Chapter 4
Skeleton
 Two divisions
 Axial skeleton

Longitudinal axis of the body
 Appendicular skeleton

Bones of limbs and girdles
 And includes
 Joints
 Cartilages
 ligaments
Bone functions
 Support
 Supports and anchors all soft organs
 Leg bones support trunk when standing
 Ribs support thoracic wall
 Protection
 Skull protects brain by enclosing it
 Vertebrae surround the spinal cord
 Ribs protect/surround vital organs
Bone functions
 Blood cell formation
 Hematopoiesis occurs in marrow cavities
 Movement
 Skeletal muscles (attached by tendons) use bones as
levers
 Storage
 Store fat inside cavities of bones
 Bones store minerals (calcium, phosphorous, etc.)
Bone classification
 206 bones in the adult human skeleton
 Two types of osseous (bone)
 Compact bone

Dense, looks smooth and homogenous
 Spongy bone

Composed of small pieces with lots of open spaces
Bone classification
 Bones are classified by shape
 Long bones
 Longer than they are wide
 Shaft with “heads” at both ends
 Mostly compact
 Bones of limbs
 Short bones
 Cube shaped
 Spongy
 Bones of wrist and ankle
 Bones in tendons (sesamoid bones) like patella
Bone classification
 Flat bones
 Thin, flat, curved
 Two thin layers of compact bone, surrounding a layer of
spongy bone
 Bones of skull, ribs, sternum
 Irregular bones
 Don’t fit in any other category
 Vertebrae and hip bones
Gross anatomy of bones
 Long bones
 Diaphysis
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Shaft, makes up most of long bones
Composed of compact bone
Covered by periosteum (connective tissue); connected by
Sharpey’s fibers
 Epiphyses
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

Ends of long bones
Thin layer of compact bone enclosing spongy bone
Covered by articular cartilage (hyaline cartilage) to decrease
friction
Gross anatomy of bones
 Long bones in adults
 Epiphysis is covered by the epiphyseal line (remnant of
the epiphyseal plate)
 Epiphyseal plates add length to long bones
 At the end of puberty, hormones stop the growth the
plates are replaced with bone leaving only the “lines”
Gross anatomy of bones
 In adults
 Cavity of shaft stores fat (yellow marrow)
 Spongy bone of flat bones and epiphyses of some long
bones make RBCs (red marrow)
 In infants
 Cavity of shaft makes RBCs (red marrow)
Bone markings
 Reveal where muscles, tendons, ligaments are attached
 Reveal where blood vessels and nerves pass
 Two categories
 Projections or processes – grow out from the bone
surface
 Depressions or cavities – indentations in bone
 All terms beginning with “T” are projections
 All terms beginning with “F” (except facet) are
depressions
Microscopic bone anatomy
 Compact bone has passageways for nerves and blood
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vessels.
Passageways allow for nutrient / waste exchange
Osteocytes (mature bone cells) are found in cavities of
the bone matrix (lacunae).
Lacunae are arranged in circles called lamellae.
Lamellae surround the Haversian canals, which run
lengthwise and hold the blood vessels and nerves.
Canaliculi radiate out of the Haversian canals to the
lacunae to provide all bone cells with nutrients.
Microscopic bone anatomy
 Volkmann’s canals run at right angles to the shaft to
connect blood vessels
 The elaborate network of canals keeps bone well
nourished and allows bone to heal quickly.
 Calcium salts give b0ne the hardness
 Collagen fibers provide flexibility and great tensile
strength.
Bone formation
 Bones form using hyaline cartilage as models
 Process called ossification has 2 phases
 1. hyaline cartilage completely covered with osteoblasts
(bone-forming cells)
 2. enclosed hyaline cartilage is digested away leaving a
medullary cavity inside the bone
Bone formation
 By birth 0r shortly after, all hyaline cartilage has been
converted to bone except
 articular cartilages (cover bone ends)
 Persist for life to reduce friction at joints
 New cartilage forms on the external surface while “old”
cartilage is replaced with bony matrix
 epiphyseal plates
 Allow longitudinal growth
Bone formation
 Bones must widen (appositional growth)
 Osteoblasts in periosteum add bone to the external
surface of the diaphysis
 Osteoclasts in the endosteum remove bone from the
inner surface of the diaphysis wall
 Controlled by hormones (growth hormone and sex
hormones)
 Ends during adolescence
Bone remodeling
 Bones are continually changing in response to two
factors
 Calcium levels in blood

Parathyroid hormone (PTH) determines when bone is broken
down to release calcium to the blood
 Pull of gravity and muscles

