The Skull: Overview, Structure, and Anatomical Relations

The Skull **1. Overview and Function of the Head** - **Location**: The most cranial region of the body, supported by the **cervical vertebrae**. - **Function**: - Houses the **brain**, **sense organs** (vision, hearing, balance, smell, taste). - Contains the initial...

The Skull **1. Overview and Function of the Head** - **Location**: The most cranial region of the body, supported by the **cervical vertebrae**. - **Function**: - Houses the **brain**, **sense organs** (vision, hearing, balance, smell, taste). - Contains the initial portions of the **alimentary** and **respiratory** systems (oral and nasal cavities). - Provides attachment for facial and neck muscles. **2. Structure of the Cranium** **A. Divisions of the Cranium** **1. Neurocranium (Brain Box)** - Forms the **superior and dorsal part** of the cranium. - **Function**: Protects the **brain**, **meninges**, and sense organs (vision, hearing, balance). - **Composition**: Eight bones: - **Unpaired (median) bones**: - Frontal. - Ethmoid. - Sphenoid. - Occipital. - **Paired bones**: - Parietal. - Temporal. - **Subdivision**: - **Calvaria (cranial vault)**: - Formed by the **frontal**, **parietal**, **sphenoid**, **temporal**, and **occipital bones**. - Composed of flattened, squamous portions. - **Cranial Base**: - Includes parts of the **ethmoid**, **frontal**, **sphenoid**, **temporal**, and **occipital bones**. - **Boundary**: A plane connecting the **glabella** (between the supraciliary arches) to the **external occipital protuberance**. **2. Viscerocranium (Facial Skeleton)** - Forms the **inferior and ventral part** of the cranium. - **Function**: Houses the **oral cavity**, **nasal cavities**, and **paranasal sinuses**, along with the organs of **taste** and **smell**. - **Composition**: 14 bones: - **Paired bones**: - Nasal. - Lacrimal. - Maxilla. - Zygomatic. - Palatine. - Inferior nasal concha (turbinate). - **Unpaired bones**: - Vomer. - Mandible. - **Bone Types**: - **Irregular bones**: Maxilla, mandible, palatine, zygomatic, and inferior nasal concha. - **Flat bones**: Nasal, lacrimal, and vomer. **B. Continuity and Articulations** - The neurocranium and viscerocranium are **continuous** and articulate through: - **Synarthroses**: Immovable joints that unite the bones into a single structure. - **Temporomandibular Joints (TMJs)**: The only **synovial joints** of the cranium, allowing movement of the mandible (a key feature of mammals). **3. Characteristics of Cranial Bones** **A. Flat Cranial Bones** - Found in both the neurocranium and viscerocranium. - **Structure**: - **Two compact bone tables** (internal and external). - Separated by a spongy layer called **diploë**. - **Internal Table Features**: - Contains **vascular sulci** for blood vessels. - **Digitate impressions** correspond to the gyri of the brain. Frontal view of the cranium - The **frontal view of the cranium** (anterior or facial view) highlights: - Most of the **viscerocranium** (facial skeleton). - The anterior and superior portion of the **neurocranium**, mainly the **frontal bone**. **1. Major Components of the Frontal View** **A. Frontal Bone (Neurocranium)** - **Squamous Part**: - Forms the **forehead** and the superior boundary of the frontal view. - **Frontal Tuber (Eminence)**: Rounded prominence on each side of the forehead. - **Supraorbital Margin**: Marks the upper boundary of the **orbital cavities**. - Contains the **supraorbital notch or foramen**, transmitting the **supraorbital nerve and vessels**. - **Supraciliary Arches**: Bony ridges above the orbital margins, prominent laterally. - **Glabella**: Smooth midline prominence between the supraciliary arches. - **Sutures**: - **Frontonasal Suture**: Between the **frontal bone** and **nasal bones**. - **Frontomaxillary Suture**: Between the **frontal bone** and the **frontal process of the maxilla**. - **Fronozygomatic Suture**: Between the **frontal bone** and the **zygomatic bone**. **B. Nasal Bones and Piriform Aperture (Viscerocranium)** - **Nasal Bones**: - Located between the orbital cavities. - Joined by the **internasal suture**, forming the superior portion of the **piriform aperture** (nasal cavity entrance). - **Piriform Aperture**: - Bony opening of the nasal cavity. - **Borders**: - **Superiorly**: Delimited by the **nasal bones**. - **Laterally and Inferiorly**: Formed