Download Bones, Part 1: The Axial Skeleton

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prepared by
Leslie Hendon
University of Alabama,
Birmingham
•  Composed of 206 named bones grouped into
two divisions
Part 1
Bones, Part 1:
The Axial
Skeleton
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•  Axial skeleton (80 bones)
•  Appendicular skeleton (126 bones)
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The Axial Skeleton
(in green)
Skull
•  Formed from 80
named bones
•  Consists of skull,
vertebral column,
and bony thorax
•  Consists of:
•  Bones, cartilage, joints, and ligaments
7
CHAPTER
The Skeleton
Cranium
Facial bones
The Axial Skeleton
Cranium
Clavicle
Scapula
Sternum
Rib
Humerus
Vertebra
Radius
Ulna
Carpals
Thoracic cage
(ribs and
sternum)
Vertebral
column
Sacrum
Clavicle
Scapula
Rib
Humerus
Vertebra
Radius
Ulna
Bones of
pelvic girdle
Tibia
Tibia
Fibula
Figure 7.1a
The Skull
Zygomatic bone
Infraorbital foramen
Maxilla
Mandible
Figure 7.1b
•  Is the body’s most complex bony structure
•  Formed by cranial and facial bones
•  The cranium
Frontal bone
Squamous part
of frontal bone
Nasal bone
Sphenoid bone
(greater wing)
Temporal bone
Ethmoid bone
Lacrimal bone
(b) Posterior view
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The Cranium
•  Formed by cranial and facial bones
Parietal bone
Lower
limb
Fibula
Tarsals
Metatarsals
Phalanges
(a) Anterior view
Upper
limb
Carpals
Phalanges
Metacarpals
Femur
Phalanges
Metacarpals
Femur
Patella
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Bones of
pectoral
girdle
Glabella
Frontonasal suture
Supraorbital foramen
(notch)
Supraorbital margin
Superior orbital fissure
•  Encloses and protects brain
•  Provides attachment for head and neck
muscles
Optic canal
Inferior orbital fissure
Middle nasal concha
Ethmoid
Perpendicular plate bone
Inferior nasal concha
Vomer
Mental
foramen
Mental
protuberance
(a) Anterior view of skull
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Figure 7.6a
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1
The Face
The Cranium
Bones of cranium (cranial vault)
•  Facial bones serve to
•  Form framework of the face
•  Form cavities for the sense organs of sight,
taste, and smell
•  Provide openings for the passage of air and
food
•  Hold the teeth in place
•  Anchor muscles of the face
Coronal
suture
Squamous
suture
Lambdoid
suture
Facial
bones
(a) Cranial and facial divisions of the skull
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Overview of Skull Geography
Overview of Skull Geography
•  Facial bones form anterior aspect
•  Cranium is divided into cranial vault and the
base
•  Internally, prominent bony ridges divide skull
into distinct fossae
•  The skull contains smaller cavities
Anterior cranial
fossa
Temporal lobe
of cerebrum
Frontal lobe
of cerebrum
Cerebellum
Middle cranial
fossa
Posterior cranial
fossa
(b) Superior view of the cranial fossae
Cranial
fossae
•  Middle and inner ear cavities—in lateral
aspect of cranial base
•  Nasal cavity—lies in and posterior to the
nose
•  Orbits—house the eyeballs
•  Air-filled sinuses—occur in several bones
around the nasal cavity
Posterior
Middle
Anterior
(c) Lateral view of cranial fossae showing the contained
brain regions
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Figure 7.2b, c
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Overview of Skull Geography
Cranial Bones
•  The skull contains approximately 85 named
openings
•  Formed from eight large bones
•  Foramina, canals, and fissures
•  Provide openings for important structures
•  Spinal cord
•  Blood vessels serving the brain
•  12 pairs of cranial nerves
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Figure 7.2a
•  Paired bones include
•  Temporal bones
•  Parietal bones
•  Unpaired bones include
•  Frontal bone
•  Occipital bone
•  Sphenoid bone
•  Ethmoid bone
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2
Parietal Bones and Sutures
Parietal Bones and Sutures
•  Parietal bones form superior and lateral parts
of skull
•  Four sutures of the cranium
•  Four sutures of the cranium (continued)
•  Coronal suture—runs in the coronal plane
•  Located where parietal bones meet the
frontal bone
•  Squamous suture—occurs where each
parietal bone meets a temporal bone inferiorly
