Muscles of Facial Expression in Otolemur, With a Comparison to Lemuroidea presented by: Amy Christine

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Muscles of Facial Expression in Otolemur, With a
Comparison to Lemuroideapresented by Amy
Christine

• Burrows, Anne M., and Timothy D. Smith. 2003.
  Muscles of Facial Expression in Otolemur, With a
  Comparison to Lemuroidea. Anatomical Record 274A
  827-836.

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Background

• Facial expression has become highly derived and
  differentiated in mammals relative to more
  primitive vertebrates.
• The basic developmental portions of this
  musculature are the undifferentiated platysma and
  sphincter colli profundus sheets.
• Muscles of facial expression are involved in
  various activities, such as mastification,
  vision, and respiration, but their major role is
  nonverbal communication, such as close proximity
  social signing.

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Background

• In primates, binocular vision, increased visual
  activity, and convergence are so well developed
  that close-range visual cues, such as facial
  expressions, take on special importance in social
  interactions.

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Background

• As the phylogenetic scale progresses from
  prosimians to humans, complexity of facial
  musculature and corresponding actions increase.
• Form and function of the facial musculature have
  been well described in catarrhines, but they are
  relatively poorly understood in prosimians.
• In earlier studies of Otolemur, only seven
  muscles were reported on the facial musculature
  occipitofrontalis m., atollens aurem m.,
  attrahens aurem m., retrahens aurem m.,
  orbicularis palpebrum m., orbicularis orism., and
  the nasal region mm.

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Background

• Prosimian muscles of facial expression were
  examined in the greater bushbabies, O.
  crassicaudatus (large-eared bushbaby) and O.
  garnettii (small-eared bushbaby).
• Family Galagonidae
• Nocturnal and like forests/woodlands.

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Materials and Methods

• 10 preserved heads from O. crassicaudatus and 8
  from O. garnettii were obtained from Duke
  University Medical Center.
• Brains and calvariae had been removed in previous
  experiments.
• A midline incision was made over the nasal and
  oral regions down into the neck to separate the
  left and right portions of the face.
• As much superficial facial musculature was
  removed as possible to leave none behind,
  creating a facemask.

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Materials and Methods

• Face masks were allowed to dry for 30-60 min in
  order to remove remaining fascia and other
  connective tissue.
• Text and diagrams from earlier studies (Ruge 1885
  and Murie Mivart 1872) were used to help
  identify muscles.

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Results

• Appearance of facial muscles in the O. garnettii.
  
• Yellow are superficial, pink are deeper.
• Retrahens aurem m. is not shown here b/c the
  calvariae was removed it was not possible to
  evaluate the attachements.

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Results Discussion

• 17 muscles in Otolemur were found as opposed to 7
  in the previous study, indicating that Otolemur
  facial expression is far more complex than
  previously described.
• The number and arrangement of muscles found
  closely resembles the condition of Lemur.
• It is apparent that Otolemur cannot be regarded
  as having a more primitive arrangement than any
  of the members of the Lemuroidea.

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Results Discussion

• Few differences between the two tested types of
  bushbabies were noted. Except O. garnetti appears
  to have a more robust, distinct musculature
  associated with the ear and oronasal regions.
• These muscles include orbitoauricularis,
  nasalis, and sphincter colli muscles. Which move
  the ear complex, nares, mysticial vibrissae, and
  the skin around it.
• This may be due to the higher degree of
  territorial displays in the O. garnettii, a
  difference in diet, and also localizing prey.

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Phylogenetic Aspects

• There is a reduction of the attachment of the
  occipitofrontalis/ attrahens aurem/ attollens
  aurem grouping to the ear in lemuroids compared
  to Otolemur.
• Previous authors have described complex movement
  of the external ear in Otolemur social
  interactions, while similar descriptions for
  lemuroids are lacking (where expressions of the
  mouth are more common).
• Considering the far greater number of muscles
  found in Otolemur, and their similar arrangement
  relative to lemuroids, these results may be
  useful for ongoing research into taxonomic
  relationships b/w the lorisoids and lemuroids,
  and the position of Otolemur relative to other
  Galaginae.