by the **maxillae**. - **Inferior Midline**: Interrupted by the **anterior nasal spine**, a bony projection of the maxilla. **C. Maxillae** - **Body of the Maxillae**: - Forms the lateral and inferior portions of the piriform aperture. - **Infraorbital Foramen**: Located below the orbit; transmits the **infraorbital nerve and vessels**. - **Canine Fossa**: Depression lateral to the infraorbital foramen, above the canine tooth. - **Palatine Processes**: - Contribute to the **floor of the piriform aperture** and the **roof of the oral cavity**. - Joined medially by the **intermaxillary suture** (inferior to the anterior nasal spine). - **Alveolar Processes**: - House the roots of the upper teeth (**maxillary dental arcade**). - **Alveolar Yokes**: Bony ridges over the roots of the teeth. - **Incisive Fossa**: Depression in the alveolar process near the central incisors. **D. Zygomatic Bones** - Form the **cheek prominences** and lateral walls of the orbits. - Articulate with: - **Maxilla** via the **zygomaticomaxillary suture**. - **Frontal Bone** via the **frontozygomatic suture**. **E. Mandible** - Located inferiorly, below the maxillae. - **Parts of the Mandible in the Frontal View**: - **Alveolar Part**: - Houses the roots of the lower teeth (**mandibular dental arcade**). - Protrusions correspond to tooth roots, similar to the maxilla. - **Mental Foramen**: - Located laterally on the mandible, near the premolars. - Transmits the **mental nerve and vessels**. - **Mandibular Symphysis**: - Median ridge marking the fusion of the two halves of the mandible during development. - Continues inferiorly as the **mental protuberance**, forming the chin. - **Oblique Line**: - Begins laterally from the mental foramen and extends upward, forming the base of the coronoid process. **2. Anatomical Relations in the Frontal View** **A. Neurocranium and Viscerocranium Connections** - The **frontal bone** of the neurocranium articulates with the bones of the viscerocranium at key sutures: - **Frontonasal Suture** (frontal + nasal bones). - **Frontomaxillary Suture** (frontal + maxillae). - **Fronozygomatic Suture** (frontal + zygomatic bones). **B. Orbit and Surrounding Structures** - The **orbital cavities** dominate the central portion of the frontal view. - **Supraorbital Foramen/Notch** (superiorly). - **Infraorbital Foramen** (inferiorly, maxilla). **C. Nasal and Oral Regions** - The **piriform aperture** and **nasal bones** mark the superior and central portions of the nasal region. - The **alveolar processes** of the maxillae and mandible define the **oral region**, including the dental arcades and associated fossae and foramina. Superior view of the cranium - The **calvaria** (cranial vault) appears **convex** in the superior view, with a smooth, dome-like shape. - Composed of: - **Anteriorly**: Squamous part of the **frontal bone**. - **Laterally**: Paired **parietal bones**. - **Posteriorly**: Squamous part of the **occipital bone**. **2. Cranial Bones and Sutures** **A. Cranial Bones** 1. **Frontal Bone (Squamous Part)**: - Forms the anterior portion of the calvaria. 2. **Parietal Bones**: - Located laterally, these paired bones dominate the central region of the calvaria. - Feature the **parietal tubers (eminences)**, slight bulges where the bone is thickest. 3. **Occipital Bone (Squamous Part)**: - Forms the posterior portion of the calvaria. - Contains the **external occipital protuberance**, a palpable bony prominence at the lower point of the superior view. **B. Sutures** The cranial bones are interconnected by **jagged, dentate sutures**, which provide strength and stability: 1. **Coronal Suture**: - Between the **frontal bone** and the **parietal bones**. 2. **Sagittal Suture**: - Lies on the **midline**, connecting the two **parietal bones**. - The **vertex**, the highest point of the calvaria, is located approximately halfway along this suture. 