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•  Sagittal suture—occurs where right and left
parietal bones meet superiorly
•  Lambdoid suture—occurs where the parietal
bones meet the occipital bone posteriorly
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Sutural Bones
The Skull— Posterior View
Sagittal suture
•  Small bones that occur within sutures
•  Irregular in shape, size, and location
•  Not all people have sutural bones
Parietal bone
Sutural bone
Lambdoid
suture
Occipital bone
Superior nuchal line
External occipital
protuberance
Inferior nuchal line
External occipital crest
Occipital
condyle
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Inferior Aspect of the Skull
Hard
palate
Maxilla
(palatine process)
Palatine bone
(horizontal plate)
Zygomatic bone
Vomer
Temporal bone
(zygomatic process)
Mandibular fossa
Styloid process
Mastoid process
Temporal bone
(petrous part)
Basilar part of
the occipital bone
Occipital bone
External occipital
protuberance
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Figure 7.5
Lateral Aspect of the Skull
Incisive fossa
Intermaxillary suture
Median palatine suture
Infraorbital foramen
Maxilla
Sphenoid bone
(greater wing)
Pterygoid process
Coronal suture
Foramen ovale
Temporal bone
Foramen spinosum
Foramen lacerum
Carotid canal
External acoustic meatus
Stylomastoid
foramen
Jugular foramen
Occipital condyle
Inferior nuchal line
Superior nuchal line
External occipital crest
(a) Inferior view of the skull (mandible removed)
Occipitomastoid
suture
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Frontal bone
Sphenoid bone
(greater wing)
Parietal bone
Ethmoid bone
Lacrimal bone
Squamous suture
Nasal bone
Lacrimal fossa
Zygomatic
bone
Coronoid
process
Maxilla
Zygomatic process
Lambdoid suture
Occipital bone
External occipital
protuberance
Occipitomastoid
suture
Alveolar
margins
Mandible
Mental foramen
External acoustic
meatus
Mastoid process
Foramen magnum
Mandibular
condyle
Styloid
process
Mandibular
notch
Mandibular ramus
Mandibular angle
(b) Photograph of right side of skull
Figure 7.7a
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Figure 7.4b
3
The Temporal Bone
The Sphenoid Bone
Optic
canal
External acoustic
meatus
Lesser wing
Squamous
region
Mastoid
region
Greater
wing
Sella
turcica
Foramen rotundum
Foramen ovale
Foramen spinosum
Body of sphenoid
Zygomatic
process
Mastoid process
Mandibular
fossa
Styloid process
Tympanic
region
(a) Superior view, as in Figure 7.9
Figure 7.8
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The Sphenoid Bone
Body of sphenoid
Figure 7.10a
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The Ethmoid Bone
Lesser
wing
Superior
orbital
fissure
Crista galli
Greater
wing
Olfactory
foramina
Pterygoid
process
Orbital
plate
Cribriform
plate
Left
lateral
mass
Ethmoidal
air cells
(b) Posterior view
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Facial Bones
Figure 7.10b
Perpendicular
plate
Middle
nasal concha
Figure 7.12
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Facial Bones
Frontal bone
•  Unpaired bones
•  Mandible and vomer
•  Paired bones
• 
• 
• 
• 
• 
• 
Maxillae
Zygomatic bones
Nasal bones
Lacrimal bones
Palatine bones
Inferior nasal conchae
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Parietal bone
Squamous part
of frontal bone
Nasal bone
Sphenoid bone
(greater wing)
Temporal bone
Ethmoid bone
Lacrimal bone
Zygomatic bone
Infraorbital foramen
Maxilla
Mandible
Glabella
Frontonasal suture
Supraorbital foramen
(notch)
Supraorbital margin
Superior orbital fissure
Optic canal
Inferior orbital fissure
Middle nasal concha
Ethmoid
Perpendicular plate bone
Inferior nasal concha
Vomer
Mental
foramen
Mental
protuberance
(a) Anterior view of skull
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Figure 7.6a
4
Mandible
Temporomandibular
joint
Mandibular notch
Maxillary Bones
Mandibular fossa
of temporal bone
Coronoid
process
Mandibular
condyle
Articulates with
frontal bone
Frontal process
Mandibular foramen
Orbital surface
Zygomatic
process
(cut)
Alveolar
margin
Mental
foramen
Ramus
of
mandible
Mandibular
angle
Alveolar
margin
Body of mandible
(b) Maxilla, right lateral view
(a) Mandible, right lateral view
Figure 7.13a
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Maxillary Bones
Maxilla
(palatine process)
