OSTEOLOGY The Skull The Skull 1 2 The

OSTEOLOGY The Skull

The Skull • 1. 2. 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 Neurocranium Viscerocranium 10/20/2021 2

The Skull Frontal coronal suture Parietal Occipital Temporal Sphenoid 10/20/2021 3

The Skull Lacrimal Nasal Zygomatic Nasal Maxilla Inferior Nasal Conchae Inferior maxilla Nasal conchae Vomer 10/20/2021 Vomer Mandible 4

Frontal Bone • Squamous (flat) portion forms the skeleton of the forehead Frontal Bone Squamous portion • Fontal bone forms the roof of the orbit Nasion Frontal bone Glabella Nasion • Nasion is an area where the frontal bone intersects with the nasal bones Orbital portion • Glabella- smooth, slightly depressed area located just superior to the nasion 10/20/2021 5

Frontal Bone • Supraorbital marginmarks 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 10/20/2021 Supraorbital notch Superciliary arch Zygomatic process Supraorbital margin 6

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- Zygomaticofacial small foramen for passage of the foramen 10/20/2021 zygomaticofacial nerve Frontal process Temporal process 7

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 Infraorbital foramen Alveolar process Piriform aperture Maxilla • Surrounds most of the pear -shaped piriform aperture 10/20/2021 8

Maxillae • Frontal processes of the maxillae articulates with the frontal bone • Zygomatic processes of the maxillae articulates with the zygomatic bones • Anterior nasal spinesharp prominence at inferior aspect of the piriform aperture frontal process • Intermaxillary suturesite where the two maxilla are united in the median plane Zygomatic process 10/20/2021 Anterior nasal spine Intermaxillary suture 9

• 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 10/20/2021 Perpendicular plate Middle & Inferior concha Vomer 10

Mandible • U-shaped bone with alveolar process that houses the mandibular teeth • Mental foramen- located inferior to 2 nd 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 Alveolar process • Ramus is the vertical portion 10/20/2021 Ramus Body Mental foramen Mental protuberance 11

Osteology Lateral Aspect of the Skull 10/20/2021 12

Lateral Aspect of the Skull 1. Parietal bone 2. Frontal bone 3. Occipital bone 4. Temporal bone 5. Sphenoid bone 6. Mandible 7. Zygomatic bone 8. Maxillae 9. Lacrimal bone 10. Nasal bone 10/20/2021 1. 2. 9. 5. 4. 10. 3. 7. 8. 6. 13

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 Coronal suture Temporal lines Parietal Lambdoid suture • Articulates with occipital bone via lambdoid suture • Pterion-site where 4 cranial bones articulateimportant clinical implications 10/20/2021 pterion 14

Temporal Bones • • • Paired bones that form the inferior lateral aspect of skull Squamous 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 10/20/2021 Mastoid process Zygomatic arch 15

Temporal Bones • 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 External acoustic meatus Styloid process 10/20/2021 16

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 protrusionarticular tubercle that is important in the mechanics of the TMJ • Mandibular fossa- deep recess that accepts the condyle of the mandiblealso important region of the TMJ 10/20/2021 Articular tubercle Mandibular fossa 17

Zygomatic bone • Forms major portion of the cheek • Temporal process that articulates with the zygomatic arch Zygomatic arch Frontal process • Frontal process that articulates with the frontal bone • Zygomaticofacial foramen – small foramen generally visible 10/20/2021 Zygomaticofacial foramen Temporal process 18

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 10/20/2021 Lambdoid suture External Occipital protuberance 19

Sphenoid Bone • • 1. 2. 3. 4. • 10/20/2021 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 20

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 Greater wing • 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 10/20/2021 Pterygoid hamulus Pterygoid process 21

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 Alveolar the maxillae foramen • Pterygopalatine fossa is a small but important space located medial to the fissure 10/20/2021 Pterygomaxillary Fissure Tuberosity of maxilla 22

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 Lacrimal bone Nasal bone • Prominent anterior nasal Nasal spine at the inferior aspect spine of the piriform aperture 10/20/2021 23

Mandible • 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 10/20/2021 Condylar process Coronoid process Angle 24

Mandible Condylar Process Mandibular foramen Infant Coronoid process Mylohyoid line Lingula Ramus Alveolar Part (crest) Mental foramen Body 10/20/2021 25

Mandible Mandibular notch Condylar process Ramus Body Mental spines Bone loss due to tooth loss 10/20/2021 26