3. **Lambdoid Suture**: - Joins the **parietal bones** with the **occipital bone**. **3. Key Landmarks** **A. Vertex** - The **vertex** is the **highest point** of the calvaria. - Located on the **sagittal suture**, midway between the coronal and lambdoid sutures. **B. Parietal Foramina** - Small openings near the **parietal tubers (eminences)**, situated on either side of the sagittal suture. - Allow passage of **emissary veins**, which connect the scalp\'s venous system to the cranial venous sinuses. **C. External Occipital Protuberance** - A prominent bony **relief** on the occipital bone. - Marks the **lowest point** visible from the superior view of the calvaria. - Palpable externally through the skin. Lateral view of the cranium - The **lateral surface** of the cranium includes: - **Neurocranium**: Formed by the **frontal**, **parietal**, **temporal**, **occipital**, and **sphenoid bones**. - **Viscerocranium**: Formed by the **zygomatic bone**, **maxilla**, and **mandible**. - **Key Functional Areas**: - The **temporal fossa**, housing the temporalis muscle. - The **zygomatic arch**, connecting the neurocranium and viscerocranium. - The **mandible**, which articulates with the temporal bone at the **temporomandibular joint (TMJ)**. **1. Anatomical Features of the Lateral Cranium** **A. Temporal Region and Temporal Fossa** 1. **Superior Temporal Line**: - Originates from the **zygomatic process of the frontal bone**. - Extends posteriorly to the **asterion** (junction of the parietal, temporal, and occipital bones). - Separates the **calvaria** from the **cranial base**. 2. **Temporal Fossa**: - A shallow depression inferior to the superior temporal line. - **Boundaries**: - **Anteriorly**: Posterior border of the **zygomatic bone**. - **Inferiorly**: **Zygomatic arch** and **infratemporal crest** of the greater wing of the sphenoid. - **Contents**: Houses the **temporalis muscle**, its nerves, and vessels. - Communicates with the **infratemporal fossa** below the zygomatic arch. **B. Zygomatic Arch and Associated Structures** - **Zygomatic Arch**: - Formed by the **temporal process of the zygomatic bone** and the **zygomatic process of the temporal bone**. - Provides an attachment site for the **masseter muscle**. - **Zygomatic Bone**: - Positioned **anteriorly to the temporal fossa**. - Contributes to the **cheek prominence** and the **lateral wall of the orbital cavity**. **C. Mandible** - **Ramus of the Mandible**: - Superior border gives rise to: - **Coronoid Process**: Covered by the zygomatic arch; insertion for the **temporalis muscle**. - **Condylar Process**: Articulates with the temporal bone at the **TMJ**. - **Masseteric Tuberosity**: - Roughened area on the ramus, located superior to the **angle of the mandible**. - Provides attachment for the **masseter muscle**. - **Body of the Mandible**: - Extends forward and curves upward into the **alveolar process**, housing the lower teeth. - Contains the **mental foramen** near the premolars, which transmits the **mental nerve and vessels**. **D. Other Key Features of the Lateral View** **1. Neurocranium** - **External Acoustic Meatus**: - Opening in the **temporal bone** for the passage of sound waves into the ear. - **Mastoid Process**: - Located posterior to the external acoustic meatus. - Serves as an attachment point for neck muscles (e.g., **sternocleidomastoid**). **2. Viscerocranium** - **Orbital Cavity**: - Opens anteriorly, bordered by the **zygomatic bone** and **maxilla**. - Contains the structures of the eye and associated vessels and nerves. - **Maxilla**: - **Body of the Maxilla**: Forms the lateral and inferior borders of the orbital cavity. - **Alveolar Process**: Houses the upper teeth. **2. Key Anatomical Landmarks** **A. Sutures** - The lateral view showcases sutures connecting the bones of the cranium: - **Coronal Suture**: Between the frontal and parietal bones. - **Squamous Suture**: Between the parietal and temporal bones. - **Lambdoid Suture**: Between the parietal and occipital bones. **B. Craniometric Points** - **Asterion**: - Junction of the parietal, temporal, and occipital bones. - Marks the posterior termination of the superior temporal line. **C. Bony Openings** - **Mental Foramen**: On the mandible, near the premolars, for passage of the **mental nerve and vessels**. - **External Acoustic Meatus**: Opening in the temporal bone for the ear canal. **3. Functional Relevance** **A. Muscle Attachments** - The **temporal fossa** and **zygomatic arch** provide anchor points for the **temporalis** and **masseter muscles**, critical for mastication. **B. Temporomandibular Joint (TMJ)** - Formed by the **condylar process** of the mandible and the **temporal bone**. - Dysfunction in the TMJ can lead to jaw pain, limited motion, and clicking sounds. Inferior view of cranium: - **Inferior Projection**: Displays both neurocranial and viscerocranial