HEAD & NECK ANATOMYTABLE OF CONTENTS1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. Superficial Face and Scalp Temporal and Infratemporal Fossae Osteology of the Skull Cranial Fossae Orbit Eye and Retina External and Middle Ear Anterior Triangles of the Neck Posterior Triangles of the Neck Pharynx Nasal Cavity and Pterygopalatine Fossa Larynx Oral Cavity Oral and Nasal Mucosa Pharyngeal Arches and Facial Development List of Structures to be Identified 1 8 15 21 25 29 33 37 46 48 52 55 60 66 70 77

Superficial Face and ScalpThe numerous muscles of facial expression originate from bones of the facial skeleton and insert onto the skin of the face. These muscles show much variation in terms of their relation to one another AND in terms of their overall development. These muscles atrophy with age, therefore age has a significant effect on how these muscles will appear over time. All the muscles of facial expression develop from an embryological structure known as the 2nd branchial arch and migrate into the superficial face; therefore they all share the same motor innervation branches of the Facial Nerve (CN VII) Muscles of facial expression form a blanket covering the facial skeleton; Occipitofrontalis & Platysma mm are also part of this grp; due to embryologic origin share same innervation. Muscles of facial expression act together in groups (act in concert with each other). This is due to the fact that their fibers interlace & thus they act together (in groups) to alter the size/shape of the orifices of the face. Many of the Muscles of facial expression insert together at a central point at the corner of the mouth known as the Modiolus. The muscles of facial expression will be presented as seven pairs grouped together because they have a similar function or location on the face: Pair # 1: Two circular muscles 1. Obicularis Oculi m: has 3 parts a.) Orbital portion - originates from bone around the orbit, function: close the eye tightly b.) Palpebral portion - located upon the upper & lower eyelids, function: close the eye lightly (i.e. blinking) blinking keeps the cornea & sclera moist and clean *c.) Lacrimal portion - very small to non-existant; if present it is located beneath (posterior/deep to) palpebral portion, helps moisten eye by holding the eyelids against the eyeball also helps with proper drainage of tears by squeezing the lacrimal sac 2. Obicularis Oris m: Surrounds the mouth and functions to close the mouth and pucker/purse the lips (the kissing muscle) Pair # 2: Elevators of the Upper Lip 1. Levator Labii Superioris originates inferior to the eye (maxilla) inserts in the upper lip functions to raise the upper lip Partially overlies the levator anguli oris 2. Levator Labii Superioris Alequae nasi - thin muscle located just lateral to the nose inserting into the upper lip functions to elevate the upper lip and opens (flares) the nostril Pair # 3: Insert onto Angles of the Mouth 1. Levator anguli oris originates below the eye (canine fossa of maxilla). inserts into the angle of the mouth (modiolus). functions to elevate the corner of the mouth. deep to Zygomaticus muscles.

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2. Depressor anguli oris originates from the inferior aspect of the body of the mandible. Inserts into the angle of the mouth (modiolus). functions to move the angle of the mouth inferiorly (frowning). assisted by posterior fibers of the Platysma. Pair # 4: Depressors of the Lower Lip 1. Depressor labii inferioris originates from the mandible, lateral to the mentalis muscle. inserts into the lower lip (merging with orbicularis oris muscle). functions to depress the lower lip. also draws the lower lip slightly laterally. 2. Mentalis originates from the mental protuberance of the mandible. Inserts into the skin of the chin (mentolabial sulcus). functions to elevate and protrude the lower lip and elevates the skin of the chin (pouting). Pair # 5: Originates from Zygomatic Arch 1. Zygomaticus major originates from lateral aspect of zygomatic bone. inserts into the corner of the mouth (modiolus). functions to draw the corner of the mouth superiorlaterally (smile). 2. Zygomaticus minor originates from zygomatic bone (medial to zygomaticus major). Inserts into the skin of the upper lip and the orbicularis oris muscle. functions to raise the upper lip (contempt). Also functions to deepen the nasolabial sulcus (sadness). Pair # 6: Muscles of the Nose 1. Procerus originates from fascia aponeurosis covering nasal bone and lateral nasal lateral nasal cartilage. inserts into the skin of the inferior forehead between the eyebrows. functions to depress medial end of eyebrows and wrinkle skin over dorsum of nose (dislike or disdain). 2. Nasalis (Compressor naris) Originates from superior portion of canine ridge of maxilla. Inserts in skin over nasal cartilages. functions to draw the ala (sides) of nose medially towards the septum (close the nostril). Pair # 7: Run in the Anterior-Posterior Plane 1. Risorius originates from Parotid fascia and skin over buccal area extremely superficial. inserts into the corner of the mouth (modiolus). functions to widen the orifice of the mouth (grinning or grimacing). 2. Buccinator Originates from mandible, alveolar processes of maxilla and mandible, and the pterygomanidibular raphe. Inserts into the angle of the mouth (modiolus) and the orbicularis oris. functions to press the cheek against molars; resists distension (when blowing), and keeps the cheek taut (smiling). Deeper plane than other muscles of facial expression.

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Miscellaneous Muscles of Facial Expression 1. Platysma originates from subcutaneous tissue of infraclavicular and supraclavicular regions. inserts into the base of the mandible, skin of cheek and lower lip. functions to depress mandible and tense skin over neck (shaving). 2. Occipitofrontalis Frontal: originates from epicranial aponeurosis and inserts in skin of forehead and eyebrows. Functions to elevate brow and wrinkle skin of forehead (surprise). Occipital: originates from superior nuchal line and inserts into epecranial aponeurosis. Functions to retract scalp; increase tension on frontalis belly. 3. Corrugator supercilii originates from medial end of superciliary arch. inserts into skin superior to middle of supraorbital margin and supercilliary arch. functions to draw eyebrows medially and inferiorly (worry or concern). Facial Nerve (Cranial Nerve VII): Exits skull via the stylomastoid foramen. Pierces the parotid gland, and as it passes through, divides into 5 major divisions or branches. Branches from superior to inferior: Temporal (Ten) Zygomatic (Zebras) Buccal (Bashed) Marginal/Mandibular (My) Cervical (Car) These nerves are responsible for innervating the muscles of facial expression. Just as it exits the stylomastoid foramen the facial nerve sends a motor branch to the following muscles as well: Posterior belly of the digastric muscle * Stylohyoid muscle * Platysma * These muscles will be studied later. Paralysis of the facial nerve results in a condition known as Bells Palsy. Approximately half the face does not function mask like appearance. Most common part of nerve affected is near the stylomastoid foramen. Patient is unable to close lips & eyelids on the affect side Eye on the affected side is unlubricated Cannot whistle or blow Cannot chew effectively Since the buccinator muscle is paralyzed/weak food and saliva dribble out of the mouth Trigeminal Nerve (Cranial Nerve V): Each of the 3 divisions of the Trigeminal nerve helps to supply the face with sensory innervation. Each division sends several named branches to supply the face. They are as follows: Ophthalmic Division (V1) Maxillary Division (V2) Mandibular Division (V3)

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Ophthalmic Division (V1): purely sensory; It passes through the cavernous sinus and exits the skull by way of the Superior Orbital Fissure. use the mneumonicLaSSIE to identify the terminal branches: Lacrimal - structures superior to the lateral canthus of the eye Supraorbital superior to the orbit Supratrochlear superior to the medial canthus of the eye Infratrochlear the region of the medial canthus External nasal - anterior and lateral aspect of the external nose Maxillary Division (V2): Purely sensory Passes through cavernous sinus and leaves skull via Foramen Rotundum Principle branches: Zygomaticotemproal lateral and superior to orbit Zygomaticofacial lateral and inferior to the orbit Infraorbital Large nerve inferior to the orbit Alveolar nerves: Posterior superior Middle superior Anterior superior Mandibular (V3): Sensory & Motor (we will cover motor later on); Sensory branches in the face: Leave the skull through the foramen ovale to enter the infratemporal fossa Divides into anterior and posterior divisions Posterior Division = sensory Auriculotemporal anterior to ear and superiorly into temporal region Buccal cheek and oral mucosa Mental lower lip Anterior Division = motor Parotid Region Parotid Gland: 1. Large superficially located salivary gland closely related in position to: Ramus of the mandible anterior to the gland Mastoid Process & External ear - posterior to gland 2. Passes along the edge of the ramus of mandible to extend to the pharynx medially 3. Several lymph nodes appear on its surface 4. Structure: Composed of several lobules Covered by a dense CT capsule Drained by the parotid duct (Stensons duct) Parotid duct runs anteriorly from surface of gland Parotid duct runs parallel to the zygomatic arch, approximately 1 finger breadth below it 5. Course of Parotid duct: Passes across the masseter muscle Turns medially at the anterior border of masseter Pierces the buccinator muscle Ends at the tip of the parotid papilla located in mucosa adjacent to the 2nd upper molar on each side 6. Structures that traverse/travel within portions of the parotid gland: Branches of Facial Nerve (CN VII)

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Retromandibular vein Terminal branches of the External Carotid Artery (ECA)

