OSTEOLOGY

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OSTEOLOGY

• The Skull

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The Skull
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
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The Skull
Parietal
coronal suture
Frontal
Occipital
Temporal
Sphenoid
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The Skull
Lacrimal
Nasal
Zygomatic
Maxilla
Inferior Nasal Conchae
Mandible
Vomer
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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
Squamous portion
Glabella
Nasion
Orbital portion
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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
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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

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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
Piriform aperture
Alveolar process
Maxilla
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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

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• 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

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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

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Osteology

• Lateral Aspect of the Skull

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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

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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

pterion
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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

Squamous
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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

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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

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Zygomatic bone

• 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

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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
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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

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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

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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
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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

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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

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Mandible
Condylar Process
Mandibular foramen
Infant
Coronoid process
Mylohyoid line
Lingula
Ramus
Alveolar Part (crest)
Mental foramen
Body
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Mandible
Mandibular notch
Condylar process
Ramus
Body
Mental spines
Bone loss due to tooth loss
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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
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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

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Infant Skull

• Superior Lateral Aspects

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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
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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

Fontanelles- membranous gaps (soft spots) in
skull that permit growth
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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
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Osteology

• External Aspect of the Cranial Base

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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
• Basilar Region
• Condylar Region
• Squamous Region

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Cranial Base- Occipital

• 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

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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
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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
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Osteology

• Internal Aspect of the Cranial Base

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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
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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
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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
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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

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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

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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
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Middle Cranial Fossa

• 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

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Middle Cranial Fossa

• Middle cranial fossa presents five important
  foramina
• Superior orbital fissure for passage of CNs III,
  IV, V1 VI ophthalmic veins
• Foramen rotundum which transmits the maxillary
  nerve (V2)
• Foramen ovale- which transmits the mandibular
  nerve (V3)

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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
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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
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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
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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
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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
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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
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Osteology of the Orbit

• Seven bones articulate to make each orbit
• Frontal
• Zygomatic
• Maxillary
• Lacrimal
• Ethmoid
• Palatine
• Sphenoid

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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