Hard
palate
Palatine bone
(horizontal plate)
Zygomatic bone
Vomer
Temporal bone
(zygomatic process)
Mandibular fossa
Styloid process
Mastoid process
Temporal bone
(petrous part)
Basilar part of
the occipital bone
Occipital bone
Infraorbital
foramen
Anterior nasal
spine
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Figure 7.13b
Other Bones of the Face
Incisive fossa
Intermaxillary suture
Median palatine suture
Infraorbital foramen
Maxilla
Sphenoid bone
(greater wing)
Pterygoid process
Foramen ovale
Foramen spinosum
Foramen lacerum
Carotid canal
External acoustic meatus
Stylomastoid
foramen
Jugular foramen
Occipital condyle
Inferior nuchal line
•  Zygomatic bones
•  Form lateral wall of orbits
•  Nasal bones
•  Form bridge of nose
•  Lacrimal bones
•  Located in the medial orbital walls
•  Palatine bones
•  Complete the posterior part of the hard palate
Superior nuchal line
External occipital crest
External occipital
protuberance
Foramen magnum
(a) Inferior view of the skull (mandible removed)
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Figure 7.7a
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Other Bones of the Face
Special Parts of the Skull
•  Vomer
• 
• 
• 
• 
•  Forms the inferior part of the nasal septum
•  Inferior nasal conchae
•  Thin, curved bones that project medially form
the lateral walls of the nasal cavity
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Orbits
Nasal cavity
Paranasal sinuses
Hyoid bone
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5
Nasal Cavity
Nasal Septum
Frontal sinus
Superior, middle, and
inferior meatus
Superior
nasal concha
Middle
nasal concha
Ethmoid
bone
Ethmoid
bone
Crista galli
Cribriform
plate
Frontal sinus
Inferior nasal concha
Nasal bone
Sella turcica
Nasal bone
Sphenoid sinus
Perpendicular
plate of
ethmoid bone
Anterior nasal spine
Sphenoid
bone
Pterygoid
process
Septal
cartilage
Maxillary bone
(palatine process)
Sphenoid
sinus
Palatine bone
(perpendicular
plate)
Palatine bone
(horizontal plate)
Hard
Palatine process
palate of maxilla
(a) Bones forming the left lateral wall of the nasal cavity
(nasal septum removed)
Figure 7.14a
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Paranasal Sinuses
Alveolar margin
of maxilla
(b) Nasal cavity with septum in place showing the contributions of the
ethmoid bone, the vomer, and septal cartilage
Figure 7.14b
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Paranasal Sinuses
Frontal
sinus
Ethmoidal
air cells
(sinus)
Sphenoid
sinus
Maxillary
sinus
•  Air-filled sinuses are located within
• 
• 
• 
• 
Vomer
Palatine bone
Frontal bone
Ethmoid bone
Sphenoid bone
Maxillary bones
(a) Anterior aspect
Frontal
sinus
Ethmoidal
air cells
•  Lined with mucous membrane
•  Lighten the skull
Sphenoid
sinus
Maxillary
sinus
(b) Medial aspect
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Orbits
Figure 7.15a, b
The Hyoid Bone
Roof of orbit
Supraorbital notch
Superior
orbital fissure
Lesser wing of
sphenoid bone
Orbital plate of
frontal bone
Lateral wall of orbit
Medial wall
Sphenoid body
Orbital plate
of ethmoid bone
Frontal process
of maxilla
Lacrimal bone
Zygomatic process
of frontal bone
Greater wing of
sphenoid bone
Orbital surface of
zygomatic bone
Inferior orbital fissure
Infraorbital groove
Zygomatic bone
(b) Contribution of each of the seven
bones forming the right orbit
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Optic canal
Nasal bone
Floor of orbit
Infraorbital foramen
Orbital process of
palatine bone
Orbital surface of
maxillary bone
Zygomatic bone
Figure 7.16b
•  Lies inferior to the
mandible
•  The only bone
with no direct
articulation with
any other bone
•  Acts as a
movable base for
the tongue
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Greater horn
Lesser horn
Body
Figure 7.17
6
The Vertebral Column
The Vertebral Column
•  Formed from 26 bones in the adult
•  Transmits weight of trunk to the lower limbs
•  Surrounds and protects the spinal cord
•  Serves as attachment sites for muscles of the
neck and back
•  Held in place by ligaments
•  Anterior and posterior longitudinal ligaments
•  Ligamentum flavum
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The Vertebral Column
Regions and Normal Curvatures
C1
2
3
4
5
6
7
T1
2
3
4
5
6
7
8
9
10
11
12
L1
2
3
4
5
Anterior view