Venous Drainage: The facial vein is the largest and most important vein draining the face. Closely follows the facial artery, however, it is superficial to the submandibular gland. Courses obliquely downward crosses over the margin of body of mandible Clinically significant anastomoses, because it drains: Face Tonsils Soft palate Submandibular gland Pterygoid venous plexus (through the deep facial vein) Cavernous sinus (through the superior ophthalmic vein) The superficial temporal vein helps to drain the lateral aspect of the face Courses inferiorly to join the maxillary vein Union of the maxillary and superficial temporal veins leads to the formation of the retromandibular vein. Retromandibular (anterior division) and facial vein unite to form common facial vein, and this empties into the internal jugular vein. If an infection occurs in the upper face (danger triangle) potentially the bacteria can migrate from this region via the facial vein into the cranium. Facial vein infection then can spread by its interconnections (ophthalmic & infraorbital veins) to the pterygoid plexus and into the cavernous sinus and thus reach the brain causing meningitis or encephalitis. Arterial Supply: Superficial face is supplied by branches of the External Carotid Artery. Superficial temporal (is smaller of the 2 terminal branches of ECA maxillary is other) Begins deep within the parotid posterior to the neck of the mandible Ascends superficial to the posterior portion of the zygomatic process of the temporal bone ends in the scalp by dividing into: frontal & parietal branches Superficial Temporal gives off the transverse facial artery. Transverse facial artery arises from the superficial temporal artery before it leaves the parotid gland. Runs in close proximity to parotid duct & zygomatic branch of Facial N. Facial Artery the chief artery of the face Course: Runs deep to the submanibular gland Wraps around the inferior border of mandible @ the anterior edge of masseter m. Enters face from its inferior boundary Courses over the face to the medial angle of the eye Runs deep to majority of the muscles of facial expression Especially zygomatic major & levator labii superioris Exception Buccinator & levator anguli oris Principle branches of the facial artery: Inferior Labial A. to the lower lip Superior Labial A. to the upper lip

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Angular Artery continuation of the Facial A. Begins at the inferior & external margin of the nostril (naris) Runs lateral to the nose to the medial canthus (medial angle) of the eye. This artery anastomoses freely with other arteries terminating on the face a s well as with its counterpart in the midline *Important Anastomosis: The External Carotid Artery system anastomoses with the Internal Carotid Artery system. The angular artery meets up with the external branches of the ophthalmic artery. Facial Artery also supplies the submandibular gland and an area know as the submandibular triangle. SCALP

Veins:

Superficial veins within the subcutaneous layer Emissary veins: connect the veins of the loose connective tissue layer to the dural venoussinuses *The emissary veins are not consistent in that they can vary in number from region to region. *Diploic veins are not the same as emissary veins - the diploic veins supply the bones of the cranium (especially of the calveria).

Arteries: External Carotid Artery (ECA) provides the major blood supply to the scalp by way of the: 1. Occipital arteries 2. Posterior auricular arteries 3. Superficial Temporal Arteries Small contribution from two other arteries: supra-orbital & supratrochlear aa., these are branches of the ophthalmic artery (a branch of the internal carotid artery) supply forehead and anterior scalp The scalp begins in the region of the eyebrows with posterior & lateral extensions: supraorbital ridge > bony structure deep to the eyebrows and also serves as the anterior boundary for the scalp. superior nuchal line > posterior boundary of the scalp zygomatic arch > lateral boundary If one takes the first letter of each layer of the scalp, the result is the actual word S C A L P: 1. Skin - contains hair follicles, sweat glands, and sebaceous glands Ducts of the sebaceous glands can become clogged. This leads to the development of a small swelling called a "Wen"

2. Connective tissue - the second layer is a layer of very tough connective tissue layer:

contains arteries, veins & nerves of the scalp. Do not confuse with the 4th layer of scalp which is loose CT A laceration to the scalp usually bleeds profusely due to the fact that the blood vessels are "held open" by this dense connective tissue. Rich sensory innervation is located in this layer: contributions from CN V & the upper cutaneous cervical nerves Anteriorly: Ophthalmic Division (V1) of Cranial nerve V

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Laterally: Mandibular division (V3) of CN V Posteriorly: Upper Cervical Nerves (C2 & C3) specifically: greater occipital nerve, lesser occipital nerve, greater auricular nerve

3. Aponeurotic layer - consists of 2 muscles of "facial expression plus connective tissue

Anteriorly: Frontalis Muscle Posteriorly: Occipitalis Muscle Together these 2 muscles form the Epicranius muscle (aka. Occipitofrontalis m.) Galea aponeurotica (aka. Epicranial aponeurosis) is the broad aponeurosis that lies between these 2 muscles The Galea Aponeurotica, Frontalis m., Occipitalis m., all combine to make a "helmet" Infection or hemorrhaging in the scalp may cause pooling under this layer within the loose CT layer (4th layer). Infection can potentially spread by way of emissary veins to reach structures such as the meninges. Scalp infection will NOT pass into the neck because of the muscular & facial attachments creating the helmet Layers S.C.A are actually tightly fixed together and move together. However, the aponeurotic layer is loosely bound to the layer of loose CT. They move through the 4th layer (loose connective tissue) This provides a natural cleavage plane and allows for scalping type of injuries to occur (i.e. with machinery or automobile accidents)

4. Loose connective tissue layer - contains emissary veins

emissary veins connect the veins of the dense CT layer (passing through this loose CT layer) to the venous sinuses of the skull Fluids (i.e. blood or pus) from injury or pathology can collect in this layer of loose CT and travel throughout the region of the scalp; in fact, fluids (i.e blood) can continue into the region of the eyelids pool/accumulate in the eyelids Ecchymosis black eye sometimes this region is referred to as the subaponeurotic space

5. Periostium - fibrous tissue that closely adheres to the bones of the skullperiosteum (pericranium) is continuous with the fibrous layer (endosteal layer) of the dura mater at the cranial sutures.

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Temporal FossaBorders: Superior & posterior: superior temporal line Anterior: frontal & zygomatic bones Inferior: zygomatic arch & infratemporal crest Medial (floor): pterion (frontal, parietal, temporal & sphenoid bones) Lateral: zygomatic arch Bones of the temporal fossa: Parietal Temporal Sphenoid (greater wing) Frontal (very small portion) Inferiorly, at the zygomatic arch the temporal fossa communicates with the infratemporal fossa. Pterion: Junction of parietal, temporal, sphenoid & frontal bones. Middle meningeal artery (supplies the meninges and the skull) runs deep to the pterion and is particularly vulnerable to injury (rupture) in this region. Rupture of this artery leads to an epidural (aka. Extra-dural) hematoma - serious & possibly life threatening. Superficial to Deep 1. Skin 2. Subcutaneous fascia (recall that the top 2 layers of the scalp reach/extend down to the zygomatic arch). 3. Superficial Temporal A & V, Auriculotemporal n. branch of V3, and Temporal branch of the facial nerve. 4. Temporal fascia (dense fascia) boundaries: i. superior - superior temporal line ii. inferior - zygomatic arch 5. Temporalis Muscle. 6. Anterior & Posterior Deep Temporal vein, artery & nerve; these structures supply, innervate, and drain the temporalis muscle respectively. Muscles Temporalis: Originates from a broad attachment: Superficial fibers - inferior temporal line & floor of the temporal fossa; Deep fibers - infratemporal crest. Inserts onto the coronoid process of the mandible & small part of the anterior ramus of the mandible. Innervated by the deep temporal brs (anterior & posterior) from the Mandibular Nerve (V3). Functions to close (elevate) the jaw; posterior fibers (somewhat horizontal in orientation) assist with retraction. Masseter: Originates from superficial fibers - inferior border of zygomatic arch; deep fibers - medial surface of the zygomatic arch (essentially Masseter is in the inferior part of the temporal fossa due to this attachment). Insertion: superficial fibers onto the angle of mandible & part of ramus; deep fibers onto the lateral aspect of coronoid process of the mandible. Innervated by the nerve to the masseter (V3) - muscular branch that passes through mandibular notch along w/the blood supply (these are sacrificed in lab to gain access to the infratemporal fossa)

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Functions to elevate the mandible (close the jaw) and protract the mandible (pull jaw slightly forward); deep fibers may aid in retraction of the jaw.

Infratemporal FossaGeneral Considerations: Wedge-shaped; located inferior to the temporal fossa, between the ramus of the mandible laterally & structures comprising the wall of the pharynx medially. It is open to the neck posteroinferiorly. Borders: superior the zygomatic arch serves as the superior boundary inferior - no real boundary, mainly the posterior aspect of submandibular region. anterior - maxilla and the inferior orbital fissure posterior several structures, including: external auditory meatus, small portion of the SCM, styloid process, internal carotid artery, internal jugular vein, condyle of the mandible, and the deep lobe of the parotid gland. lateral - ramus of the mandible, zygomatic process of temporal bone & zygomatic bone (temporal process). medial - lateral pterygoid plate & pharyngeal musculature (the superior pharyngeal constrictor and 2 muscles of the soft palate, levator veli palatini, and tensor veli palatini) Located in the medial superior border is a ledge of bone called the infratemporal crest, which runs along a portion of greater wing of sphenoid to the squamous portion of the temporal bone

Superomedially, the roof is formed partially by the inferior surfaces of the greater wing of thesphenoid and the temporal bone, and contains: foramen ovale foramen spinosum petrotympanic fissure

Anterior wall is formed by part of the posterior surface of the maxilla and the pyramidal processof the palatine bone. Anterior Wall contains: the alveolar foramen, and the upper part opens as the infraorbital fissure leading to the orbit.

Lateral wall is formed by the medial surface of the ramus of the mandible. Lateral wall contains: the opening to the mandibular canal Medial wall is formed anteriorly by the lateral plate of the pterygoid process; posteriorly by thepharynx and two small muscles of the soft palate (tensor and levator veli palatini mm.). Medial wall contains: pterygomaxillary fissure in its anterior aspect which allows structures to pass between the infratemporal fossa & the pterygopalatine fossa.

1. 2. 3. 4. 5. 6.

Bony Landmarks Articular tubercle of the temporal bone: anterior limit of the TMJ. Mandibular Fossa of the temporal bone: receives head of the mandible to create the TMJ. Postglenoid tubercle of the temporal bone: posterior limit of the TMJ. Condyloid process of the mandible: with its neck and head. Ramus and Angle of the mandible. Coronoid process and mandibular notch.

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7. Maxillary tuberosity and pyramidal process of the palatine bone. 8. Pterygomaxillary fissure: medial boundary of the infratemporal fossa. This fissure iscontinuous with the inferior orbital fissure superiorly, and the pterygopalatine fossa medially.