Calvaria • 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 Bregma Coronal suture Sagittal suture Emissary foramen Lambda 10/20/2021 Lambdoid suture 27

Calvaria • Inferior aspect of the skull cap presents several Diploe 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 10/20/2021 Grooves for middle meningeal artery Granular foveolae Groove for superior sagittal sinus 28

Infant Skull Superior & Lateral Aspects 10/20/2021 29

Infant Skull • Bones forming the calvaria & some parts of the cranial base develop by Anterior 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 Sphenoidal • Posterior • Mastoid • 10/20/2021 sphenoidal Posterior Mastoid 30

Infant Calvaria • Anterior Fontanelle (soft spot) is the future site of the bregma • By about 18 -24 monthsthe 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 10/20/2021 Fontanelles- Anterior fontanelle Posterior fontanelle 31 membranous gaps (soft spots) in skull that permit growth

Infant Skull • Mastoid & sphenoidal fontanelles fuse early in infancy • Palpation of fontanelles during infancy enables physicals to determine: 1. Growth progress of the frontal & parietal bones 2. Degree of hydration of the infant (a depressed fontanelle indicates dehydration) 3. Level of intracranial pressure-bulging fontanelle indicates increased pressure on the brain 10/20/2021 Anterior Sphenoidal Posterior Mastoid 32

Osteology External Aspect of the Cranial Base 10/20/2021 33

Cranial Base • 1. 2. 3. 4. 5. 6. • 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 10/20/2021 1 2 3 4 5 6 34

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 10/20/2021 Palatine processes Horizontal plate of the Palatine bone Posterior nasal spine 35

Cranial Base- Palate • Posterior to the central incisors is a small depression-incisive fossa with a pair of canalsincisive canals for the passage of the nasopalatine nerves Incisive canals Greater and Lesser Palatine foramina • Posterolaterally are the greater & lesser palatine foramen for passage of the nerves & vessels of the same name 10/20/2021 36

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) 10/20/2021 Vomer Choanae 37

Cranial Base- Sphenoid • Three parts of the sphenoid bone can be appreciated on the inferior aspect of skull: 1. Greater wing 2. Medial pterygoid plate Greater wing Lateral pterygoid plate Medial pterygoid plate 3. Lateral pterygoid plate • Pterygoid fossa is between the two pterygoid plates 10/20/2021 38

Cranial Base- Sphenoid • • • Foramen ovale for passage of the mandibular division (V 3) of the trigeminal nerve Foramen ovale Auditory Tube-groove Foramen spinosum- for passage of the middle meningeal artery Groove for the pharyngotympanic (auditory) tube lies medial to spinosum 10/20/2021 Foramen spinosum 39

Cranial Base- Temporal • Mastoid processprominence 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 10/20/2021 EAM Mastoid process 40

Cranial Base- Temporal • Styloid process- thin bony process extending inferior & anteriorly • Styloid serves as attachment site for numerous muscles & ligaments Mandibular fossa Styloid process • Mandibular fossaarticular surface that accepts the condyle of the mandible forming the TMJ 10/20/2021 41

Cranial Base- Temporal • Two important foramen can be identified on the inferior aspect of the temporal bone: Carotid canal • Stylomastoid foramenlocated between the mastoid & styloid Stylomastoid 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 10/20/2021 42

Cranial Base- Occipital • 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: 1. Basilar Region 2. Condylar Region 3. Squamous Region 10/20/2021 1 2 Foramen magnum 3 43

Cranial Base- Occipital • • Basilar portion presents a small tuberclepharyngeal tubercle for attachment of the pharyngeal constrictors Foramen lacerum (jagged-shaped) is located lust lateral to the basilar portion 10/20/2021 Foramen lacerum Pharyngeal tubercle 44

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 Jugular foramen Occipital condyle Hypoglossal canal for passage of the hypoglossal nerve (CN XII) 10/20/2021 45

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 10/20/2021 46

Osteology Internal Aspect of the Cranial Base 10/20/2021 47

Cranial Base • Internal aspect of the cranial base is divided into three major regions or fossae: 1. Anterior cranial fossa 2. Middle cranial fossa 3. Posterior cranial fossa 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 10/20/2021 48

Anterior Cranial Fossa Ethmoid • Frontal lobes of the brain occupies the anterior cranial fossa • Fossa is formed by the: 1. Orbital portion of the frontal bone 2. Ethmoid bone in the middle 3. Lesser wing of the sphenoid 10/20/2021 Orbital portion of the frontal bone Lesser wing of the sphenoid 49