Stress on the bone determines where bone matrix is broken
down or formed to keep the skeleton as strong as possible
Rickets
 A disease in children when bones fail to calcify
 Bowing of weight bearing bones occurs
 Due to lack of calcium and/or vitamin D in the diet
(Vit. D is needed to absorb calcium)
 NOT common in US where good nutrition is stressed
 Milk
 Bread
 Juices fortified with Vit. D
Bone Fractures
 Fractures (breaks) occur due to twists or smashes of
the bone in youth; thinning and weakening in elderly
 Clean breaks that don’t penetrate the skin are “closed”
(simple) fractures
 Breaks where bone penetrates the skin are “open” or
compound fractures
Bone Fractures: treatment
 Reduction is the realignment of broken bone ends
 Closed reduction: bone ends are coaxed back into
normal position by the physician’s hands
 Open reductions: surgery is required to secure the
bone ends with pins or wires
 In both cases, the bone is also immobilized with a cast
to help initiate healing (6-8 weeks in adults, young
adults; much longer in elderly)
Bone repair
 4 parts
 Hematoma forms (blood filled swelling due to ruptures
in the vessels) causing some bone cells to die
 Fibrocartilage callus forms (contains cartilage matrix,
bone matrix, and collagen) to begin splinting the bone;
also includes regrowth of blood vessels
 Bony callus is formed to replace the early fibrocartilage
 Bony callus is remodeled in response to mechanical
stresses to produce a more permanent and strong
“patch” at the injury site
Axial Skeleton
 3 parts
 Skull
 Bony thorax (ribs and sternum)
 Vertebral column
Skull
 Formed by two sets of bones
 Cranium encloses the brain tissue
 Facial bones hold eyes in anterior position and allow
facial muscles to show feelings
 Connected by joints
 All but one bone are connected by interlocking sutures
(immovable joints)
 Mandible (jawbone) is attached by a freely movable
joint
Cranium
 Composed of 8 large, flat bones
 All are single bones except the parietal and temporal
(these are paired bones)
Cranium
 Frontal bone
 Forehead
 Bony projections under eyebrows
 Superior part of each orbit
Cranium
 Parietal bones
 Paired bones
 Most of superior / lateral walls
 Meet at the sagittal suture
 Form the coronal suture where they meet the frontal
bone
Cranium
 Temporal bones
 Paired bones
 Inferior to the parietal bones (meet them at the squamous
sutures
 Has several important bone markings
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External auditory meatus – bony canal to the eardrum
Styloid process – needlelike projection inferior to the auditory
meatus; neck muscle attachment point
zygomatic process – thin bridge of bone that joins the zygomatic
bone
Mastoid process – rough projection posterior and inferior to the
auditory meatus; neck muscle attachment point and location of
mastoid sinuses
Cranium
 Temporal bone markings continued
 Jugular foramen – at the junction of the occipital and
temporal bones allows passage of jugular vein which
drains oxygen poor blood from the brain
 Carotid canal – anterior to the jugular foramen; allows
passage of the carotid artery which “feeds” the brain
Cranium
 Occipital bone
 Most posterior bone of cranium
 Floor and back wall
 Joins parietal bones at the lambdoid suture
 Contains the foramen magnum – surrounds the lower
part of the brain and allows the spinal cord to attach to
the brain
 Occipital condyles (lateral on both sides of the foramen
magnum); rest on 1st vertebra of the spinal column
Cranium
 Sphenoid bone
 Spans the width of the skull and forms the floor of the
cranial cavity
 At the midline is the sella turcica which holds the
pituitary gland in place
 Foramen ovale posterior to the sella turcica allows nerve
fibers of cranial nerve V to pass to the muscles of the
mandible
 Central part contains the sphenoid sinuses
Cranium
 Ethmoid bone
 Irregular shape; lies anterior to the sphenoid
 Roof of the nasal cavity
 Part of medial walls of orbits
 Crista galli projects from the superior surface (brain
covering attaches here)
 On each side are holes (cribriform plates) to allow nerve
fibers to carry impulses from olfactory receptors to the
brain
Cranium
 Facial bones
 14 bones, 12 are paired; only mandible and vomer are
single
 Maxillae fuse to form the upper jaw; are joined to all
other facial bones except mandible; carry upper teeth
 Palantine processes form anterior part of upper palate
 Paranasal sinuses (of maxiallae) surround nasal cavity;
lighten the skull; and amplify sound
 Palantine bones – posterior to the palantine processes;
make up the posterior part of the hard palate
Cranium
 Facial bones continued
 Zygomatic bones (cheekbones)-form lateral walls of
orbits
 Lacrimal bones – form part of medial walls of orbits; has
a groove for tears
 Nasal bones – bridge of nose
 Vomer bone – one bone in the median line of nasal
cavity; forms nasal septum
 Inferior conchae – thin curved bones projecting from
the lateral walls of nasal cavity
Cranium
 Facial bones continued
 Mandible – lower jaw, largest and strongest in the face;
joins temporal bones on each side; freely moveable joint;
holds lower teeth
 Hyoid bone – does not articulate directly with any other
bone; suspended in mid-neck region above larynx;
anchored to styloid process by ligaments; moveable base
for the tongue; attachment for neck muscles that
raise/lower larynx in swallowing and speaking
Fetal skull
 Very small face compared to size of the cranium
 ¼ the total body length of the infant (compared to 1/8
the body length of an adult)
 Contains fontanels (soft spots) where cranial bones
have not yet fused
 allows for growth of the brain in late pregnancy and
early infancy
 Allows the skull to be slightly compressed during birth
Vertebral column
 Axial support for the body
 Extends from skull to pelvis where it transmits weight
to lower limbs
 26 irregular bones connected and reinforced by
ligaments
 Flexible, curved structure
 Vertebrae protect/surround the spinal cord
Vertebral column
 Before birth, spine has 33 separate bones
 9 of them fuse to form two composite bones (sacrum
and coccyx)
 Of the 24 single bones, 7 are cervical (neck), 12 are
thoracic, 5 are lumbar (lower back)
Vertebral column
 Intervertebral discs (pads of flexible fibrocartilage)
separate the vertebrae adding cushion and providing
shock absorption
 Young people have discs with high water content that
makes the discs spongy and compressible
 Older people lose water content with age making the
discs hard and less compressible
Intervertebral disc problems
 Drying of the discs and weakening of the ligaments
causes older people to be susceptible to herniated
discs
 If the disc protrudes inward and presses on the spinal
cord or spinal nerves, numbness and pain result
Abnormal spinal curvatures
 Scoliosis
 Bending/curving of the spine to left or right of the body
midline
 Kyphosis
 Abnormal protruding curve of the spine in the upper
thoracic area (hump back)
 Lordosis
 Abnormal inward curve of the lumbar region (sway
back)
Common features of vertebrae
 Body (centrum) - disc-like, weight-bearing part, facing
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anteriorly
Vertebral arch – arch formed from the joining of all
posterior extensions (laminae and pedicles)
Vertebral foramen – canal through which the spinal
cord passes
Transverse processes – two lateral projections from the
vertebral arch
Spinous process – single projection arising from the
posterior aspect of the vertebral arch
Common features of vertebrae
 Superior and inferior articular processes – paired
projections lateral to the vertebral foramen, allowing
vertebrae to form joints with adjacent vertebrae
Cervical vertebrae
 7 of them (identified as C1 – C7)
 Neck region
 First two are known as the “atlas” and “axis”
 Atlas (C1) has no body

