Textbook Ch. 9 Skeletal System

Transcription

CHAPTER 8
SKELETAL
SYSTEM
CHAPTER OUTLINE
Divisions of Skeleton, 210
Axial Skeleton, 213
Skull, 213
Cranial bones, 227
Facial bones, 229
Hyoid bone, 230
Vertebral column, 231
Sternum, 235
Ribs, 235
Appendicular Skeleton, 236
Upper extremity, 236
Lower extremity, 241
Skeletal Differences in Men and Women, 247
Cycle of Life, 248
The Big Picture, 248
Mechanisms of Disease, 248
Case Study, 251
KEY TERMS
appendicular skeleton
axial skeleton
cranium
fontanel
pelvic girdle
J
shoulder girdle
sinus
suture
thorax
vertebra
ust as skeletal tissues are organized to form bones, the
bones are organized or grouped to form the major subdivisions of the skeletal system described below. The
rigid bones lie buried within the muscles and other soft tissues, thus providing support and shape to the body. An understanding of the relationship of bones to each other and to
other body structures provides a basis for understanding the
function of many other organ systems. Coordinated movement, for example, is possible only because of the way bones
are joined in joints and the way muscles are attached to those
bones. In addition, knowledge of the placement of bones
210
within the soft tissues assists in locating and identifying
other body structures.
The adult skeleton is composed of 206 separate bones. Variations in the total number of bones in the body may occur as a
result of certain anomalies such as extra ribs or from failure of
certain small bones to fuse in the course of development.
In Chapter 7 the basic types of skeletal tissue, including
bone and cartilage, were discussed. Comparisons between
the structural and functional characteristics of dense (compact) and cancellous (spongy) bone provided the background for study in this chapter of individual bones and
their interrelationships in the skeleton. Chapter 9 takes your
studies one step farther, by considering articulations—that
is, how the bones form joints.
DIVISIONS OF SKELETON
The human skeleton consists of two main divisions—the axial skeleton and the appendicular skeleton (Figure 8-1).
Eighty bones make up the axial skeleton. This includes
74 bones that form the upright axis of the body and six tiny
middle ear bones. The appendicular skeleton consists of
126 bones—more than half again as many as in the axial
skeleton. Bones of the appendicular skeleton form the appendages to the axial skeleton: the shoulder girdles, arms,
wrists, and hands and the hip girdles, legs, ankles, and feet.
One of the first things you should do in studying the skeleton is to familiarize yourself with the names of individual
bones listed in Table 8-1. Next, look at Table 8-2, which lists
some terms often used to name or describe bone markings—
specific features on an individual bone. After this preparation, begin a step-by-step exploration of the skeletal system
by studying the illustrations, text, and tables that constitute
the rest of this chapter.
A picture is worth a thousand words. The illustrations
and tables contained in this chapter were carefully selected
and compiled to assist you in visualizing and organizing the
material discussed. If, in addition to your textbook, you have
access to individual bones or an articulated skeleton in a laboratory setting, frequent reference to chapter illustrations
Skeletal System
Chapter 8
Figure 8-1 Skeleton. A, Anterior view.
Continued
211
212
Unit 2
Support and Movement
Figure 8-1, cont’d Skeleton. B, Posterior view.
Skeletal System
Chapter 8
213
Table 8-1 Bones of Skeleton (206 Total)*
Part of Body
AXIAL SKELETON (80 BONES TOTAL)
Name of Body
Skull (28 bones total)
Cranium (8 bones)
Face (14 bones)
Ear bones (6 bones)
Hyoid bone (1)
Spinal column
(26 bones total)
Sternum and ribs
(25 bones total)
Frontal (1)
Parietal (2)
Temporal (2)
Occipital (1)
Sphenoid (1)
Ethmoid (1)
Nasal (2)
Maxillary (2)
Zygomatic (malar) (2)
Mandible (1)
Lacrimal (2)
Palatine (2)
Inferior nasal conchae
(turbinates) (2)
Vomer (1)
Malleus (hammer) (2)
Incus (anvil) (2)
Stapes (stirrup) (2)
APPENDICULAR SKELETON (126 BONES TOTAL)
Part of Body
Name of Body
Upper extremities
(including shoulder girdle)
(64 bones total)
Lower extremities
(including hip girdle)
(62 bones total)
Clavicle (2)
Scapula (2)
Humerus (2)
Radius (2)
Ulna (2)
Carpals (16)
Metacarpals (10)
Phalanges (28)
Innominate (2)
Femur (2)
Patella (2)
Tibia (2)
Fibula (2)
Tarsals (14)
Metatarsals (10)
Phalanges (28)
Cervical vertebrae (7)
Thoracic vertebrae (12)
Lumbar vertebrae (5)
Sacrum (1)
Coccyx (1)
Sternum (1)
True ribs (14)
False ribs (10)
*An inconstant number of small, flat, round bones known as sesamoid bones (because of their resemblance to sesame seeds) are found in various tendons in which considerable
pressure develops. Because the number of these bones varies greatly between individuals, only two of them, the patellae, have been counted among the 206 bones of the body. Generally, two of them can be found in each thumb (in flexor tendon near metacarpophalangeal and interphalangeal joints) and great toe plus several others in the upper and lower
extremities. Wormian bones, the small islets of bone frequently found in some of the cranial sutures, have not been counted in this list of 206 bones because of their variable
occurrence.
Box 8-1 HEALTH MATTERS
Mastoiditis
and tabular material will prove immensely helpful in your
study efforts.
AXIAL SKELETON
astoiditis (mas-toy-DYE-tis), or inflammation of the
air spaces within the mastoid portion of the temporal bone, can produce very serious medical problems unless treated promptly. Infectious material frequently finds
its way into the mastoid air cells from middle ear infections.
The mastoid air cells do not drain into the nose, as do the
paranasal sinuses. As a result, infectious material that accumulates may erode the thin bony partition that separates
the air cells from the cranial cavity. Should this occur, the
inflammation may spread to the brain or its covering
membranes.