9. Foramen ovale (V3 & acc. meningeal a.) and Foramen spinosum (middle meningeal a. &recurrent meningeal n.).

10. Spine of the sphenoid bone: gives the foramen spinosum its name.

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Principle Contents of the Infratemporal Fossa the inferior portion of the temporalis muscle; the medial and lateral pterygoid muscles; these, along with the masseter, comprise the muscles of mastication; the temporomandibular joint (TMJ); the sphenomandibular & stylomandibular ligaments; the maxillary artery and its branches (3 segments); the mandibular nerve [CN V3] & its branches; sensory branches of the facial nerve [CN VII] - chorda tympani; branches of the glossopharyngeal nerve [CN IX] as they head to a gap between the superior and middle pharyngeal constrictor muscles; the pterygoid plexus of veins; the otic ganglion.

Muscles Lateral Pterygoid: thick triangular muscle Originates as two (2) heads: Superior & Inferior Superior from the infratemporal crest. Inferior from the lateral surface of the lateral pterygoid plate. Inserts uniquely into TMJ and mandible: Superior head inserts into capsule & disc of the TMJ. Inferior head inserts onto the anterior surface of the neck of the mandible at the pterygoid fovea. Innervation is via the nerve to the lateral pterygoid (branch of V3). Functions primarily to open the jaw and protrude the jaw via the inferior head; superior head acts on the articular disc. Works also to grind food. Medial Pterygoid: Deep to Lat. Pterygoid; runs parallel to Masseter. Originates also as two (2) heads: Deep & Superficial Deep from the medial surface of the lateral pterygoid plate. Superficial from the tuberosity of the maxilla & the pyramidal plate of palatine. Inserts onto the medial surface of the mandible near the angle. Innervated by the medial pterygoid n. (branch of V3). Functions to elevate and protrude the mandible. Works also to grind food. Movements of the Jaw Protraction (anterior movement): Lateral pterygoid (most imp. muscle), assisted by medial pterygoid, some limited contribution from the masseter Retraction (posterior movement): Posterior fibers of Temporalis & Deep fibers of Masseter. Elevation (closing): Temporalis, Masseter, Medial Pterygoid. Depression (opening): Lateral Pterygoid, Digastric (primarily ant. belly), Mylohyoid, Geniohyoid, Infrahyoid, and Gravity (extremely important). Lateral Displacement (grinding & chewing): Ipsilateral masseter & temporalis, Contralateral medial & lateral pterygoids. Muscles act in a series, not all at once.

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Temperomandibular Joint (TMJ) All the muscles acting on the mandible directly or indirectly influence the function of the temporomandibular joint. Muscular dysfunction can create improper joint biomechanics. Due to the significant neurovascular structures in this area, TMJ dysfunction has the potential to manifest as headaches, dizziness, ear popping, and jaw pain. Althought the entire TMJ complex itself is not part of the Infratemporal fossa, it is important to consider it when discussing this region: Several TMJ components serve as borders of the infratemporal fossa; Several components of the TMJ are among the structures contained within the infratemporal fossa. The TMJ has close relationships the with the following structures of the infratemporal fossa: Facial nerve as it travels toward its entrance to the substance of the parotid gland Auriculotemporal nerve sends articular branches to the TMJ Irritation/Inflammation from TMJ dysfunction can cause referred pain to other regions supplied by this nerve Lateral Pterygoid & Medial Pterygoid muscles: the lingual & inferior alveolar nerves pass between these 2 muscles; improper biomechanics of the TMJ may contribute to spasm within these muscles and thereby place low grade pressure on these nerves leading to abnormal sensation in the jaw and inferolateral oral cavity The TMJ: Joint that occurs between the condyle (head) of the mandible and the temporal bone (specifically the mandibular fossa) of the skull. It is a synovial (diarthrodial) joint, but unlike other synovial joints it does not contain the usual hyaline cartilage, rather it has a dense irregular connective tissue articular disc. It is a modified hinge type joint, composed of right and left ellipsoidal joints forming a bicondylar articulation. Each joint is divided into a superior and inferior part by an articular disc. The superior portion provides a gliding (sliding) movement. The inferior portion provides for a hinge movement. Ligaments The Ligaments of the TMJ function to help limit the movement of the joint, but they do not stabilize it or prevent excessive movement due to force. Temporomandibular (lateral) ligament is closest in proximity to the joint: runs diagonally (posterior & inferior) from the margin of the articular tubercle (of the temporal bone) to the neck of the mandible; limits the inferior and posterior movement of the TMJ. Sphenomandibular ligament is medial to the temporomandibular joint: runs from the spine of the sphenoid bone at the base of the skull to the lingula on the medial side of the ramus of the mandible; limits anterior and lateral movement of the TMJ. Stylomandibular ligament is also medial to the TMJ: runs from the styloid process of the temporal bone to the posterior margin and angle of the mandible; also limits anterior and lateral movement of the TMJ. Joint Capsule The synovial membrane of the joint capsule lines all non-articular surfaces of the upper and lower compartments of the joint, and attaches to the margins of the articular disc.

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The fibrous membrane of the joint capsule encloses the temporomandibular joint complex, and is attached to the articular disc at its periphery to the inner aspect of the fibrous membrane. The superior head of the lateral pterygoid muscle also attaches to the articular disc to aid in its displacement during jaw opening & closing.

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Borders of the TMJ Anteriorly: Insertion of the lateral pterygoid muscle. Posteriorly: External auditory meatus; Deep lobe of the Parotid gland; Auriculotemporal nerve; Superficial temporal artery and vein. Superiorly: bones of the middle cranial fossa. Medially: Spine of sphenoid & the foramen spinosum. Laterally: Subcutaneous connective tissue. Contents of the TMJ Articular tubercle - located on the temporal bone Mandibular fossa posterior to the articular tubercle Condyle of the mandible (head and neck) Articular disc: Divides the joint into superior & inferior compartments Attached to the joint capsule Postglenoid tubercle Note: Unlike most synovial joints, the TMJ is lined with dense connective tissue, not the usual hyaline cartilage. Movements of the TMJ

Each TMJ is divided into a superior & inferior compartment by its articular disc. Each part is a separate functional unit with its own specific movement: 1st movement lower compartment: hinge movement (rotational). occurs first - result is opening the jaw. 2nd movement upper compartment: only acts after the hinge movement has completed. sliding/gliding movement along the eminence, leading to full opening (depression) & protrusion of the mandible.

Maxillary Artery It is largest of the 2 terminal brs of the External Carotid Artery. Arises posterior to neck of the mandible. Divided into 3 regional parts by the lateral pterygoid muscle: Mandibular part passes anteriorly, deep to the neck of the mandibular condyle Pterygoid part passes across the lateral pterygoid (it may pass either superficial or deep to the muscle) Pterygopalatine part the portion of the maxillary artery after it passes through the pterygomaxillary fissure to enter the infratemporal fossa

Mandibular Part (4-1): Deep auricular artery to the external auditory meatus (EAM). Anterior Tympanic internal aspect of tympanic membrane. Middle Meningeal important artery, enters the foramen spinosum and supplies the dura mater and internal aspect of the skull. Accessory Meningeal passes through the foramen ovale to help supply the meninges.

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Inferior Alveolar passes through the mandibular foramen to supply the mandibular dentition(teeth) and emerge as the mental a.

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Pterygoid part (3-3): Several muscular branches to: Masseteric a. (passes through mandibular notch) and gives off twig to the TMJ. Internal (medial) & External (lateral) pterygoid aa. (typically 2). Anterior & Posterior Deep temporal arteries: To portions of muscle with same name (temporalis). Ascend between the deep fibers of this muscle and the bones of the temporal fossa. Buccal artery to the cheek (travels with long buccal nerve) to supply buccal fat pad, buccinator muscle, and buccal aspect of oral mucosa. Pterygopalatine part (4-1-I): Posterior superior alveolar to posterior maxillary teeth. Infraorbital passes through the inf. Orbital fissure to the infraorbital foramen & canal, and gives off: Middle & Anterior superior alveolar aa. that supply the maxillary teeth. Infraorbital artery - continues anterior emerging from the infraorbital foramen to supply the face in the region of the orbit; considered the termination of the Maxillary a. Descending palatine a. gives off the following branches greater palatine a. - hard palate. lesser palatine a. - soft palate. Pharyngeal artery to the pharynx. Artery of the pterygoid canal through canal of same name. Sphenopalatine artery to the nasal cavity.

External Carotid ArteryBranches of the External Carotid Artery: SALFOP SuperT Max 1. Superior Thyroid a. to thyroid, infrahyoid region & larynx. 2. Ascending Pharyngeal a. to pharynx, prevertebral muscles, meninges (via jugular & hypoglossal canals), tympanic membrane, soft palate. 3. Lingual a. to tongue & oral mucosa, suprahyoid region, sublingual gland, tonsils. 4. Facial a. to submandibular gland, lips, nose, facial muscles, and angle of the eye. 5. Occipital a. to sternocleidomastoid m., meninges and posterior scalp. 6. Posterior Auricular a. to tympanic membrane, ear, posterior scalp. 7. Superficial Temporal a. to parotid gland, ear, face, zygomatic & temporal regions of the face. Gives off the transverse facial a. before ascending. 8. Maxillary a. already covered.

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Trigeminal Nerve (Mandibular Division; V3) This nerve is a mixed nerve carrying both motor and sensory fibers. The mandibular nerve (mandibular division of Trigeminal Nerve) is derived from a structure known asthe 1st Branchial Arch: All muscles derived from the 1st branchial arch are innervated by branches of the mandibular nerve. The Mandibular division of CN V exits the middle cranial fossa by passing through the foramen ovale, and enters the infratemporal fossa. There are several branches that come directly off the Stem of the nerve as it emerges from the foramen ovale into the infratemporal fossa. Recurrent meningeal br. re-enters cranium through foramen spinosum to innervate meninges. N. to medial pterygoid m. via otic ganglion (no synapse). N. to tensor tympani m. via otic ganglion (no synapse). N. to tensor veli palatini m. via otic ganglion (no synapse). The remainder of the mandibular division of CN V is divided into Anterior and Posterior divisions, with the Anterior being primarily motor, and the Posterior being primarily sensory.

