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Chapter 8
The Skeletal System
• Overview of the skeleton
• The skull
• The vertebral column and
thoracic cage
• The pectoral girdle and
upper limb
• The pelvic girdle and
lower limb
Overview of the Skeleton
• Regions of the skeleton
– axial skeleton forms the central axis
• skull, vertebral column, ribs, sternum and sacrum
– appendicular skeleton includes the limbs & girdles
• Number of bones
– 206 in typical adult skeleton
• varies with development of sesamoid bones (patella)
– start at 270 at birth, decreases with age as bones fuse
• Surface markings defined in Table 8.2
• 4 regions of the skeleton = skull, vertebral column &
thorax, upper and lower limbs and girdles
Surface Features of Bones
Axial & Appendicular Skeleton
• Axial skeleton in
yellow
– skull, vertebrae,
sternum, ribs,
sacrum & hyoid
• Appendicular
skeleton in blue
–
–
–
–
pectoral girdle
upper extremity
pelvic girdle
lower extremity
Major Skull Cavities
• Cranial cavity holds brain
• Orbit contains eyeball &
extraocular muscles
• Ethmoid sinus
• Nasal cavity
• Maxillary sinus
• Oral cavity
The Skull
• 22 bones joined together by sutures
• Cranial bones surround cranial cavity
– 8 bones in contact with meninges
• frontal, parietal,
– calvaria (skullcap) forms roof & walls
• Facial bones support teeth & form nasal cavity
& orbit
– 14 bones with no direct contact with brain or
meninges
– attachment of facial & jaw muscles
Cranial Fossa
• 3 basins that comprise the cranial floor or base
– anterior fossa holds the frontal lobe of the brain
– middle fossa holds the temporal lobes of the brain
– posterior fossa contains the cerebellum
• Swelling of the brain may force tissue through foramen
magnum resulting in death
Frontal Bone
• Forms forehead and part
of the roof of the cranium
• Forms roof of the orbit
• Contains frontal sinus
Parietal Bone
• Forms cranial roof and
part of its lateral walls
• Bordered by 4 sutures
– coronal, sagittal, lambdoid
and squamous
Temporal lines
• Marked by temporal lines
of temporalis muscle
Temporal Bone
• Forms lateral wall & part
of floor of cranial cavity
– squamous part
• zygomatic process
• mandibular fossa & TMJ
– tympanic part
• external auditory meatus
• styloid process for muscle
attachment
– mastoid part
• mastoid process
– mastoiditis from ear infection
• mastoid notch
– digastric muscle
Petrous Portion of Temporal Bone
• Forms part of cranial floor
– separates middle from
posterior cranial fossa
• Houses middle and inner
ear cavities
– receptors for hearing and
sense of balance
– internal auditory meatus is
opening for CN VII
(vestibulocochlear nerve)
Openings in Temporal Bone
• Carotid canal
– passage for internal
carotid artery supplying
the brain
• Jugular foramen
– irregular opening between
temporal & occipital
bones
– passageway for drainage
of blood from brain to
internal jugular vein
Occipital Bone
• Rear & much of base of skull
• Foramen magnum holds spinal
cord
• Skull rests on atlas at occipital
condyles
• Hypoglossal canal transmits
hypoglossal nerve (CN XII)
supplying tongue muscles
• External occipital protuberance
for nuchal ligament
• Nuchal lines mark neck muscles
Sphenoid Bone
• Lesser wing
• Greater wing
• Body of sphenoid
• Medial and lateral
pterygoid processes
Sphenoid Bone
• Body of the sphenoid
– sella turcica contains deep
pit (hypophyseal fossa)
– houses pituitary gland
• Lesser wing
– optic foramen contains optic
nerve & ophthalmic a.