Anterior Cranial Fossa • Frontal crest- a median bony extension from the frontal bone Crista galli • 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 10/20/2021 Frontal crest Foramen cecum 50

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 Cribriform plate Optic canal for passage of the optic nerve (CN II) and the ophthalmic Optic canal artery can be appreciated within the lesser wing of the sphenoid 10/20/2021 51

Middle Cranial Fossa • Temporal lobes of the brain occupy the middle cranial fossa • Fossa is formed by the: 1. Greater wing of the sphenoid 2. Squamous portion of the temporal bone 3. Petrous portion of the temporal bone 10/20/2021 Greater wing of sphenoid Squamous portion temporal bone Petrous portion temporal bone 52

Middle Cranial Fossa • Sella turcica- the saddlelike bony formation located on the superior aspect of the body of the sphenoid • Sella turcica is surrounded by anterior & posterior clinoid processes 10/20/2021 Sella turcica Anterior and Posterior clinoids 53

Middle Cranial Fossa • Sella turcica is composed of three parts: 1. Hypophyseal fossa (pituitary fossa) 2. Tuberculum sellae (saddle horn) 3. Dorsum Sellae (back of the saddle) • Tuberculum sellae Hypophyseal fossa Dorsum sellae Sella turcica- essentially houses and guards the pituitary gland 10/20/2021 54

Middle Cranial Fossa • Middle cranial fossa presents five important foramina: 1. Superior orbital fissure for passage of CN’s III, IV, V 1 & VI & ophthalmic veins 2. Foramen rotundum which transmits the maxillary nerve (V 2) Superior orbital fissure Foramen rotundum Foramen ovale 3. Foramen ovalewhich transmits the mandibular nerve (V 3) 10/20/2021 55

Middle Cranial Fossa 4. Foramen spinosum which transmits the middle meningeal artery 5. Foramen lacerumnothing is transmitted vertically thru this foramen although the internal carotid artery and some nerves pass across the Foramen lacerum foramen horizontally • Grooves for the greater & lesser petrosal nerves are located along the anterior slope of the petrous portion of the temporal bone 10/20/2021 Foramen spinosum Petrosal grooves 56

Middle Cranial Fossa • Petrous portion of the temporal bone houses the middle and inner ear cavities • Arcuate eminencemarks 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 10/20/2021 Trigeminal impression Arcuate eminence 57

Posterior Cranial Fossa • The largest & deepest of the three fossae • Cerebellum, pons and medulla occupy the posterior fossa Occipital bone • Formed mainly by the occipital bone and the petrous & mastoid portions of the temporal bone 10/20/2021 Temporal bone Petrous portion 58

Posterior Cranial Fossa • Clivus marks the anterior portion of the occipital bone • Foramen magnumlarge foramen that marks the transition from the medulla to the spinal clivus cord • Posterior to the foramen magnum is the internal occipital crest and internal occipital protuberance 10/20/2021 Occipital crest Internal occipital protuberance 59

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 Jugular cranial nerves: foramen 1. Glossopharyngeal (CN IX) 2. Vagus (CN X) 3. Accessory (CN XI) 10/20/2021 Groove for the Sigmoid sinus Transverse Sinus groove 60

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 Internal acoustic meatus canal • Hypoglossal canal for the hypoglossal nerve (CN XII) lies superior to the margin of the foramen magnum 10/20/2021 61

Cribrifrom plate-CN I Superior Orbital Fissure CN III, IV, V 1 & VI Optic Canal CN II Foramen Rotundum- CN V 2 Foramen Ovale-CN V 3 Hypoglossal Canal CN XII Internal Acoustic Meatus. CN VII & VIII 10/20/2021 Jugular Foramen- CN IX, X and XI 62

Osteology of the Orbit • Seven bones articulate to make each orbit: 1. Frontal 2. Zygomatic 3. Maxillary 4. Lacrimal 5. Ethmoid 6. Palatine 7. Sphenoid 10/20/2021 superior 1 lateral 7 2 5 6 4 medial 3 inferior 63

Osteology of the Orbit • Optic canal- transmits the optic nerve and ophthalmic artery • Superior orbital fissuretransmits CN III, IV, V 1 & VI • Inferior orbital fissure & groove- transmits the infraorbital vessels & nerve • Anterior & posterior ethmoidal foraminatransmits vessels & nerves with same name 10/20/2021 Ethmoidal foramina Optic canal Superior orbital fissure Inferior orbital fissure & groove 64