1. Muscles of mandible By: Abdul Muhaimin (D11 A007)
Reference: Veterinary anatomy of domestic animal (Book)

2. Mandibular muscles
Comprise muscle of mastication and superficial muscles of mandibular space.
Innervated by mandibular nerve (trigeminal nerve)
Responsible for movement jaw (mastication)
Covers mandibular space and hyoid apparatus ventrally.
Different species have their own structure of muscle for mastication.

3. Mandibular muscle Muscle of mastication
Masseter muscle
Medial and lateral pterygoid muscles
Temporal muscle
Superficial muscles of mandibular space
Digastric muscle
Mylohyoid muscle

4. Muscle of mastication Masseter muscle Origin Insertion Extend
Broad multipennate muscle
Multiple tendinous intersections
Origin
From ventral border of zygomatic arch and facial crest
Insertion
On the lateral aspect of mandible
Extend
From facial notch to temporomandibular joint.

5. Masseter muscle In carnivores, it is separated into 3 layers
Superficial, middle, deep (by tendinous sheets)
Superficial portion is the strongest
Middle layer is the weakest
In pig, these three layers are firmly fused
Tendinous intersections are pronounced, forming 5 distinct parts in the ox.
Change in fibre direction between each portion increases masticatory force of this muscle

6. Masseter muscle
In horse, it shows up to 15 tendinous intermuscular strands which are orientated sagitally and divide muscle into multiple layers.
Both sides masseter muscles act together will force upper and lower jaw together
Mandible can be move to the side of contracting muscle (grinding in herbivores)

7. Pterygoid muscle
Pass from palatine, pterygoid and sphenoid bones to the medial aspect of mandible.
Lateral pterygoid muscle is smaller than medial one.
In carnivores, both are fused at their origin
Horse: medial pterygoid muscle is covered by lateral one. Mandibular nerve passes across lateral surface of medial pterygoid muscle (separating 2 pterygoid muscles).

8. Pterygoid muscle
Pterygoid and masseter muscles contract bilaterally will raise mandible, but if working unilaterally, will draw mandible to side of contracting muscle.
Lateral portion also able to move mandible rostrally (mouth open)

9. Temporal muscle Size varying in different species depending size fossa
The strongest muscle of head in carnivores.
Dolichocephalic dogs: temporal muscle meets corresponding muscle of opposite side in midline (form mid-line sulcus)
Brachycephalic dogs: two muscles don’t meet, no sulcus visible

10. Temporal muscle
Ruminant: temporal muscle is indistinct but visible in horse
Horse: temporal muscle however do not well developed compared to other masticatory muscles.
It raises mandible acting together with other masticatory muscles.

11. Superficial muscle of mandibular space
Assist muscles of mastication. Cover ventral side of lingual muscles in mandibular space.
Digastric muscle
Single bellied muscle in domestic animal (except horse)
Horse: has caudal and rostral bellies
Other domestic mammals: evolutionary bipartite structure is indicated by a fibrous intersection.

12. Digastric muscle
Rostral part is innervated by mylohyoid nerve (branch of mandibular nerve)
Caudal part by digastric branch of facial nerve
In carnivores: it is strong single-bellied muscle with delicate tendinous strands (mark division between rostral and caudal portion)
Ruminants: tendinous intersection between two bellies is indistinct.
Horse: rostral belly depresses mandible and opens mouth

13. Mylohyoid muscle Form sling between inner surface of body of mandible
Innervated by mylohyoid nerve (branch of mandibular nerve), assigned to mandibular group
Can also be seen as lingual muscle (its function)
Supports tongue and raises it towards palate