Anterior Division (MOTOR division): Buccal n. (aka. Buccinator n. & long buccal n.) EXCEPTION: sensory to the external cheek and oral cavity Anterior & Posterior Deep Temporal nn. provide innervation to the temporalis m. Nerve to the lateral pterygoid m. Nerve to the masseter m. Posterior Division (SENSORY division): There is at least one special thing about each of these nerves. 1. Auriculotemporal n. sensory to the anterior ear and temporal region. Special #1: Lesser petrosal nerve (preganglionic parasympathetic) is derived from the glossopharyngeal nerve (CN IX) and runs to the otic ganglion where it synapses. The postganglionic fibers leaving the otic ganglion join (run with) the auriculotemporal n. to supply secretomotor fibers to the parotid gland. Special #2: The auriculotemporal n. splits to encircle the middle meningeal artery (before it passes through the foramen spinosum) and then reunites to continue along its course in front of the ear. 2. Lingual N. sensory innervation to the anterior 2/3 of the tongue. Special #1: Receives the chorda tympani n (CN VII), which exits the petrotympanic fissure to enter the infratemporal fossa. Chorda tympani supplies special visceral afferent (SVA) fibers for taste to the anterior two-thirds of the tongue. Chorda tympani fibers traveling in the lingual nerve also carry preganglionic parasympathetics (GVE) which run to the submandibular ganglion to synapse. Postganglionic fibers from the submandibular ganglion provide the secretomotor innervation to the submandibular & sublingual glands. 3. Inferior Alveolar N. passes through the mandibular foramen, enters the mandibular canal, and supplies sensory innervation to the mandibular (lower) teeth. It then continues anteriorly & exits the mental foramen at which point it becomes known as the mental nerve.

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Special #1: Before entering the mandibular foramen, the inferior alveolar nerve gives off a nerveknown as the nerve to the mylohyoid. The nerve to the mylohyoid runs anteriorly & inferiorly to supply motor innervation to the anterior belly of the digastric muscle & the mylohyoid muscle.

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OSTEOLOGY OF THE SKULLBONE GROWTH The bones of the skull grow (ossify) by one of three methods: 1. Intramembranous growth - begins as a connective tissue membrane. This type of growth occurs in the bones which make up the calvaria (skull cap). For example, the frontal, zygomatic, mandible and parietal bones develop by this method. 2. Cartilaginous growth - begins as a "cartilage model" (prototype). The inferior nasal concha and ethmoid bones develop in this manner . 3. Mixed - part intramembranous and part cartilaginous. The sphenoid, vomer, occipital, and temporal bones fall into this category. The bones of the cranial vault are made up of three layers. The outermost and innermost layers are quite strong and are therefore known as the outer and inner tables, respectively. These two layers surround a spongy layer known as the diploe. Hematopoiesis occurs in the diploe. Veins located within this layer are known as diploic veins, and they anastomose with the intracranial dural venous sinuses. SUTURES The bones of the skull meet at very irregular lines known as sutures. Sutures are of two general types: 1) interlocking (serrated) or 2) overlapping (squamous). The bones of the skull continue to grow until the sutures fuse. Some important sutures for you to learn are: 1. Sagittal (interparietal} - located between the two parietal bones. 2. Coronal - between the frontal and two parietal bones. 3. Lambdoidal - between the occipital and parietal bones. 4. Squamosal - laterally placed suture between the temporal bone and parietal bones. The frontal suture is of less importance. This midline suture separates the frontal bone into right and left halves until approximately five (5) to six (6) years of age. If this suture persists beyond the sixth year, it becomes known as the metopic suture. Other sutures exist between most of the bones of the skull, and often are named by the bones involved, such as the nasomaxillary, frontosphenoid, sphenosquamosal, and occipitomastoid sutures. Wormian bones (aka. Sutural bones) these are small bones that are encased or surrounded completely by the sutures. They are most commonly seen along the lamboidal suture or at the pterion. FONTANELLES The large bones of the calvaria do not meet perfectly at the time of birth. The resulting "gaps" or "soft spots" are covered by skin, connective tissue, and the meninges and are called fontanelles. The two largest fontanelles are listed below. 1. Anterior fontanelle - located at junction of sagittal and coronal sutures. The intersection of these two sutures is known as the bregma after the anterior fontanelle has filled in with bone. This fontanelle disappears at approximately one and one-half years postnatal. 2. Posterior fontanelle - smaller of the two is located at the junction of the lambdoidal and the sagittal sutures. The intersection of these two sutures is known as the lambda after this fontanelle has been replaced by bone. This fontanelle obliterates approximately three months after birth.

BONY LANDMARKS OF THE SKULL

INDIVIDUAL BONES OF THE SKULL There are a total of 22 bones forming the skull. They include: Neurocranium: Parietal (2) Temporal (2) Frontal (1) Occipital (1) Sphenoid (1) Ethmoid (1) Viscerocranium: Mandible (1) Maxilla (2) Palatine (2) Zygomatic (2) Lacrimal (2) Vomer (1) Nasal (2) Inferior nasal concha (2) The first 8 bones form the Neurocranium (cranial vault), while the remaining bones form the Viscerocranium (face). NEUROCRANIUM: PARIETAL:

1. Rectangular in shape 2. Interparietal (sagittal) suture very irregular 3. Pits on inside of bone near interparietal suture formed by arachnoid granulations are called granular fovea 4. Grooves formed by branches of middle meningeal artery on inside (medial aspect) of bone 5. Parietal eminence on lateral aspect 6. Superior and inferior temporal lines for origin of temporal fascia and temporalis muscle, respectively. TEMPORAL: The temporal bone is made up of four parts: squamous, petrous, tympanic and mastoid portions. Structures located on the external surface: 1. External auditory meatus 2. Zygomatic process 3. Stylomastoid foramen 4. At birth, the external auditory meatus and the middle ear are shallow 5. Mastoid process absent at birth Structures located on the internal surface: 1. Internal auditory meatus 2. Petrous portion (medial aspect of squamous portion also seen here) 3. Region of superior petrosal sinus 4. Middle and inner ear within petrous part FRONTAL: 1. Orbital plates related to anterior cranial fossa 2. Superciliary arches above orbits 3. Glabella is the region between the two superciliary arches 4. Supraorbital foramen (sometimes notch) above medial aspect of orbit OCCIPITAL: External view: 1. External occipital protuberance (inion) 2. Nuchal lines: supreme, superior, and inferior Internal view: 1. Basiocciput (clivus) 2. Foramen magnum 3. Internal occipital protuberance 4. Condyloid canal 5. Hypoglossal canal Inferior view (Norma basalis): 1. Foramen magnum 2. Occipital condyles 3. Basiocciput 4. Pharyngeal tubercle SPHENOID:

The unpaired sphenoid bone is the most complex bone of the skull (probably of the entire body). It articulates with eight other bones [frontal, occipital, parietal, ethmoid, temporal, vomer, zygoma, and palatine bones (do not have to know for test)], and is therefore referred to as the keystone of the skull. The body of the sphenoid bone articulates with the basiocciput at an important junction known as the basisphenoid synchondrosis. This synchondrosis (n.b. not a suture) is related to development (growth) of the face during and after puberty (a secondary sex characteristic). A cavernous sinus (dural venous sinus) lies on either side of the body of the sphenoid bone.

Posterosuperior view: 1. Lesser wings 2. Greater wings; together with lesser wings forms the bat wing appearance of this bone. 3. Sella turcica (tuberculum sella, dorsum sella, and hypophyseal fossa) 4. Anterior and posterior clinoid processes 5. Optic canal 6. Groove for internal carotid artery 7. Groove for optic chiasma Inferior view: 8. Pterygoid processes each with medial and lateral pterygoid plates 9. Pterygoid hamulus associated with medial plate 10. Scaphoid fossa (for origin of tensor veli palatini m.) 11. Pterygoid canal 12. Right and left sphenoid sinus (separated by septum) Canals/foramina: 13. Superior orbital fissure, foramen rotundum, foramen ovale, foramen spinosum, foramen lacerum (Junction of sphenoid, temporal, and occipital bones), opening of carotid canal. ETHMOID: 1. Unpaired bone 2. Crista galli -for attachment of falx cerebri 3. Cribriform plate 4. Anterior, middle, and posterior ethmoidal air cells 5. Perpendicular plate -forms superior portion of nasal septum 6. Superior and middle conchae -with meatus beneath each 7. Lamina papyracea VISCEROCRANIUM: MANDIBLE: Body (horizontal), ramus (vertical), and angle. Anterior view: 1. Mental foramen 2. Mental protuberance 3. Mental tubercle (lateral aspect of protuberance) 4. Symphysis menti -fuses early Lateral view: 1. Coronoid process - anterosuperior process 2. Condyloid process - posterosuperior process consisting of head and neck 3. Oblique line - inferior to coronoid process 4. Mandibular notch found between the two processes of the ramus Posterior view: 1. Mandibular foramen - for inferior alveolar n. and a. 2. Lingula - attachment of sphenomandibular ligament. 3. Mylohyoid groove - continues inferiorly (and slightly anteriorly) from mandibular foramen on internal aspect of mandible. Created by the passage of the n. and a. to the mylohyoid. 4. Mandibular canal - route of inferior alveolar n. and a. within mandible after entering mandibular foramen. 5. Mylohyoid line - origin of mylohyoid muscle from medial aspect of body. 6. Sublingual fossa - fossa for sublingual gland located above the mylohyoid line.

