Craniofacial Muscles

92 M. Lewis et al.
lost leading to prosthetic replacement. The different embryological origin and innervation
of these muscles compared to somatic skeletal muscle coupled with their changing
and unique functions have led to the possibility of structural specialisation within
the muscles of mastication. Of the muscles in this group, the masseter muscle has
undergone most investigation particularly in relation to its ease of access compared
to the other muscles of the group.
6.2 Anatomy
The temporalis muscle is a fan-shaped muscle arising from the whole of the temporal
fossa except for that part formed by the zygomatic bone together with the deep
surface of the temporal fascia (Fig. 6.1 ). The anterior and posterior fi bres converge
to attach, via a tendon, to the medial surface, the apex, and the anterior and posterior
borders of the coronoid process and the anterior border of the ramus of the mandible
nearly as far forward as the last molar tooth. The anterior fi bres act to elevate the
mandible whilst the posterior fi bres are principally involved in drawing the mandible
back after protrusion of the jaw but also provide a backward pull during closing
of the jaw. Electromyographic investigations suggest the muscle is active during
forced elevation of the mandible but not in slow elevation.
The medial pterygoid muscle arises as two heads: the super fi cial head from the
bone around the maxillary tuberosity, and a deep head from the medial surface of
the lateral pterygoid plate. The muscle fi bres pass downwards, backwards and laterally
to insert into the deep surface of the angle of the mandible. The medial pterygoid
works in combination with the masseter and anterior fi bres of temporalis to
Fig. 6.1 The muscles of mastication. The masseter, temporalis, and medial pterygoid muscles are
responsible for jaw closure, whereas the lateral pterygoid muscle is associated with jaw opening
and facilitates lateral and protrusive mandibular movements