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11/10/2016 Anatomy #10 Skull Nour Erekat Farah Behari Views of the skull Objectives: Describe the anterior and posterior views of skull both internally and externally Describe the lateral view of skull both internally and externally Describe the superior and inferior views of skull both internally and externally Describe the base of the skull and its major foramina as well as the structures that pass through them The skull is made up of bones that are grouped into two groups based on the overall structure that they participate in forming. One group consists of the bones that form the cranium (neurocranium). The cranium is the cavity that houses the brain, its different meninges and blood vessels. The other group consists of bones that form the face called facial bones. All cranial bones (frontal, occipital, sphenoid and ethmoid) are single-unpaired, except for two, the parietal and temporal bones. Regarding the facial bones, they are the exact opposite of the cranial bones, 2 are unpaired or single (the mandible and vomer) whereas all the others (nasal, maxillae, zygomatic, lacrimal, palatine, inferior nasal conchae) are paired. Anterior view of the skull The blue bone is the frontal bone There are 2 orbits; each orbit is a cavity called the eye socket and contains the eyeball. The supraorbital margin of the orbit is formed by the frontal bone At the medial third of the supraorbital margin , there is the supraorbital foramen(canal) Supraorbital ridge just above the supraorbital margin there is a ridge called the supraorbital ridge (also called superciliary arch or brow ridge), and in between the two ridges is a flattened part of the frontal bone called the glabella Glabella The frontal air sinuses (one group of the paranasal sinuses) lie deep within the frontal bone, specifically deep to the superciliary ridges. “Sinus≡ airspace” The yellow colored bone is the maxilla. 2 maxillae form the upper jaw. The frontal process of the maxilla ascends upward to articulate with the frontal bone; thereby it’s called the frontal process of the maxilla. Each maxilla exhibits a frontal process so we have two frontal processes of the maxillae. Below the inferior margin of the orbit there is a foramen perforating each maxilla called the infraorbital (below the orbit) foramen. The alveolar arch is the part of the maxilla that descends projecting forward and craving the roots of the different teeth; it is formed by the alveolar processes of the two maxillae. The two maxillae join and articulate in the midline at the intermaxillary (between the two maxillae) suture. The anterior nasal apertures (heart shaped opening) are formed by the lower borders of the nasal bones above and the maxillae below. There are 3 pairs of conchae which are just moony shelves projecting from the lateral wall of the nasal cavity the superior nasal conchae the middle nasal conchae Both middle and superior nasal conchae are part of the ethmoid bone, specifically the lateral mass of the ethmoid bone. The inferior nasal conchae, which are separate facial bones or entities. The nasal cavity is divided into two halves by the nasal septum which is an osteocartilagenous structure. There are two bony parts forming the nasal septum, the perpendicular or vertical plate of the ethmoid bone anteriosuperiorly and the vomer posteroinferiorly. The mandible is mainly divided into: The body of the mandible which has 2 major foramina adjacent to the second premolar teeth and the vertical rami The orange colored bones in the first figure are the zygomatic bones. The zygomatic bone produces the prominence of the cheek. There are two foramina in the zygomatic bone, the zygomaticofacial and the zygomaticotemporal foramina, which are named according to the nerves that they transmit (zygomaticofacial and zygomaticotemporal nerves). The zygomatic bone articulates medially with the maxilla and laterally with the temporal bone. Bridge of the nose This is the image of a real or plastic skull; you must recognize the following: The part of the zygomatic arch formed by the temporal process of the zygomatic bone the frontal bone articulating with the two nasal bones that form the bridge of the nose the anterior nasal apertures leaving into the two halves of the nasal cavity and the septum dividing between them the middle nasal concha which is part of the ethmoid bone and the inferior nasal concha which is a fascial bone 2 maxillae meeting at the intramaxillary suture 2 zygomatic bones and the small part of the zygomatic arch formed by the temporal process of the zygomatic bone the mandible’s horizontal body and two vertical rami Lateral view of the skull The anterosuperior part of the skull if formed by the frontal bone (single-unpaired); the parietal bones (paired) lie posterior to the frontal bone. The parietal bone articulates with the frontal bone at the coronal suture occipital bone posteriorly at the lambdoid suture other parietal bone superiorly in the midline at the sagittal suture The zygomatic bone is articulating with the frontal bone superiorly, maxillae medially and zygomatic process of the temporal bone laterally to form the zygomatic arch. The purple colored bone is the temporal bone which has the following main parts: the temporal squama which is the