OSTEOLOGY The Skull

The Skull The skull is divided into two parts: Neurocranium The skull is divided into two parts: Neurocranium- which forms a protective case or “vault” around the brain Viscerocranium- which forms the anterior part of the skull including the orbits, nasal cavities and upper/lower jaw bones Viscerocranium 11/22/2018

The Skull Parietal coronal suture Frontal Occipital Temporal Sphenoid 11/22/2018

The Skull Lacrimal Nasal Zygomatic Maxilla Inferior Nasal Conchae Mandible maxilla Nasal Inferior conchae Vomer Lacrimal Nasal Zygomatic Maxilla Inferior Nasal Conchae Mandible Vomer 11/22/2018

Frontal Bone Squamous (flat) portion forms the skeleton of the forehead Fontal bone forms the roof of the orbit Nasion is an area where the frontal bone intersects with the nasal bones Glabella- smooth, slightly depressed area located just superior to the nasion Frontal Bone Frontal bone Nasion Glabella Squamous portion Glabella Nasion Orbital portion 11/22/2018

Frontal Bone Supraorbital margin- marks the boundary between the squamous and orbital portions Supraorbital notch or foramen is for the passage of the supraorbital nerve and vessels A prominent ridge just superior to the supraorbital margin is the superciliary arch (more pronounced in males) Zygomatic process of the frontal bone articulates with the zygomatic bone Supraorbital notch Superciliary arch Zygomatic process Supraorbital margin 11/22/2018

Zygomatic Bones Cheek bones Forms a portion of the lateral wall of the orbit Frontal Process of the zygomatic bone articulates with the frontal bone Temporal process of the zygomatic bone articulates with the temporal bone Zygomaticofacial foramen- small foramen for passage of the zygomaticofacial nerve Frontal process Temporal Zygomaticofacial foramen 11/22/2018

Maxillae Forms the upper jaw Alveolar processes of the maxillae includes the sockets and supporting bone for the maxillary teeth Maxillae form the floor of the orbit Large infraorbital foramen for passage of the infraorbital nerve & vessels Surrounds most of the pear-shaped piriform aperture Infraorbital foramen Alveolar process Piriform aperture Maxilla 11/22/2018

Maxillae Frontal processes of the maxillae articulates with the frontal bone Zygomatic processes of the maxillae articulates with the zygomatic bones Anterior nasal spine- sharp prominence at inferior aspect of the piriform aperture Intermaxillary suture- site where the two maxilla are united in the median plane frontal process Anterior nasal spine Intermaxillary suture Zygomatic 11/22/2018

Seen within the piriform aperture are the scrolled middle nasal conchae (part of the ethmoid bone) & the inferior nasal conchae Vomer bone along with the perpendicular plate of the ethmoid bone which together form the bony nasal septum can also be identified with the piriform aperture Vomer Middle & Inferior concha Perpendicular plate 11/22/2018

Mandible U-shaped bone with alveolar process that houses the mandibular teeth Mental foramen- located inferior to 2nd premolar for passage of the mental nerve and vessels Mental protuberance- a triangular elevation of bone that forms the prominence of the chin Mental tubercle- located just lateral to the protuberance Body is the horizontal portion Ramus is the vertical portion Ramus Body Mental foramen Mental protuberance Alveolar process 11/22/2018

Lateral Aspect of the Skull Osteology Lateral Aspect of the Skull

Lateral Aspect of the Skull 1. 4. 2. 3. 6. 9. 8. 10. 5. 7. Parietal bone Frontal bone Occipital bone Temporal bone Sphenoid bone Mandible Zygomatic bone Maxillae Lacrimal bone Nasal bone 11/22/2018

Parietal Bones Paired bones that form the lateral & superior cranium Temporal Lines- mark the attachment site of the temporalis muscle & fascia Articulates with frontal bone via coronal suture Articulates with occipital bone via lambdoid suture Pterion-site where 4 cranial bones articulate-important clinical implications Parietal Coronal suture Lambdoid suture Temporal lines pterion 11/22/2018

Temporal Bones Paired bones that form the inferior lateral aspect of skull Temporal bone is described as having a flat squamous portion and a mastoid process (site of attachment of several muscles) Zygomatic arch extends anteriorly to articulate with the zygomatic bone Mastoid process Zygomatic arch Squamous 11/22/2018

Temporal Bones External acoustic meatus Styloid process External acoustic meatus (ear canal) and the pointed styloid process are considered to be located the tympanic portion of the temporal bone Styloid process serves as the attachment site for several muscles and the stylohyoid ligament 11/22/2018

Temporal Bones Mandible and a portion of the zygomatic arch removed in this view Located on the inferior aspect of the arch is a small bony protrusion- articular tubercle that is important in the mechanics of the TMJ Mandibular fossa- deep recess that accepts the condyle of the mandible-also important region of the TMJ Articular tubercle Mandibular fossa 11/22/2018