Transverse processes receive the occipital condyles of skull; allows
nodding or “yes” motion
 Axis (C2) is a pivot for rotation

Allows rotating from side-to-side or “no” motion
 Typical cervical vertebrae (C3-C7) are smallest and lightest
 Spinous processes are are short and divided into two branches
 Tranverse processes have foramina for arteries to pass
Thoracic vertebrae
 (T1-T12)
 Longer than cervical vertebrae
 Body is somewhat heart-shaped
 Have two articulating surfaces on each side to receive
ribs
 Spinous process is long and hooks sharply downward
Lumbar vertebrae
 (L1-L5) have massive, block-like bodies
 Sturdiest vertebrae
 Carry most of the stress
Sacrum
 Formed by the fusion of five vertebrae
 Superiorly articulates with L5
 Inferiorly articulates with the coccyx
 Wing-like alae articulate laterally with the hip bones to
form sacroiliac joints
 Forms posterior wall of pelvis
 Contains the sacral canal (lower continuation of the
vertebral canal)
Coccyx
 Formed from the fusion of 3-5 tiny, irregular vertebrae
 “tailbone” or remnant of a tail that other vertebrates
have
Bony thorax
 Sternum
 Ribs
 Thoracic vertebrae
 Often called the thoracic cage (cone shaped protection
around thoracic cavity (enclosing the heart, lungs, and
major blood vessels)
Sternum
 Flat bone
 Fusion of 3 bones (manubrium, body, xiphoid process)
 Attached to first 7 pairs of ribs
 3 landmarks
 Jugular notch