flat part of the bone the tympanic part that forms the bony part of the auditory tube the styloid process which is the narrow slender process projecting downwards the mastoid process posteriorly the external auditory meatus The mandible: Notice the mandibular notch which separates the coronoid process anteriorly and condylar process posteriorly. The condylar process consists of the head (above the neck) and the neck. The green colored bone is the greater wing of the sphenoid The pterion of the skull is the thinnest and weakest area of the lateral side of the skull. It is where the anteroinferior corner of the parietal bone articulates with the greater wing of the sphenoid. It can also be thought of as the site of articulation of the frontal bone, temporal, parietal, and greater wing of the sphenoid. This area is potential for fractures as it is the weakest area of the skull. The most important point regarding the pterion is that it overlies the anterior division of the middle meningeal artery (a branch of the maxillary artery), so whenever the skull is traumatized laterally resulting in a fracture, the middle meningeal artery ruptures leading to epidural hematoma. Posterior margin of the zygomatic process Zygomatic process of the frontal bone The different parts of the temporal bone as seen laterally: Zygomatic process of the temporal bone articulating with the temporal process of the zygomatic bone forming the zygomatic arch Temporal squama Tympanic plate Mastoid and styloid processes From the posterior margin of the zygomatic process of the frontal bone temporal lines begin and diverge as they arch backward forming two lines, the superior temporal line and the inferior temporal line. Below the inferior temporal line, there is a depression called the temporal fossa. The temporal fossa contains the pterion. The part of the greater wing of the sphenoid below the temporal fossa is called the infratemporal crest of the greater wing of the sphenoid. Below the infratemporal crest there is the infratemporal fossa. In the medial wall of the infratemporal fossa is a downward projecting process of the greater wing of the sphenoid called the pterygoid process; it lies posterior to the maxilla, in between there is a fissure called the pterygomaxillary fissure. Medial to this fissure is the pterygopalatine fossa. (So it can be thought of this way: the pterygomaxillary fissure is the lateral gate or door leading into the pterygopalatine fossa medially.) In the medial wall of the pterygopalatine fossa is a foramen called the sphenopalatine foramen which is the communication between the pterygopalatine fossa and nasal cavity medially. The pterygopalatine fossa is located below the apex of the orbit and posterior to it so you expect it to communicate with the orbit anteriorly to the inferior orbital fissure, now superiorly the sphenopalatine fossa articulates with the medial cranial fossa so the cranial cavity through a foramen called foramen rotundum. Posterior view of the skull The parietal bones articulate with each other in the midline at the sagittal suture and articulate with the posterior occipital bone at the lambdoid suture. The different parts of the occipital bone as seen posteriorly in the midline are: The external occipital protuberance; which is a roughened elevation (prominence) The 2 superior nuchal lines; which extend laterally on either side of the external occipital protuberance towards the temporal bones. The 2 inferior nuchal lines; which are parallel to the superior nuchal lines. Superior view of the skull Whenever you dissect a cadaver using an electric saw you remove the upper part of the skull called the calvarium (calvaria) The calvarium is made up anteriorly of the frontal bone which articulates with the two parietal bones at the coronal suture, and posteriorly of the two parietal bones that articulate at the sagittal suture. Occasionally, the two halves of the frontal bones fail to fuse leaving a midline metopic suture. Inferior view of the skull Posterior nasal aperture The hard palate lies anteriorly. The hard palate is formed by the palatine process of the maxillae anteriorly and the horizontal plate of the palatine bone posteriorly. In the midline anteriorly, there is the incisive foramen and posterolaterally there are the greater and lesser palatine foramina. The two choanae or posterior nasal apertures are located above the posterior edge of the hard palate; they are the site of communication between the nasal cavity and the nasopharynx. These choanae are bordered by the vomer medially, and by the medial pterygoid plate of the sphenoid bone. (Explanation of the pterygoid plate: From the greater wing of the sphenoid projects a downward process called the pterygoid process; the pterygoid process consists of two plates, the medial pterygoid plate and the lateral pterygoid plate) The inferior end of the pterygoid plate is prolonged forming the pterygoid hamulus. Posterolateral to the lateral pterygoid plate is the large oval-shaped foramen called foramen ovale. Posterolateral to the foramen ovale is the foramen spinosoum. Posterolateral to the foramen spinosoum is a small prominence projecting downwards which is the spine of the sphenoid. Anterolaterally on the temporal bone is the mandibular fossa. Anterior to the mandibular fossa