structures. - **Three Regions**: - **Anterior Region**: From the incisors to the posterior border of the bony palate. - **Middle Region**: From the posterior palate to the anterior margin of the foramen magnum. - **Posterior Region**: From the foramen magnum to the external occipital protuberance. **1. Anterior Region** **A. Maxillae and Bony Palate** - **Maxillary Dental Arcade**: Houses the upper teeth. - **Bony Palate**: Formed by: - **Palatine Processes of the Maxillae**. - **Horizontal Plates of the Palatine Bones**. - **Sutures**: - **Cruciform Suture**: Intersection of the **median palatine suture** and **transverse palatine suture**. **B. Foramina and Features** - **Incisive Fossa**: Contains the **incisive foramina**, openings for the **nasopalatine nerve** and vessels. - **Greater Palatine Foramen**: Located posteriorly, allows passage of the **greater palatine nerve and vessels**. - **Lesser Palatine Foramina**: Openings in the **pyramidal process** of the palatine bone, transmitting **lesser palatine nerves and vessels**. **C. Lateral Structures** - **Zygomatic Process of the Maxilla** and **Zygomatic Bone**: - Contribute to the **zygomatic arch**, articulating with the **zygomatic process of the temporal bone**. **2. Middle Region** **A. Sphenoid and Pterygoid Processes** - **Pterygoid Processes of the Sphenoid**: - **Medial Plate**: Extends into the **pterygoid hamulus**. - **Lateral Plate**: Forms part of the **infratemporal fossa**. - **Pterygoid Fossa**: Space between the medial and lateral plates. - **Choanae**: Posterior nasal openings, bordered by: - Medially: **Vomer** (articulating with the sphenoid). - Laterally: **Medial Plates of the Pterygoid Processes**. - Inferiorly: **Horizontal Plates of the Palatine Bones**. **B. Foramina and Openings** - **Foramen Ovale**: Passage for the **mandibular nerve (V3)**. - **Foramen Spinosum**: Passage for the **middle meningeal artery**. - **Foramen Lacerum**: Closed by fibrocartilage in living subjects. - **Carotid Canal**: Entrance of the **internal carotid artery**. - **Stylomastoid Foramen**: Exit for the **facial nerve (CN VII)**. - **Jugular Foramen**: Passage for: - **Internal jugular vein**. - **Glossopharyngeal nerve (CN IX)**, **vagus nerve (CN X)**, and **accessory nerve (CN XI)**. **C. Temporal Bone Structures** - **Mandibular Fossa**: Articulation site for the **condylar process** of the mandible. - Divided by the **tympanosquamous fissure**, which transmits the **chorda tympani**. - **External Acoustic Meatus**: Opening for the ear canal. - **Styloid Process**: Attachment for muscles and ligaments. **3. Posterior Region** **A. Occipital Bone and Foramen Magnum** - **Foramen Magnum**: - Allows passage of: - **Medulla oblongata**. - **Vertebral arteries**. - **Accessory nerve (spinal root)**. - **Pharyngeal Tubercle**: On the basilar part, attachment for the **pharyngobasilar fascia**. **B. External Occipital Features** - **External Occipital Protuberance**: Prominent midline projection. - **Nuchal Plane**: - Divided by the **inferior nuchal line** and bounded superiorly by the **superior nuchal line**. - Provides attachment for muscles of the neck and back. **C. Temporal Bone and Occipital Condyles** - **Mastoid Process**: - Contains the **mastoid notch**, attachment for the **digastric muscle**. - **Jugular Process**: - Stabilizes the occipital condyle. - **Occipital Condyles**: Articulate with the **atlas (C1)**, forming the atlanto-occipital joint. Occipital view of the cranium - The **occipital view** (posterior view) of the cranium reveals the structures of the **neurocranium**, particularly: - The **occipital bone** (squamous part). - Posterior portions of the **parietal bones**. - The **mastoid processes** of the **temporal bones**. **1. Key Features of the Occipital View** **A. Sutures and Craniometric Point** 1. **Sagittal Suture**: - Runs along the midline, separating the **parietal bones**. 2. **Lambdoid Suture**: - Arches posteriorly, connecting the **parietal bones** to the **occipital bone**. 3. **Lambda**: - Craniometric point marking the intersection of the **sagittal** and **lambdoid sutures**. **B. External Surface of the Occipital Bone** 1. **External Occipital Protuberance**: - A prominent midline projection on the squamous part of the occipital bone. - Serves as an attachment site for the **nuchal ligament** and other soft tissues. 