Zygomatic bone Forms major portion of the cheek Temporal process Frontal process Zygomatic arch Zygomaticofacial foramen Forms major portion of the cheek Temporal process that articulates with the the zygomatic arch Frontal process that articulates with the frontal bone Zygomaticofacial foramen – small foramen generally visible 11/22/2018

Occipital Bone Forms the posterior aspect of the skull Articulates with the parietal bone via the lambdoid suture Prominent palpable elevation located posteriorly is the external occipital protuberance Lambdoid suture External Occipital protuberance 11/22/2018

Sphenoid Bone Irregular shaped bone that forms a portion of the orbit, lateral aspect of skull and a portion of the cranial base Sphenoid can be divided into 4 parts: Greater wing Lesser wing Pterygoid processes Body Some portions of the sphenoid can only be seen inside the cranial cavity Sphenoid Bone 11/22/2018

4 portions of Sphenoid Bone Portion of zygomatic arch and mandible removed in this view Greater wing articulates with the temporal, parietal & frontal bones at the pterion Pterygoid processes are two thin plates of bone that serve as attachment sites for muscles Pterygoid hamulus-small hook of bone extending from the medial pterygoid plate- tensor veli palatini tendon courses around this Greater wing Pterygoid process hamulus 11/22/2018

Maxillae Portion of zygomatic arch and mandible removed in this view Posterior aspect of the maxillae is referred to as the tuberosity of maxillae Small alveolar foramina for the posterior superior alveolar nerves & vessels Pterygomaxillary fissure-tear-drop shaped fissure between the sphenoid and tuberosity of the maxillae Pterygopalatine fossa is a small but important space located medial to the fissure Pterygomaxillary Fissure Alveolar foramen Tuberosity of maxilla 11/22/2018

Lateral Aspect of Skull Nasal bone can also identified as it articulates with the frontal bone and the maxillae Lacrimal bone- which houses the lacrimal sac van be identified within the orbit Prominent anterior nasal spine at the inferior aspect of the piriform aperture Nasal spine bone Lacrimal bone 11/22/2018

Mandible Angle Condylar process Coronoid Condylar process is located at the superior part of the ramus and involved in the articulation of the mandible with the temporal bone (TMJ) Coronoid process is located just anterior and serves as the attachment site for the temporalis muscle Angle of mandible is between the ramus and body 11/22/2018

Mandible Condylar Process Mandibular foramen Coronoid process Infant Coronoid process Mylohyoid line Lingula Ramus Alveolar Part (crest) Mental foramen Body 11/22/2018

Mandible Mandibular notch Condylar process Ramus Body Mental spines Bone loss due to tooth loss 11/22/2018

Calvaria Bregma Emissary foramen- small, inconsistent (not always present) foramina for passage of emissary veins Bregma- is the landmark formed by the intersection of the sagittal & coronal sutures Lambda-is the landmark formed by the intersection of the sagittal & lambdoid sutures Coronal suture Sagittal suture Emissary foramen Lambdoid suture Lambda 11/22/2018

Calvaria Inferior aspect of the skull cap presents several features: Vascular grooves for branches of the middle meningeal artery Granular Foveolae- pits formed by arachnoid granulations (site of CSF transfer) Groove for the superior sagittal sinus-large venous channel within the dura mater Diploe- cancellous bone containing red marrow Groove for superior sagittal sinus Grooves for middle meningeal artery Diploe Granular foveolae 11/22/2018

Superior & Lateral Aspects Infant Skull Superior & Lateral Aspects

Infant Skull Bones forming the calvaria & some parts of the cranial base develop by intramembranous ossification Whereas-most parts of the cranial base develop by endochondral ossification Bones in the infant skull are separated by areas of fibrous tissue membranes- the fontanelles: Anterior Posterior Mastoid sphenoidal Anterior Posterior Mastoid Sphenoidal 11/22/2018

Infant Calvaria Anterior Fontanelle (soft spot) is the future site of the bregma By about 18-24 months- the surrounding bones fuse together and is no longer palpable Posterior Fontanelle is triangular and marks the future site of the lambda Fusion of surrounding bones occurs by about 12 months Anterior fontanelle Posterior Fontanelles- membranous gaps (soft spots) in skull that permit growth 11/22/2018

Infant Skull Mastoid & sphenoidal fontanelles fuse early in infancy Palpation of fontanelles during infancy enables physicals to determine: Growth progress of the frontal & parietal bones Degree of hydration of the infant (a depressed fontanelle indicates dehydration) Level of intracranial pressure-bulging fontanelle indicates increased pressure on the brain Anterior Posterior Mastoid Sphenoidal 11/22/2018

External Aspect of the Cranial Base Osteology External Aspect of the Cranial Base