• Greater wing -- 3 foramen
– foramen rotundum & ovale
for brs. trigeminal nerve
– foramen spinosum for
meningeal artery
Sphenoid Bone
• Sphenoid sinus
Ethmoid Bone
• Found between the orbital cavities
• Forms lateral walls and roof of nasal
cavity
• Cribriform plate & crista galli
• Ethmoid air cells form ethmoid sinus
• Perpendicular plate forms part of
nasal septum
• Concha or turbinates on lateral wall
Ethmoid Bone
• Superior & middle concha
• Perpendicular plate of nasal
septum
Maxillary Bones
• Forms upper jaw
– alveolar processes are bony points
between teeth
– alveolar sockets hold teeth
• Forms inferomedial wall of orbit
– infraorbital foramen
• Forms anterior 2/3’s
of hard palate
– incisive foramen
– cleft palate
Locations of Paranasal Sinuses
Frontal
Ethmoid
Maxillary
Sphenoid
• Maxillary sinus fills maxillae bone
• Other bones containing sinuses are frontal, ethmoid &
sphenoid.
Palatine Bones
• L-shaped bone
• Posterior 1/3 of the hard
palate
• Part of lateral nasal wall
• Part of the orbital floor
Zygomatic Bones
• Forms angles of the
cheekbones and part of
lateral orbital wall
• Zygomatic arch is formed
from temporal process of
zygomatic bone and
zygomatic process of
temporal bone
Lacrimal Bones
• Form part of medial wall
of each orbit
• Lacrimal fossa houses
lacrimal sac in life
– tears collect in lacrimal
sac and drain into nasal
cavity
Nasal Bones
• Forms bridge of nose and
supports cartilages of
nose
• Often fractured by blow
to the nose
Inferior Nasal Conchae
• A separate bone
• Not part of ethmoid like
the superior & middle
concha or turbinates
Vomer
• Inferior half of the nasal
septum
• Supports cartilage of
nasal septum
Mandible
• Only bone of the skull that can move
– jaw joint formed between mandibular fossa
of temporal bone & condyloid process
• Holds the lower teeth
• Attachment of muscles of mastication
– temporalis muscle onto coronoid process
– masseter muscle onto angle of mandible
• Mandibular foramen
• Mental foramen
Ramus, Angle and Body of Mandible
Bones Associated With the Skull
• Auditory ossicles
– malleus
– incus
– stapes
• Hyoid bone
– suspended from styloid
process of skull by
stylohyoid muscle and
ligament
– greater & lesser cornua
The Skull in Infancy & Childhood
• Spaces between unfused skull
bones called fontanels
– filled with fibrous membrane
– allow shifting of bones during
birth & growth of brain in
infancy
– fuse by 2 years of age
• 2 frontal bones fuse by age six
– metopic suture
• Skull reaches adult size by 8 or
9 causing heads of children to
be larger in proportion to trunk
General Features of the Vertebral Column
• 33 vertebrae & discs of
fibrocartilage between them
• Five vertebral groups
–
–
–
–
–
7 cervical in the neck
12 thoracic in the chest
5 lumbar in lower back
5 sacral fused into the sacrum
4 coccygeal fused into
coccyx
• Variations in number of
lumbar and sacral vertebrae
Newborn Spinal Curvature
• Spine exhibits one
continuous C-shaped
curve
• Known as primary
curvature
Adult Spinal Curvatures
• S-shaped vertebral column
with 4 curvatures
• Secondary curvatures
develop after birth
– lifting head as it begins to
crawl develops cervical
curvature
– walking upright develops
lumbar curvature
Abnormal Spinal Curvatures
• Result from disease,
posture, paralysis or
congenital defect
• Scoliosis from lack
of proper
development of one
vertebrae
• Kyphosis is from
osteoporosis
• Lordosis is from
weak abdominal
muscles
General Structure of a Vertebra
• Body
• Series of vertebral foramen
form the vertebral canal
• Neural arch
– 2 lamina
– 2 pedicles
• Processes
– spinous
– transverse
– articular (superior & inferior)
Intervertebral Foramen & Discs
• Intervertebral foramen
– formed from vertebral
notches of adjacent vertebrae
– passageway for spinal nerves
• Intervertebral discs
– bind vertebrae together
– absorb shock
– inner gelatinous nucleus
pulposus surrounded by
annulus fibrosus (ring of
fibrocartilage)
– herniated disc puts pressure
