Part 5

• Digastricus (biventer)


  • Origin: arises from the paracondylar process of the occipital bone
  • Insertion: body of the mandible
  • Action: only muscle that opens the jaw, aided by gravity
  • Innervation: Rostral part - mandibular nerve, Caudal part - facial nerve

  
• Masseter muscle


  • Origin: Zygomatic arch
  • Insertion: Masseteric fossa; the ventrolateral surface of the ramus of the mandible, and the angular process
  • Action: closes the jaw
  • Innervation: Trigeminal nerve

  
• Temporalis


  • Origin: arises from the temporal fossa
  • Insertion: coronoid process of the mandible
  • Action: closes the jaw
  • Innervation: Trigeminal nerve
• Medial and Lateral Pterygoid Muscles

  • Origin: Arises from the pterygoid palatine fossa
  • Insertion: medial surface and caudal margin of the ramus and the angular process
  • Action: closes the jaw
  • Innervation: Trigeminal nerve

  
• Muscles of Facial Expression

  • Muscles that move the skin and appendages of the face and head
  • Facial expression or mimetic muscles
  • Generally thin cutaneous muscles innervated by the facial nerve

  
• Platysma


  • Origin: Cutaneous muscle that passes from the dorsal median raphe of the neck to the angle of the mouth
  • Insertion: radiates into the orbicularis oris in the lips
  • Action: Draw the angle of the mouth caudally
  • Innervation: Facial nerve

  
• Buccinator (Trumpeter's muscle)


  • Origin: it attaches to the alveolar margins of the mandible and maxilla and the adjacent buccal mucosa
  • Action: Contraction draws the cheek inwards against the teeth
  • Innervation: facial nerve
• Levator nasolabialis


  • Origin: Arises from the maxillary bone, courses rostroventrally
  • Insertion: Attaches to the edge of the superior lip and on the naris
  • Action: Contraction causes the dilation of the nostrils and raises the upper lip
  • Innervation: Facial nerve

  
• Orbicularis oris


  • Origin: Lies near the free borders of the lips and extends from one lip to the other around the angle of the mouth
  • Insertion: The fibers of each side at the median plane in the incisor region of both jaws
  • Action: Contraction closes the lips by drawing them together into the shape of an "O"
  • Innervation: Facial nerve

  
• Zygomaticus (Smiling muscle)


  • Origin: Arises from the zygomatic arch
  • Action: draws the angle of the mouth caudally and external ear cranially and ventrally
  • Innervation: Facial nerve

  
• Mentalis


  • Origin: Arises from the pterygoid palatine fossa
  • Action: Contraction stiffens the apical region of the lowerlip
  • Innervation: Facial nerve
• Frontalis


  • Origin: A thin sheet of muscle overlying the temporalis muscle
  • Action: Contraction draws the scutular cartilage forward and raises the eyebrow
  • Innervation: Facial nerve
• Orbicularis oculi


  • Origin: Attached medially to the medial palbepral ligament
  • Insertion: The fibers of each side at the median plane in the incisor region of both jaws
  • Action: Close the palpebral fissure
  • Innervation: Facial nerve

  
• Retractor anguli oculi lateralis

  • Origin: Passes directly caudally from the lateral palpebral angle to blend with the temporal fascia
  • Action: Assist in the closing of the eye
  • Innervation: Facial nerve
• Levator anguli oculi medialis


  • Origin: Passes directly from the medial palpebral angle to attach to the frontal bone
  • Action: raises the upper lid and erects the eyebrow
  • Innervation: Facial nerve

  
• Extraocular Muscles


  • Seven extrinsic muscles
  • Two oblique muscles
  • Four rectus muscles
  • One retractor bulbi muscle

  
• Extraocular Muscle Insertions


  • All extrinsic muscles insert on the fibrous coat of the eyeball, sclera, and near the equator of the eyeball
  • Rectus muscle inserts closer to the corneoscleral junction
• Extraocular Muscle Actions


  • Dorsal rectus (elevates the globe)
  • Ventral rectus (depresses the globe)
  • Lateral rectus (turns the globe temporally/laterally)
  • Retractor bulbi (retracts the globe)

  
• Extraocular Muscle Innervation


  • Lateral rectus and retractor bulbi are innervated with the abducent nerve
  • Other three recti are innervated with oculomotor nerve
  • Dorsal oblique is innervated by the trochlear nerve
  • Ventral oblique is innervated by the oculomotor nerve
• Rostral auricular muscles


  • Superficial sculutoauricularis
  • Deep sculutoauricularis
  • Frontoscutularis
  • Frontalis
  • Zygomaticoauricularis

  
• Dorsal auricular muscles


  • Interscutularis
  • Parietoscutularis
  • Parietoauricularis
• Caudal auricular muscles


  • Cervicoscutularis
  • Superficial cervicoauricularis
  • Middle cervicoauricularis
  • Deep cervicoauricularis
  • Paratodiauricularis
  • Styloauricularis
• Styloglossus


  • Origin: Arises from the stylohyoid bone, passes rostroventrally lateral to the palatine tonsil
  • Insertion: Middle of the tongue
  • Action: Retracts and elevates the tongue
  • Innervation: Hypoglossal nerve

  
• Genioglossus


  • Origin: Arises from the intermandibular articulation and adjacent surface of the body of the mandible
  • Action: caudal fibers protrude the tongue and rostral fibers retract the apex
  • Innervation: Hypoglossal nerve
• Hyoglossus


  • Origin: Arises from the thyrohyoid and the basihyoid and passes into the root of the tongue
  • Action: Retracts and depresses the tongue
  • Innervation: Hypoglossal nerve