M
SKULL
Twenty-eight irregularly shaped bones form the skull (Figures 8-2 to 8-8). Figures 8-2 through 8-7 show the articulated bones of the skull in full or sectioned views. Figure 8-8
is a multipart series highlighting the individual bones and
shows their relationship to the skull as a whole. As you study
the skull, refer often to the illustrations and the descriptive
information contained in Tables 8-3 to 8-5. The skull consists of two major divisions: the cranium, or brain case, and
the face. The cranium is formed by eight bones, namely,
Text continued on p. 227
214
Unit 2
Table 8-2 Terms Used to Describe Bone Markings
Term
Meaning
Term
Meaning
Angle
Body
Condyle
A corner
The main portion of a bone
Rounded bump; usually fits into a fossa on
another bone, forming a joint
Moderately raised ridge; generally a site for
muscle attachment
Bump near a condyle; often gives the
appearance of a “bump on a bump”; for
muscle attachment
Flat surface that forms a joint with another
facet or flat bone
Long, cracklike hole for blood vessels and
nerves
Round hole for vessels and nerves
(pl. foramina)
Depression; often receives an articulating
bone (pl. fossae)
Distinct epiphysis on a long bone, separated
from the shaft by a narrowed portion
(or neck)
Line
Similar to a crest but not raised as much
(is often rather faint)
Edge of a flat bone or flat portion of edge of
a flat area
Tubelike opening or channel (pl. meati)
A narrowed portion, usually at the base of a
head
A V-like depression in the margin or edge
of a flat area
A raised area or projection
Curved portion of a bone, like a ram’s horn
(pl. rami)
Cavity within a bone
Similar to a crest but raised more; a sharp,
pointed process; for muscle attachment
Groove or elongated depression (pl. sulci)
Large bump for muscle attachment (larger
than tubercle or tuberosity)
Oblong, raised bump, usually for muscle
attachment; small tuberosity is called a
tubercle
Crest
Epicondyle
Facet
Fissure
Foramen
Fossa
Head
Margin
Meatus
Neck
Notch
Process
Ramus
Sinus
Spine
Sulcus
Trochanter
Tuberosity
Table 8-3 Cranial Bones and Their Markings
Bones and
Markings
Frontal
Supraorbital
margin
Frontal sinuses
Frontal tuberosities
Superciliary
ridges
Supraorbital
foramen
(sometimes
notch)
Glabella
Parietal
Description
Forehead bone; also forms most of roof
of orbits (eye sockets) and anterior
part of cranial floor
Arched ridge just below eyebrow, forms
upper edge of orbit
Cavities inside bone just above supraorbital margin; lined with mucosa;
contain air
Bulge above each orbit; most prominent part of forehead
Ridges caused by projection of frontal
sinuses; eyebrows lie superficial to
these ridges
Foramen or notch in supraorbital
margin slightly medial to its midpoint; transmits supraorbital nerve
and blood vessels
Smooth area between superciliary
ridges and above nose
Prominent, bulging bones behind
frontal bone; forms top sides of
cranial cavity
Bones and
Markings
Sphenoid
Body
Greater wings
Lesser wings
Sella turcica
(or Turk’s
saddle)
Sphenoid sinuses
Pterygoid
processes
Description
Keystone of cranial floor; forms its midportion; resembles bat with wings
outstretched and legs extended downward posteriorly; lies behind and
slightly above nose and throat; forms
part of floor and sidewalls of orbit
Hollow, cubelike central portion
Lateral projections from body, form
part of outer wall of orbit
Thin, triangular projections from
upper part of sphenoid body; form
posterior part of roof of orbit
Saddle-shaped depression on upper
surface of sphenoid body; contains
pituitary gland
Irregular mucosa-lined, air-filled spaces
within central part of sphenoid
Downward projections on either side
where body and greater wing unite;
comparable to extended legs of bat if
entire bone is likened to this animal;
form part of lateral nasal wall
Skeletal System
Chapter 8
215
Table 8-3 Cranial Bones and Their Markings—cont’d
Bones and
Markings
Optic foramen
Superior orbital
fissure
Foramen rotundum
Foramen ovale
Foramen lacerum
Foramen spinosum
Temporal
Squamous portion
Mastoid portion
Petrous portion
Mastoid process
Mastoid air cells
External auditory
meatus (or canal)
Zygomatic process
Internal auditory
meatus
Mandibular fossa
Styloid process
Description
Bones and
Markings
Opening into orbit at root of lesser
wing; transmits optic nerve
Slitlike opening into orbit; lateral to
optic foramen; transmits third, fourth,
and part of fifth cranial nerves
Opening in greater wing that transmits
maxillary division of fifth cranial nerve
mandibular division of fifth cranial
nerve
Opening at the junction of the sphenoid, temporal, and occipital bones;
transmits branch of the ascending
pharyngeal artery
the middle meningeal artery to
supply meninges
Stylomastoid
foramen
Form lower sides of cranium and part
of cranial floor; contain middle and
inner ear structures
Thin, flaring upper part of bone
Rough-surfaced lower part of bone
posterior to external auditory meatus
Wedge-shaped process that forms part
of center section of cranial floor
between sphenoid and occipital
bones; name derived from Greek
word for stone because of extreme
hardness of this process; houses
middle and inner ear structures
Protuberance just behind ear
Mucosa-lined, air-filled spaces within
mastoid process
Tube extending into temporal bone
from external ear opening to tympanic membrane
Projection that articulates with malar
(or zygomatic) bone
Fairly large opening on posterior
surface of petrous portion of bone;
transmits eighth cranial nerve to
inner ear and seventh cranial nerve
on its way to facial structures
Oval-shaped depression anterior to external auditory meatus; forms socket
for condyle of mandible
Slender spike of bone extending downward and forward from undersurface
of bone anterior to mastoid process;
often broken off in dry skull; several
neck muscles and ligaments attach to
styloid process
Condyles
Jugular fossa
Jugular foramen
Carotid canal
(or foramen)
Occipital
Foramen magnum
External occipital
protuberance
Superior nuchal
line
Inferior nuchal line
Internal occipital
protuberance
Ethmoid
Horizontal
(cribriform) plate
Crista galli
Perpendicular plate
Ethmoid sinuses
Superior and
middle conchae
(turbinates)
Lateral masses
Description
Opening between styloid and mastoid
processes where facial nerve emerges
from cranial cavity
Depression on undersurface of petrous
portion; dilated beginning of internal
jugular vein lodged here
Opening in suture between petrous
portion and occipital bone; transmits
lateral sinus and ninth, tenth, and
eleventh cranial nerves
Channel in petrous portion; best seen
from undersurface of skull; transmits
internal carotid artery
Forms posterior part of cranial floor
and walls
Hole through which spinal cord enters
cranial cavity
Convex, oval processes on either side of
foramen magnum; articulate with depressions on first cervical vertebra
Prominent projection on posterior
surface in midline short distance
above foramen magnum; can be felt
as definite bump
Curved ridge extending laterally from
external occipital protuberance
Less well-defined ridge paralleling superior
nuchal line a short distance below it
Projection in midline on inner surface of
bone; grooves for lateral sinuses extend
laterally from this process and one for
sagittal sinus extends upward from it
Complicated irregular bone that helps
make up anterior portion of cranial
floor, medial wall of orbits, upper
parts of nasal septum, and sidewalls
and part of nasal roof; lies anterior to
sphenoid and posterior to nasal bones
Olfactory nerves pass through numerous holes in this plate
Meninges (membranes around the
brain) attach to this process
Forms upper part of nasal septum
Honeycombed, mucosa-lined air spaces
within lateral masses of bone
Help to form lateral walls of nose
Compose sides of bone; contain many
air spaces (ethmoid cells or sinuses);
inner surface forms superior and
middle conchae
216
Unit 2
Figure 8-2 Anterior view of the skull.
Skeletal System
Figure 8-3 Skull viewed from the right side.
Chapter 8
217
218
Unit 2
Figure 8-4 Floor of the cranial cavity.
Skeletal System
Figure 8-5 Skull viewed from below.
Chapter 8
219
220
Unit 2
Figure 8-6 Left half of the skull viewed from within.
Figure 8-7 Bones that form the left orbit.
Skeletal System
Chapter 8
Figure 8-8 Bones of the skull. A, Right parietal bone viewed from the lateral side. B, Right temporal bone
viewed from the lateral side. C, Frontal bone viewed from the front and slightly above.
Continued
221
222
Unit 2
Figure 8-8, cont’d Bones of the skull. D, Occipital bone viewed from below. E, Sphenoid bone. E1, Superior
view; E2, posterior view.
Skeletal System
Chapter 8
Figure 8-8, cont’d Bones of the skull. F, Ethmoid bone. F1, Superior view; F2, lateral view; F3, anterior view.
G, Vomer. G1, Anterior view; G2, lateral view.
Continued
223
224
Unit 2
Figure 8-8, cont’d Bones of the skull. H, Right maxilla. H1, Medial view; H2, lateral view. I, Right zygomatic
bone viewed from the lateral side.
Skeletal System
Chapter 8
Figure 8-8, cont’d Bones of the skull. J, Right palatine bone. J1, Medial view; J2, anterior view. K, Right
lacrimal bone viewed from the lateral side. L, Right nasal bone viewed from the lateral side.
Continued
225
226
Unit 2
Figure 8-8, cont’d
Bones of the skull. M, Right half of the mandible. M1, Medial view; M2, lateral view.
Skeletal System
frontal, two parietal, two temporal, occipital, sphenoid, and
ethmoid (Table 8-3). The 14 bones that form the face are two
maxilla, two zygomatic (malar), two nasal, mandible, two
lacrimal, two palatine, two inferior nasal conchae
(turbinates), and vomer (Table 8-4). Note that all the face
bones are paired except for the mandible and vomer. All cranial bones, on the other hand, are single (unpaired) except
for the parietal and temporal bones, which are paired. The
frontal and ethmoid bones of the skull help shape the face
but are not numbered among the facial bones.