on spinal nerve or spinal cord
Typical Cervical Vertebrae
• Small body and larger vertebral foramen
• Transverse process short with transverse foramen for
protection of vertebral arteries
• Bifid or forked spinous process in C2 to C6
• C7 vertebra prominens
The Unique Atlas and Axis
• Atlas (C1) supports the skull
– concave superior articular facet
• nod your head in “yes” movement
– ring surrounding large vertebral
foramen
• anterior & posterior arch
• Axis (C2)
– dens or odontoid process is held in
place inside the vertebral foramen of
the atlas by ligaments
– allows rotation of head -- “no”
Atlas & Axis Articulation
Typical Thoracic Vertebrae
• More massive body than cervical but smaller than lumbar
• Spinous processes pointed and angled downward
• Superior articular facets face posteriorly permitting some rotation
between adjacent vertebrae
• Rib attachment
– superior and inferior costal facets on vertebral body and transverse costal
facets at ends of transverse processes for articulation of ribs
Lumbar Vertebrae
• Thick, stout body and blunt, squarish spinous process
• Superior articular processes face medially
– lumbar region resistant to twisting movements
Sacrum (Anterior View)
• 5 separate sacral
vertebrae fuse by age 26
• Anterior surface
– smooth & concave
– sacral foramina were
intervertebral foramen
• nerves & blood vessels
– 4 transverse lines indicate
line of fusion of vertebrae
Sacrum (Posterior View)
• Rough surface of sacrum
• Spinous processes have
fused into median sacral
crest
• Transverse processes fuse
into lateral sacral crest
• Posterior sacral foramina
• Sacral canal ends as sacral
hiatus
• Auricular surface is part of
sacroiliac joint
Coccyx
• Single, small, triangular bone
– 4 small vertebrae fused by age of 30
– Co1 to Co4
• Provides attachment site for
muscles of pelvic floor
• Cornua
– hornlike projections on Co1 for
ligaments attach coccyx to sacrum
• Fractured by fall or during
childbirth
Thoracic Cage
• Consists of thoracic
vertebrae, sternum & ribs
• Attachment site for
pectoral girdle and many
limb muscles
• Protects many organs
• Rhythmically expanded by
respiratory muscles to
draw air into the lungs
Rib Structure
Tubercle
Head
• Flat blade called a shaft
– inferior margin has costal groove for
nerves & vessels
• Proximal head & tubercle are
connected by neck
• Articulation
– head with body of vertebrae
– tubercle with transverse process
Numbered Rib Articulations
True and False Ribs
• True ribs (1 to 7) attach
to sternum with hyaline
cartilage
• False ribs (8-12)
– 11-12 are floating and not
attached to sternum
• 12 pairs of ribs in both
sexes
Pectoral Girdle
• Attaches upper extremity to the body
• Scapula and clavicle
• Clavicle attaches medially to the sternum and
laterally to the scapula
– sternoclavicular joint
– acromioclavicular joint
• Scapula articulates with the humerus
– humeroscapular or shoulder joint
– easily dislocated because of its loose attachment
Clavicle
• S-shaped bone, flattened dorsoventrally
• Inferior surface marked by muscle & ligament attachments
• Sternal end is rounded -- acromial end is flattened
Scapula
•
•
•
•
•
Triangular plate that dorsally overlies ribs 2 to 7
Spine ends as acromion process
Coracoid process for muscle attachment
Subscapular, infraspinous and supraspinous fossa
Glenoid fossa is shallow socket for head of humerus
Scapular Features
Upper Limb
• 30 bones per limb
• Brachium or arm contains the humerus
• Antebrachium or forearm contains the radius &
ulna (radius on thumb side)
• Carpus or wrist contains 8 small bones arranged
in two rows
• Manus or hand contains 19 bones in 2 groups
– 5 metacarpals in the palm
– 14 phalanges in the fingers
Humerus
• Hemispherical head forms shoulder
joint above anatomical neck
• Muscles attach to greater & lesser
tubercles and deltoid tuberosity
• Intertubercular groove holds biceps
tendon
• Rounded capitulum articulates with
radius
• Pulleylike trochlea articulates with
