The Parotid Region of the Face

The parotid region is actually part of the neck but it extends into the facial region as well. It also must be studied before the infratemporal region can be examined. We will examine the parotid region from superficial to deep pointing out the gland itself and the structures running through it.
 
The parotid gland is a superficial structure located in the upper neck above the posterior belly of the digastric muscle. It is a salivary gland that has a large duct  (pd) which crosses the masseter muscle to pierce the buccinator muscle opposite the upper 2nd molar tooth. The duct can frequently be rolled between the finger and the masseter muscle. The skin overlying the lower pole of the gland is supplied by the greater auricular nerve (ga), a branch of the cervical plexus. You have already identified the branches of the facial nerve appearing at the upper and anterior edges of the gland (yellow).
If the parotid gland is carefully removed, you can identify the structures located within it. The first plane is the venous plane and consists of the retromandibular vein (rm) and its tributaries and branches:
  • st--superficial temporal
  • rm--retromandibular vein
  • m--maxillary vein
  • ad--anterior division
  • f--facial
  • cf--common facial
  • pd--posterior division
  • pa--posterior auricular
  • ej--external jugular
The common facial vein empties into the internal jugular vein and the external jugular into the subclavian vein near its junction with the internal jugular.
When the venous plane is removed we reach the important nervous plane. The importance of this plane is the presence of the facial (VII) nerve. The facial nerve leaves the skull through the stylomastoid foramen and immediately enters the deep part of the parotid gland where it gives off its branches:
  • posterior auricular (pa)
  • motor branch to posterior belly of digastric (db)
  • temporal branch (t)
  • zygomatic branch (z)
  • buccal branches (b)
  • mandibular branch (m)
  • cervical branch (c)
Deep to the nerves lies the arterial plane which includes terminal parts of  the external carotid artery and its branches:
  • external carotid artery (EC)
  • occipital artery (oc)
  • maxillary artery (m)
  • transverse facial artery (tf)
  • superficial temporal artery
The deepest part of the parotid region is the parotid bed and houses the deep part of the gland which fills the small space between the neck of the condyle of the mandible (nc) and the mastoid process (m). Other structures forming the floor of this space are the :
  • styloid process (sp)
  • stylohyoid muscle (sh)
  • stylopharyngeus muscle (sph)
  • posterior belly of the digastric muscle (pbd)
The gland becomes infected and swollen in mumps. If you have had the mumps, you will realize just how difficult it is to open your mouth. Now, you can see why this is so. When you open the mouth, you narrow the parotid bed space and compress the deep parotid gland between the neck of the condyle and the mastoid process.

The Infratemporal Fossa and Muscles of Mastication

The infratemporal fossa is a small space between the ramus of the mandible and the lateral pterygoid plate of the sphenoid. On a skull, it is big enough for maybe 1 1/2 fingers but it has many things in it. Following is a tabulation of the infratemporal fossa and all of its contents.
The lateral wall of the infratemporal fossa is noted in the 1st image and consists of the
  • ramus (4)
    • coronoid process (1)
    • head of condyle (2)
    • neck of condyle (3)
  • body (5)
  • angle (6)
Medial wall:
lateral pterygoid plate (1)
Roof;
greater wing of sphenoid (3)
includes foramen ovale & foramen
spinosum
Posteriorly:
styloid process (4)
There are four muscles of mastication on each side that control the movement of the mandible:
  • masseter
  • medial pterygoid
  • lateral pterygoid
  • temporalis
The lateral pterygoid is the main muscle that opens the mouth. It is helped from gravity and a couple of neck muscles. It opens the jaw by pulling forward on the neck of the mandible and causing the jaw to drop.

 
    The artery entering the infratemporal fossa is the maxillary branch of the external carotid artery. As can be seen, it has many branches (11 in all). You will probably not be responsible for all of them but I have included them all for completeness.