2. **External Occipital Crest**: - Descends from the external occipital protuberance to the **foramen magnum**. - Provides attachment for the **nuchal ligament**. 3. **Nuchal Lines**: - **Superior Nuchal Line**: - Extends laterally from the external occipital protuberance. - Divides the squamous part into: - **Occipital Plane**: Superior to the line. - **Nuchal Plane**: Inferior to the line. - Serves as an attachment site for neck muscles (e.g., **trapezius**). - **Inferior Nuchal Line**: - Runs parallel to the superior nuchal line, crossing the **external occipital crest**. - Further subdivides the **nuchal plane** into four portions. **C. Mastoid Processes of the Temporal Bones** - Located laterally, these bony projections serve as attachment points for the **sternocleidomastoid** and other neck muscles. **2. Functional Relevance** **A. Muscle Attachments** - The **superior** and **inferior nuchal lines** provide anchorage for muscles critical to head and neck movements, such as: - **Trapezius**. - **Sternocleidomastoid**. - **Splenius capitis**. Intercranial surface of the cranial bone - The **intracranial surface of the cranial base** forms the floor of the cranial cavity. - Divided into **three cranial fossae**, aligned in an anteroposterior and superoinferior plane: 1. **Anterior Cranial Fossa**: Most superior, supports the frontal lobes. 2. **Middle Cranial Fossa**: Intermediate, supports the temporal lobes and pituitary gland. 3. **Posterior Cranial Fossa**: Most inferior, houses the cerebellum, brainstem, and associated structures. **1. Anterior Cranial Fossa** **A. Boundaries and Floor** - **Anterior Boundary**: Orbital part of the frontal bone. - **Posterior Boundary**: Free edge of the **lesser wings of the sphenoid** and the **prechiasmatic sulcus** of the sphenoid body. - **Floor Composition**: - **Frontal Bone**: Orbital parts forming the roof of the orbits. - **Ethmoid Bone**: Cribriform plate and crista galli. - **Sphenoid Bone**: Body and lesser wings. **B. Key Features and Openings** 1. **Frontal Bone**: - **Foramen Cecum**: Located near the frontal crest, transmits an emissary vein connecting the nasal cavity to the superior sagittal sinus. 2. **Ethmoid Bone**: - **Cribriform Plate**: Perforated with numerous foramina for the **olfactory nerves (CN I)**, transmitting sensory signals from the nasal cavity. - **Crista Galli**: Vertical projection anchoring the **falx cerebri**, a dural fold. 3. **Sphenoid Bone**: - **Anterior Clinoid Processes**: Medial projections of the lesser wings, providing attachment for the **tentorium cerebelli**. - **Ethmoidal Foramina** (Anterior and Posterior): Passage for ethmoidal vessels and nerves connecting the anterior cranial fossa with the orbit. **2. Middle Cranial Fossa** **A. Boundaries and Floor** - **Anterior Boundary**: Lesser wings of the sphenoid. - **Posterior Boundary**: Superior border of the petrous part of the temporal bone and the dorsum sellae. - **Floor Composition**: - **Sphenoid Bone**: Body and greater wings. - **Temporal Bone**: Petrous and squamous parts. **B. Key Features and Openings** **1. Central Structures** - **Sella Turcica (Turkish Saddle)**: - Houses the **pituitary gland** within the **hypophysial fossa**. - **Dorsum Sellae**: Posterior ridge of the sella, separating the middle and posterior fossae. - **Prechiasmatic Sulcus**: Groove anterior to the sella, holding the optic chiasm. - **Optic Canal**: - Located at the termination of the prechiasmatic sulcus. - Transmits the **optic nerve (CN II)** and the **ophthalmic artery** to the orbit. - **Carotid Sulcus**: - Lateral groove on the body of the sphenoid, housing the **internal carotid artery** within the **cavernous sinus**. - **Foramen Lacerum**: - Found at the junction of the sphenoid and temporal bones. Filled with fibrocartilage in life, it is not a true passageway. **2. Lateral Structures** - **Foramina of the Greater Wing of the Sphenoid**: - **Foramen Rotundum**: Transmits the **maxillary nerve (CN V2)** to the pterygopalatine fossa. - **Foramen Ovale**: Transmits the **mandibular nerve (CN V3)**, accessory meningeal artery, and lesser petrosal nerve. - **Foramen Spinosum**: Passage for the **middle meningeal artery**, vein, and meningeal branch of the mandibular nerve. - **Superior Orbital Fissure**: - Between the greater and lesser wings. - Transmits the **oculomotor nerve (CN III)**, **trochlear nerve (CN