Cervical curvature
(concave)
7 vertebrae, C1 – C7
•  The Vertebral column has five major regions
Spinous
process
Transverse
processes
Thoracic
curvature
(convex)
12 vertebrae,
T1 – T12
7 cervical vertebrae of the neck region
12 thoracic vertebrae
5 lumbar vertebrae
Sacrum—five fused bones
•  Inferior to lumbar vertebrae
•  Coccyx—inferior to sacrum
• 
• 
• 
• 
Intervertebral
discs
Intervertebral
foramen
Lumbar
curvature
(concave)
5 vertebrae, L1 – L5
Sacral
curvature
(convex) 5 fused
vertebrae sacrum
Coccyx
4 fused vertebrae
Right lateral view
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Figure 7.18
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Regions and Normal Curvatures
Regions and Normal Curvatures
•  Curvatures of the spine
•  Curvatures increase resilience of spine
•  Thoracic and sacral curvatures
•  Cervical and lumbar curvatures
•  Concave posteriorly
•  Thoracic and sacral curvatures
•  Convex posteriority
•  Primary curvatures
•  Present at birth
•  Lumbar curvature
•  Develops when baby begins to walk
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7
Ligaments of the Spine
Ligaments of the Spine
Intervertebral
disc
Supraspinous ligament
•  Major supporting ligaments
Anterior
longitudinal
ligament
Transverse process
Sectioned
spinous process
•  Anterior longitudinal ligament
•  Attaches to bony vertebrae and
intervertebral discs
•  Prevents hyperextension
•  Posterior longitudinal ligament
•  Narrow and relatively weak
•  Attaches to intervertebral discs
Intervertebral foramen
Posterior longitudinal
ligament
Ligamentum flavum
Interspinous
ligament
Anulus fibrosus
Nucleus pulposus
Inferior articular process
(a)
Sectioned body
of vertebra
Median section of three vertebrae, illustrating the composition
of the discs and the ligaments
Posterior longitudinal
ligament
Anterior longitudinal
ligament
Body of a vertebra
Intervertebral disc
(b) Anterior view of part of the spinal column
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Figure 7.19a, b
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Ligaments of the Spine
Intervertebral Discs
•  Are cushion-like pads between vertebrae
Vertebral spinous process
(posterior aspect of vertebra)
Spinal cord
Nucleus pulposus
of intact disc
Spinal nerve root
Transverse
process
•  Composed of
•  Nucleus pulposus
•  Anulus fibrosus
Herniated portion
of disc
Anulus fibrosus
of disc
Nucleus
pulposus
of disc
(c) Superior view of a herniated intervertebral disc
Herniated nucleus
pulposus
(d) MRI of lumbar region of vertebral column in sagittal
section showing normal and herniated discs
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Intervertebral Discs
Figure 7.19c, d
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General Structure of Vertebrae
Lamina
•  Nucleus pulposus
Posterior
Spinous
process
Transverse
process
Vertebral
arch
•  Gelatinous inner sphere
•  Absorbs compressive stresses
Superior
articular
process
and
facet
•  Anulus fibrosus
•  Outer fings formed of ligament
•  Inner rings formed of fibrocartilage
•  Contain the nucleus pulposus
Pedicle
Vertebral
foramen
Anterior
PLAY
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Body
(centrum)
Spine (horizontal)
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Figure 7.20
8
General Structure of Vertebrae
Regions Vertebral Characteristics
•  Common structures to all regions
•  Specific regions of the spine perform specific
functions
•  Types of movement that occur between
vertebrae
• 
• 
• 
• 
• 
• 
• 
Body
Vertebral arch
Vertebral foramen
Spinous process
Transverse process
Superior and inferior articular processes
Intervertebral foramina
•  Flexion and extension
•  Lateral flexion
•  Rotation in the long axis
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Cervical Vertebrae
Cervical Vertebrae
•  Seven cervical vertebrae (C1–C7)—smallest
and lightest vertebrae
•  C3–C7 are typical cervical vertebrae
•  Body is wider laterally
•  Spinous processes are short and bifid (except
C 7)
•  Vertebral foramen are large and triangular
•  Transverse processes contain transverse
foramina
•  Superior articular facets face
superoposteriorly
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Cervical Vertebrae
Table 7.2a
The Atlas
Dens of axis
Transverse ligament
of atlas
C1 (atlas)
C2 (axis)
C3
