THE SKELETON
CHAPTER 7
9/30/2007
Introduction
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A strong, yet light, internal support for
the human body
The skeleton is adapted for the
protection, locomotor, and
manipulative functions
The upright stance increases the ability of
the skeletal muscle to resist gravity
Introduction



The skeleton maintains its upright
position through a series of
compensating curves
The skeleton accounts for approximately
20% of the body mass
The 206 bones of the body are grouped
into the axial and appendicular skeleton
Introduction
Axial skeleton
 Forms the long axis
of the body
 80 bones in three
major regions
– Skull
– Vertebral column
– Bony thorax
• Ribs
• Sternum
Appendicular
 Bones of upper &
lower extremities and
girdles
 126 bones in three
major regions
– Girdles
• Shoulder girdle
• Pelvic girdle
– Upper extremity
– Lower extremity
THE SKULL
SECTION I
The Skull
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The skull is the body’s most complex
bony structure
It is formed by two sets of bones, the 8
cranial bones and the 14 facial bones
These 22 bones combine to form the
cranial cavity and the facial features
In addition, there are 3 bones in each
inner ear to assist in sound transmission
The Skull: Introduction

The bones of the skull provide . . .
– A case to house the brain, the cranium
– A framework for the face
– Cavities to house the organs of sight, taste,
and smell
– Passages for air and food
– Attachment sites for the teeth
– Attachment sites for muscle
The Skull: Introduction

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Most bones of the skull are flat bones
Except for the mandible, all bones are
firmly united by interlocking sutures
The major sutures of the skull are . . .
–
–
–
–

Coronal
Sagittal
Squamosal
Lambdoidal
(Between Frontal & Parietal)
(Between Parietal bones)
(Between Parietal & Temporal)
(Between Parietal & Occipital)
Other skull sutures connect facial bones
and are named after these structures
________
________
Sagittal
Coronal
Lambdoid
Squamous
Overview of Skull Geography

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Facial bones form the anterior aspect
The cranial bones enclose the brain
Vault

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The cranial vault
or calvaria forms
the superior,
lateral, and
posterior aspects
of skull
The cranial base
forming the
inferior aspect of
skull
Cranial Base

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Cranial base forms
the skull’s inferior
aspect
Three prominent
ridges divide the
base into fossae
The brain rests on
these cranial fossae
completely
enclosed by the
cranial vault
The brain occupies
the cranial cavity
Cavities of the Skull

In addition to the large cranial cavity
there are many smaller cavities
–
–
–
–
Middle and inner ear cavities
Nasal cavity
Orbits of the eyes
Several bones contain air filled sinuses
• Sinuses surrounding the nasal cavity are referred
to as the paranasal sinuses
– The skull has about 85 named openings
(foramina, canals and fissures)
Cranium


The 8 cranial bones include; 2 parietal, 2
temporal frontal, occipital, sphenoid, ethmoid
The cranium is self-bracing allowing the bones
to be thin, yet strong
Frontal bone

Forms the
anterior
portion of
the cranium,
the forehead,
roofs of the
orbits, and
most of the
anterior
cranial fossa
Frontal bone - landmarks
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Frontal
squama
Supraorbital
margins
Supraorbital
foramen
Orbits
Anterior
cranial fossa
Glabella
Frontal
sinuses
Parietal bones
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Forms most of
the superior &
lateral aspects
of the skull
Articulates
with other
cranial bones
to form four
major sutures
Parietal
Parietal bones - landmarks

The four largest sutures cranial sutures,
Coronal, Sagittal, Lambdodial, Squamosal
Occipital bone

Articulates with
parietal &
temporal
Occipital bone
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Joins w/ sphenoid
in the cranial
floor
Forms internal
walls of posterior
cranial fossa
Occipital bone Ext. landmarks

Foramen magnum,
Occipital condyles,
External occipital
protuberance,
Nuchal lines,
External occipital
crest
Occipital bone - Int. landmarks

Hypoglossal canal, Posterior cranial fossa
Temporal Bone
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Forms the inferolateral aspects of
the skull
Parts of the
cranial floor
Divided into four
regions;
squamous
tympanic,
mastoid, and
petrous-(int)
Temporal Bone


The internal
petrous region
contributes to
the cranial base
The petrous
region and the
sphenoid bone
form the
middle cranial
fossa
Temporal Bone - landmarks