there is an articular tubercle. These two structures form the upper articulating surfaces or temporomandibular joint. Posterior to the mandibular fossa is the external auditory meatus and the tympanic plate that forms the bony part of the external auditory meatus. The tympanic plate of the temporal bone has the supranatal crest in the lateral surface of the squamous part of the temporal bone as well as the supranatal triangle and supranatal spine. The squamotympanic fissure separates between tympanic plate posteriorly and the mandibular fossa anteriorly. The medial end of the squamotympanic fissure called the tympani exits or leaves the tympanic cavity. The styloid process: medial to the styloid process is a rocky Portion of the temporal bone called the petrous part of the temporal bone. In the inferior surface of the petrous portion is an opening of the carotid canal called the carotid foramen through which the internal carotid artery passes. At the medial end of the petrous part of the temporal bone is a foramen called foramen lacerum. The foramen lacerum is basically formed between: 1. petrous part of the temporal bone 2. Sphenoid bone. 3. Basilar part of the occipital bone Note: this foramen is covered with fibrous tissue and cartilage during life. Posteriorly, between the petrous part of the temporal bone and the occipital bone is a jugular foramen which is medial to the styloid process and is formed by a deep notch of the petrous part of the temporal bone and a shallower notch on the occipital bone. In this foramen the sigmoid sinus becomes the internal jugular vein, in addition, the glossopharyngeal, vagus and accessory nerves pass through this foramen (9, 10&11 cranial nerves). Parts of the occipital bone: 1. Pharyngeal tubercle which is a small prominence on the undersurface of the basilar part (the most anterior part) of the occipital bone in the midline. This pharyngeal tubercle gives attachment to the raphe of the pharynx; the pharyngeal raphe is where the tendons of the constrictor muscles of the pharynx (superior, middle and inferior) insert. There are also the two occipital condyles where the tendons of constrictor muscles of the pharynx (superior, middle, inferior) insert. 2. Occipital condyles articulate with the superior aspect of the lateral masses of the first cervical vertebra (atlas); the two occipital condyles are on either side of the foramen magnum. There is the foramen magnum in the inferior part of the bone; within this foramen the medulla oblongata connects with the spinal cord and the vertebral arteries, spinal arteries and accessory (XI) nerve pass. Superior to the foramen magnum is the external occipital protuberance which is the most prominent projection of the posterior surface of the bone. The two superior nuchal lines extend laterally from the protuberance. 3. Hypoglossal canal is superior to the occipital condyle and it is for transmission of the hypoglossal nerve. 4. External occipital protuberance is posterior to the foramen magnum in the midline. . Base of the skull The calvarium is the skullcap (top of the cranial cavity-roof of the skull) while the vault of the skull is the inner space of the cranium occupied by the brain. When you remove the calvaria, you can see the floor of the cranial cavity which is referred to as the base of the skull. The base of the skull is basically a depression that is divided into 3 cranial fossae which lie at three different levels (anterior, middle and posterior). The neurocranium is the braincase of the skull; it is divided into the base and the calvarium. The calvarium can be used alternatively with the vault of the skull which is the space in the skull within the neurocranium occupied by the brain 1. The anterior cranial fossa: the highest and most anterior The orbital plate of the frontal bone form its floor In the midline, there are two structures: the crista gali which is an upward projection of the ethmoid bone and the cribriform (perforated) plate through which the fibers of the olfactory never (cranial nerve 1) pass. 2. The middle cranial fossa is posterior to the anterior fossa and is separated from it by the lesser wings of the sphenoid bone It looks like a butterfly with a narrow middle portion formed by the body of the sphenoid bone and two lateral expansions formed by the greater wings of the sphenoid bone it’s also made up of parts of the temporal and parietal bones In the greater wing there is the optic canal which transmits the optic nerve and ophthalmic artery (a branch of internal carotid artery) separating the lesser wing from the greater is the superior orbital fissure (transmits the superior ophthalmic artery) There is the foramen rotundum (transmits the maxillary division of the trigeminal nerve), posterolateral to it is the foramen ovale (transmits the mandibular division of the trigeminal nerve-cranial nerve #5) and finally foramen spinosum (transmits the middle meningeal artery). The Superior orbital fissure transmits the superior ophthalmic nerve. 3. The posterior cranial fossa which is the most posterior, largest and deepest fossa It is separated from the middle cranial fossa by the petrous part of the temporal bone In this fossa is the internal acoustic (auditory) meatus which transmits the 7th and 8th cranial nerves Edited by: Cyrine katanani