IV)**, **abducens nerve (CN VI)**, **ophthalmic nerve (CN V1)**, and ophthalmic veins to the orbit. **3. Temporal Bone Structures** - **Trigeminal Impression**: Depression on the petrous part for the **trigeminal ganglion**. - **Hiatus for Greater and Lesser Petrosal Nerves**: Grooves for parasympathetic nerve fibers. - **Tegmen Tympani**: Thin bony plate forming the roof of the middle ear cavity. **3. Posterior Cranial Fossa** **A. Boundaries and Floor** - **Anterior Boundary**: Posterior edge of the dorsum sellae and superior petrous ridge. - **Posterior Boundary**: Internal occipital protuberance. - **Floor Composition**: - **Occipital Bone**: Basilar part, cerebellar fossae, and clivus. - **Temporal Bone**: Petrous part and mastoid region. **B. Key Features and Openings** **1. Foramen Magnum** - Largest opening, allowing passage of: - **Medulla oblongata**. - **Vertebral arteries**. - **Accessory nerve (spinal root)**. - **Dural veins**. **2. Venous Grooves** - **Transverse Sinus Groove**: Extends laterally from the internal occipital protuberance. - **Sigmoid Sinus Groove**: Leads to the **jugular foramen**, carrying venous blood to the internal jugular vein. **3. Temporal Bone Openings** - **Internal Acoustic Meatus**: Transmits the **facial nerve (CN VII)** and **vestibulocochlear nerve (CN VIII)**. - **Jugular Foramen**: Passage for the **glossopharyngeal (CN IX)**, **vagus (CN X)**, and **accessory nerves (CN XI)**, as well as the internal jugular vein. - **Hypoglossal Canal**: Transmits the **hypoglossal nerve (CN XII)**. Orbital cavity - The orbital cavities are **quadrangular pyramids**: - **Base**: The orbital opening faces anteriorly. - **Walls**: Four surfaces (roof, floor, medial, lateral). - **Apex**: Posterior tip where the **optic canal** opens into the middle cranial fossa. - **Orientation**: The major axes of the orbits are directed forward and laterally, with the superior margin of the orbital opening anterior to the inferior and medial margins. **1. Boundaries of the Orbital Opening** **A. Superior Margin (Supraorbital Margin)** - Formed by the **frontal bone**: - **Squamous part** (middle). - **Zygomatic process** (lateral). - **Nasal part** (medial). - Contains the **supraorbital notch** (or **supraorbital foramen**) for the **supraorbital nerve and vessels**. **B. Inferior Margin (Infraorbital Margin)** - Formed by the **body of the maxilla** (medially) and the **zygomatic bone** (laterally). **C. Medial Margin** - Formed by the **frontal process of the maxilla**. **D. Lateral Margin** - Composed of the **zygomatic bone** and the **zygomatic process of the frontal bone**. **2. Walls of the Orbital Cavity** **A. Roof (Superior Wall)** - Formed by: - **Orbital part of the frontal bone** (anteriorly). - **Lesser wings of the sphenoid** (posteriorly). - Features: - **Fossa for the Lacrimal Gland**: Lateral depression housing the lacrimal gland. - **Anterior and Posterior Ethmoidal Foramina**: Connect the orbit to the anterior cranial fossa, allowing passage of ethmoidal vessels and nerves. **B. Floor (Inferior Wall)** - Formed by: - **Orbital surface of the maxilla** (anteriorly). - **Orbital process of the perpendicular plate of the palatine bone** (posteriorly). - **Orbital surface of the zygomatic bone** (laterally). - Features: - **Infraorbital Groove and Canal**: Transmits the **infraorbital nerve and vessels**. - Lies above the **maxillary sinus**, making it susceptible to fractures and infections. **C. Medial Wall** - Formed by: - **Frontal process of the maxilla**. - **Lacrimal bone** (forming the groove for the **lacrimal sac**). - **Orbital plate of the ethmoidal labyrinth** (posteriorly). - **Lesser wing of the sphenoid** (posteriorly). - Features: - **Nasolacrimal Canal**: Drains tears from the lacrimal sac into the nasal cavity. **D. Lateral Wall** - Formed by: - **Frontal bone** (superiorly). - **Zygomatic bone** (anteriorly). - **Greater wing of the sphenoid** (posteriorly). - Features: - **Zygomatico-Orbital Foramen**: Transmits the **zygomatic nerve**. - **Superior Orbital Fissure**: Separates the lateral wall from the roof **3. Apex of the Orbit** - The apex of the orbital cavity is located posteriorly and contains: - **Optic Canal**: Transmits the **optic nerve (CN II)** and the **ophthalmic artery** from the middle cranial fossa to the orbit. **4. Fissures and Foramina** **A. Superior Orbital