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Muscles of Mastication
• The muscles that are responsible for
mastication are in general strong and showed
marked species-specific variations due to the
different anatomy of the whole masticatory
apparatus, including the skeletal components,
the teeth and the temporo-mandibular joint.
The masseter muscle
• The masseter muscle is a broad
multipemnnate (bilateral symmetrical) muscle
with mutiple tendinous insertions. It
originates from the ventral border of the
zygomatic arch and the facial crest and inserts
the lateral aspect of the mandble, extending
from the facial notch to the
temporomandibular joint.
Mandibular muscles of the dog
Mandibular muscles of the horse
Layers of masseter muscle
• The masseter muscles of carnivores is
seperated into three layers (superficial,
middle, deep) by tendinous sheets (Fig. 2-4).
• The superficial portion is strongest and
originates from the rostral half of the
zygomatic arch, passes over the ramus of
mandible caudoventrally and partly inserts on
the ventrolateral surface of the mandible.
Layers of masseter muscle
• The rest of the muscle passes around the
ventral border of the mandible and the
angular process to insert on the ventromedial
side, where it covers the digastric muscle.
• The middle layer, the weakest part of the
masseter muscle, originates from the ventral
border of the zygomatic arch, medial to the
superficial layer and inserts on the lateral
surface of the mandible.
Layers of masseter muscle
• It is not possible to isolate the rostral origin of
the deep layer, since it is fused to the
temporalis muscl; caudally it originates from
the medial surface of the zygomatic arch.
• In the pig the three layers are firmly fused and
difficult to dissect.
• In the ox, the tendinous intersections are
pronounced forming five distinct parts.
• The change of the fibre direction between
each portion increases the masticatory forceof
the muscle. The superficial portion extends
from the facial tubercurosity to the caudal
border of the mandible.
• The deep layer originates from the facial crest
and zygomatic arch, passes caudoventrally
and inserts on the lateral surface of the
mandibular ramus.
• The masseter muscle of the horse shows up to
fifteen tendinous intermuscular strands,
which are originated sagitally and divide the
muscle into multiple layers.
• The superficial layers arise from the facial
crest, pass caudoventrally and insert on the
ventral and caudal borders of the mandible.
• The deep layers originate from the zygomatic
arch, pass over the ramus of mandible in a
horizontal direction and unites with the
superficial portions, with which they insert on the
lateral surface of the ramus of mandible.
• If the masseter muscles of both sides act
together, they force the upper and lower jaw
together; if acting singly, they move the mandible
to the side of the contracting muscle, which is
essential for the grinding process of herbivores.
The Pterygoid muscles
• The pterygoid muscles pass on the palatine,
pterygoid and sphenoid bones to the medial
aspect of the mandible (Fig.2-5).
• The lateral pterygoid muscle is the smaller of
the two. It originates from the pterygoid
process of the basisphenoid bone, passes
caudoventrally and inserts on the medial
surface of the ramus of mandible near the
condylar process.
• The much larger medial pterygoid muscle
occupies a position of the medial surface of
the mandible similar to that of the masseter
laterally.
• It extends from the basisphenoid and palatine
bones to the ventral border of the mandible
and the medial surface of the ramus of the
mandible.
The Temporal Muscle
• The temporal muscle occupies the temporal
fossa, its size varying in the different species
depending on the size of the fossa (Fig. 2-2and23).
• It originates from the temporal crest which forms
the edge of the temporal fossa, and from the
temporal fascia.
• From there it extends downward, covered by the
auricular muscles, and inserts on the coronoid
process of the mandible.
Temporal muscle
• It is the strongest muscle of the head in
carnivores.
• The margins of its origin are the temporal line,
the nuchal crest, the zygomatic process of the
temporal bone and the medial surface of the
temporal fossa (Fig. 2-4).
• From its extensive origin the muscle bundles
curve cranioventerally beneath the zygomatic
arch and the orbital ligament and pass around
the coronoid process of the madible, to which it
inserts.
Temporal muscle
• A tendinous branch fuses with the deep layer of the
masseter muscle.
• In dolichocephalic (having a relatively long skull) dogs,
the temporal muscle meets the corresponding muscle
of the opposite side in the midline and forms a midline
sulcus(a groove or furrow)
• In brachycephalic (having a relatively broad, short
skull) dogs, the two muscle do not meet and therefore
no sulcus is visible, except for a small indentation (a
deep recess or notch on the edge or surface of
something) between the interparietal bones in some
breeds of dog.
Temporal muscle
• While the temporal muscle is indistinct in
ruminants, it is visible under the skin in the horse.
• However, even in the horse, the temporal muscle
is not well developedcompared to the other
masticatory muscles.
• It originates from the borders of the temporal
fossa, the temporal line, external sagittal crest,
the nuchal crest and the pterygoid crest and the
surface of the temporal fossa which it occupies
completely.
Temporal muscle
• It partly fuses with the masseter and inserts to
the coronoid process of the mandible.
• It raises the mandible, acting together with
the other masticatory muscles.
Name
Innervation
Origin
Insertion
Function
Masseter muscle
Masseteric nerve of
the mandibular nerve
Facial crest and
zygomatic arch
Raises and draw
mandibular
sidewards
Lateral pterygoid
muscle Branch to
lateral pterygoid of the
mandibular nerve
Medial pterygoid
muscle
Branch to medial
pterygoid of the
mandibular nerve
Temporal muscle
Deep temporal nerve
of the mandibular N
Pterygoid process of
the sphenoid bone
Lateral surface of
the mandible and
intermandibular
region
Medial surface of
the mandible and
the condylar process
Medial surface of
the mandible
Raises mandible
Coronoid process of
the mandible
Raises mandible in
order to close the
mouth
Pterygoid process of
the sphenoid and
pterygoid bones and
the perpendicular
plate
Temporal fossa
Raises, pushes and
draws the
mandible forward
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