Cranial Bones
The frontal bone forms the forehead and the anterior part
of the top of the cranium (see Figure 8-8, C). It contains
mucosa-lined, air-filled spaces, or sinuses—the frontal
sinuses. The frontal sinuses, with similar sinuses in the
sphenoid, ethmoid, and maxillae, are often called paranasal
Chapter 8
227
sinuses because they have narrow channels that open into the
nasal cavity (Figure 8-9). Paranasal sinuses are also discussed
in Chapter 23, pp. 687-688. A portion of the frontal bone
forms the upper part of the orbits. It unites with the two
parietal bones posteriorly in an immovable joint, or
suture—the coronal suture. Several of the more prominent
frontal bone markings are described in Table 8-3.
The two parietal bones give shape to the bulging topside
of the cranium (see Figure 8-8, A). They form immovable
joints with several bones: the lambdoidal suture with the occipital bone, the squamous suture with the temporal bone
and part of the sphenoid, and the coronal suture with the
frontal bone.
The lower sides of the cranium and part of its floor are
fashioned from two temporal bones (see Figure 8-8, B).
They house the middle and inner ear structures and contain
the mastoid sinuses, notable because of the occurrence of
Table 8-4 Facial Bones and Their Markings
Bones and
Markings
Palatine
Horizontal plate
Mandible
Body
Ramus
Condyle (or head)
Neck
Alveolar process
Mandibular
foramen
Mental foramen
Coronoid process
Angle
Maxilla
Description
Bones and
Markings
Form posterior part of hard palate,
floor, and part of sidewalls of nasal
cavity and floor of orbit
Joined to palatine processes of maxillae
to complete part of hard palate
Alveolar process
Maxillary sinus
(antrum of
Highmore)
Palatine process
Lower jawbone; largest, strongest bone
of face
Main part of bone; forms chin
Process, one on either side, that projects
upward from posterior part of body
Part of each ramus that articulates with
mandibular fossa of temporal bone
Constricted part just below condyles
Teeth set into this arch
Opening on inner surface of ramus;
transmits nerves and vessels to lower
teeth
Opening on outer surface below space
between two bicuspids; transmits
terminal branches of nerves and
vessels that enter bone through
mandibular foramen; dentists inject
anesthetics through these foramina
Projection upward from anterior part
of each ramus; temporal muscle
inserts here
Juncture of posterior and inferior
margins of ramus
Upper jaw bones; form part of floor of
orbit, anterior part of roof of mouth,
and floor of nose and part of sidewalls of nose
Infraorbital
foramen
Lacrimal groove
Description
Arch containing teeth
Large mucosa-lined, air-filled cavity
within body of each maxilla; largest
of sinuses
Horizontal inward projection from
alveolar process; forms anterior and
larger part of hard palate
Hole on external surface just below
orbit; transmits vessels and nerves
Groove on inner surface; joined by
similar groove on lacrimal bone to
form canal housing nasolacrimal
duct
Nasal
Small bones forming upper part of
bridge of nose
Zygomatic
Cheekbones; form part of floor and
sidewall or orbit
Lacrimal
Thin bones about size and shape of fingernail; posterior and lateral to nasal
bones in medial wall of orbit; help
form sidewall of nasal cavity, often
missing in dry skull
Interior Nasal
Conchae
(turbinates)
Thin scroll of bone forming shelf along
inner surface of sidewall of nasal
cavity; lies above roof of mouth
Vomer
Forms lower and posterior part of nasal
septum; shaped like the blade of a
plough
228
Unit 2
Table 8-5 Special Features of the Skull
Feature
Description
Feature
Description
Sutures
Immovable joints between skull
bones
Line of articulation along top curved
edge of temporal bone
Joint between parietal bones and
frontal bone
Joint between parietal bones and occipital bone
Joint between right and left parietal
bones
Air Sinuses
Spaces, or cavities, within bones; those
that communicate with nose called
paranasal sinuses (frontal, sphenoidal,
ethmoidal, and maxillary); mastoid
cells communicate with middle ear
rather than nose, therefore not included among paranasal sinuses
Squamous
Coronal
Lambdoidal
Sagittal
Fontanels
Frontal
(or anterior)
Occipital
(or posterior)
Sphenoid (or
anterolateral)
Mastoid (or
posterolateral)
“Soft spots” where ossification is incomplete at birth; allow some compression of skull during birth; also
important in determining position
of head before delivery; six such
areas located at angles of parietal
bones
At intersection of sagittal and coronal
sutures (juncture of parietal bones
and frontal bone); diamond shaped;
largest of fontanels; usually closed by
11⁄2 years of age
At intersection of sagittal and lambdoidal sutures (juncture of parietal
bones and occipital bone); triangular; usually closed by second month
At juncture of frontal, parietal, temporal, and sphenoid bones
At juncture of parietal, occipital, and
temporal bones; usually closed by
second year
Orbits Formed by
Frontal
Ethmoid
Lacrimal
Sphenoid
Zygomatic
Maxillary
Palatine
Roof of orbit
Medial wall
Medial wall
Lateral wall
Lateral wall
Floor
Floor
Nasal Septum
Formed by
Partition in midline of nasal cavity;
separates cavity into right and left
halves
Perpendicular
plate of ethmoid
bone
Forms upper part of septum
Vomer bone
Forms lower, posterior part
Cartilage
Forms anterior part
Wormian Bones
Small islets of bone in sutures
Malleus, Incus,
Stapes
Tiny bones, referred to as auditory ossicles, in middle ear cavity in temporal
bones; resemble, respectively, miniature hammer, anvil, and stirrup
Figure 8-9 The paranasal sinuses.
Skeletal System
mastoiditis, an inflammation of the mucous lining of these
spaces. For a description of several other temporal bone
markings, see Table 8-3.
The occipital bone creates the framework of the lower,
posterior part of the skull (see Figure 8-8, D). It forms immovable joints with three other cranial bones—the parietal,
temporal, and sphenoid—and a movable joint with the first
cervical vertebra. Table 8-3 lists a description of some of its
markings.
The shape of the sphenoid bone resembles a bat with its
wings outstretched and legs extended down and back. Note
in Figures 8-4 and 8-8, E, the location of the sphenoid bone
in the central portion of the cranial floor. Here it serves as
the keystone in the architecture of the cranium, anchoring
the frontal, parietal, occipital, and ethmoid bones. The sphenoid bone also forms part of the lateral wall of the cranium
Box 8-2 HEALTH MATTERS
The Cribriform Plate
eparation of the nasal and cranial cavities by the cribriform plate of the ethmoid bone has great clinical significance. The cribriform plate is perforated by many small
openings, which permit branches of the olfactory nerve responsible for the special sense of smell to enter the cranial
cavity and reach the brain. Separation of these two cavities
by a thin, perforated plate of bone presents real hazards. If
the cribriform plate is damaged as a result of trauma to the
nose, it is possible for potentially infectious material to
pass directly from the nasal cavity into the cranial fossa. If
fragments of a fractured nasal bone are pushed through
the cribriform plate, they may tear the coverings of the
brain or enter the substance of the brain itself.
S
Chapter 8
229
and part of the floor of each orbit (see Figures 8-2 and 8-3).
The sphenoid bone contains fairly large mucosa-lined, airfilled spaces—the sphenoid sinuses (see Figure 8-6). Several
prominent sphenoid markings are described in Table 8-3.
The ethmoid, a complicated, irregular bone, lies anterior
to the sphenoid but posterior to the nasal bones. It helps
fashion the anterior part of the cranial floor (see Figures 8-4
and 8-8, F), the medial walls of the orbits (see Figures 8-2
and 8-7), the upper parts of the nasal septum (see Figure 8-2)
and of the sidewalls of the nasal cavity (Figure 8-10), and the
part of the nasal roof (the cribriform plate) perforated by
small foramina through which olfactory nerve branches
reach the brain. The lateral masses of the ethmoid bone are
honeycombed with sinus spaces (see Figure 8-9). For more
ethmoid bone markings, see Table 8-3.
