): eyelids cover eyeball completely at the apex of the eyelids movement, and thus AU43/45 is coded. e) and f): eyelids cover eyeball only partially at the apex, and thus AU47 is coded. Other AUs are present (e.g. AU41).
Fig 11.
AU109+110—Nose Wrinkler + Upper Lip Raiser.
The arrow indicates the direction of movement that is seen when the upper lip is pulled towards the inner eye corner.
Fig 12.
The arrow indicates the direction of movement when the upper lip is pulled towards the ears.
Fig 13.
Left: AU25 and AU27 are present; Centre: AU12 is added to AU25+AU27; Right: AU110 is added to AU25+AU27+AU12.
Fig 14.
A: Neutral; B: AU16 pulls the lower lip downwards medially; C: AU16 pulls the lower lip downwards medially and laterally; D: AU16 pulls the lower lip further down (AU12 also present).
Fig 15.
A: Neutral; B: AU16 pulls the lower lip downwards medially and laterally (AU12 also present); C: AU16 pulls the lower lip further down laterally (AU110+AU12 also present); D: AU16 pulls the whole lower lip further down (AU110+AU12 also present).
Fig 16.
Left: AU25 and AU27 are present; Right: AU118 is added to AU25+AU27.
Fig 17.
Left: AU25 and AU27 are present; Right: AU118 is added after mouth closure.
Fig 18.
Left: Neutral; Right: AU118 is present during AD19—Tongue Show.
Fig 19.
Tree gouging action with AU27—Mouth Stretch at its apex (adapted from [76]).