Fig. 5: The evolutionally unique human mastication.

a Selective co-ordination of jaw-adductor muscles in the horizontal phase of closure of the human unilateral chewing cycle. Frontal view (top left), frontal view of a transverse section of the left first molars (right) and an inferior view of the upper left premolars and the canine (left, below). Food-tooth contacts of the BAT-area (“EXC”) activates the temporal (large arrow, 1) and masseter (large arrow, 2) muscles. With the narrowing gape the upper and lower canines are also contacted. In the BAT-area, the lingual inclines of the paracones, and the buccal inclines of the protoconids are guiding the movement of mandible to be approximately parallel (dashed arrow) to the path of the lower canine against the lingual slope of the ipsilateral upper canine (solid arrows). The gliding, inhibitory ANT-contact silences (“INH”) the activity of the temporal-masseter-complex. b The medial glide of mandible continues to be driven by the antagonist, horizontally oriented group of muscles, the inferior belly of the lateral pterygoid (large arrow, 3), and the medial pterygoid muscles (large arrow, 4). The food bolus is crushed in the central fossae of the BAT between the buccal aspect of the protocone and the lingual aspect of the protoconid, that are almost perpendicular to the paracone-protoconid-canine-guided medial movement of mandible.