Cranial Base Inferior aspect of the skull presents six different bones: Palatine processes of the maxillae Palatine bone Sphenoid bone Vomer Temporal Occipital bone Numerous foramina can also be identified 1 2 3 4 5 6 11/22/2018

Cranial Base- Palate Hard palate is formed by the palatine processes of the maxillae and the horizontal plates of the palatine bone Small prominence projecting posteriorly form the hard palate in the median plane is the posterior nasal spine Palatine processes Horizontal plate of the Palatine bone Posterior nasal spine 11/22/2018

Cranial Base- Palate Posterior to the central incisors is a small depression-incisive fossa with a pair of canals- incisive canals for the passage of the nasopalatine nerves Posterolaterally are the greater & lesser palatine foramen for passage of the nerves & vessels of the same name Incisive canals Greater and Lesser Palatine foramina 11/22/2018

Cranial Base-Vomer Vomer-thin, flat unpaired bone in the midline that forms a major portion of the bony nasal septum On either side of the vomer are two large openings- choanae (posterior nasal apertures) Vomer Choanae 11/22/2018

Cranial Base- Sphenoid Three parts of the sphenoid bone can be appreciated on the inferior aspect of skull: Greater wing Medial pterygoid plate Lateral pterygoid plate Pterygoid fossa is between the two pterygoid plates Greater wing Medial pterygoid plate Lateral pterygoid plate 11/22/2018

Cranial Base- Sphenoid Foramen ovale for passage of the mandibular division (V3) of the trigeminal nerve Foramen spinosum- for passage of the middle meningeal artery Groove for the pharyngotympanic (auditory) tube lies medial to spinosum Foramen ovale Auditory Tube-groove Foramen spinosum 11/22/2018

Cranial Base- Temporal Mastoid process- prominence located posteriorly on the temporal bone Mastoid serves as the attachment site for the SCM and posterior belly of the digastric muscles External acoustic meatus (EAM) is located just anterior to the mastoid EAM Mastoid process 11/22/2018

Cranial Base- Temporal Styloid process- thin bony process extending inferior & anteriorly Styloid serves as attachment site for numerous muscles & ligaments Mandibular fossa- articular surface that accepts the condyle of the mandible forming the TMJ Mandibular fossa Styloid process 11/22/2018

Cranial Base- Temporal Two important foramen can be identified on the inferior aspect of the temporal bone: Stylomastoid foramen- located between the mastoid & styloid processes is a small foramen for the passage of the facial nerve (CN VII) Carotid canal- passage for the internal carotid artery into the cranial cavity Carotid canal Stylomastoid foramen 11/22/2018

Cranial Base- Occipital 1 2 3 Foramen magnum Occipital bone forms the posterior and inferior aspects of the skull Foramen Magnum- a large foramen for passage of the spinal cord Foramen magnum divides the occipital bone into 3 parts: Basilar Region Condylar Region Squamous Region 11/22/2018

Cranial Base- Occipital Pharyngeal tubercle Foramen lacerum Basilar portion presents a small tubercle- pharyngeal tubercle for attachment of the pharyngeal constrictors Foramen lacerum (jagged-shaped) is located lust lateral to the basilar portion 11/22/2018

Cranial Base- Occipital Condylar portion presents the occipital condyles that articulate with the atlas Jugular foramen- large foramen between the occipital & temporal bones for passage of cranial nerves: IX, X, XI and the internal jugular vein Hypoglossal canal for passage of the hypoglossal nerve (CN XII) Jugular foramen Hypoglossal canal Occipital condyle 11/22/2018

Cranial Base- Occipital Squamous portion presents the palpable external occipital protuberance Superior & inferior nuchal lines project laterally and are sites for muscular attachments Superior & inferior nuchal lines External occipital protuberance 11/22/2018

Internal Aspect of the Cranial Base Osteology Internal Aspect of the Cranial Base

Cranial Base Internal aspect of the cranial base is divided into three major regions or fossae: Anterior cranial fossa Middle cranial fossa Posterior cranial fossa These three fossae lie at different levels and form the bowl-shaped floor of the cranial cavity Anterior cranial fossa Middle cranial fossa Posterior cranial fossa 11/22/2018

Anterior Cranial Fossa Ethmoid Frontal lobes of the brain occupies the anterior cranial fossa Fossa is formed by the: Orbital portion of the frontal bone Ethmoid bone in the middle Lesser wing of the sphenoid Orbital portion of the frontal bone Lesser wing of the sphenoid 11/22/2018

Anterior Cranial Fossa Frontal crest- a median bony extension from the frontal bone Foramen cecum is located at the base of the crest and is a small foramen for passage a vessels during development Crista galli- ridge of bone projecting superiorly from the ethmoid bone and serves as the attachment for the cerebral falx Frontal crest Crista galli Foramen cecum 11/22/2018