Zygomatic
process
– Meets the
zygomatic
bone
– Forms the
cheek

Mandibular
fossa
– Receives
condyle of
mandible
Temporal Bone - landmarks

External
Auditory
Meatus
– Middle and
inner ear

Styloid
process
– Muscle of
tongue

Mastoid
process
– Muscles of
neck
Temporal bones - landmarks

Jugular
foramen
– Entry point for
the Jugular
artery

Internal
acoustic meatus
– Entry point for
the auditory
nerve
Jugular Foramen
Temporal bones - landmarks

Stylomastoid
foramen
– exit for facial
nerve

Carotid canal
– entrance for
the carotid
artery which
supplies blood
to cerebral
hemispheres
Sphenoid bone

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Bone spanning the
width of middle
cranial fossa
Articulates as
central wedge of
all cranial bones
Consists of central
body and three
processes; greater
and lesser wings
and pterygoid
process (pos. view)
Sphenoid - landmarks
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Sella turcica (enclosure for pituitary gland)
Optic foramina (passage of optic nerves)
Superior orbital fissure (Nerves III, IV, V enter orbit)
Foramen rotundum & ovale (Cranial Nerve V to face)
Foramen spinosum (Middle meningeal artery)
Ethmoid bone
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Forms most of
the area between
the nasal cavity
& orbits of eyes
Lies between
nasal bones &
sphenoid
Complex shape
gives rise to
nasal septum,
sinuses and
cribiform plate
Ethmoid bone - landmarks

Cribiform plates
– Forms roof of
nasal cavity

Olfactory formina
– Olfactory nerves
enter brain

Crista galli
– Attachment of the
dura mater which
secures brain in
cavity
Ethmoid bone - landmarks

Perpendicular
plate
– Forms superior
part of nasal
septum

Lateral mass
– House ethmoid
sinuses

Nasal concha
– Project into nasal
cavity

Orbital plates
– Medial walls of
orbits
Facial bones
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Consists of 14
bones w/ only
mandible and
vomer unpaired
Others include
maxillae,
lacrimals,
nasals,
zygomatics,
inferior nasal
conchae, and
palatines (not
pictured)
Mandible
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Forms the lower
jaw
Largest,
strongest bone of
the face
It has a body
and two
upwardly
projecting
sections called
rami
Houses lower
dentition
Mandible - landmarks
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Mandibular angle
Mandibular notch
Coronoid process
Mandibular
condyle
Alveolar margin
Mandible formina
Mental formina
Ramus of
mandible
Maxillary bone
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Forms upper
jaw and central
portion of facial
skeleton
Fused medially
Articulates with
all facial bones
except mandible
Upper dentition
Forms 2/3 of
hard palate of
the mouth
Zygomatic
process
Maxillary
bone
Maxillary bones - landmarks

Alveolar margin
– Upper dentition

Frontal process
– Forms lateral
aspects of nose

Zygomatic
process
– Articulates with
zygomatic bone

Maxillary
sinuses
– (Fig. 7.11)
Maxillary bones - landmarks

Palatine
processes
– Forms roof of
mouth

Incisive fossa
– Passage of
nerves and
blood vessels

Infraorbital
foramen
– Infraorbital
nerve and blood
vessel to face
Palatine Process
Maxillary bones - landmarks

Inferior
orbital fissure
– Located deep
within the
orbit
– Permits
passage of the
zygomatic
nerve,
maxillary
nerve, and
blood vessels
to reach face
Zygomatic bones
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Commonly called
the cheekbones
Form prominences
of cheeks and
inferolateral
margins of orbits
Articulate with the
Zygomatic process
of temporal bone
and Zygomatic
process of maxallae
Zygomatic
Process of
Temporal
Zygomatic
bone
Nasal bones
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Forms bridge
of the nose
Thin,
rectangular
shape
Fused medially
Articulate with
the frontal bone
and maxillary
bones laterally
Nasal cartilages
Lacrimal Bones
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Forms part of
the medial
border of each
orbit
Articulates with
frontal, ethmoid
& maxillae
Forms part of
Lacrimal fossa
– Permits tears to
drain from orbit
to nasal cavity
Lacrimal Bones