7. Submandibular fossa - fossa for the submandibular gland located below the mylohyoid line. 8. Digastric fossa - located within the anterior aspect of the submandibular fossa. 9. Mental spine (genial tubercle) - anteriormost aspect of inside surface of mandible - origin of geniohyoid m. 10. Mandibular teeth and alveolar processes. MAXILLA: Medial view: 1. Lateral wall of nasal cavity 2. Maxillary sinus 3. Incisive canal and foramen - for nasopalatine n. and a. 4. Frontal process (nasal process) - separates nasal bones from orbit. 5. Palatine part (forms anterior aspect of hard palate) - meets palatine part (process) of opposite side at intermaxillary suture. Anterior view: 1. Infraorbital foramen - inferior to orbit 2. Maxillary teeth and alveolar processes 3. Incisive fossa - above incisors 4. Canine fossa - above and lateral to canines 5. Orbital surface - forms floor of orbit 6. Anterior nasal spine Lateral view: 1. Zygomatic process 2. Infratemporal surface - forms anterior wall of infratemporal fossa 3. Tuberosity - posterior, rounded portion associated with third molar PALATINE: 1. Paired bones 2. Horizontal process (plate) - forms posterior aspect of hard palate articulates with same process of opposite side and contains greater and lesser palatine foramina. 3. Vertical process (perpendicular plate) - extends superiorly to orbit, aids in formation of pterygopalatine fossa. 4. Pyramidal process - small portion lodged between maxilla and lateral pterygoid plate. ZYGOMATIC: 1. Paired bones 2. Frontal process 3. Temporal process 4. Maxillary process 5. Zygomaticofacial foramen 6. Zygomaticotemporal foramen 7. Zygomatic arch arch formed by union of zygomatic process of temporal bone with temporal process of zygomatic bone LACRIMAL: 1. Helps form medial wall of orbit - very small, paired bone 2. Forms entrance of nasolacrimal ("tear") duct

VOMER: 1. Unpaired bone 2. Forms inferior and posterior aspect of bony nasal septum. 3. Articulates with (I) palatine process of maxilla, (2) horizontal plate of palatine bone, (3) perpendicular plate of ethmoid bone, (4) body of sphenoid bone and 5) septal cartilage. 4. Creates left and right choanae from the posterior nasal aperture.

NASAL BONES: 1. Form anterosuperior aspect of bony nose 2. Separated by internasal suture 3. Nasion - region where internasal suture meets frontal bone INFERIOR NASAL CONCHA: 1. Separate bone from ethmoid (superior and middle conchae) on lateral wall of nasal cavity 2. Inferior meatus lies underneath (inferiorly) BONES WHICH FORM LATERAL WALL OF NASAL CAVITY: 1. Maxilla 2. Inferior nasal concha 3. Ethmoid (superior and middle conchae) 4. Palatine [vertical (process) plate] 5. Sphenoid (medial pterygoid plate) 6. Lacrimal 7. Nasal PARANASAL SINUSES: 1. Frontal 2. Ethmoidal (anterior, middle, and posterior ethmoidal air cells) 3. Sphenoidal 4. Maxillary

CRANIAL FOSSAEThe cranial vault consists of the bones of the skull which cover and protect the brain. In addition, the cranial vault contains the dural reflections (e.g. falx cerebri) which help to support the brain and create the important venous sinuses and, of course, the cranial vault contains the brain itself. The floor of the cranial vault is rather complex and consists of three cranial fossae (anterior, middle, and posterior). Each fossa contains many foramina which allow passage of nerves, arteries, and veins entering and leaving the cranial vault. BONES OF THE CRANIAL VAULT The bones comprising the outside of the cranial vault are: (1) frontal, (2) sphenoid (greater wing), (3) parietal, (4) temporal, and (5) occipital. The pterion is the region where these bones (with the exception of the occipital) meet. The frontal branch of the middle meningeal artery runs along the medial surface of this region. The calvaria ("skullcap," "roof of the skull") consists of the superior aspects of the frontal, parietal (both left and right), and occipital bones and, therefore, covers the superiormost portion of the brain. When this region is removed with the aid of a saw (there are no sutures which run directly in this transverse plane), the underlying dura mater is exposed. Removal of the brain and meninges exposes the floor of the cranial cavity which consists of the, anterior, middle, and posterior cranial fossae. ANTERIOR CRANIAL FOSSA The anterior cranial fossa extends from the anterior limit of the cranial vault to the posterior edge of the lesser wings of the sphenoid bone. This fossa contains portions of the frontal, ethmoid, and sphenoid bones. The frontal lobes of the brain rest within the anterior cranial fossa. ETHMOID BONE The ethmoid bone is located in the center of the anterior fossa and consists of the: 1. crista galli - centrally located peak which serves as attachment for the falx cerebri. 2. cribriform plate - small sieve-like plate of bone located on each side of the crista galli. The fibers of the olfactory nerve (approximately 20 per small foramen) pass from the olfactory mucosa to the olfactory bulb through the many openings in this structure. SPHENOID BONE The portions of the sphenoid bone which lie within the anterior cranial fossa are: 1. lesser wings - forms posterior limit of the anterior fossa, ends medially as the anterior clinoid processes. These processes serve as attachments for the anterior extent of the tentorium cerebelli and the diaphragma sella. 2. body - the anterior aspect of the body of the sphenoid (jugum) joins the two lesser wings centrally. The body of the sphenoid is hollow and divided by a midline septum. When lined with mucosa, the centrally located empty spaces of the sphenoid are known as the right and left sphenoidal sinuses. FRONTAL BONE The portions of the frontal bone which participate in the anterior cranial fossa are: 1. orbital plates - these thin plates of bone form the majority of the floor of the anterior cranial fossa. They separate this fossa from the orbits below, and are very irregular in shape due to pressure from the gyri of the frontal lobes (cerebral impressions). 2. frontal crest - midline posterior projection of the anterior portion of the frontal bone. This crest along with the crista galli of the ethmoid bone serves as attachment sites for the falx cerebri.

3. foramen cecum - foramen located between the frontal crest and the crista galli. Allows for passage of an emissary vein between the superior sagittal sinus and the nasal cavity. MIDDLE CRANIAL FOSSA This fossa is located posteriorly and inferiorly to the anterior cranial fossa and extends from the lesser wings of the sphenoid to the petrous ridge of the temporal bone. It could be thought of as a "step down" from the anterior cranial fossa. The fossa is formed by: (1) a very small portion of the lesser wing of the sphenoid bone (optic canal), (2) the greater wing of the sphenoid, (3) the body of the sphenoid bone, (4) the petrous part of the temporal bone, and (5) the squamous part of the temporal bone. This region contains the anterior aspect of the temporal lobes (temporal poles) of the telencephalon. The middle cranial fossa contains many foramina for the passage of vessels and nerves. This fossa also contains the sella turcica (Turkish saddle) which consists of: 1. tuberculum sella - anterior border of the sella turcica. 2. dorsum sella - posterior border of the sella turcica. The posterior clinoid processes project from the superior and lateral limits of this process. The posterior clinoid processes also serve as attachments for the tentorium cerebelli and the diaphragma sella. The diaphragma sella is the dural reflection which covers the hypophysis cerebri (pituitary gland), and therefore runs between all four clinoid processes. 3. hypophyseal fossa - central depression between the tuberculum sella and the dorsum sella which houses the pituitary gland. FORAMINA OF THE MIDDLE FOSSA OPTIC CANAL: The optic canal resides within the lesser wings of the sphenoid bone just inferior and medial to the anterior clinoid processes. Two important structures pass through it: 1. optic nerve - this is the large sensory nerve of sight (actually a peripheral extension of the diencephalon). It runs from the retina to the optic tracts (some fibers cross in the centrally located optic chiasma). 2. ophthalmic artery - this branch of the internal carotid artery supplies the vast majority of the orbit and its contents, including the eye itself. NOTE: The next four foramina are positioned in the form of a crescent (half-moon), the convexity of the crescent abuts the sella turcica medially. The concavity faces laterally. These foramina will be discussed from anterior to posterior. SUPERIOR ORBITAL FISSURE: Located between the lesser and greater wings of the sphenoid bone, this fissure contains the following: 1. ophthalmic veins -drain the orbit and connect the facial v. with the cavernous sinus. 2. oculomotor n. (CN III) - motor nerve to many extraocular muscles (see orbit). 3. trochlear n. (CN IV) - motor nerve to the superior oblique m. (an extraocular m.). 4. ophthalmic division of the trigeminal n. (CN V1) - sensory to orbit and its contents and the superior face (see face). 5. abducens n. (CN VI) - to the lateral rectus m. FORAMEN ROTUNDUM: Opening into the pterygopalatine fossa, this foramen contains the maxillary division of the trigeminal n. (CN V2) which is sensory to the face and nasal cavity. FORAMEN OVALE: 1. mandibular division of the trigeminal n. (CN V3) - sensory to lower face and motor to muscles of mastication. 2. accessory meningeal a. -branch maxillary a.

FORAMEN SPINOSUM: Smallest of the above foramen and contains: 1. middle meningeal a. -from maxillary a., supplies majority of dura mater and bones of calvaria. 2. recurrent meningeal n. -given off after V3 exits foramen ovale. This nerve returns through this foramen to supply sensory innervation to anterior dura.

