Muscles of facial expression in the chimpanzee (Pan troglodytes): descriptive, comparative and phylogenetic contexts - PubMed (original) (raw)
Comparative Study
Muscles of facial expression in the chimpanzee (Pan troglodytes): descriptive, comparative and phylogenetic contexts
Anne M Burrows et al. J Anat. 2006 Feb.
Abstract
Facial expressions are a critical mode of non-vocal communication for many mammals, particularly non-human primates. Although chimpanzees (Pan troglodytes) have an elaborate repertoire of facial signals, little is known about the facial expression (i.e. mimetic) musculature underlying these movements, especially when compared with some other catarrhines. Here we present a detailed description of the facial muscles of the chimpanzee, framed in comparative and phylogenetic contexts, through the dissection of preserved faces using a novel approach. The arrangement and appearance of muscles were noted and compared with previous studies of chimpanzees and with prosimians, cercopithecoids and humans. The results showed 23 mimetic muscles in P. troglodytes, including a thin sphincter colli muscle, reported previously only in adult prosimians, a bi-layered zygomaticus major muscle and a distinct risorius muscle. The presence of these muscles in such definition supports previous studies that describe an elaborate and highly graded facial communication system in this species that remains qualitatively different from that reported for other non-human primate species. In addition, there are minimal anatomical differences between chimpanzees and humans, contrary to conclusions from previous studies. These results amplify the importance of understanding facial musculature in primate taxa, which may hold great taxonomic value.
Figures
Fig. 2
Right side of facial mask from Pan troglodytes. This is a view of the deep surface of the face as dissected away from the skull.
Fig. 1
Abstracts of facial expression musculature in Pan troglodytes. (a) Lateral view; (b) frontal view. In both diagrams, yellow represents the most superficially located musculature, red represents the most deeply located musculature and orange represents muscles located intermediate to the others. For both views: 1 – superficial head, occipitalis muscle, 2 – deep head, occipitalis muscle, 3 – posterior auricularis muscle, 4 – superior auricularis muscle, 5 – anterior auricularis muscle, 6 – frontalis muscle, 7 – tragicus muscle, 8 – platysma muscle, 9 – risorius muscle, 10 – superficial head, zygomaticus major muscle, 11 – zygomaticus minor muscle, 12 – orbicularis occuli muscle, 13 – levator labii superioris muscle, 14 – levator labii superioris alaeque nasi muscle, 15 – caninus muscle, 16 – depressor septi muscle, 17 – orbicularis oris muscle, 18 – depressor anguli oris muscle, 19 – depressor labii inferioris muscle, 20 – mentalis muscle, 21 – depressor supercilli muscle, 22 – procerus muscle, and 23 – corrugator supercilli muscle.
Fig. 6
Composite figure of the (a) right midfacial and orbital regions, (b) orbicularis oris muscle and associated musculature, and (c) right lower lip and mental regions. All figures are of the deep surface of the facial masks. Note the especially thick and expansive orbicularis oris muscle in Pan troglodytes.
Fig. 3
Right side of head from Pan troglodytes. (a) Dissection of the platysma muscle and its attachments to the orbicularis oris and occipitalis (deep head) muscles. The portion of the zygomaticus major muscle shown here is the superficial head. (b) Dissection of the facial mask away from the deeper structures. Note the more caudal fibres of risorius muscle and the deep and superficial heads of zygomaticus major muscle.
Fig. 4
Composite figure of the (a) right pinna, (b) right occipital region from a caudal view, and (c) right scalp and pinna region from the deep surface of the facial mask.
Fig. 5
Right side of face from Pan troglodytes with superciliary region shown in dissection. This is a skin flap from the frontal region pulled down to the level of the superciliary arch.
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