Lacrimal fossa
– Permits tears to
drain from orbit
to nasal cavity
Palatine bones
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
The horizontal
plates forms the
posterior portion
of hard palate
Vertical plate
forms part of the
posterolateral
wall of nasal
cavity and a
small portion of
orbit
Palatine bones - landmarks

Horizontal plate
– Posterior
section of hard
palate

Vertical plate
– Part of the
posteriolateral
walls of nasal
cavity

Orbital surface
– Part of inferior
medial aspect of
orbit
Vomer


Forms part of
the nasal
septum
Discussed with
the nasal cavity
Vomer - landmarks

Plow shape
– Divides nasal
septum into
right and left
parts
Inferior Nasal Conchae
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Form lateral
walls of nasal
cavity
Project
medially from
the lateral
walls of nasal
cavity
Largest of
nasal conchae
Inferior Nasal Conchae - Landmark
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The Inferior
nasal conchae
is just one of
three in the
nasal cavity
Superior and
middle concha
are on the
Ethmoid bone
Nasal cavity

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The nasal cavity is constructed of bone
and hyaline cartilage
The cavity is divided into right and left
parts by the nasal septum
Superior, middle and inferior nasal
concha project into the cavity
The nasal septum and conchae are lined
with mucus-secreting mucosa
Nasal cavity
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Roof of the
cavity is the
cribriform
plates of
ethmoid
Lateral walls
are the superior,
middle, and
inferior
conchae, and
vertical plates of
palatines
Nasal cavity
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Floor of cavity is
formed by
palatine
processes of the
maxillae and the
palatine bones
Septum is
formed by vomer
and the
perpendicular
plate of ethmoid
Palatine
The Orbits
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The orbits are bony cavities within which
the eyes are encased and cushioned by fatty
tissue
The muscles that move the eyes and the tear
producing lacrimal glands are housed
within the orbit
Formed by frontal, sphenoid, maxilla,
zygomatic, lacrimal, palatine & ethmoid
Contain superior & inferior orbital fissures
Optic foramina
The Orbits
Paranasal sinuses
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Five skull bones; frontal, sphenoid,
ethmoid, and the paired maxillary
contain mucus-lined, air-filled sinuses
Cluster around nasal cavity
Connected to nasal cavity to allow air to
enter and mucus to drain
Lighten skull, warm and humidify air,
enhance voice resonance
Paranasal sinuses

Note positioning
around nasal
cavity
Paranasal sinuses
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Sphenoid sinus
Frontal sinus
Ethmoidal air
cells
Maxillary
sinuses
Hyoid bone
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Not really a part of the skull, it is unique
in that it is the only bone that does not
articulate with any other bone
Positioned just inferior to the mandible
Anchored by stylohyoid ligaments to the
styloid processes of temporal bone
Acts as a movable base for the tongue
Hyoid bone

Body
– Neck muscle
attachment

Greater horn
– Neck muscle
attachment

Lesser horn
THE VERTEBRAL COLUMN
SECTION II
Vertebral Column:
General Characteristics
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Formed from 26 irregular bones in adult
It contains four distinct curvatures
It provide axial support for the trunk
Transmits weight of trunk to lower limbs
Protects spinal cord
Attachment site for ribs and muscles
Separated by intervertebral discs
There are 24 vertebrae, a sacrum (5 fused)
and a coccyx (4 fused)
General
Characteristics

Alignment
– Anterior/ posterior
– Lateral

Curvatures
– Compensatory
curves

Features
– Weight bearing
– Muscle attachment
– Protection
Regional
Characteristics

Cervical C1-C7
– Neck / movable

Thorasic T1-T12
– Rib cage / limited
movement

Lumbar L1-L5
– Low back / movable

Sacral 5 fused
– Joins the pelvis

Coccyx 4 fused
– Terminus
Characteristics - Ligaments

Ligaments hold the
vertebral column in
an upright position
– The broad Anterior
Longitudinal
Ligament prevents
hyperextension and
is quite strong
– The cord like
Posterior
Longitudinal
Ligament prevents
hyperflexion and is
relatively weak
Characteristics - Ligaments

Ligaments
also connect
specific
vertebra and
support disc
position
– Supraspinos
ligament
– Ligamentum
flavum
– Interspinous
ligament
Characteristics - Ligaments
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The ligamentum flavum connects the
lamina of adjacent vertebrae
The ligamentum flavum contains
significant amount of elastic fibers and is
especially strong
The ligament stretches forward, then
recoils as we straighten to an erect
position
Intervertebral Discs
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Intervertebral discs are cushion like pads
interposed between vertebra
The discs provide compressibility of the
spine and resist tension on the spine
Compression flattens discs
Discs are thickest in the cervical and
lumbar regions to which improves
flexibility
Intervertebral Discs