Facial Bones
The two maxillae serve as the keystone in the architecture of
the face just as the sphenoid bone acts as the keystone of the
cranium. Each maxilla articulates with the other maxilla and
also with a nasal, a zygomatic, an inferior concha, and a palatine bone (see Figure 8-8, H). Of all the facial bones, only the
mandible does not articulate with the maxillae. The maxillae
form part of the floor of the orbits, part of the roof of the
mouth, and part of the floor and sidewalls of the nose. Each
maxilla contains a mucosa-lined space, the maxillary sinus
(see Figure 8-9). This sinus is the largest of the paranasal sinuses, that is, sinuses connected by channels to the nasal cavity. For other markings of the maxillae, see Table 8-4.
Unlike the upper jaw, which is formed by the articulation
of the two maxillae, the lower jaw, because of fusion of its
halves during infancy, consists of a single bone, the mandible
(see Figure 8-8, M). It is the largest, strongest bone of the
face. It articulates with the temporal bone in the only mov-
Figure 8-10 Bones of the nasal cavity.
230
Unit 2
able joint of the skull. Its major markings are identified in
Table 8-4.
The cheek is shaped by the underlying zygomatic, or
malar, bone (see Figure 8-8, I). This bone also forms the
outer margin of the orbit and, with the zygomatic process of
the temporal bone, makes the zygomatic arch. It articulates
with four other facial bones: the maxillary, temporal, frontal,
and sphenoid bones.
Shape is given to the nose by the two nasal bones,
which form the upper part of the bridge of the nose (see
Figure 8-8, L), and by the septal cartilage, which forms the
lower part (see Figure 8-10). Although small, the nasal
bones enter into several articulations: with the perpendicular plate of the ethmoid bone, the cartilaginous part of
the nasal septum, the frontal bone, the maxillae, and each
other.
An almost paper-thin bone, shaped and sized about like a
fingernail, lies just posterior and lateral to each nasal bone. It
helps form the sidewall of the nasal cavity and the medial
wall of the orbit. Because it contains a groove for the nasolacrimal (tear) duct, this bone is called the lacrimal bone
(see Figure 8-8, K). It joins the maxilla, frontal bone, and
ethmoid bone.
The two palatine bones join to each other in the midline
like two Ls facing each other. Their united horizontal portions
form the posterior part of the hard palate (see Figure 8-8, J).
The vertical portion of each palatine bone forms the lateral
wall of the posterior part of each nasal cavity. The palatine
bones articulate with the maxillae and the sphenoid bone.
There are two inferior nasal conchae (turbinates). Each
one is scroll-shaped and forms a kind of ledge projecting
into the nasal cavity from its lateral wall. In each nasal cavity
there are three such ledges. The superior and middle conchae (which are projections of the ethmoid bone) form the
upper and middle ledges. The inferior concha (which is a
separate bone) forms the lower ledge. They are mucosacovered and divide each nasal cavity into three narrow, irregular channels, the nasal meati. The inferior nasal conchae
form immovable joints with the ethmoid, lacrimal, maxilla,
and palatine bones.
Two structures that enter into the formation of the nasal
septum have already been mentioned—the perpendicular
plate of the ethmoid bone and the septal cartilage. One other
structure, the vomer bone, completes the septum posteriorly
(see Figures 8-8, G, and 8-10 and Table 8-5). It forms immovable joints with four bones: the sphenoid, ethmoid,
palatine, and maxillae.
Special features of the skull include sutures, fontanels (Figure 8-11), sinuses, orbits, nasal septum, wormian bones, and
the auditory ossicles; all of which are described in Table 8-5.
HYOID BONE
The hyoid bone is a single bone in the neck—a part of the
axial skeleton (Table 8-6). Its U shape may be felt just above
the larynx (voice box) and below the mandible where it is
suspended from the styloid processes of the temporal bones
(Figure 8-12). Several muscles attach to the hyoid bone.
Among them are an extrinsic tongue muscle and certain
muscles of the floor of the mouth. The hyoid claims the distinction of being the only bone in the body that articulates
with no other bones.
1. Name the eight bones of the cranium and describe how
they fit together.
2. Name the 14 bones of the face and describe how they
fit together.
3. Which bone is the only bone that normally does not form a
joint with any other bone of the skeleton?
Figure 8-11 Skull at birth. A, Viewed from the side (lateral). B, Viewed from above (superior).
Skeletal System
VERTEBRAL COLUMN
The vertebral, or spinal, column forms the longitudinal axis
of the skeleton. It is a flexible rather than a rigid column because it is segmented. As Figure 8-13 shows, the vertebral
column consists of 24 vertebrae plus the sacrum and coccyx.
Joints between the vertebrae permit forward, backward, and
sideways movement of the column. Consider too these further facts about the vertebral column. The head is balanced
on top, the ribs are suspended in front, the lower extremities
Chapter 8
231
are attached below, and the spinal cord is enclosed within. It
is indeed the “backbone” of the body.
The seven cervical vertebrae constitute the skeletal framework of the neck (see Figure 8-13). The next 12 vertebrae are
called thoracic vertebrae because of their location in the posterior part of the chest or thoracic region. The next five, the
lumbar vertebrae, support the small of the back. Below
the lumbar vertebrae lie the sacrum and coccyx. In the adult
the sacrum is a single bone that has resulted from the fusion
Table 8-6 Hyoid, Vertebrae, and Thoracic Bones and Their Markings
Bones and
Markings
Description
Hyoid
U-shaped bone in neck between
mandible and upper part of larynx;
distinctive as only bone in body not
forming a joint with any other bone;
suspended by ligaments from styloid
processes of temporal bones
Vertebral
Column
General
features
Body
Pedicles
Lamina
Neural arch
Spinous process
Transverse processes
Superior articulating
processes
Not actually a column but a flexible,
segmented curved rod; forms axis of
body; head balanced above, ribs and
viscera suspended in front, and lower
extremities attached below; encloses
spinal cord
Anterior part of each vertebra (except
first two cervical) consists of body;
posterior part of vertebrae consists
of neural arch, which, in turn, consists of two pedicles, two laminae,
and seven processes projecting from
laminae
Main part; flat, round mass located anteriorly; supporting or weightbearing part of vertebra
Short projections extending posteriorly
from body
Posterior part of vertebra to which
pedicles join and from which
processes project
Formed by pedicles and laminae; protects spinal cord posteriorly; congenital absence of one or more neural
arches is known as spina bifida (cord
may protrude right through skin)
Sharp process projecting inferiorly
from laminae in midline
Right and left lateral projections from
laminae
Project upward from laminae
Bones and
Markings
Inferior articulating
processes
Spinal foramen
Intervertebral
foramina
Cervical Vertebrae
Atlas
Axis (epistropheus)
Thoracic Vertebrae
Description
Project downward from laminae; articulate with superior articulating
processes of vertebrae below
Hole in center of vertebra formed by
union of body, pedicles, and laminae;
spinal foramina, when vertebrae, superimposed one on other, form
spinal cavity that houses spinal cord
Opening between vertebrae through
which spinal nerves emerge
First or upper seven vertebrae; foramen
in each transverse process for transmission of vertebral artery, vein, and
plexus of nerves; short bifurcated
spinous processes except on seventh
vertebra, where it is extra long and
may be felt as protrusion when head
bent forward; bodies of these vertebrae small, whereas spinal foramina
large and triangular
First cervical vertebra; lacks body and
spinous process; superior articulating processes concave ovals that act
as rockerlike cradles for condyles of
occipital bone named atlas because it
supports the head as Atlas supports
the world in Greek mythology
Second cervical vertebra, so named
because atlas rotates about this bone
in rotating movements of head; dens,
or odontoid process, peglike projection upward from body of axis,
forming pivot for rotation of atlas
Next 12 vertebrae; 12 pairs of ribs attached to these; stronger, with more
massive bodies than cervical vertebrae; no transverse foramina; two
sets of facets for articulations with
Continued
232
Unit 2
Table 8-6 Hyoid, Vertebrae, and Thoracic Bones and Their Markings—cont’d
Bones and
Markings
Thoracic Vertebrae—
cont’d
Lumbar Vertebrae
Sacrum
Sacral promontory
Coccyx
Curves
Primary
Description
corresponding rib: one on body,
second on transverse process; upper
thoracic vertebrae with elongated
spinous process
Next five vertebrae; strong, massive; superior articulating processes directed
medially instead of upward; inferior
articulating processes, laterally
instead of downward; short, blunt
spinous process
Five separate vertebrae until about
25 years of age; then fused to form
one wedge-shaped bone
Protuberance from anterior, upper
border of sacrum into pelvis; of obstetrical importance because its size
limits anteroposterior diameter of
pelvic inlet
Four or five separate vertebrae in child
but fused into one in adult
Curves have great structural importance because they increase carrying
strength of vertebral column, make
balance possible in upright position
(if column were straight, weight of
viscera would pull body forward),
absorb jolts from walking (straight
column would transmit jolts straight
to head), and protect column from
fracture
Column curves at birth from head to
sacrum with convexity posteriorly;
after child stands, convexity persists
only in thoracic and sacral regions,
which therefore are called primary
curves
of five separate vertebrae, and the coccyx is a single bone that
has resulted from the fusion of four or five vertebrae.
