Anatomy of the skull Dr Rania Gabr

Objectives List the bones of the skull Identify the major sutures of the skull Identify the major surface markings of the skull Identify the major foramina in the skull List the major structures which pass through the foramina Describe the cranial fossa and its part Understand the base of the skull and its fracture Describe the structure of the mandible

The Skull It consists of flat and irregular bones It is divided into: Cranial bones which encase the brain (Neurocranium) Facial bones which form the bones of the face (Viscerocranium)

The Skull Cranial bones include: Facial bones include: (Neurocranium) Frontal 1 Ethmoid 1 Sphenoidal 1 Occipital 1 Parietal 2 Temporal 2 Facial bones include: (Viscerocranium) Maxilla 2 Zygomatic 2 Nasal 2 Palatine 2 Lacrimal 2 Inferior conchae 2 Vomer 1 Mandible 1

The Skull Frontal Maxilla Zygomatic Nasal Mandible Lacrimal z

The Skull Parietal Temporal Squamous Mastoid Styloid Tympanic Petrous Sphenoid Greater wing Lesser wing Pterygoid process Body Occipital

The Skull Petrous part of temporal Lesser wing of sphenoid Body of sphenoid Pterygoid process Ethmoid bone Crista galli Cribriform plate Perpendicular plate Vomer Palatine bone

Frontal Bone Landmarks: Squama: flat portion that forms the forehead Supraorbital margin: ridge under the eyebrow, forming the upper part of the orbit (eye socket) Supraorbital foramen: small hole within supraorbital margin for blood vessels and nerves Frontal sinuses: hollow spaces behind the squama, act as sound chambers to give the voice resonance.

Frontal Bone (Anterior View) (Blue Colored Bone)

Frontal Bone (Lateral View) (Blue Colored Bone)

Temporal bone

Temporal bone Landmarks: Squama: flat portion of the temporal bone forming the anterior and superior part of the temple Zygomatic process: process forming part of the cheek Petrous portion: internal,between the sphenoid and occipital, forming part of the floor of the cranium. Contains the ear canal and internal ear structures. Mandibular fossa: socket between squama and petrous portion, articulates with the condyle of the mandible (TMJ) External auditory meatus: opening to the ear canal Mastoid process: bony prominence behind the external auditory meatus Styloid process: looks like an elephant’s tusk located between the mastoid process and the jaw. Acts as a point of attachment for muscles and ligaments.

Temporal Bone (Lateral View) (Purple Colored Bone)

Occiput Landmarks: Foramen magnum: large hole, allowing passage of the spinal cord External occipital protuberance (EOP): prominent projection on back of occiput Nuchal lines: a superior and inferior line running laterally from the midline, serve as a point of muscle attachment

Occipital Bone (Lateral View) (Orange Bone)

Occipital Bone (Posterior View) (Orange Colored Bone)

Sphenoid Bone

Sphenoid bone Landmarks A prominent, irregular, wedge-shaped bone at the base of the skull. The sphenoid bone has been called the "keystone" of the cranial floor since it is in contact with all of the other cranial bones. Landmarks Greater wings: large lateral projections of bone that help to form the lateral border of the skull Lesser wings: smaller lateral projections of bone above the greater wings Pterygoid processes: two long downward projections from the greater wings that act as a point of muscle attachment. Sella turcica: known as the Turkish Saddle which cradles the pituitary gland.

Sphenoid Bone (Lateral View) (Green Colored Bone)

Sphenoid Bone (Floor of Cranium) (Green Colored Bone)

Ethmoid Bone An irregularly shaped, spongy bone that provides the floor of the front part of the skull and the roof of the nasal cavity. The ethmoid consists of two masses of thin plates enclosing air cells and looks like a sieve. Landmarks: Lateral masses: form most of the wall between the nasal cavity and the orbits Perpendicular plate: forms the superior portion of the nasal septum Cribriform plate: forms the roof of the nasal cavity Olfactory foramina: small holes within the cribriform plate for passage of the first cranial nerve (for smell)

Crista galli: upward extension of bone above the cribriform plate, acts as an anchoring point for one of the coverings of the brain. ( Falx cerebi) Nasal conchae (turbinates): two scroll-shaped projections (superior and middle) with a mucus membrane on either side of the nasal septum. Function to cause air turbulence and trap inhaled particles.