Discs are pads
positioned
between
vertebral
bodies
Two
components
– Anulus
fibrosus
– Nucleus
pulposus
Intervertebral Discs
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
Nucleus pulposus is the gelatinous mass
that enables the spine to absorb
compressive stress
The Anulus fibrosus has an outer ring
consisting of ligamentous tissue and an
inner ring consisting of fibrocartilage
– Functions to contain the nucleus pulposus
during compression
– Collagen fibers are organized similar to
fibers in osteons forming X’s that resist
twisting
Characteristics - discs
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Anulus fibrosus
surrounds the
outer margin
Nucleus pulposus
can shift under
pressure
Herniated or
prolapsed disc
typically occurs
posteriolaterally
compressing
nerve roots
Herniation
of disk
Characteristics - discs
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
MRI of lumbar
region showing
normal and
herniated discs
Note the
posterior
displacement
Normal
Curvatures
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Cervical and lumbar
are concave
Thoracic and are
sacral are convex
Curves increase spinal
resiliency
Primary curvatures
– Thoracic and sacral

Secondary curvatures
– Cervical and lumbar
Curves develop in response to:
Upright posture
Weight bearing
Musculature
General structure of vertebrae

Common pattern
– Body or centrum
– Vertebral arch
• lamina
• pedicle
– Vertebral
foramen
• Passage for
spinal cord
General structure of vertebrae

Seven different
processes project
from each arch
– Spinous process
– Transverse
process
– Superior and
inferior articular
processes
– Facets
General structure of vertebrae

Interlocking
pattern
– Superior and
inferior processes
interlock
– The inferior from
above and the
superior from the
vertebrae below
form a movable
joint
– The movement
contributes to
spinal rotation
Superior Articular
Process
General structure


Pedicles have
notches on their
superior and
inferior borders
Lateral openings
are called
intervertebral
foramen
– Spinal nerves
from spinal cord
exit through
these foramina
Regional Characteristic: Cervical

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
Body is oval, but wide
side to side C3 - C7
Spinous process is
short and bifid (split)
except in C7
Vertebral foramen is
triangular
Transverse processes
contain foramina for
blood vessels leading
to brain
Cervical Vertebrae C1 and C2
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The first two cervical vertebrae are named
the atlas and axis respectively
There is no intervertebral disc between
them
They are highly modified for carrying the
skull on top of the vertebral column
The atlas (C1) functions as a cradle to
support the head
The axis (C2) functions as a pivot point for
the rotation of the atlas
Cervical Vertebrae C1

Lateral masses articulates with the occipital
condyles of the skull
Cervical Vertebrae C1
Body of the
Vertebrae is
missing

Inferior articular surface articulates with C2
below
Cervical Vertebrae C2


The axis has the
odontoid process
or dens is its
unique feature
The dens is the
missing body of
the atlas which
fuses with the
atlas during
embryonic
development
Regional Characteristic: Cervical
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Spinous processes
project directly
posteriorly
Superior facets
directed
superoposteriorly
Inferior facets
directed
inferoanteriorly
Flexion/extension,
lateral flexion and
rotation
Regional Characteristic: Thoracic
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Body is larger than
cervical; heart
shaped
Spinous process is
long and sharp
Vertebral foramen is
circular
Transverse processes
project posteriorly
and bear facets for
ribs
Regional Characteristic: Thoracic
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Body bears two
costal demifacets
Spinous processes
projects inferiorly
Superior facets
directed posteriorly
Inferior facets
directed anteriorly
Rotation, limited
lateral flexion,
flexion/extension
prevented
Regional Characteristic: Lumbar
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
Body is massive and
kidney shaped
Spinous processes are
short and blunt
Vertebral foramen is
triangular
Transverse processes
are perpendicular to
spinous process but
has no special
features
Regional Characteristic: Lumbar

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
Spinous process
projects posteriorly
Superior facets
directed medially
Inferior facets
directed laterally
Flexion/extension,
some lateral flexion,
rotation prevented
Sacrum

