2. osteology. bones of the skull

what is the external skull and what is it’s function

it forms the bony skeleton of the head and protects the brain, special sense organs and the cranial parts of the respiratory and digestive systems as well as providing muscle attachment

what are the two main divisions of the skull? what do they house?

• the neurocranium (cranial vault) which houses the brain and meninges

• and the viscerocranium (facial skeleton) which houses the oral, nasal and orbital structures (OSS)

how many separate bones are in the skull

28

what type of bone ossifications are found in the skull

• intramembranous = flat bones

• endochondral = base of the skull

what is a synostosis

a type of suture or articulation - they are immobile fibrous joints between skull bones

what makes newborn skull sutures different from adult ones

in newborns they are immature and flexible allowing for growth and movement

what are the synovial joints of the skull

the TMJ and atlanto-occipital joint

what makes the TMJ special

its the only movable joint of the skull - it has a bilateral articulation with a capsule, a disc and synovial fluid

what are foramina in the skull

openings in the skull allowing nerves and blood vessels to pass through

why are immature skulls more protected from trauma than adult skulls

immature skulls are highly flexible providing a natural protection which makes it less prone to fractures unlike adult skulls which are less flexible increasing the risk of a fracture

what bones are visible in the front view of the skull

frontal bones, nasal bones, maxilla, mandible, zygomatic bones, temporal and parietal

what bones are visible laterally

temporal, zygomatic arch, sphenoid, mandible, ethmoid, occipital, external auditory meatus

what bones of skull can be seen posteriorly

occipital bone, temporal bone, parietal bone, mastoid process,

what bones are visible from the internal view

frontal, ethmoid, sphenoid, temporal, occipital, cranial fossae

at birth, how does neurocranium compare in size to viscerocranium

the neurocranium is double the size of the viscerocranium (skull size is bigger than the facial region)

where is the nasal fossa located at birth

between the orbits on the same horizontal plane

what proportion of the neonatal cranium does the facial region constitute

only 1/8th

What is the development status of the mandible and maxilla at birth?

They are in a rudimentary stage of development

which skull features have not developed yet at birth

Glabella, superciliary arches, and mastoid process.

how does the of the cranium look like in a newborn

it’s short and narrow

 What type of tissue is present due to incomplete ossification at birth

Fibrous cartilage

 Are all skull bones single structures at birth

no, some bones are in two halves

What is the state of sutures in a newborn skull?

Neotopic sutures are open; they are absent in adults

How many fontanelles are there at birth and what are they?

fontanelles are unfused ‘soft spots’ on newborn heads and there are four: anterior, posterior, anterolateral, and posterolateral.

What is the size and location of the anterior fontanelle?

4 x 2.5 cm; its the largest and at the junction of sagittal, coronal, and frontal sutures.

where is the posterior fontanelle and what is it’s shape

at the junction of sagittal and lambdoid sutures; it’s triangular in shape

What is the size and shape of the lateral fontanelles? (posterolateral and anterolateral)

Small and irregular

How do the orbits compare in size to the rest of the skull in a newborn?

the orbits are relatively large

 What is the length of the external acoustic meatus in a newborn?

short

What is the state of paranasal sinuses at birth?

Rudimentary, appearing like a cleft

What does the growth of the cranial vault depend on

cerebral maturation (brain development)

what drives the growth of the facial skeleton after birth

spatial requirements for teeth and masticatory muscle development

what are the craniometric landmarks

specific areas of the skull aiding in linear or angular head measurements

what are the frontal craniometric landmarks

• glabella

• nasion

• gnathion

• gonion

what are the base of the skull landmarks

• porion

• basion

• nasion

what are the superior craniometric landmarks

bregma, lambda, obelion, opisthocranion

what are the lateral craniometric landmarks

glabella, nasion, dacrion, pterion

how is the skull’s maximum length measured

from glabella to opisthocranion

how is the base of the skull length measured

from basion to nasion

how is the skull maximum width measured

from eurion to eurion

how is the skull height measured

from basion to bregma

what is the formula for the cranial index

(skull maximum width x 100) / skull maximum length

what cranial index range defines a brachiocephalic skull (wide skull)

80.0 - 84.9

what cranial index range defines a dolichocephalic skull (narrow skull)

70.0 - 74.9

what cranial index defines a mesocephalic skull (average skull)

75.0 - 79.9

what is craniometry

measurement of skull bones using planes to delimit anatomical portions

what is the purpose of craniometric measurements

to compare skull dimensions with a known database

how do craniometry, cephalometry and anthropometry differ

• craniometry = skull

• cephalometry = head

• anthropometry = human body

what are some applications of craniometry

neurosurgery, orthognathic surgery, orthodontics

how does a male skull appear compared to a female skull

• more robust

• square forehead

• prominent frontal eminence

• larger and more robust mandible

• square-shaped chin

• larger condyles

• more pronounced muscle attachments

• gonial angle of <125 degrees

• rounder orbital margins

• well-defined glabella

• pronounced mastoid process and supraorbital ridges

• temporal lines and external occipital protuberance are more prominent

at what age does the nasal spine develop

by 3 years of age

when does the dorsum sellae develop

by 5 years of age

when does occipital bone fusion occur

by 7 years of age

when do fontanelles fully close

by 2 years of age

at what age does sutural fusion complete

around 34 years

what is another method of age assessment

dental maturation and dental chronological pattern

which regions are associated with caucasoid skull type

europe, north africa, middle east, indian subcontinent, central asia

what features do caucasoid skulls exhibit

• dolichocephalic skull

• narrow nasal aperture

• moderate supraorbital margin ridging

• prominent nasal spine and steeple nasal root

• little prognathism

• narrow intraorbital distance

• prominent chin

• long, narrow palate

• less prominent cheek bones

• tendency of maxillary protrusion and mandibular retrusion

what regions are linked with the negroid skull type

sub-saharan and western africa

what features do negroid skulls exhibit

• longer skull shape

• wide nasal aperture

• strong alveolar prognathism

• low nasal root

• wide interorbital distance

• rounder forehead

• wider palate

• larger teeth

what regions show the mongoloid skull

east, south and central asia, americas, greenland, inuit, polynesia, south asia and eastern europe

what features are typical of a mongoloid skull

• round skull shape

• nasal aperture of medium width

• well developed and high cheekbones

• moderate prognathism

• short nasal spine

• shovel shaped incisors (narrower)

• foreshortened palate

• forehead is vertical

what is regions exhibit the australoid skull

australian aborigines, maori, pacific islanders, fijians, papaus

what features do australoid skulls exhibit

• broad nasal aperture

• well developed supraorbital ridging

• well developed glabella

• wide palate

• wide teeth