Concave upper border of the manubrium
 Sternal angle

Junction of the manubrium and sternal body
 Xipheisternal joint

Junction of the sternal body and xiphoid process
Ribs
 Twelve pairs of ribs form walls of the thoracic cage
 All articulate with vertebral column posteriorly and curve
downward toward the anterior body surface
 Intercostal spaces are filled with muscles that aide breathing
 True ribs
 First 7 pairs
 Attach to sternum by costal cartilages
 False ribs
 Next 5 pairs
 Attach indirectly to sternum or don’t attach at all
 Floating ribs
 Last 2 pairs of ribs have no sternal attachments
Appendicular Skeleton
 126 bones of the limbs
 Pectoral and pelvic girdles (which attach limbs to the
axial skeleton)
Shoulder girdle (pectoral girdle)
 2 bones (Clavicle and scapulae)
 Clavicle
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
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Called the “collar bone”
Attaches to the manubrium of sternum medially and to the
scapula laterally
Braces the arm away from the thorax and prevents shoulder
dislocation
Shoulder girdle
 Scapulae
 Also called “shoulder blades”
 Loosely held in place by trunk muscles
 Has 3 borders and 3 angles (p. 139)
 Glenoid cavity receives the head of the humerous
 Flat, triangular with two processes


Acromion
 Connects with the clavicle laterally at the acromioclavicular
joint
Coracoid process
 Anchors muscles in the arm
Shoulder girdle
 Exceptionally free movement due to:
 Girdle attaches to the axial skeleton only at one point
(sternoclavicular joint)
 Loose attachment of scapulae allow them to slide easily
against the thorax with muscles
 Glenoid cavity is shallow, shoulder joint is poorly
reinforced with ligaments
 Very easily dislocated!
Upper limbs
 30 separate bones in each upper limb
 Forming the arm, forearm, and hand
Arm
 Arm is formed by the humerus
 Typical long bone
 Proximal end has a round head that fits the glenoid cavity of
the scapula
 Greater and lesser tubercles are behind the head which are
sites of muscle attachment
 Deltoid tuberosity is in middle of shaft, attachment point for
deltoid muscle
 Radial groove runs down the shaft to mark the course of the
radial nerve
 Distal end has the trochlea and capitulum that articulate with
the bones of the forearm
Forearm
 Two bones
 Radius (in anatomical position) is lateral or “thumb side”
 Ulna is medial “little finger side”
 On proximal end (elbow) radius and ulna articulate at the
radioulnar joints
 Both bones connected along length by the interosseous
membrane
 Head of radius articulates with the humerus
 Radial tuberosity is the attachment for the biceps muscle
 Coronoid process and olecranon process articulate and grip
the distal end of the humerus
Hand
 Carpals, metacarpals, and phalanges
 Carpals (8) arranged in two rows of four bones
forming the carpus (wrist); bound together by
ligaments – see figure 5.22
 Metacarpals – palm; numbered 1-5 beginning on
thumb side; heads become “knuckles” when hand is
fisted
 Phalanges (14) – fingers; labeled proximal, middle, and
distal except the thumb (only has proximal and distal)
Pelvic girdle
 Formed by 2 coxal bones (ossa coxae) or hip bones
 With sacrum and coccyx form bony pelvis
 Bones are large and heavy; attached to axial skeleton
 Large, deep sockets receive the femurs; reinforced by
ligaments
 Bearing weight is most important function of this
girdle
 Also protects reproductive organs, bladder, and part of
large intestine
Hip bones
 Formed by fusion of ilium, ischium, and pubis
 Ilium – connects with sacrum (sacroiliac joint); is a
flaring bone (hip bone); iliac crest is an anatomical
landmark
 Ischium – “sitdown bone”; most inferior part of coxal
bone; ischial tuberosity receives weight when sitting;
ischial spine narrows pelvis outlet during birth; sciatic
notch allows vessels and sciatic nerve to pass
 Pubis – most anterior of coxal bone; fusion of pubic
bones anteriorly forms the pubic symphysis
(cartilaginous joint)
Acetabulum
 Deep socket
 Sight of fusion of ilium, ishcium, and pubis
 Receives head of femur
Bony pelvis
 2 parts
 False pelvis
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
Superior to true pelvis
Medial to ilia
 True pelvis
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
Lies inferior to ilia
Must have larger dimensions in females
Differences between male/female
pelvis
 Female inlet is larger / circular
 Female pelvis is shallow; bones are lighter / thinner
 Female ilia flare more laterally
 Female sacrum is shorter, less curved
 Female ischial spines are shorter and farther apart
(larger outlet)
 Female pubic arch is more rounded with greater angle
Lower limbs
 Carry total body weight when erect
 Bones are thicker and stronger
Thigh
 Femur is the only bone
 Heaviest and strongest in the body
 Proximal end has a ball like “head”, a neck and greater and
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lesser trochanters
Trochanters are separated by the intertrochanteric line
anteriorly and by the intertrochanteric crest posteriorly
Trochanters, intertrochanteric crest, and gluteal tuberosity
are sites for muscle attachment
Head of femur articulates with the deep socket of the ilium
The neck is often a fracture point for elderly
Thigh
 Femur slants medially as it runs downward
 This brings knees in line with the body’s center of
gravity (more noticeable in females due to wider
pelvis)
 On the posterior side of the distal end, lateral and
medial condyles (separated by the intercondylar
notch) articulate with the tibia
 On the anterior side of the distal end is the patellar
surface which forms a joint with the patella
Leg
 Tibia and fibula are connected along their length by an
interosseous membrane
 Tibia (shin bone) is larger and medial
 Proximal end: medial and lateral condyles articulate
with the distal end of the femur to form the knee
 Patellar ligament attaches to tibial tuberosity
 Distally, the medial malleolus forms the inner bulge of
the ankle
 Anterior crest of tibia is somewhat sharp and
unprotected (easily felt beneath skin)
Leg
 Fibula is thin and stick-like
 Articulates with the tibia proximally and distally
 not part of the knee
 Distally, lateral malleolus forms outer part of ankle
Foot
 Composed of tarsals, metatarsals, and phalanges
 Two functions
 Supports body weight
 Serves as a lever to propel the body forward in motion
Tarsus
 Posterior half of the foot
 7 tarsal bones
 Body weight carried by the two largest tarsals (calcaneus and talus)
 5 metatarsals
 Form the sole of the foot
 14 phalanges form the toes
 All toes have three phalanges except the big two which has two
 Bones of foot arranged to form 3 strong arches: two longitudinal
(medial and lateral) and one transverse
 Ligaments bind the bones together and tendons anchor muscles
and hold the foot in an arched position (but still allow “give” or
springiness (weak arches are “fallen” or cause “flat feet”)
Joints
 Articulations have 2 functions
 Hold bones together securely
 Give the rigid skeleton mobility
Joints classification
 Functional classification
 Amount of movement allowed