All the vertebrae resemble each other in certain features and
differ in others. For example, all except the first cervical vertebra have a flat, rounded body placed anteriorly and centrally,
plus a sharp or blunt spinous process projecting inferiorly in the
posterior midline and two transverse processes projecting laterally (Figure 8-14). All but the sacrum and coccyx have a central opening, the vertebral foramen. An upward projection (the
Bones and
Markings
Description
Secondary
Concavities in cervical and lumbar
regions; cervical concavity results
from infant’s attempts to hold head
erect (2 to 4 months); lumbar concavity, from balancing efforts in
learning to walk (10 to 18 months)
Sternum
Breastbone; flat dagger-shaped bone;
sternum, ribs, and thoracic vertebrae
together form bony cage known as
thorax
Main central part of bone
Flaring, upper part
Projection of cartilage at lower border
of bone
Body
Manubrium
Xiphoid process
Ribs
True ribs
False ribs
Head
Neck
Tubercle
Body or shaft
Costal cartilage
Upper seven pairs; fasten to sternum by
costal cartilages
False ribs do not attach to sternum directly; upper three pairs of false ribs
attach by means of costal cartilage of
seventh ribs; last two pairs do not
attach to sternum at all, therefore
called “floating” ribs
Projection at posterior end of rib; articulates with corresponding thoracic
vertebra and one above, except last
three pairs, which join corresponding vertebrae only
Constricted portion just below head
Small knob just below neck; articulates
with transverse process of corresponding thoracic vertebra; missing
in lowest three ribs
Main part of rib
Cartilage at sternal end of true ribs; attaches ribs (except floating ribs) to
sternum
dens) from the body of the second cervical vertebra furnishes
an axis for rotating the head. A long, blunt spinous process,
which can be felt at the back of the base of the neck, characterizes the seventh cervical vertebra. Each thoracic vertebra has
articular facets for the ribs. More detailed descriptions of separate vertebrae are given in Table 8-6. The vertebral column, as
a whole, articulates with the head, ribs, and iliac bones. Individual vertebrae articulate with each other in joints between
their bodies and between their articular processes.
Skeletal System
Figure 8-12 Hyoid bone.
Figure 8-13 The vertebral column (three views).
Chapter 8
233
234
Unit 2
Figure 8-14 Vertebrae. A, Atlas (first cervical vertebra), superior view. B, Axis (second cervical vertebra),
slightly posterior and superior view. C, Fifth cervical vertebra, superior view. D, Thoracic vertebra, superior view.
E, Lumbar vertebra, superior view. F, Sacrum and coccyx, posterior view.
Skeletal System
Chapter 8
235
Figure 8-15 Thoracic cage. Note the costal cartilages and their articulations with the body of the sternum.
Box 8-3
Vertebroplasty
ertebroplasty (ver-TEE-bro-plasty) is a new, experimental orthopedic procedure that involves the injection
of a “super glue” type of bone cement to repair fractured
and compressed (collapsed) vertebrae. In these patients the
body of one or more vertebra (generally lower thoracic
and/or lumbar segments) have undergone a compression
fracture due to trauma, tumors, or prolonged use of steroid
drugs. In the procedure, bone cement is injected by needle
into the area of compression, where it quickly hardens and
thus stabilizes and seals the fracture. Vertebroplasty is cost
effective, has a short recovery period, and in many cases
may eliminate the need for difficult and expensive spinal
surgery. The procedure is not intended for treatment of
herniated disks and other types of vertebral pathology.
V
To increase the carrying strength of the vertebral column
and to make balance possible in the upright position, the
vertebral column is curved. At birth there is a continuous
posterior convexity from head to coccyx. Later, as the child
learns to sit and stand, secondary posterior concavities necessary for balance develop in the cervical and lumbar regions
(see Figures 33-21 and 33-22, pp. 957-958).
STERNUM
The medial part of the anterior chest wall is supported by the
sternum, a somewhat dagger-shaped bone consisting of
three parts: the upper handle part, the manubrium; the middle blade part, the body; and a blunt cartilaginous lower tip,
the xiphoid process. The last ossifies during adult life. The
manubrium articulates with the clavicle and first rib,
whereas the next nine ribs join the body of the sternum, either directly or indirectly, by means of the costal cartilages
(Figure 8-15).
RIBS
Twelve pairs of ribs, together with the vertebral column and
sternum, form the bony cage known as the thoracic cage, or
simply, the thorax. Each rib articulates with both the body
and the transverse process of its corresponding thoracic vertebra. The head of each rib articulates with the body of the
corresponding thoracic vertebra, and the tubercle of each rib
articulates with the vertebra’s transverse process (Figure 8-16).
In addition, the second through the ninth ribs articulate with
the body of the vertebra above. From its vertebral attachment, each rib curves outward, then forward and downward
(see Figures 8-1 and 8-16), a mechanical fact important for
breathing. Anteriorly, each rib of the first seven pairs joins a
costal cartilage that attaches to the sternum. For this reason,
these ribs are often called the true ribs. Ribs of the remaining
five pairs, the false ribs, do not attach directly to the sternum.
Instead, each costal cartilage of pairs eight, nine, and ten attaches to the costal cartilage of the rib above it—indirectly attaching it to the sternum. Ribs of the last two pairs of false
ribs are designated as floating ribs because they do not attach
even indirectly to the sternum (see Figure 8-15).
1. Name the three types of vertebrae and how many of
each type are found in the vertebral column.
2. What bones make up the bony cage known as the
thorax? How do these bones fit together to form this
structure?
3. What is a floating rib?
236
Unit 2
Figure 8-16 Rib. A, Articulation of the ribs with thoracic vertebra. B, A rib of the left side seen from behind
(posterior).
APPENDICULAR SKELETON
UPPER EXTREMITY
The upper extremity consists of the bones of the shoulder
girdle, upper arm, lower arm, wrist, and hand. Two bones,
the clavicle and scapula, compose the shoulder girdle. Contrary to appearances, this girdle forms only one bony joint
with the trunk: the sternoclavicular joint between the sternum and clavicle. At its outer end, the clavicle articulates
with the scapula, which attaches to the ribs by muscles and
tendons, not by a joint. All shoulder movements therefore
involve the sternoclavicular joint. Various markings of the
scapula are described in Table 8-7 (see also Figure 8-17).
The humerus, or upper arm bone, like other long bones,
consists of a shaft, or diaphysis, and two ends, or epiphyses
(Figures 8-18 and 8-19). The upper epiphysis bears several
identifying structures: the head, anatomical neck, greater
and lesser tubercles, intertubercular groove, and surgical
neck. On the diaphysis are found the deltoid tuberosity and
the radial groove. The distal epiphysis has four projections—
the medial and lateral epicondyles, the capitulum, and the
trochlea—and two depressions—the olecranon and coronoid fossae. For descriptions of all of these markings, see
Table 8-7. The humerus articulates proximally with the
scapula and distally with the radius and the ulna.