FORAMEN LACERUM: The foramen lacerum is NOT located within the above mentioned crescent, but is more medially located and is formed by the imperfect junction of the sphenoid, occipital, and petrous temporal bones. This structure is actually a canal (running from inferior to superior) in a dried skull; however, in the living, the floor of this structure is covered by fibrocartilage, and is therefore more appropriately considered a region (an inferiorly sealed cylinder). Several structures are related to this "foramen:" 1. carotid canal - this canal opens onto the posterior wall of the "foramen" lacerum. Thus its contents, the internal carotid a. and carotid sympathetic plexus, pass through this region from posterior (and lateral) to anterior (and medial). 2. greater petrosal n. - this branch of the facial n. (CN VII) carries parasympathetic fibers to the nasal mucosa, palate and lacrimal gland (responsible for tearing and crying) .It exits the hiatus for this nerve posterior and lateral to the "foramen" lacerum, traverses the region lacerum from posterior (and lateral) to anterior (and medial), and reaches the pterygoid canal. Just as it enters the pterygoid canal, its fibers are joined by the deep petrosal n. (sympathetic fibers from the carotid sympathetic plexus) and together these two nerves are called the n. of the pterygoid canal as they enter the canal of the same name. An emissary v. and a small a. traverse the fibrocartilage floor of the foramen lacerum, but these structures are relatively insignificant, and you will therefore not be held responsible for them. CAVERNOUS SINUS: The cavernous sinus is a dura mater venous sinus located lateral to the body of the sphenoid bone. Several structures traverse this sinus. They are as follows: 1. internal carotid a. - runs a very tortuous course within this sinus (with its accompanying sympathetic plexus). 2. oculomotor n. (CN III) - to superior orbital fissure. 3. trochlear n. (CN IV) - to superior orbital fissure. 4. abducens n. (CN VI) - to superior orbital fissure. 5. ophthalmic division of trigeminal n. (CN VI) - to superior orbital fissure. 6. maxillary division of trigeminal (CN V2) - to foramen rotundum. POSTERIOR CRANIAL FOSSA This fossa is located posteriorly and inferiorly to the middle fossa (another "step down"), and is made up of the occipital bone and the petrous and mastoid parts of the temporal bone. The region of the occipital bone located anterior to the foramen magnum which climbs to meet the base of the sphenoid bone (basisphenoid) is known as the basiocciput, or clivus. The cerebellum, pons, and medulla rest in this fossa, and there are five (5) important foramina located in this fossa. They are listed below along with their contents. FORAMEN MAGNUM: This is the largest foramen of the cranial vault. It is unpaired and contains: 1. vertebral aa. - meet to form the single basilar a. 2. anterior spinal a. (single) and posterior spinal aa. (paired) - branches of the vertebral aa. 3. meninges - dura, arachnoid, and pia. 4. transition of spinal cord to medulla 5. spinal portion of spinal accessor): nn. (CNs XI) 6. tectorial membrane (membrana tectoria) - this is a broad, strong band which covers the odontoid process and its ligaments; it is a prolongation upward of the P.L.L of the vertebral column. It is attached to the posterior surface of the body of the axis, expanding as it ascends, it attaches to the basilar groove of the occipital bone, in front of the foramen magnum, where it blends with the cranial dura mater. 7. superior band of cruciform ligament 8. apical odontoid (dental) ligament

INTERNAL ACOUSTIC MEATUS : This opening is within the petrous part of the temporal bone. The petrous part of the temporal bone is a very dense structure which contains the inner and middle ears. Two important nerves and one artery traverse the meatus: 1. facial n. (CN VII) 2. vestibulocochlear n. [auditory n. (CN VIII)] - sensory to the Organ of Corti (hearing) and the membranous labyrinth (balance). 3. labyrinthine a. (internal auditory a.) - supplies middle ear and inner ear. JUGULAR FORAMEN: This foramen is formed by the union of the occipital bone (jugular notch) with the petrous part of the temporal bone (jugular fossa) and contains: 1. beginning of the internal iugular v. - from the sigmoid and inferior petrosal sinuses. 2. glossopharyngeal n. (CN IX) 3. vagus n. (CN X) 4. spinal accessory n. (CN XI) - union of both cranial and spinal portions. HYPOGLOSSAL CANAL: This canal runs at a right angle through the longitudinal axis of the occipital condyle and contains the hypoglossal n. (CN XII). CONDYLOID CANAL: This canal opens into the termination of the sigmoid sinus and runs posteriorly to exit the skull just behind to the occipital condyle. This foramen is frequently confused with the hypoglossal canal. It contains an emissary vein.

ORBITTHE BONY ORBIT Three bones make up the outer rim of the orbit. They are: 1. Frontal bone - superiorly. This bone also forms the roof of the orbit. 2. Zygomatic bone - laterally. 3. Maxilla - medially. This bone also forms a large part of the floor of the orbit. Several other bones help to form the inside of the orbit: 4. Lacrimal bone - located on the anterior aspect of the medial wall. This bone presents a fossa for the lacrimal sac. The fossa is surrounded by anterior (maxilla) and posterior (lacrimal bone) lacrimal crests. 5. Ethmoid bone - makes up majority of the medial wall. The portion of this bone which separates the orbit from the ethmoidal air cells is very thin and is called the lamina papyracea. 6. Sphenoid bone - lesser (optic canal) and greater wings make up a large percentage of the posterior aspect of the orbit. The superior orbital fissure lies between these two wings. The inferior orbital fissure lies between the greater wing of the sphenoid and the maxilla. The inferior and superior orbital fissures meet one another medially. 7. Palatine bone - orbital (vertical) process helps to form a small portion of the posterior floor of the orbit between the inferior orbital fissure and the maxilla. THE PALPEBRAE (eyelids) The superior and inferior palpebrae protect and aid in the lubrication of the eye. The outermost layer of the eyelid is the skin. This layer becomes continuous with the palpebral conjunctiva at a region known as the mucocutaneous junction. The palpebral conjunctiva is the mucus membrane on the inside of the eyelid. The palpebral conjunctiva becomes continuous with the orbital (bulbar) conjunctiva which serves as a protective covering for the eye itself. The eyelid has several layers associated with it. These layers are (from external to internal): 1. Skin - this layer contains sweat glands (glands of Moll) and sebaceous glands (glands of Zinn). The eyelashes are also contained in this layer at the anterior border of the mucocutaneous junction. The sebaceous glands associated with the eyelashes are known as the ciliary glands. Obstruction of these glands results in a stye. 2. Subcutaneous connective tissue - this layer of loose connective tissue allows free movement of the overlying skin. 3. Muscular layer - this layer contains the palpebral portion of the orbicularis oculi muscle. 4. Submucosal layer - the nerves which supply the eyelid are contained in this layer. 5. Tarsal plate - dense connective tissue plate which gives form to the upper (and lower) eyelids. This plate is held to the roof of the orbit by the palpebral fascia (orbital septum). The tarsal plates are held to the medial and lateral walls of the orbit by the medial and lateral palpebral ligaments, respectively. The levator palpebrae superioris muscle attaches to the superior aspect of the tarsal plate of the upper lid and functions to raise the upper lid. A small and separate portion of this muscle contains smooth muscle fibers and is known as the tarsal muscle. This small portion is innervated by sympathetic fibers from the internal carotid sympathetic plexus. The tarsal muscle is responsible for the "wide-eyed" stare of someone who is frightened and is also responsible for the drooping of the eyelid seen with a lesion of the cervical sympathetics (Homer's syndrome). 6. Tarsal glands - these rather long glands are located on the posterior aspect of the tarsal plate. The ducts of these glands empty behind the mucocutaneous junction. Secretions from these glands prevent the eyelids from sticking together and also help to form a seal between

the lids when they are closed. A chalazion is a rather painful condition in which the ducts of these glands become blocked. 7. Palpebral conjunctiva - this is the mucus membrane which forms the last layer of the eyelid and helps to moisten the eye itself. Again, this layer is continuous with the orbital (bulbar) conjunctiva [which covers the sclera (white) of the eye. The junction of the palpebral and orbital conjunctiva is known as the fornix. It is into the superior fornix that the ducts of the lacrimal gland empty. ANTERIOR VIEW OF THE EYE When viewed from the front, the eye can be seen ending medially and laterally at acute angles known respectively as the medial canthus and the lateral canthus. There are several other features of the anterior eye: 1. The space between the upper and lower lids is known as the palpebral fissure. 2. The larger medial angle of the eye is known as the lacrimal lake. 3. The lacrimal caruncle is the fleshy elevation seen in the medial angle of the eye within the lacrimal lake. This structure contains sweat glands, sebaceous glands, and cilia. The glands are responsible for the yellow and white secretion sometimes found in the eye upon arising after a night's sleep. 4. Plica semilunaris - is the connective tissue band found just lateral to the lacrimal caruncle. This structure may be homologous to the nictitating membrane ("third eyelid") seen in many other animals. The plica separates the sclera from the lacrimal lake. LACRIMAL GLAND The lacrimal gland is located in the superolateral aspect of the orbit. It's ducts drain into the superior palpebral fornix (located at the junction of the palpebral and orbital conjunctiva). LACRIMAL APPARATUS Tears flow from the superolaterally placed lacrimal gland, inferomedially to the medial canthus of the eye. 1. Puncta lacrimali - openings found on the medial aspect of the upper and lower eyelids into which the tears drain. The puncta are situated on small elevations called the lacrimal papillae. 2. Lacrimal canaliculus (duct) - canal which connects the lacrimal puncta with the lacrimal sac. This is also found on both the upper and lower palpebrae. 3. Lacrimal sac - oblong "sac" which rests within the fossa of the lacrimal bone. 4. Nasolacrimal duct - passes directly inferiorly from the lacrimal sac to the anterior aspect of the inferior meatus. This anterior drainage of the nasolacrimal duct accounts for the "sniffling" which is necessary to keep the draining tears within the nasal cavity during crying. INNERVATION OF THE LACRIMAL GLAND The motor fibers to the lacrimal gland are parasympathetic in nature. These fibers arise from the nervus intermedius portion of the seventh cranial nerve (CN VII). The specific branch of CN VII that contains the secretomotor parasympathetic fibers to the lacrimal gland is the greater petrosal nerve. This nerve courses within the hiatus for the facial nerve of the middle cranial fossa. The greater petrosal nerve continues through the foramen ("region") lacerum, where it is met by the deep petrosal nerve (sympathetic fibers), and together these two nerves form the nerve of the pterygoid canal. This nerve runs through the canal of the same name (pterygoid canal). The nerve of the pterygoid canal courses into the pterygopalatine fossa to the pterygopalatine ganglion where only the parasympathetic fibers synapse. The postganglionic parasympathetic fibers (that will eventually reach the lacrimal gland) join the maxillary nerve (V2) and follow its zygomaticotemporal branch. These postganglionic parasympathetics then join

the lacrimal nerve of V1 and follow it to the lacrimal gland supplying this gland with the secretomotor fibers it so genuinely deserves.