Fissure** - Located between the **lesser** and **greater wings of the sphenoid**. - Transmits: - **Cranial Nerves**: - **Oculomotor (CN III)**. - **Trochlear (CN IV)**. - **Abducens (CN VI)**. - **Ophthalmic Nerve (V1)** (branch of the trigeminal nerve). - **Ophthalmic Veins**. **B. Inferior Orbital Fissure** - Located between the **maxilla** and the **greater wing of the sphenoid**. - Transmits: - **Zygomatic Nerve** (branch of V2). - **Infraorbital Nerve** and vessels. - Provides access to the **pterygopalatine** and **infratemporal fossae**. **C. Zygomatico-Orbital Foramen** - Located in the lateral wall of the orbit. - Transmits the **zygomatic nerve** (branch of V2). **D. Infraorbital Foramen** - Continuation of the infraorbital canal, transmits the **infraorbital nerve and vessels** to the face. **6. Relations of the Orbital Cavity** - **Medial**: Nasal cavity. - **Superior**: Anterior cranial fossa. - **Inferior**: Maxillary sinus. - **Posterior**: Middle cranial, pterygopalatine, and infratemporal fossae. Nasal cavity - The **nasal cavities**: - **Function**: First part of the respiratory system and location of the olfactory organ. - **Shape**: Triangular prisms with anterior (piriform aperture) and posterior openings (choanae). - **Boundaries**: - **Superior**: Anterior cranial fossa. - **Inferior**: Oral cavity. - **Medial**: Nasal septum. - **Lateral**: Orbital cavities, maxillary sinuses, and pterygopalatine fossae. **1. Boundaries of the Nasal Cavities** **A. Nasal Septum (Medial Wall)** - **Composition**: - **Perpendicular Plate of the Ethmoid** (superior part). - **Vomer** (inferior and posterior parts). - **Septal Nasal Cartilage** (anterior part). - Divides the nasal cavity into **right and left halves**, which are often asymmetrical. **B. Roof (Vault)** - Formed by: - **Nasal Bones** (anteriorly). - **Nasal Spine of the Frontal Bone**. - **Cribriform Plate of the Ethmoid**: Perforated for the **olfactory nerves (CN I)**. - **Body of the Sphenoid** and **Alae of the Vomer** (posteriorly). - **Sphenoidal Sinus** opens at the anterior surface of the body of the sphenoid. **C. Floor** - Formed by: - **Palatine Processes of the Maxillae** (anterior two-thirds). - **Horizontal Plates of the Palatine Bones** (posterior third). - **Features**: - **Nasal Crest**: Along the midline, formed by the maxillae and palatine bones. - **Incisive Canals**: Connect the nasal cavities to the oral cavity. **D. Lateral Wall** - **Composition** (anterior to posterior): - **Frontal Process of the Maxilla**. - **Lacrimal Bone**: Forms the groove for the **lacrimal sac** (drains tears into the **nasolacrimal duct**). - **Medial Surface of the Ethmoidal Labyrinth**: Includes the **superior** and **middle nasal conchae**. - **Body of the Maxilla**. - **Inferior Nasal Concha** (independent bone). - **Perpendicular Plate of the Palatine Bone**. - **Medial Plate of the Pterygoid Process of the Sphenoid**. **2. Openings of the Nasal Cavities** **A. Anterior Opening (Piriform Aperture)** - **Boundaries**: - Superiorly: **Nasal Bones**. - Laterally and Inferiorly: **Nasal Notches of the Maxillae**. - Inferiorly: **Anterior Nasal Spine**. **B. Posterior Openings (Choanae)** - **Boundaries**: - Superiorly: Inferior surface of the **sphenoid body** and **alae of the vomer**. - Laterally: **Medial Plate of the Pterygoid Process**. - Inferiorly: **Horizontal Plate of the Palatine Bone**. - Medially: **Posterior Border of the Vomer**. **3. Nasal Conchae (Turbinates) and Meatuses** **A. Nasal Conchae (Turbinates)** - Projections from the lateral wall into the nasal cavity: 1. **Superior Nasal Concha**: Part of the **ethmoidal labyrinth**. 2. **Middle Nasal Concha**: Part of the **ethmoidal labyrinth**. 3. **Inferior Nasal Concha**: Independent bone. **B. Meatuses** - Spaces beneath each nasal concha: - **Superior Meatus**: - Opens into the **posterior ethmoidal cells**. - **Middle Meatus**: - Receives drainage from: - **Frontal Sinus**. - **Maxillary Sinus**. - **Anterior and Middle Ethmoidal Cells**. - Key Features: - **Ethmoidal Infundibulum**: Pathway connecting the frontal sinus and anterior ethmoidal cells. - **Uncinate Process**: Partly closes the maxillary sinus opening. - **Ethmoidal Bulla**: A prominent ethmoidal cell superior to the infundibulum. - **Inferior Meatus**: - Receives the opening of the **nasolacrimal duct**. **C. Sphenoethmoidal Recess** - Located