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
The triangular shaped structure formed
by five fused vertebrae
Forms the posterior wall of the pelvis
Articulates with L5 of the vertebral
column
Articulates with the iliac bone of the
pelvic girdle
Transfers the weight of the upper torso
and limbs to the lower extremities
Sacral


Ala are fused remnants
of transverse processes
that articulate with hip
bones to form the sacro
iliac joints of the pelvis
Sacral promontory
– Center of gravity is 1 cm
posterior of this point


Transverse line are sites
of vertebral fusion
Sacral foramina
transmit blood vessels
and nerves
Sacral




On the posterior aspect
median sacral crest are
fused spinous processes
The vertebral canal
continues inside the
sacrum as the sacral
canal
Sacral hiatus is at the
inferior end of the
sacral canal
Superior articular
surface form a joint
with the spinal column
Coccyx

Coccyx articulates with sacrum
The Bony Thorax

The thorax is the chest which includes
– Thoracic vertebrae posteriorly
– The ribs laterally
– The sternum and costal cartilages anteriorly


It is cone shaped with its broad opening
inferiorly
The thorax forms a bony cage around the
heart, lungs and major blood vessels
Functions of The Bony Thorax



Protection
Attachment point for muscles of the
back, chest, and shoulders
The intercostal muscles attach to the
thorax to lift and depress the thorax
during respiration
The Sternum


The sternum lies in the
anterior midline of the
thorax
It is three fused bones
– Manubrium
• Jugular notch
• Clavicular notch
– Sternal body
• Sternal angle
– Xiphoid process
• Xiphisternal joint
Bony Thorax



Thorax is the chest and its bony
underpinnings is called the thoracic cage
Elements consist of the thoracic vertebrae,
ribs, sternum, and costal cartilages which
secure ribs to the sternum
A cone opening inferiorly, the thorax provides
a protective cage around the vital organs of
the thoracic cavity (heart, lungs, great blood
vessels)
Bony Thorax - continued



Provides support for the shoulder girdles
Bony attachment points for muscles of the
back, chest and shoulders
Intercostal spaces between ribs are occupied
by the intercostal muscles which lift and
depress the thorax during breathing
Sternum

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
Located on the anterior
midline of the thorax
Consists of three fused
bones; manubrium,
body, and xiphoid
process
Manibrium articulates
with clavicle & 2 ribs
Body with ribs 2 - 7
Xiphoid attachment
site for abdominal
muscle
Thorax to Vertebral Column
Thorax to Vertebral Column
Ribs
Ribs


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


Twelve pairs forming thoracic cage
All attach posteriorly to thoracic vertebrae
Curve inferiorly toward anterior body surface
Ribs 1-7 attach directly to sternum by
separate costal cartilages and are referred to
as true ribs
Ribs 8-10 attach indirectly to sternum by
attaching to costal cartilages immediately
above
Ribs 11-12 have no anterior attachments and
are referred to as floating ribs
Ribs




Ribs are bowed
flat bones
Long shaft
Tear drop shaped
with a costal
groove on inner
surface
Head of rib has 2
facets to
articulate with its
vertebrae as well
as the one above
Ribs




Neck is just
beyond the head
Angle of rib
Costal cartilages
attach rib to
sternum
Attachments are
secure but
flexible
Ribs



Tubercle of rib
articulates with
transverse process
Ligaments secure
rib to transverse
process
Note how the
transverse
processes of
thoracic vertebrae
are angled
posteriorly
Disorders of the Axial Skeleton
Abnormal
Curvatures

Scoliosis
– An abnormal lateral
curvature of the
spinal column
– Curvature can
occur in an “S” or
“C” deviation
Abnormal
Curvatures

Kyphosis
– An exaggerated
dorsal curvature
in the dorsal
region
– Common is aged
individuals
because of
osteoporosis
Abnormal
Curvatures

Lordosis
– Accentuated
lumbar curvature
– Being overweight
or pregnant
causes an
excessive load up
front
The Axial Skeleton
Throughout Life



Fontanels
Cleft palate
Adult Skeletal Changes
The Fetal Skull
The Axial Skeleton
Throughout Life





Discs become thinner and more prone to
herniation
Loss of a few centimeters of height
Osteoporosis
Rigid thorax (costal cartilage ossification)
restricts breathing
Loss of bone mass in facial bones
End of Chapter 7