Two bones form the framework for the forearm: the radius on the thumb side and the ulna on the little finger side.
At the proximal end of the ulna the olecranon process projects posteriorly and the coronoid process projects anteriorly. There are also two depressions: the semilunar notch on
the anterior surface and the radial notch on the lateral surface. The distal end has two projections: a rounded head and
a sharper styloid process. For more detailed identification of
these markings, see Table 8-7. The ulna articulates proximally with the humerus and radius and distally with a fibrocartilaginous disk, but not with any of the carpal bones.
The radius has three projections: two at its proximal end,
the head and radial tuberosity, and one at its distal end, the
styloid process (see Figures 8-18 and 8-19). There are two
proximal articulations: one with the capitulum of the
humerus and the other with the radial notch of the ulna. The
three distal articulations are with the scaphoid and lunate
carpal bones and with the head of the ulna
The eight carpal bones (Figure 8-20) form what most
people think of as the upper part of the hand but what,
anatomically speaking, is the wrist. Only one of these bones
is evident from the outside, the pisiform bone, which projects
posteriorly on the little finger side as a small rounded elevation. Ligaments bind the carpals closely and firmly together
in two rows of four each: proximal row (from little finger toward thumb)—pisiform, triquetrum, lunate, and scaphoid
bones; distal row—hamate, capitate, trapezoid, and trapezium bones. The joints between the carpals and radius permit
wrist and hand movements.
Of the five metacarpal bones that form the framework of
the hand, the thumb metacarpal forms the most freely movable joint with the carpals. This fact has great significance.
Because of the wide range of movement possible between the
thumb metacarpal and the trapezium, particularly the ability
to oppose the thumb to the fingers, the human hand has
much greater dexterity than the forepaw of any animal and
has enabled humans to manipulate their environment effectively. The heads of the metacarpals, prominent as the proximal knuckles of the hand, articulate with the phalanges.
1. What bones make up the shoulder girdle? Where
does the shoulder girdle form a joint with the axial
skeleton?
2. What are the two bones of the forearm? In the anatomical position, which one is lateral?
3. Name the bones of the hand and wrist.
Text continued on p. 241
Skeletal System
Chapter 8
237
Table 8-7 Upper Extremity Bones and Their Markings
Bones and
Markings
Clavicle
Scapula
Borders
Superior
Vertebral
Axillary
Spine
Acromion process
Coracoid process
Glenoid cavity
Humerus
Head
Anatomical neck
Greater tubercle
Lesser tubercle
Intertubercular
groove
Surgical neck
Deltoid tuberosity
Radial groove
Epicondyles (medial
and lateral)
Capitulum
Trochlea
Olecranon fossa
Description
Collar bones; shoulder girdle joined to
axial skeleton by articulation of clavicles with sternum (scapula does not
form joint with axial skeleton)
Shoulder blades; scapulae and clavicles
together make up shoulder girdle
Bones and
Markings
Coronoid fossa
Radius
Head
Upper margin
Margin toward vertebral column
Lateral margin
Sharp ridge running diagonally across
posterior surface of shoulder blade
Slightly flaring projection at lateral end
of scapular spine; may be felt as tip
of shoulder; articulates with clavicle
Projection on anterior surface from
upper border of bone; may be felt in
groove between deltoid and pectoralis major muscles, about 1 inch
below clavicle
Arm socket
Long bone of upper arm
Smooth, hemispherical enlargement at
proximal end of humerus
Oblique groove just below head
Rounded projection lateral to head on
anterior surface
Prominent projection on anterior
surface just below anatomical neck
Deep groove between greater and lesser
tubercles; long tendon of biceps
muscle lodges here
Region just below tubercles; so named
because of its liability to fracture
V-shaped, rough area about midway
down shaft where deltoid muscle
inserts
Groove running obliquely downward
from deltoid tuberosity; lodges radial
nerve
Rough projections at both sides of
distal end
Rounded knob below lateral epicondyle;
articulates with radius; sometimes
called radial head of humerus
Projection with deep depression
through center similar to shape of
pulley; articulates with ulna
Depression on posterior surface just
above trochlea; receives olecranon
Radial tuberosity
Styloid process
Description
process of ulna when lower arm
extends
Depression on anterior surface above
trochlea; receives coronoid process of
ulna in flexion of lower arm
Bone of thumb side of forearm
Disk-shaped process forming proximal
end of radius; articulates with capitulum of humerus and with radial
notch of ulna
Roughened projection on ulnar side,
short distance below head; biceps
muscle inserts here
Protuberance at distal end on lateral
surface (with forearm in anatomical
position)
Ulna
Bone of little finger side of forearm;
longer than radius
Olecranon process
Elbow
Coronoid process
Projection on anterior surface of proximal end of ulna; trochlea of
humerus fits snugly between olecranon and coronoid processes
Semilunar notch
Curved notch between olecranon and
coronoid process into which trochlea
fits
Radial notch
Curved notch lateral and inferior to
semilunar notch; head of radius fits
into this concavity
Head
Rounded process at distal end; does not
articulate with wrist bones but with
fibrocartilaginous disk
Styloid process
Sharp protuberance at distal end; can be
seen from outside on posterior surface
Carpals
Wrist bones; arranged in two rows at
proximal end of hand; proximal row
(from little finger toward thumb)—
pisiform, triquetrum, lunate, and
scaphoid; distal row—hamate, capitate, trapezoid, and trapezium
Metacarpals
Long bones forming framework of palm
of hand; numbered I through V
Phalanges
Miniature long bones of fingers, three
(proximal, middle, distal) in each
finger, two (proximal, distal) in each
thumb
238
Unit 2
Figure 8-17 Right scapula. A, Anterior view. B, Posterior view. C, Lateral view. D, Posterior view showing articulation with clavicle. (The inset shows the relative position of the right scapula within the entire skeleton.)
Skeletal System
Chapter 8
Figure 8-18 Bones of the arm (right arm, anterior view). A, Humerus (upper arm). B, Radius and ulna
(forearm). C, Elbow joint, showing how the distal end of the humerus joins the proximal ends of the radius and
ulna. (The inset shows the relative position of the right arm bones within the entire skeleton.)
Figure 8-19 Bones of the arm (right arm, posterior view). A, Humerus (upper arm). B, Radius and ulna
(forearm). C, Elbow joint, showing how the distal end of the humerus joins the proximal ends of the radius and
ulna. (The inset shows the relative position of the right arm bones within the entire skeleton.)
239
240
Unit 2
Figure 8-20 Bones of the hand and wrist. A, Dorsal view of the right hand and wrist. B, Palmar view of the
right hand and wrist.
Skeletal System
Chapter 8
241
Box 8-4 FYI
Palpable Bony Landmarks
ealth professionals often identify externally palpable
bony landmarks when dealing with the sick and injured.
Palpable bony landmarks are bones that can be touched
and identified through the skin. They serve as reference
points in identifying other body structures.
There are externally palpable bony landmarks throughout
the body. Many skull bones, such as the zygomatic bone, can
be palpated. The medial and lateral epicondyles of the
humerus, the olecranon process of the ulna, and the styloid
process of the ulna and the radius at the wrist can be palpated on the upper extremity. The highest corner of the
shoulder is the acromion process of the scapula.
When you put your hands on your hips, you can feel
the superior edge of the ilium, called the iliac crest. The anterior end of the crest, called the anterior superior iliac
spine, is a prominent landmark used often as a clinical reference. The sacral promontory is a prominent anteriorly
projecting ridge or border on the superior aspect of the
sacrum. It often serves as a palpable reference point when
measuring the pelvis during obstetrical examinations. The
medial malleolus of the tibia and the lateral malleolus of
the fibula are prominent at the ankle. The calcaneus or heel
bone is easily palpated on the posterior aspect of the foot.