Bones of the face Maxilla The second largest bones of the face, after the mandible and form, by their union, the whole of the upper jaw. They hold the upper teeth, and connect on the left and right to the zygomatic bones (cheek bones). Each assists in forming the boundaries of three cavities, namely, the 1-roof of the mouth, 2-the floor and lateral wall of the nose, and 3- the floor of the orbit.

Maxilla

Landmarks: Infra Orbital foramen: hole below the orbit, for blood vessels and nerves Alveolar process: arch of the maxilla containing the upper teeth Palatine process: horizontal projection of the maxilla forming the anterior ¾ of the hard palate.

Zygomatic Bones Commonly referred to as the cheekbone. It is situated at the upper and lateral part of the face: it forms the prominence of the cheek and part of the lateral wall and floor of the orbit. It articulates with the zygomatic arch of the temporal bone.

Vomer One of the unpaired facial bones of the skull. Located in the midsagittal line, and attaches to the sphenoid, the ethmoid, the left and right palatine bones, and the left and right maxillary bones.

Inferior Nasal Conchae Extends horizontally along the lateral wall of the nasal cavity and consists of a lamina of spongy bone, curled upon itself like a scroll. Inferior Nasal Conchae

Smallest and most fragile bone of the face, is situated at the front part of the Medial of the orbit. Contains the lacrimal sac and the naso-lacrimal duct. Lacrimal Bones Lacrimal bone

Nasal Bones Varying in size and form in different individuals They are placed side by side at the middle and upper part of the face and form, by their junction, "the bridge" of the nose

Cranial Fossa It is the cavity of the skull Divides into: Anterior cranial fossa Middle cranial fossa Posterior cranial fossa

Anterior Cranial Fossa Formed of: Orbital plate of frontal bone Cribriform plate of ethmoid Crista galli Lesser wing of sphenoid Occupied by: Frontal lobe of the cerebrum Optic nerves Olfactory bulb and tract

Middle Cranial Fossa Formed of: Greater wing of sphenoid Body of sphenoid Squamous part of temporal bone Anterior part of petrous bone It occupied by: Temporal lobe of the cerebrum

Posterior Cranial Fossa Formed of: Sphenoid part of clivus Posterior part of petrous bone Occipital bone It shows the following land marks: Groove for transverse sinus Groove for sigmoid sinus Internal occipital protuberance It is occupied by: Cerebellum Brain stem

Base of The Skull Most of the bones are seen in other views

Foramina of the Skull Foramina are found within the skull bones They vary in size and shape They transmit nerves, blood vessels and dura matter

Foramina of the Skull

Foramina of the Skull Supraorbital Infraorbital Mental

The following must be identified: Nasion Inion Bregma Lambda External occipital protuberance Parietal eminence Zygomatic arch

Sutures of the Skull Sutures are fibrous joints articulating the skull bones They include: Coronal Sagittal Lambdoid Pterion

Skull Fontanelles Fontanelles are spaces between some of the skull bones of infants. They permit easy growth of the brain. They permit overlapping of skull bones during labor. They include: 1. Anterior Fontanelle Lies between Frontal and Parietal Bones Closed by 18 months of age 2. Posterior Fontanelle Lies between Parietal and Occipital Bones Closed by end of 1st year 3. Anterolateral Fontanelle 4. Posterolateral Fontanelle

The Mandible It is a flat bone Identify the following: Head(condylar process) Mandibular notch Coronoid process Ramus Angle Body Mylohyoid line Submandibular fossa Digastric fossa Mandibular foramen Mental foramen

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