above and behind the **superior nasal concha**. - Opens into the **sphenoidal sinus** and contains the **sphenopalatine foramen** (passage for vessels and nerves from the pterygopalatine fossa). **D. Common Meatus** - Medial space between the nasal conchae and the nasal septum. **4. Relations of the Nasal Cavities** - **Medial**: Nasal septum. - **Lateral**: Orbital cavities and maxillary sinuses. - **Superior**: Anterior cranial fossa. - **Inferior**: Oral cavity. - **Posterior**: Pharynx, pterygopalatine fossa, and infratemporal fossa. Joints and ligaments of the cranium **1. Cranial Synarthroses** **A. Types of Synarthroses** 1. **Serrate Sutures** (Interlocking edges): - **Coronal Suture**: Between the frontal and parietal bones; inferior part forms the **limbous suture**. - **Sagittal Suture**: Between the two parietal bones. - **Lambdoid Suture**: Between the parietal and occipital bones; also called the **denticulate suture**. - **Metopic Suture** (variably present): Between the two primordia of the frontal bone, typically fusing in early childhood. 2. **Squamous Suture** (Overlapping edges): - Between the parietal bone and the squamous part of the temporal bone; inferiorly, it transitions into a **limbous suture**. 3. **Plane Sutures** (Flat edges): - Found between most bones of the **viscerocranium**. 4. **Schindylesis**: - Specialized joint between the **alae of the vomer** and the **sphenoidal rostrum**. **B. Synchondroses** - **Spheno-occipital Synchondrosis**: - Cartilaginous joint between the body of the sphenoid and the basilar part of the occipital bone. - Becomes a **synostosis** (bony fusion) in adulthood. **C. Gomphoses (Dentoalveolar Syndesmoses)** - Specialized fibrous joints anchoring teeth in the **dental alveoli** of the maxilla and mandible. **2. Temporomandibular Joint (TMJ)** **A. Overview and Structure** - A **synovial condylar joint**, allowing movements of the mandible relative to the cranium. - **Unique Features**: - Lined with **fibrocartilage** rather than hyaline cartilage. - Divided into two compartments by an **articular disc**. - The **right and left TMJs** always move in coordination. **B. Articulating Surfaces** **1. Temporal Bone** - **Articular Surface**: - **Articular Tubercle**: Saddle-shaped and located anterior to the mandibular fossa. - **Mandibular Fossa**: Divided into three continuous planes: - **Posterior Inclined Plane**: Extends to the articular eminence. - **Preglenoid Plane**: Flat region anterior to the articular eminence. - **Entoglenoid Process**: Medial structure forming the medial glenoid plane. **2. Mandibular Head (Condylar Process)** - **Ellipsoidal shape**: - Major axis: 15--20 mm (posterior-medial orientation). - Minor axis: 8--10 mm. - The axes of both mandibular heads converge posteriorly at an angle of **145--160°** near the basion. **C. Articular Disc** - **Fibrocartilaginous structure** dividing the joint cavity into: - **Superior Temporodiscal Compartment**: Allows gliding movements. - **Inferior Condylodiscal Compartment**: Allows hinge movements. - **Attachments**: - Adheres to the joint capsule at its periphery. - Secured to the mandibular head by **medial** and **lateral ligaments**. - Posteriorly anchored by **superior** and **inferior plates**, separated by a venous plexus that acts as a shock absorber. **D. Joint Capsule and Ligaments** 1. **Joint Capsule**: - Superior attachment: From the articular tubercle to the petrotympanic fissure. - Inferior attachment: Around the neck of the mandible. 2. **Reinforcing Ligaments**: - **Temporomandibular Ligament (Lateral Ligament)**: - Most important; consists of two bundles: - **Superficial Oblique Bundle**: Oriented at 70° to the horizontal plane, from the articular tubercle to the neck of the mandible. - **Deep Horizontal Bundle**: From the lateral pole of the mandibular head to the neck of the mandible. 3. **Accessory Ligaments**: - **Stylomandibular Ligament**: From the **styloid process** to the posterior margin of the ramus and angle of the mandible. - **Sphenomandibular Ligament**: From the **spine of the sphenoid** to the **lingula of the mandible**. **E. Movements of the TMJ** - **Hinge Movements**: Opening and closing of the mouth. - **Gliding Movements**: Protrusion, retraction, and lateral displacement. - **Coordination**: Dysfunction in one TMJ affects the other due to their anatomical and functional linkage.