ulna
• Olecranon fossa holds olecranon
process of ulna in straightened arm
• Forearm muscles attach to medial &
lateral epicondyles
Ulna and Radius
• Radius
– head is disc that rotates freely
during pronation & supination
• articulates with the capitulum
– radial tuberosity for biceps muscle
• Ulna
– olecranon and trochlear notch form
proximal end
– radial notch holds head of ulna
• Interosseous membrane
– ligament attaches radius to ulna
along interosseous margin of each
bone
Carpal Bones
• Form the wrist
– allows flexion, extension,
abduction & adduction
• 2 rows of 4 bones each
– proximal row is scaphoid,
lunate, triquetrum &
pisiform
– distal row is trapezium,
trapezoid, capitate &
hamate
Metacarpals and Phalanges
• Phalanges are bones of
the fingers
– thumb or pollex has
proximal & distal phalanx
– fingers have proximal,
middle & distal phalanx
• Metacarpals are bones of
the palm
– base, shaft & head
Pelvic Girdle
• Composed of 4 bones:
right & left os coxae,
sacrum and coccyx
• Supports trunk on the legs
& protects viscera
• Each os coxae is joined to
the vertebral column at the
sacroiliac joint
• Anteriorly, pubic bones are joined by pad of fibrocartilage
to form pubic symphysis
• False and true pelvis are separated at pelvic brim
• Infant’s head passes through pelvic inlet & outlet
Os Coxae (Hip Bone)
• Acetabulum is hip joint socket
• Ilium is superior portion
– iliac crest and iliac fossa
– greater sciatic notch contains sciatic nerve
• Pubis is anterior portion
– body, superior and inferior ramus
• Ischium is posterolateral portion
–
–
–
–
ischial tuberosity bears body weight if sit
ischial spine
lesser sciatic notch lies between ischial spine & tuberosity
ischial ramus joins inferior pubic ramus
Comparison of Male & Female
• Female less massive, shallower pubic arch greater than
100 degrees, and pubic inlet round or oval
• Male heavier, upper pelvis nearly vertical, coccyx more
vertical, and pelvic inlet heart-shaped, outlet smaller
Femur
• Nearly spherical head &
constricted neck
– ligament to fovea capitis
• Greater & lesser trochanters
for muscle attachment
• Posterior ridge called linea
aspera
• Medial & lateral condyles
and epicondyles found
distally
• Smooth patellar surface on
anterior femur
Patella and Tibia
• Patella is triangular sesamoid
bone
• Tibia is thick, strong weightbearing bone on medial side of
leg
– broad superior head with 2 flat
articular surfaces
• medial & lateral condyles
– roughened anterior surface can be
palpated below the patella
(tibial tuberosity)
– distal expansion is medial
malleolus
Fibula
• Slender lateral strut that
helps stabilize the ankle
• Does not bear any of the
body’s weight
– use as spare bone tissue to
replace bone elsewhere
• Head is proximal end
• Lateral malleolus is distal
expansion
• Joined to tibia by
interosseous membrane
The Ankle and Foot
• Tarsal bones are shaped & arranged
differently from carpal bones due to
load-bearing role of the ankle
• Talus is most superior tarsal bone
– forms ankle joint with tibia & fibula
– sits upon calcaneus & articulates with
navicular
• Calcaneus forms heel (achilles tendon)
• Distal row of tarsal bones
– cuboid, medial, intermediate and lateral
cuneiforms
The Foot
• Remaining bones of foot are similar
in name & arrangement to the hand
• Metatarsal I is proximal to the great
toe (hallux)
– base, shaft and head
• Phalanges
– 2 in great toe
• proximal and distal
– 3 in all other toes
• proximal, middle & distal
Foot Arches
• Sole of foot does not normally
rest flat on the ground
• 3 springy arches absorb stress of
walking
– medial longitudinal arch extends
from heel to hallux
– lateral longitudinal arch extends
from heel to little toe
– transverse arch extends across the
middle of the foot
• Arches held together by short,
strong ligaments
– pes planis (flat feet)
X ray of the Right Foot
Bipedalism and Upright Stance
Bipedalism and Limb Adaptations
Bipedalism and Head Position