Inferior articular
process
•  C1 is termed the atlas
•  Lacks a body and spinous process
•  Supports the skull
•  Superior articular facets receive the occipital
condyles
Bifid spinous
process
•  Allows flexion and extension of neck
Transverse processes
•  Nodding the head “yes”
C7 (vertebra
prominens)
(a) Cervical vertebrae
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Figure 7.22a
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9
The Atlas
C1
The Atlas
C1
Posterior
Posterior tubercle
Lateral
masses
Posterior arch
Transverse
foramen
Superior articular
facet
Anterior arch
Anterior tubercle
(a) Superior view of atlas (C1)
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Figure 7.21a
The Axis
•  Has a body and spinous process
•  Dens (odontoid process) projects superiorly
•  Formed from fusion of the body of the atlas
with the axis
•  Acts as a pivot for rotation of the atlas and
skull
•  Participates in rotating the head from side to
side
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Thoracic Vertebrae (T1—T12)
Posterior
Posterior
arch
Posterior tubercle
Transverse
process
Lateral
masses
Inferior
articular
facet
Anterior
arch
Transverse foramen
Facet for dens
(b) Inferior view of atlas (C1)
Anterior tubercle
Figure 7.21b
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The Axis
C2
Posterior
Inferior
articular
process
Transverse
process
Dens
(c) Superior view of axis (C2)
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Spinous process
Lamina
Pedicle
Superior
articular
facet
Body
Figure 7.21c
Thoracic Vertebrae
•  All articulate with ribs
•  Have heart-shaped bodies from the superior
view
•  Each side of the body of T1–T10 bears
demifacts for articulation with ribs
•  T1 has a full facet for the first rib
•  T10–T12 only have a single facet
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Table 7.2b
10
Thoracic Vertebrae
Lumbar Vertebrae (L1—L5)
•  Spinous processes are long and point
inferiorly
•  Vertebral foramen are circular
•  Transverse processes articulate with
tubercles of ribs
•  Superior articular facets point posteriorly
•  Inferior articular processes point anteriorly
•  Bodies are thick and robust
•  Transverse processes are thin and tapered
•  Spinous processes are thick, blunt, and point
posteriorly
•  Vertebral foramina are triangular
•  Superior and inferior articular facets directly
medially
•  Allows flexion and extension—rotation
prevented
•  Allows rotation and prevents flexion and
extension
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Lumbar Vertebrae
Lumbar Vertebrae
Superior
articular
process
Transverse
process
Body
Intervertebral
disc
Inferior
articular
process
Spinous
process
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Sacrum (S1—S5)
• 
• 
• 
• 
• 
Shapes the posterior wall of pelvis
Formed from 5 fused vertebrae
Superior surface articulates with L5
Inferiorly articulates with coccyx
Sacral promontory
•  Where the first sacral vertebrae bulges into
pelvic cavity
Table 7.2c
(c) Lumbar vertebrae
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Figure 7.22c
Sacrum
•  Sacral foramina
•  Ventral foramina
•  Passage for ventral rami of sacral spinal
nerves
•  Dorsal foramina
•  Passage for dorsal rami of sacral spinal
nerves
•  Center of gravity is 1 cm posterior to sacral
promontory
•  Ala—develops from fused rib elements
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11
Sacrum
Coccyx
Body
Sacral promontory
Ala
Sacral
canal
Facet of superior
articular process
Body of
first
sacral
vertebra
Auricular
surface
Transverse
ridges (sites
of vertebral
fusion)
Median
sacral
crest
Anterior
Posterior
sacral
sacral
foramina
foramina
Apex
Coccyx
Coccyx
•  Is the “tailbone”
•  Formed from 3—5 fused vertebrae
•  Offers only slight support to pelvic organs
Lateral
sacral
crest
Sacral
hiatus
(b) Posterior view
(a) Anterior view
Figure 7.23
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The Thoracic Cage
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The Thoracic Cage
Jugular notch
Clavicular notch
Manubrium
•  Forms the framework of the chest
•  Components
Sternal angle
Body
Xiphisternal
joint
Xiphoid
process
True
ribs
(1–7
•  Thoracic vertebrae—posteriorly
•  Ribs—laterally
•  Sternum and costal cartilage—anteriorly
•  Protects thoracic organs