    Maxillary artery

    • deep auricular (da)
    • anterior tympanic (at)
    • middle meningeal (mm)
    • accessory middle meningeal (amm)
    • inferior alveolar (ia)
    • buccal (b)
    • deep temporal (dt)
    • posterior superior alveolar (psa)
    • descending palatine (dp)
    • infraorbital (io)
    • sphenopalatine (sp)
    External carotid artery (ec)
    • occipital (oc)
    • transverse facial (tf)
    • superficial temporal (st)


    The sphenopalatine and descending palatine arteries pass through a small space between the pterygoid process of the sphenoid and the maxilla, the pterygomaxillary fissure.

The mandibular nerve (V3) is the nerve of the infratemporal fossa and is responsible for supplying the muscles of mastication plus two tensor muscles: 1) tensor palati and 2) tensor tympani. The branches are as follows:
  • deep temporal (dt)
  • auriculotemporal (at)
  • inferior alveolar (ia)
    • nerve to the mylohyoid (nmh)
  • lingual (l)
  • buccal (b)
  • branches to lateral pterygoid (not labeled)
Not shown:
  • meningeal branch
  • nerve to masseter

The Temporomandibular Joint (TMJ)

The temporomandibular joint (tmj) is a synovial type joint separated by an interarticular disc. The disc splits the joint into two separate joints. The upper joint (ujc) is between the mandibular (articular) fossa of the temporal bone and the articular disk and provides a sliding motion when the lateral pterygoid contracts and pulls the condyle and disc forward. 

The lower joint (ljc) is between the articular disc and the head of the condyle of the mandible. The action here is a hinge-like action, in which the mandible drops, thereby opening the mouth.

When dentition or muscle action is not in proper alignment, the joint can be secondarily affected and pain can ensue. This is TMJ disease and requires dental specialists to correct the problem.

Table of Muscles

Muscle
Origin
Insertion
Action
Nerve Supply
masseter zygomatic arch ramus & angle of mandible closes mouth muscular branch (V3)
medial pterygoid medial surface of lateral pterygoid plate and maxillary tuberosity medial surface of ramus and angle of mandible closes mouth and helps protrude mandible muscular branch (V3)
lateral pterygoid upper head: greater wing of sphenoid
lower head: lateral surface of lateral pterygoid plate
upper head: articular disc
lower head: neck of condyle
open and protrudes mandible, moves mandible side to side muscular branch (V3)
temporalis temporal fossa coronoid process and anterior border of ramus closes and retracts mandible muscular branch (V3)

Summary of Items in This Lesson

Bones
Mandible
body
angle
ramus
condyle
head
neck
coronoid process
mental foramen

Temporal bone
Mastoid process
styloid process
stylomastoid foramen
mandibular (or articular) fossa
Temporomandibular joint
articular disc
Sphenoid bone
greater wing
foramen ovale
foramen spinosum
pterygoid process
lateral pterygoid plate
Pterygomaxillary fissure
Posterior surface of maxilla
posterior superior alevolar foramina

Muscles

Masseter
Medial pterygoid
Lateral pterygoid
upper belly
lower belly
Temporalis

Nerves

Mandibular division of trigeminal (V3)
auriculotemporal
deep temporal
inferior alveolar
nerve to mylohyoid
lingual
chorda tympani
buccal
muscular branches
muscles of mastication
tensor palati
tensor tympani
 

Nerves (contd.)

Facial (VII)
posterior auricular
tympanic
zygomatic
buccal
mandibular
cervical
branch to posterior belly of the digastric

Arteries

external carotid
occipital
maxillary
inferior alveolar
middle meningeal
accessory middle meningeal (if present)
deep temporal
buccal
posterior superior alveolar branches
descending palatine
sphenopalatine
infraorbital
transverse facial
superficial temporal

Veins

superficial temporal
maxillary
retromandibular
anterior division
facial
common facial
posterior division
posterior auricular
external jugular

Viscera

parotid gland
parotid duct

Orbit and Ear   Anterior Triangles of Neck


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