MUSCLES OF THE ORBIT The muscles of the orbit are known as the extraocular muscles. These muscles include: 1. Levator palpebrae superioris - this muscle elevates the upper eyelid. The following four muscles are known as the recti muscles. They all originate from the anulus tendineus, a fibrous ring which encircles the junction of the superior and inferior orbital fissures. This region is rather medially placed and therefore the muscles must travel laterally as well as anteriorly to reach the eye. 2. Superior rectus m. - inserts upon the superior aspect of the sclera (outer white layer of the eye) and moves the eye superiorly and medially. 3. Inferior rectus m. - inserts onto the sclera of the inferior aspect of the eye. This muscle moves the eye inferiorly as well as medially. N.B. From posterior to anterior, the orbit is directed in a medial to lateral direction. This explains the medial pull of the superior and inferior rectus muscles. 4. Medial rectus m. - inserts onto the medial aspect of the eye and moves it in the same direction (adduction). 5. Lateral rectus m. - inserts onto the lateral aspect of the eye and moves it laterally (abduction). The next two muscles do NOT originate from the anulus tendineus: 6. Superior oblique m. - originates from the body of the sphenoid, passes anteriorly through the superomedial aspect of the orbit, hooks around a connective tissue pulley called the trochlea, continues posterolaterally inferior to the superior rectus m. to insert onto the posterolateral aspect of the superior part of the eye. This muscle moves the eye inferiorly and laterally. 7. Inferior oblique m. - originates from the anteromedial aspect of the orbit on the maxilla bone and runs laterally and somewhat posteriorly underneath (inferior to) the inferior rectus m. to insert onto the posterolateral aspect of the inferior part of the eye. This muscle functions to move the eye superiorly and laterally. INNERVATION OF THE EXTRAOCULAR MUSCLES 1. Oculomotor nerve (CN III) - divides into a superior and an inferior division. The superior division innervates the levator palpebrae superioris muscle and the superior rectus. The inferior division innervates the medial and inferior rectus muscles as well as the inferior oblique muscle. 2. Trochlear nerve (CN IV) - innervates the superior oblique muscle. 3. Abducens nerve (CN VI) - innervates the lateral rectus muscle. NERVES OF THE ORBIT The ophthalmic division of the trigeminal nerve (CN VI) supplies sensory innervation to the orbit and external eye. This division enters the orbit through the superior orbital fissure and then divides into three primary branches, the lacrimal nerve, the frontal nerve, and the nasociliary nerve. 1. Lacrimal nerve - runs along the superior and lateral aspect of the orbit to supply sensory innervation to the lacrimal gland and the lateral aspect of the eye and the upper and lower palpebrae. The postganglionic parasympathetics which are secretomotor to the lacrimal gland (from preganglionics from CN VII) join this nerve after running with the zygomaticotemporal branch of V2. 2. Frontal nerve - courses along the roof of the orbit superior to the levator palpebrae superioris muscle. This nerve divides into a more medial supratrochlear nerve (which supplies sensory innervation to the skin above the medial canthus and a portion of the scalp) and the more lateral supraorbital nerve which supplies the superior palpebra and the scalp above. 3. Nasociliary nerve - this nerve crosses above the optic nerve from lateral to medial. It gives off many branches:

A. Communicating branch to the ciliary ganglion this branch contributes sensory fibers to the eye but first runs through the ciliary ganglion (without synapsing). It then reaches the eye by running through the short ciliary nerves. B. Long ciliary nerves - these nerves also provide sensory innervation to the eye (cornea, sclera, ciliary body). They run directly to the posterior aspect of the eye. C. Posterior ethmoidal nerve - to the posterior and middle ethmoidal air cells. D. Anterior ethmoidal nerve - to the middle and anterior ethmoidal air cells. This nerve runs a complex course to end as the external nasal nerve which supplies the external nose. E. Infratrochlear nerve - terminal branch of the nasociliary n. This nerve runs beneath the trochlea of the superior oblique muscle and supplies the medial canthus, lower eyelid, and surrounding region. CILIARY GANGLION This ganglion is located between the optic nerve and the lateral rectus muscle. Sensory and sympathetic fibers run through this ganglion without synapsing in it. Parasympathetic fibers from the oculomotor nerve (CN III) also reach the ganglion and are THE ONLY MODALITY OF FIBERS WHICH SYNAPSE IN THE CILIARY GANGLION. The short ciliary nerves (several in number) connect the ciliary ganglion to the posterior aspect of the eye. The short ciliary nerves therefore supply all three modalities to the eye (parasympathetic, sympathetic, and sensory). Each of these fiber types has a unique course: 1. Parasympathetic fibers - from the Edinger-Westphal nucleus of the oculomotor nerve (CN III). These fibers travel to the inferior division of CN III (specifically the branch to the inferior oblique muscle). They then run to the ciliary ganglion where they synapse. The postganglionics then course to the eye through the short ciliary nerves where they cause constriction of the pupil (sphincter pupillae m.) and contraction of the ciliary muscle. These two actions, along with ocular convergence, are known together as accommodation. Accommodation allows one to focus on a near object after looking at a distant one. 2. Sympathetic fibers - the postganglionic sympathetic fibers originate in the superior cervical ganglion. They participate in the internal carotid plexus and then "hitch a ride" with VI through the superior orbital fissure and into the orbit. These fibers course through the ciliary ganglion, the short ciliary nerves, and end by innervating the dilator pupillae muscle. This muscle causes dilation of the pupil. Sympathetic fibers also reach the eye via long ciliary nerves (of the nasociliary n.). Therefore, the long ciliary nerves provide both sensory and sympathetic innervation to the eye. 3. Sensory fibers - reach the ciliary ganglion via the communicating branch from the nasociliary nerve VI. They continue through the ganglion (without synapsing) and help to supply sensory innervation to the eye via short ciliary nerves. The long ciliary nerves also supply sensory innervation to the eye. OPHTHALMIC ARTERY The ophthalmic artery supplies blood to the orbit including the eye itself. This artery follows a course very similar to the nasociliary nerve in that it courses across the superior aspect of the optic nerve from lateral to medial. The ophthalmic artery has many branches: 1. Meningeal branches - supply anterior meninges. 2. Lacrimal a. - to the same gland. This artery also gives off an anterior choroidal artery which supplies anterior aspect of the vascular tunic of the eye (choroids layer). 3. Central retinal a. - enters the optic nerve and ramifies along the inside of the retina. This is the artery which is seen during a fundoscopic examination of the eye. 4. Long and short choroidal arteries - to the choroid layer of the eye. 5. Frontal divides and gives off:

6. supraorbital a., 7. anterior ethmoidal a. 8. posterior ethmoidal a. 9. supratrochlear arteries. These arteries generally follow the course of the nerves of the same name. 10. Branches to eyelids. 11. External branch to nose - terminal branch of ophthalmic a.

THE EYEThe eye is a highly specialized organ of photoreception, a process which involves the conversion of different quanta of light energy into nerve action potentials. The photoreceptors are modified dendrites of two types of cells, rod cells and cone cells. The rods are integrated into a system which is receptive to light of differing intensity; this is perceived in a form analogous to a black and white photographic image. The cones are of three functional types receptive to one of the basic colors blue, green and red; they constitute a system by which colored images may be perceived. The rod and cone receptors and a system of primary integrating neurons are located in the inner layer of the eye, the retina. All the remaining structures of the eye serve to support the retina or to focus images of the visual world upon the retina. The eye is essentially an orb, with a diameter of approximately 2.5cm. Each eye sits loosely in the orbit, surrounded by fat and connective tissue. Due to the nature of the surrounding fascia, movements of the eye are essentially unrestricted, except for the resistance of the other extraocular muscles. The eye contains several unique elements which aid in the transduction of light into action potentials by the retina. These include the cornea (primary refraction/focusing of light entering the eye), lens (secondary focusing of objects onto the retina), iris (controls the amount of light falling onto the retina), aqueous and vitreous humors, and the layers making up the eyeball proper: corneo-scleral layer, uveal (vascular) layer, and the neural layer or retina. The autonomic nervous system controls the focusing of images onto the retina, and the amount of light entering the eye via its connections to smooth muscles located in the iris and the ciliary body. The eye is broken into three chambers: an anterior chamber (between the cornea and iris), a posterior chamber (between the iris and the lens), and a postremal (vitreous) chamber (behind the lens). The anterior and posterior chambers are filled with the watery aqueous humor, while the postremal chamber is filled with the gelatinous vitreous humor. The eye is made up of three basic layers: the outer corneo-scleral layer, the intermediate uveal layer (vascular layer), and the inner retinal layer. Corneo-scleral Layer: The corneo-scleral layer forms a tough, fibro-elastic capsule which supports the eye. External to the sclera is bulbar fascia. The external surface (episclera) is connected by a loose system of collagen fibers to a dense layer of connective tissue called Tenons capsule, which comes in contact with the conjunctiva at the junction of the cornea and sclera. The outer sclera consists of dense, fibro-elastic connective tissue, the fibers of which are arranged in bundles parallel to the surface. The sclera is the posterior 5/6ths of the eye, and is opaque. It provides insertion for the extra-ocular muscles. The sclera varies in thickness, being thickest posteriorly and thinnest at the coronal equator of the globe. The anterior one-sixth, the cornea, is transparent and has a smaller radius of curvature than the sclera. The cornea is the principal refracting medium of the eye and roughly focuses an image on to the retina; the focusing power of the cornea depends mainly on the radius of curvature of its external surface. The corneo-scleral junction is known as the limbus and is marked internally and externally by a shallow depression. The cornea is an avascular structure consisting of five layers. The outer surface is lined by stratified squamous epithelium about five cells thick. This layer is contiguous with the bulbar conjunctiva. This epithelium is supported by a specialized basement membrane known as Bowman's Membrane which is particularly prominent in man. The bulk of the cornea, the substantia propria, consists of a highly regular form of dense collagenous connective tissues. Fibroblasts and occasional leucocytes are scattered in the corneal ground substance. The inner surface of the cornea is lined by a layer of flattened endothelial cells which are supported by a very thick elastic basement membrane known as Descemet's Membrane. The cornea is sustained by diffusion of metabolites from the aqueous humor and the blood vessels of the limbus; some oxygen is derived directly from the external environment.