Anterior Cranial Fossa On either side of the crista galli is a “sievelike” Cribriform plate for passage of the olfactory axons into the cranial cavity Optic canal for passage of the optic nerve (CN II) and the ophthalmic artery can be appreciated within the lesser wing of the sphenoid Cribriform plate Optic canal 11/22/2018

Middle Cranial Fossa Temporal lobes of the brain occupy the middle cranial fossa Fossa is formed by the: Greater wing of the sphenoid Squamous portion of the temporal bone Petrous portion of the temporal bone Greater wing of sphenoid Squamous portion temporal bone Petrous portion temporal bone 11/22/2018

Middle Cranial Fossa Sella turcica- the saddle-like bony formation located on the superior aspect of the body of the sphenoid Sella turcica is surrounded by anterior & posterior clinoid processes Sella turcica Anterior and Posterior clinoids 11/22/2018

Middle Cranial Fossa Sella turcica is composed of three parts: Hypophyseal fossa Tuberculum sellae Dorsum sellae Sella turcica is composed of three parts: Hypophyseal fossa (pituitary fossa) Tuberculum sellae (saddle horn) Dorsum Sellae (back of the saddle) Sella turcica- essentially houses and guards the pituitary gland 11/22/2018

Middle Cranial Fossa Middle cranial fossa presents five important foramina: Superior orbital fissure for passage of CN’s III, IV, V1 & VI & ophthalmic veins Foramen rotundum which transmits the maxillary nerve (V2) Foramen ovale- which transmits the mandibular nerve (V3) Superior orbital fissure Foramen rotundum Foramen ovale 11/22/2018

Middle Cranial Fossa Foramen spinosum which transmits the middle meningeal artery Foramen lacerum- nothing is transmitted vertically thru this foramen although the internal carotid artery and some nerves pass across the foramen horizontally Grooves for the greater & lesser petrosal nerves are located along the anterior slope of the petrous portion of the temporal bone Foramen spinosum Petrosal grooves Foramen lacerum 11/22/2018

Middle Cranial Fossa Petrous portion of the temporal bone houses the middle and inner ear cavities Arcuate eminence- marks the roof of the anterior semicircular canal of the inner ear cavity Trigeminal impression is located just anteromedial the eminence-which marks the location of the sensory ganglion of the trigeminal nerve Trigeminal impression Arcuate eminence 11/22/2018

Posterior Cranial Fossa The largest & deepest of the three fossae Cerebellum, pons and medulla occupy the posterior fossa Formed mainly by the occipital bone and the petrous & mastoid portions of the temporal bone Occipital bone Temporal bone Petrous portion 11/22/2018

Posterior Cranial Fossa Clivus marks the anterior portion of the occipital bone Foramen magnum- large foramen that marks the transition from the medulla to the spinal cord Posterior to the foramen magnum is the internal occipital crest and internal occipital protuberance clivus Occipital crest Internal occipital protuberance 11/22/2018

Posterior Cranial Fossa Broad grooves show the horizontal course of the transverse and S-shaped sigmoid sinuses (both dural venous sinuses) Sigmoid sinus empties into the large jugular foramen which also transmits several cranial nerves: Glossopharyngeal (CN IX) Vagus (CN X) Accessory (CN XI) Jugular foramen Groove for the Sigmoid sinus Transverse Sinus groove 11/22/2018

Posterior Cranial Fossa Internal acoustic meatus is located just anterosuperior to the jugular foramen Internal acoustic meatus transmits the facial nerve (CN VII) and vestibulochochlear nerve (CN VIII) along with the labyrinthine artery Hypoglossal canal for the hypoglossal nerve (CN XII) lies superior to the margin of the foramen magnum Internal acoustic meatus Hypoglossal canal 11/22/2018

Superior Orbital Fissure CN III, IV, V1 & VI Cribrifrom plate-CN I Optic Canal CN II Superior Orbital Fissure CN III, IV, V1 & VI Hypoglossal Canal CN XII Jugular Foramen- CN IX, X and XI Internal Acoustic Meatus- CN VII & VIII Foramen Rotundum- CN V2 Foramen Ovale-CN V3 11/22/2018

Osteology of the Orbit Seven bones articulate to make each orbit: 1 2 3 4 5 7 medial lateral superior inferior Seven bones articulate to make each orbit: Frontal Zygomatic Maxillary Lacrimal Ethmoid Palatine Sphenoid 6 11/22/2018

Osteology of the Orbit Optic canal- transmits the optic nerve and ophthalmic artery Superior orbital fissure- transmits CN III, IV, V1 & VI Inferior orbital fissure & groove- transmits the infraorbital vessels & nerve Anterior & posterior ethmoidal foramina- transmits vessels & nerves with same name Inferior orbital fissure & groove Optic canal Superior fissure Ethmoidal foramina 11/22/2018