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Immovable joints (synarthroses) - axial
Slightly movable joints (amphiarthroses) - axial
Freely movable joints (diarthroses) – appendicular
 Structural classification
 Fibrous (most immovable)
 Cartilaginous (most amphiarthrotic)
 Synovial (freely movable)
Fibrous joints
 Bones are united by fibrous tissue
 Sutures in the skull (irregular edges of the bones are
bound by connective tissue fibers)
 Syndesmoses have longer connective fibers so some
“give” is allowed (joints that join the tibia and fibula)
Cartilaginous Joints
 Bone ends covered with cartilage
 Slightly movable joints (amphiarthrotic) such as pubic
symphysis and intervertebral joints
 Epiphyseal plates of growing long bones and
cartilaginous joints between ribs and sternum are
immovable (synarthrotic)
Synovial joints
 Articulating bone ends are separated by a cavity
containing synovial fluid
 Have 4 distinguishing features
 Articular cartilage covers the ends of the bones
 Joint surfaces are enclosed by a capsule of fibrous
connective tissue, lined with synovial membrane
 Articular capsule encloses the cavity filled with synovial
fluid
 Fibrous capsule is reinforced with ligaments
Types of synovial joints
 Determined by shape
 6 types
 Plane
 Hinge
 Pivot
 Condyloid
 Saddle
 Ball-and-socket
Plane joints
 Articular surfaces are flat
 Only allow short slipping or gliding
 Movements are nonaxial (does not involve rotation
around an axis)
 Ex: intercarpal joints of wrist
Hinge joints
 Cylindrical end of one bone fits into the trough-
shaped surface of another bone
 Angular movement allowed in one plane
 Ex: elbow, ankle, phalanges
 Also considered uniaxial (or on one axis)
Pivot joints
 Round end of one bone fits into a sleeve or ring of
bone (and ligaments)
 Can only turn on long axis (uniaxial)
 Ex: proximal radioulnar joint and joint between atlas
and axis vertebrae
Condyloid joints
 Egg-shaped articular surface of one bone fits into an
oval concavity in another
 Allow movement side-to-side AND back-and-forth
(biaxial)
 Bone cannot rotate around long axis
 ex: knuckles
Saddle joints
 Articular surfaces have both convex and concave areas
(like a saddle)
 Biaxial joints allow same movements as condyloid
joints
 Ex: carpometacarpal joints of thumb
Ball-and-socket joints
 Spherical head of one bone fits into the round socket
of another
 Multiaxial joints allow movement in all axes including
rotation
 Ex: shoulder and hip