Uveal Layer: The middle layer, the uvea or uveal tract, is a highly vascular layer which is made up of three components: the choroid, ciliary body and the iris. The choroid lies between the sclera and retina in the posterior five-sixths of the eye. It provides nutritive support for the retina and is heavily pigmented, thus absorbing light which has passed through the retina. Anteriorly, the choroids merges with the ciliary body which is a circumferential thickening of the uvea lying beneath the limbus. The ciliary body surrounds the coronal equator of the lens, and is attached to it by the suspensory ligaments or zonule. The lens is a biconvex transparent structure, the shape of which can be varied to provide fine focus of the corneal image upon the retina. The ciliary body contains smooth muscle, the tone of which controls the shape of the lens via the suspensory ligament. The lens, suspensory ligament and ciliary body partition the eye into a large posterior compartment and a smaller anterior compartment. The iris, the third component of the uvea, forms a diaphragm extending in front of the lens from the ciliary body so as to incompletely divide the anterior compartment into two chambers; these are known, somewhat confusingly, by the terms, anterior and posterior chamber. The highly pigmented iris acts as an adjustable diaphragm which regulates the amount of light reaching the retina. The aperture of the iris is called the pupil. The anterior and posterior chambers contain a watery fluid, the aqueous humor, which is secreted into the posterior chamber by the ciliary body and circulated through the pupil to drain into a canal at the angle of the anterior chamber, the canal of Schlemm. The aqueous humor is a source of nutrients for the nonvascular lens and cornea, and acts as an optical medium which is non-refractive with respect to the cornea. The pressure of aqueous humor maintains the shape of the cornea. The large, posterior compartment of the eye contains a gelatinous mass known as the vitreous body consisting of so-called vitreous humor .The vitreous body supports the lens and retina from within as well as providing an optical medium which is non-refractive with respect to the lens. In life, the vitreous body contains a canal which extends from the exit of the optic nerve to the posterior surface of the lens; this socalled hyaloid canal represents the course of the degenerated hyaloid artery which supplied the vitreous body during embryological development. The vitreous body and hyaloid canal are rarely preserved in histological preparations. Retinal Layer: The photosensitive retina forms the inner lining of most of the posterior compartment of the eye and terminates along a scalloped line, the ora serrata, behind the ciliary body. Anterior to the ora serrata, the retinal layer continues as a non-photosensitive epithelial layer which lines the ciliary body and the posterior surface of the iris. The visual axis of the eye passes through a depression in the retina called the fovea which is surrounded by a yellow pigmented zone, the macula lutea. The foveal retina is the area of greatest visual acuity and contains only cone photoreceptors. Afferent nerve fibers from the retina converge to form the optic nerve which leaves the eye via numerous perforations through apart of the sclera known as the lamina cribrosa. The retina overlying the lamina cribrosa, the optic papilla (optic disc) is devoid of photoreceptors and is thus referred to as the blind spot. Classically, the retina is divided into ten distinct histological zones. These layers represent the arrangement of five functional groups of neurons. The outermost cell layer of the retina consists of pigmented epithelial cells resting on the choroid. Three functional layers of neurons extend to the inner limiting membrane of the retina: the outer layer (lying adjacent to the pigmented epithelium) consists of rod and cone receptor cells; the intermediate layer consists of a network of interneurons and bipolar cells which integrate sensory inputs from the receptor cells before transmission to the CNS; the innermost layer comprises the ganglion cells, the cell bodies of afferent axons passing to the CNS in the optic nerve. The fifth functional group of cells are support cells, known as Muller cells, which extend between the outer and inner limiting membranes. The outer limiting membrane merely represents a

dense zone of junctional complexes between Muller cells and the photoreceptor cells. The inner limiting membrane represents the basement membrane separating the bases of the Muller cells from the vitreous body. Rod photoreceptors are long, slender cells. The single dendrite of each cell extends beyond the outer limiting membrane as the rod proper. The rod proper consists of inner and outer segments connected by a thin, eccentric strand (stalk) of cytoplasm containing microtubule doublets similar to those of cilia (but without the inner pair of microtubules). The inner segment contains a prominent Golgi apparatus and many mitochondria. The outer segment has a regular, cylindrical shape and contains a stack of flattened membranous discs which incorporate the visual pigment rhodopsin (visual purple). The rods are ensheathed by cylindrical, cytoplasmic processes extending from the outer pigmented epithelial cells. The membranous discs of the rods are continuously shed from the end of each rod and phagocytized by the pigmented epithelial cells; the discs are continuously replaced from the inner segment of the rod. Cone photoreceptors are similar in basic structure to the rod cells, but they differ in several important details, especially in the outer segment. The outer segment of the receptor proper is a long, conical structure containing membranous invaginations instead of discs. The spaces between the invaginations are continuous with the extracellular environment. The invaginations are not shed like the discs of the rods, although the tips of the cones are invested by processes of pigmented epithelial cells. The cones contain pigments (iodopsin) preferentially receptive to blue, green or red light. The bodies of the cone cells are generally continuous with the inner segment of the cone proper without an intervening dendritic process. The nuclei of cone cells thus form a row of nuclei immediately inside the outer limiting membrane. The dimensions of the rods and cones differ in various parts of the retina as do the numerical proportions of rods and cones, with rods being more numerous and located peripherally, and the cones being located more centrally near the fovea. The photoreceptor cells are connected to the ganglion cells by a variety of bipolar neurons, each of which may synapse with several interneurons in the outer plexiform layer. Similarly, these interneurons may synapse with more than one ganglion cell in the inner plexiform layer. Horizontal cells, with their cell bodies amongst those of the bipolar cells, make lateral connections in the outer plexiform layer between groups of rod and cone receptors. A variety of other interneurons, known as amacrine cells, which lack axons but have numerous dendrites, also have their cell bodies in the bipolar layers; these cells form integrative connections in the inner plexiform layer between the bipolar cells and the ganglion cells. Axons of the ganglion cells form the layer immediately adjacent to the inner limiting membrane; the axons are interspersed with neuroglia similar to those of the CNS. This layer also contains the retinal vascular system derived from the central artery of the optic nerve. Near the fovea, the bipolar cells, interneurons and ganglion cells are pushed laterally to allow the light an unobstructed path to the photoreceptor layer, thus providing the highest visual acuity (due to the decreased refraction of light). The fovea is also devoid of any large blood vessels which could also interfere with light transmission to the photoreceptors. The fovea and surrounding macula are dependant on diffusion from the underlying choroids vessels for their metabolic needs. In order to reach the photoreceptors, photons (light) must pass through blood vessels and several layers of cells and their processes. At the fovea, that part of the retina with the most visual acuity, the inner layers are flattened laterally so as to present less of a barrier to the light reaching the receptor units. In the fovea, the receptors are almost exclusively cones and there is an almost one to one ratio of ganglion cells to photoreceptors. Afferent nerve fibers from the retina converge to form the optic nerve which leaves the eye via numerous perforations through a part of the sclera known as the lamina cribrosa. The retina overlying the lamina cribrosa, the optic papilla (optic disc) is devoid of photoreceptors and is thus referred to as the blind spot.

The optic nerve and retina develop embryologically as an outgrowth of the primitive forebrain. Thus the optic nerve is invested by the meninges. The dura mater becomes continuous with its developmental equivalent, the sclera, while the pia-arachnoid continues into the eye as the uveal layer.

Blood Supply: The blood supply of the eye is derived from the ophthalmic artery via two separate systems, the retinal and uveal systems. The retina is supplied by a central artery passing in the substance of the optic nerve. This central artery of the retina branches from the centre of the optic papilla to give rise to end arteries which radiate over the surface of the retina; this system provides a unique view of the microcirculation when observed with an instrument called the ophthalmoscope. The uvea is supplied by branches of the ophthalmic artery which perforate the sclera. Venous drainage of the eye is through the choroidal vessels (ciliary veins) to the vorticose veins to either the superior or inferior ophthalmic veins, which eventually drain into the cavernous sinus. The scleral venous sinus is a specialized vascular structure encircling the anterior chamber, and is responsible for draining the excess aqueous humor (via the canal of Schlemm) to the venous circulation. Venous drainage of the retina is via the central vein of the retina which normally drains directly into the cavernous sinus (but may join the ophthalmic veins). Miscellaneous: Within the bony orbital cavity, the eye is supported by a loose packing of fatty connective tissue. The exposed surface of the eye is protected by the eyelids. The mucus-secreting epithelium lining the inner surface of the eyelids is reflected at the superior and inferior fornices on to the exposed surface of the sclera and is known as the conjunctiva. The conjunctiva and cornea are moistened and cleansed by watery secretions from the lacrimal gland, a small flattened gland located at the upper lateral aspect of the eye. Modified sebaceous glands and apocrine sweat glands of the eyelid provide a superficial oily layer which inhibits evaporation. Tears drain to the inner aspect of the eye and thence into the nasal cavity via the nasolacrimal duct.

EXTERNAL EARAURICLE Auricle (pinna) - The auricle is composed of elastic cartilage covered by a thin skin extending into the external acoustic meatus. The auricle is held to the skull by ligaments and muscle. The parts of the auricle are: 1. Helix - the rim of the auricle on the superior and posterior free margin. 2. Antihelix - internal to the helix. A semicircular prominence located anterior and inferior to the helix. Its superior portion divides into the crura. 3. Concha Deep fossa anterior to the antihelix. 4. Tragus - Small projection immediately anterior to the external opening of the ear.