•  Supports shoulder girdle and upper limbs
•  Provides attachment sites for muscles
False
ribs
(8–12)
Intercostal
spaces
L1
Vertebra
Floating ribs (11, 12)
(a) Skeleton of the thoracic cage, anterior view
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The Thoracic Cage
T2
Figure 7.24a
•  Formed from three sections
Jugular notch
•  Manubrium—superior section
•  Articulates with medial end of clavicles
•  Body—bulk of sternum
•  Sides are notched at articulations for costal
cartilage of ribs 2–7
•  Xiphoid process—inferior end of sternum
•  Ossifies around age 40
Sternal angle
Heart
T9
Costal cartilage
Costal margin
Sternum
T3
T4
Sternum
Xiphisternal
joint
(b) Midsagittal section through the thorax, showing
the relationship of surface anatomical landmarks
of the thorax to the vertebral column
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Figure 7.24b
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Sternum
Ribs
•  Anatomical landmarks
•  All ribs attach to vertebral column posteriorly
•  Jugular notch
•  Central indentation at superior border of the
manubrium
•  Sternal angle
•  A horizontal ridge where the manubrium
joins the body
•  Xiphisternal joint
•  Where sternal body and xiphoid process
fuse
•  Lies at the level of the 9th thoracic vertebra
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•  True ribs - superior seven pairs of ribs
•  Attach to sternum by costal cartilage
•  False ribs—inferior five pairs of ribs
•  Ribs 11–12 are known as floating ribs
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Ribs
Facets for articulation
with vertebrae
Shaft
Head
Neck
Ribs
Articular facet
on tubercle
Articular facet
on tubercle of rib
Spinous process
Shaft
Junction with
costal cartilage
Costal groove
Costal angle
(a) A typical rib (rib 6, right), posterior view
Angle
of rib
Transverse costal facet
(for tubercle of rib)
Ligaments
Superior costal facet
(for head of rib)
Neck of rib
Body of vertebra
Head of rib
Head of rib
Intervertebral disc
Neck of rib
Tubercle of rib
Shaft
Crosssection
of rib
Costal groove
Superior costal facet
(for head of rib)
Sternum
Figure 7.25a, b
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Disorders of the Axial Skeleton
Disorders of the Axial Skeleton
•  Cleft palate
•  Abnormal spinal curvatures
•  A common congenital disorder
•  Right and left halves of palate fail to fuse
medially
•  Stenosis of the lumbar spine
•  Narrowing of the vertebral canal
•  Can compress roots of spinal nerves
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Body of
thoracic
vertebra
(c) Superior view of the articulation between a rib and a
thoracic vertebra
Costal cartilage
(b) Vertebral and sternal articulations of a typical true rib
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Transverse
costal facet
(for tubercle
of rib)
Figure 7.25c
•  Scoliosis—an abnormal lateral curvature
•  Kyphosis—an exaggerated thoracic
curvature
•  Lordosis—an accentuated lumbar curvature;
“swayback”
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13
The Axial Skeleton Throughout Life
Fontanelles
•  Membrane bones begin to ossify in second
month of development
•  Bone tissue grows outward from ossification
centers
•  Fontanels
•  Unossified remnants of membranes
Frontal suture
Frontal bone
Ossification
center
Posterior fontanelle
(a) Superior view
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Parietal bone
Occipital
bone
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Fontanelles
Figure 7.28a
The Axial Skeleton Throughout Life
Parietal bone
Frontal bone
Ossification
center
Sphenoidal
fontanelle
Temporal bone
(squamous
portion)
Posterior
fontanelle
Anterior
fontanelle
Mastoid
fontanelle
Occipital bone
•  Many bones of the face and skull form by
intramembranous ossification
•  Endochondral bones of the skull
• 
• 
• 
• 
Occipital bone
Sphenoid
Ethmoid bones
Parts of the temporal bone
(b) Lateral view
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Figure 7.28b
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The Axial Skeleton Throughout Life
•  Aging of the axial skeleton
•  Water content of the intervertebral discs
decreases
•  By age 55, loss of a few centimeters in height
is common
•  Thorax becomes more rigid
•  Bones lose mass with age
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