Parotid Region and Muscles of Mastication Parotid Gland Shape: Irregular pyramid with an upper end, anterior end and a lower end Has 3 surfaces: lateral (superficial), anteromedial and posteromedial External acoustic meatus sternomastoid Ramus of mandible sternomastoid Masseter muscle Position: Wedged between the ramus of mandible and the sternomastoid Its upper end fits into the external acoustic meatus Its lower end reaches down to the angle of the mandible Overlaps the masseter ms (ant) and the sternomastoid (post) Accessory parotid gland A small semi-detached part of the gland lies on the masseter between the zygomatic arch and parotid duct Anteromedial surface Posteromedial Lateral surface

Capsule: The gland is ensheathed by a capsule derived from the deep cervical fascia Attached superiorly to the zygomatic arch Deeply, it is attached to the angle of mandible and styloid process, forming the stylomandibular ligament The stylomandibular ligament separates the parotid gland from the submandibular gland External acoustic meatus Z y g o m a t i c a r c h Mastoid process Styloid process Stylo-mandibular ligament Stylo-mandibular ligament Medial veiw Lateral veiw

Relations Lateral surface: Anteromedial surface: Skin, superficial fascia, platysma Great auricular nerve Preauricular lymph nodes TMJ Ramus Anteromedial surface: Posterior border of the ramus of mandible Temporomandibular joint (TMJ) Insertion of medial pterygoid muscle (on the inner surface of the ramus) Masseter muscle (on the outer surface of the ramus)

Sternomastoid & posterior Posteromedial surface: Mastoid process, sternomastoid ms, and posterior belly of digastric ms. Styloid process and muscles attached to it The styloid process separates the gland from the carotid sheath and its contents (ICA & IJV) Terminal part of ECA The medial border of the gland is in contact with the lateral wall of pharynx Styloid process Sternomastoid & posterior belly of digastric Upper end: Fits below the external acoustic meatus ECA ICA & IJV

Structures within the substance of the parotid gland Main structures: Terminal part of ECA: deep in position Retromandibular V: intermediate in position Facial N: superficial in position Auriculotemporal nerve Superficial temporal vessels Parotid gland Terminal branches of facial nerve Posterior auricular vein Posterior branch of retromandibular v. External jugular vien Common facial vein Anterior branch of retromandibular v. IJV

How structures enter and leave the gland ECA, enters the gland through its posteromedial surface and divides into superficial temporal and maxillary arteries Superficial temporal artery: leaves the gland through its upper end Maxillary artery: leaves the gland through its anteromedial surface Maxillary vein: enters the gland through the anteromedial surface Superficial temporal vein: enters the gland through the upper end Retromandibular vein, formed inside the gland by union of maxillary and superficial temporal veins It divides into anterior and posterior divisions, which leave the gland through its lower end The posterior division joins the posterior auricular vein to form the external jugular vein The anterior division joins the anterior facial vein to form the common facial vein Facial nerve, comes out of stylomastoid foramen and enters the gland through its posteromedial surface It divides into 5 terminal branches within the substance of the gland Branches of facial nerve: leave through the upper end (temporal branches), anteromedial surface (zygomatic and buccal branches) and lower end (marginal mandibular and cervical branches) Auriculotemporal nerve: enters through the anteromedial surface and leaves through the upper end

Parotid duct: Surface anatomy of the parotid duct Two inches long Arises from the anterior border of the gland Runs on the masseter below the zygomatic arch and accessory parotid gland It runs between the upper and lower buccal branches of facial nerve The buccal branch of mandibular nerve runs below the duct It receives a small duct from the accessory parotid duct At the anterior border of masseter, it turns medially piercing the buccal pad of fat, buccopharyngeal fascia, the buccinator muscle and the buccal mucosa Opens into the vestibule of the mouth opposite the upper second molar tooth Parotid duct Opening of parotid duct Buccinator Buccal pad of fat Masseter Surface anatomy of the parotid duct Represented by the middle third of a line between the lower border of the tragus and a point midway between the ala of the nose and the red margin of upper lip The duct can be palpated on the anterior border of masseter on contracting the muscle

Nerve supply: Arterial supply: ECA Lesser petrosal nerve Arterial supply: ECA Venous drainage: Retromandibular Vein Lymph drainage: Preauricular lymph nodes Tympanic plexus CN IX Inferior salivary nucleus Tympanic branch of CN IX Otic ganglion Nerve supply: Sensory: auriculotemporal nerve Sympathetic: plexus around ECA Parasympathetic: postganglionic fibres from the otic ganglion carried by the auriculotemporal nerve Auriculotemporal nerve ICA The preganglionic fibres arise from the inferior salivary nucleus in the brain stem, run with CN IX, then through its tympanic branch to join the tympanic plexus, fibres are then carried by the lesser petrosal nerve which leaves through the foramen ovale and terminates in the otic ganglion

Temporal fossa A shallow fossa on the side of the head Boundaries: Temporal lines A shallow fossa on the side of the head Boundaries: Zygomatic arch, below Temporal lines, above Frontozygomatic process, anteriorly Supramastoid crest, posteriorly Temporal fossa Contents: Temporalis muscle, covered by temporal fascia Deep temporal nerves and vessels Auriculotemporal nerve Superficial temporal artery Zygomatic arch Deep temporal nerves T e m p o r a l i s M u s c l e Auriculotemporal nerve

Muscles of Mastication Temporalis ms. Origin: floor of temporal fossa & inner surface of temporal fascia Insertion: coronoid process of the mandible Action: Elevation of the mandible (anterior and middle fibers) Retraction of the protruded mandible (posterior fibers) Nerve supply: deep temporal nerves (anterior division of mandibular nerve) Temporalis Muscle Masseter ms. Origin: lower border and inner surface of zygomatic arch Insertion: outer surface of the ramus of mandible Action: elevation of the mandible Nerve supply: nerve to masseter (anterior division of mandibular nerve) Coronoid process of mandible Temporal fascia Temporal fascia Covers the temporal fossa and temporalis muscle Superiorly, it is attached superiorly to the superior temporal line Inferiorly, it is attached to upper border of zygomatic arch Its deep surface gives origin to temporalis muscle Temporalis Masseter

Superficial & deep heads Upper & lower heads of lateral pterygoid Lateral pterygoid ms. Origin: by two heads upper head: infratemporal crest and infratemporal surface of greater wing of sphenoid lower head: lateral surface of lateral pterygoid plate Insertion: pterygoid fovea (front of the neck of mandible) capsule and articular disc of temporomandibular joint Action: protrusion of the mandible pulls the head of mandible forwards (during opening the mouth) side to side movement of the mandible (chewing) (acting with medial pterygoid, alternately with the muscles of the contralateral side) Nerve supply: nerve to lateral pterygoid (anterior division of mandibular n) Articular disc of TMJ Superficial & deep heads of medial pterygoid Lateral pterygoid TMJ Medial pterygoid ms. Origin: by two heads superficial head: tuberosity of the maxilla deep head: medial surface of lateral pterygoid plate Insertion: inner surface of the ramus of mandible Action: Elevation & protrusion of the mandible side to side movement (chewing) Nerve supply: nerve to medial pteryoid (trunk of mandibular n) medial pterygoid