On the anterior aspect of the lower extremity, examples of
palpable bony landmarks include the patella, or kneecap;
the anterior border of the tibia, or shin bone; and the
metatarsals and phalanges of the toes. Try to identify as
many of the externally palpable bones of the skeleton as
possible on your own body. Using these as points of reference will make it easier for you to visualize the placement
of other bones that cannot be touched or palpated
through the skin.
H
LOWER EXTREMITY
Bones of the hip, thigh, lower leg, ankle, and foot constitute
the lower extremity (Table 8-8). Strong ligaments bind each
coxal bone (os coxae, or innominate bone) to the sacrum posteriorly and to each other anteriorly to form the pelvic girdle
(Figures 8-21 and 8-26), a stable, circular base that supports
the trunk and attaches the lower extremities to it. In early
life, each coxal bone is made up of three separate bones.
Later, they fuse into a single, massive irregular bone that is
broader than any other bone in the body. The largest and uppermost of the three bones is the ilium; the strongest and
lowermost, the ischium; and the anteriorly placed pubis.
Numerous markings are present on the three bones (see
Table 8-8 and Figures 8-21 and 8-22).
The pelvis can be divided into two parts by an imaginary
plane, called the pelvic inlet. The edge of this plane, outlined
in Figure 8-21, is called the pelvic brim, or brim of the true
pelvis. The structure above the pelvic inlet, termed the false
pelvis, is bordered by muscle in the front and bone along the
sides and back. The structure below the pelvic inlet, the so-
called true pelvis, creates the boundary of another imaginary
plane, called the pelvic outlet. It is through the pelvic outlet
that the digestive tract empties. The female reproductive
tract also passes through the pelvic outlet; this is a fact of
great importance in childbirth. The pelvic outlet is just large
enough for the passage of a baby during delivery; however,
careful positioning of the baby’s head is required. Measurements such as those shown in Figure 8-21 are routinely
made by obstetricians to ensure successful delivery. Despite
its apparent rigidity, the joint between the pubic portions of
each coxal bone, the symphysis pubis, softens prior to delivery. This allows the pelvic outlet to expand to accommodate
the newborn’s head as it passes out of the birth canal. The
tiny coccyx bone, which protrudes into the pelvic outlet,
sometimes breaks when the force of labor contractions
pushes the newborn’s head against it.
The two thigh bones, or femurs, have the distinction of
being the longest and heaviest bones in the body. Several
prominent markings characterize them. For example, three
projections are conspicuous at each epiphysis: the head and
242
Unit 2
Figure 8-21 The female pelvis.
A, Pelvis viewed from above. Note
that the brim of the true pelvis
(dotted line) marks the boundary
between the superior false pelvis
(pelvis major) and the inferior true
pelvis (pelvis minor). B and C, Pelvis
viewed from below. Comparison
of the male and female pelvis is
shown in Figure 8-26.
Figure 8-22 Right coxal bone. The right coxal bone is disarticulated
from the skeleton and viewed from the side with the bone turned so
as to look directly into the acetabulum.
Skeletal System
greater and lesser trochanters proximally and the medial and
lateral condyles and adductor tubercle distally (Figure 8-23).
Both condyles and the greater trochanter may be felt externally. For a description of the various femur markings, see
Table 8-8.
The largest sesamoid bone in the body, and the one that is
almost universally present, is the patella, or kneecap, located
in the tendon of the quadriceps femoris muscle as a projection to the underlying knee joint. Although some individuals
have sesamoid bones in tendons of other muscles, lists of
bone names usually do not include them because they are not
always present, are not found in any particular tendons, and
Chapter 8
243
are less important. (See the footnote in Table 8-1.) When the
knee joint is extended, the patellar outline may be distinguished through the skin, but as the knee flexes, it sinks into
the intercondylar notch of the femur and can no longer be
easily distinguished.
The tibia is the larger and stronger and more medially
and superficially located of the two leg bones. The fibula is
smaller and more laterally and deeply placed. At its proximal
end it articulates with the lateral condyle of the tibia. The
proximal end of the tibia, in turn, articulates with the femur
to form the knee joint, the largest and one of the most stable
joints of the body. Distally the tibia articulates with the
Table 8-8 Lower Extremity Bones and Their Markings
Bones and
Markings
Coxal
Ilium
Ischium
Pubic bone (pubis)
Acetabulum
Iliac crests
Iliac spines
Anterior superior
Anterior inferior
Posterior superior
Posterior inferior
Greater sciatic
notch
Ischial tuberosity
Ischial spine
Symphysis pubis
Superior ramus
of pubis
Inferior ramus
Pubic arch
Pubic crest
Pubic tubercle
Description
Bones and
Markings
Large hip bone; with sacrum and
coccyx, forms basinlike pelvic cavity;
lower extremities attached to axial
skeleton by coxal bones
Upper, flaring portion
Lower, posterior portion
Medial, anterior section
Hip socket; formed by union of ilium,
ischium, and pubis
Upper, curving boundary of ilium
Obturator foramen
Prominent projection at anterior end of
iliac crest; can be felt externally as
“point” of hip
Less prominent projection short distance below anterior superior spine
At posterior end of iliac crest
Just below posterior superior spine
Large notch on posterior surface of
ilium just below posterior inferior
spine
Large, rough, quadrilateral process
forming inferior part of ischium; in
erect sitting position body rests on
these tuberosities
Pointed projection just above
tuberosity
Cartilaginous, amphiarthrotic joint
between pubic bones
Part of pubis lying between symphysis
and acetabulum; forms upper part of
obturator foramen
Part extending down from symphysis;
unites with ischium
Angle formed by two inferior rami
Upper margin of superior ramus
Rounded process at end of crest
True pelvis (or
pelvis minor)
Pelvic brim
(or inlet)
False pelvis (or
pelvis major)
Pelvic outlet
Pelvic girdle (or
bony pelvis)
Femur
Head
Neck
Greater trochanter
Description
Large hole in anterior surface of os
coxa; formed by pubis and ischium;
largest foramen in body
Boundary of aperture leading into true
pelvis; formed by pubic crests, iliopectineal lines, and sacral promontory; size and shape of this inlet have
obstetrical importance, because if
any of its diameters are too small,
infant skull cannot enter true pelvis
for natural birth
Space below pelvic brim; true “basin”
with bone and muscle walls and
muscle floor; pelvic organs located in
this space
Broad, shallow space above pelvic brim,
or pelvic inlet; name “false pelvis” is
misleading, because this space is actually part of abdominal cavity, not
pelvic cavity
Irregular circumference marking lower
limits of true pelvis; bounded by tip
of coccyx and two ischial tuberosities
Complete bony ring; composed of two
hip bones (ossa coxae), sacrum, and
coccyx; forms firm base by which
trunk rests on thighs and for attachment of lower extremities to axial
skeleton
Thigh bone; largest, strongest bone of
body
Rounded upper end of bone; fits into
acetabulum
Constricted portion just below head
Protuberance located inferiorly and laterally to head
Continued
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Unit 2
Table 8-8 Lower Extremity Bones and Their Markings—cont’d
Bones and
Markings
Description
Small protuberance located inferiorly
and medially to greater trochanter
Intertrochanteric line Line extending between greater and
lesser trochanter
Prominent ridge extending lengthwise
Linea aspera
along concave posterior surface
Supracondylar ridges Two ridges formed by division of linea
aspera at its lower end; medial supracondylar ridge extends inward to
inner condyle, lateral ridge to outer
condyle
Large, rounded bulges at distal end of
Condyles
femur; one medial and one lateral
Blunt projections from the sides of the
Epicondyles
condyles; one on the medial aspect
and one on the lateral aspect
Small projection just above medial
Adductor tubercle
condyle; marks termination of
medial supracondylar ridge
Smooth depression between condyles
Trochlea
on anterior surface; articulates with
patella
Intercondyloid fossa Deep depression between condyles on
posterior surface; cruciate ligaments
(notch)
that help bind femur to tibia lodge in
this notch
Lesser trochanter
Patella
Kneecap; largest sesamoid bone of
body; embedded in tendon of
quadriceps femoris muscle
Tibia
Shin bone
Bulging prominences at proximal end
of tibia; upper surfaces concave for
articulation with femur
Upward projection on articular surface
between condyles
Sharp ridge on anterior surface
Condyles
Intercondylar
eminence
Crest
fibula and also with the talus. The latter fits into a boxlike
socket (ankle joint) formed by the medial and lateral malleoli, projections of the tibia and fibula, respectively. For other
tibial markings, see Table 8-8 and Figure 8-23.
Structure of the foot is similar to that of the hand, with certain differences that adapt it for supporting weight (Figure 824). One example of this is the much greater solidity and the
more limited mobility of the great toe compared to the thumb.
Then, too, the foot bones are held together in such a way as to
form springy lengthwise and crosswise arches (Figure 8-25).
This is architecturally sound, because arches furnish more supporting strength per given amount of structural material than
any other type of construction. Hence the two-way arch construction makes a highly stable base. The longitudinal arch has
Bones and
Markings
Tibial tuberosity
Medial malleolus
Fibula
Lateral malleolus
Tarsals
Calcaneus
Description
Projection in midline on anterior
surface
Rounded downward projection at distal
end of tibia; forms prominence on
medial surface of ankle
Long, slender bone of lateral side of
lower leg
Rounded prominence at distal end of
fibula; forms prominence on lateral
surface of ankle
Bones that form heel and proximal or
posterior half of foot
Heel bone
Talus
Uppermost of tarsals; articulates with
tibia and fibula; boxed in medial and
lateral malleoli
Longitudinal
arches
Tarsals and metatarsals so arranged as to
form arch from front to back of foot
Medial
Formed by calcaneus, talus, navicular,
cuneiforms, and three medial
metatarsals
Lateral
Formed by calcaneus, cuboid, and two
lateral metatarsals
Transverse (or
metatarsal) arch
Metatarsals and distal row of tarsals
(cuneiforms and cuboid) so articulated as to form arch across foot;
bones kept in two arched positions by
means of powerful ligaments in sole
of foot and by muscles and tendons
Metatarsals
Long bones of feet
Phalanges
Miniature long bones of toes; two in
each great toe; three in other toes
an inner, or medial, portion and an outer, or lateral, portion.
Both are formed by the placement of tarsals and metatarsals.
Specifically, some of the tarsals (calcaneus, talus, navicular, and
cuneiforms) and the first three metatarsals (starting with the
great toe) form the medial longitudinal arch. The calcaneus
and cuboid tarsals plus the fourth and fifth metatarsals shape
the lateral longitudinal arch. The transverse arch results from
the relative placement of the distal row of tarsals and the five
metatarsals. (See Table 8-8 for specific bones of different
arches.) Strong ligaments and leg muscle tendons normally
hold the foot bones firmly in their arched positions. Not infrequently, however, these weaken, causing the arches to flatten—
a condition aptly called fallen arches, or flatfeet (see Figure 825, B). Look at Figure 8-25, D, to see what high heels do to the
Skeletal System
Chapter 8
Figure 8-23 Bones of the thigh and leg. A, Right femur, anterior surface. B, Anterior aspect of the right knee
skeleton. C, Right tibia and fibula, anterior surface. D, Posterior aspect. (The inset shows the relative position of
the bones of the thigh and leg within the entire skeleton.)
245
246
Unit 2
position of the foot. They give a forward thrust to the body,
which forces an undue amount of weight on the heads of the
metatarsals. Normally the tarsals and metatarsals have the major role in the functioning of the foot as a supporting structure,
with the phalanges relatively unimportant. The reverse is true
for the hand. Here, manipulation is the main function rather
than support. Consequently, the phalanges of the fingers are all
important, and the carpals and metacarpals are subsidiary.
In Chapter 7 sesamoid bones were described as unique irregular bones generally found embedded in the substance of
tendons close to joints. Although the kneecap, or patella, is
the largest of the sesamoid bones, they also appear quite fre-
Figure 8-24 The foot. A, Bones of the right foot viewed from above. Tarsal bones consist of cuneiforms,
navicular, talus, cuboid, and calcaneus. B, Posterior aspect of the right ankle skeleton and inferior aspect of the
right foot skeleton. C, X-ray film of left foot showing prominent sesamoid bones near the distal end (head) of
the first metatarsal bone of the great toe.
Figure 8-25 Arches of the foot. A, Longitudinal arch. Medial portion formed by calcaneus, talus, navicular,
cuneiforms, and three metatarsals; lateral portion formed by calcaneus, cuboid, and two lateral metatarsals.
B, “Flatfoot” results when there is a weakening of tendons and ligaments attached to the tarsal bones. Downward pressure by the weight of the body gradually flattens out the normal arch of the bones. C, Transverse
arch in the metatarsal region of the left foot. D, High heels throw the weight forward, causing the heads of the
metatarsals to bear most of the body’s weight. (Arrows show direction of force.)
Skeletal System
Chapter 8
247
quently in tendons near the distal end (head) of the first
metatarsal bone of the big toe (Figure 8-24, C).
SKELETAL DIFFERENCES
IN MEN AND WOMEN
General and specific differences exist between male and female skeletons. The general difference is one of size and
weight, the male skeleton being larger and heavier. The specific differences concern the shape of the pelvic bones and
cavity. Whereas the male pelvis is deep and funnel shaped
with a narrow subpubic angle (usually less than 90 degrees),
the female pelvis, as Figure 8-26 shows, is shallow, broad,
Box 8-5 SPORTS AND FITNESS
Chondromalacia Patellae
hondromalacia patellae is a degenerative process
that results in a softening (degeneration) of the articular surface of the patella. The symptoms associated with
chondromalacia of the patella are a common cause of knee
pain in many individuals—especially young athletes. The
condition is usually caused by an irritation of the patellar
groove, with subsequent changes in the cartilage on the
underside of the patella. The most common complaint is of
pain arising from behind or beneath the kneecap, especially during activities that require flexion of the knee, such
as climbing stairs, kneeling, jumping, or running.
C
Figure 8-26 Comparison of male and female bony pelvis.
Table 8-9 Comparison of Male and Female Skeletons
Portion of Skeleton
Male
Female
General Form
Bones heavier and thicker
Muscle attachment sites more massive
Joint surfaces relatively large
Bones lighter and thinner
Muscle attachment sites less distinct
Joint surfaces relatively small
Skull
Forehead shorter vertically
Mandible and maxillae relatively larger
Facial area more pronounced
Processes more prominent
Forehead more elongated vertically
Mandible and maxillae relatively smaller
Facial area rounder, with less pronounced features
Processes less pronounced
Narrower in all dimensions
Deeper
Pelvic outlet relatively small
Long, narrow, with smooth concavity (sacral
curvature); sacral promontory more
pronounced
Less movable
Less than a 90-degree angle
Relatively deep
Turned more inward
Wider in all dimensions
Shorter and roomier
Pelvic outlet relatively large
Short, wide, flat concavity more pronounced in a
posterior direction; sacral promontory less
pronounced
More movable and follows posterior direction of
sacral curvature
Greater than a 90-degree angle
Relatively shallow
Turned more outward and further apart
Narrow
Wide
Pelvis
Pelvic cavity
Sacrum
Coccyx
Pubic arch
Symphysis pubis
Ischial spine, ischial
tuberosity, and anterior
superior iliac spine
Greater sciatic notch
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Unit 2
and flaring, with a wider subpubic angle (usually greater
than 90 degrees). The childbearing function obviously explains the necessity for these and certain other modifications of the female pelvis. These and other differences between the male and female skeleton are summarized in
Table 8-9, p. 247.
1. Which three bones fuse during skeletal development
to form the coxal (hip) bone?
2. List the bones of the lower extremity, indicating their
positions in the skeleton.
3. What is the functional advantage of foot arches?
4. Name two differences between typical male and female
skeletons.
CYCLE OF LIFE
Skeletal System
he changes that occur in the body’s skeletal framework
over the course of life result primarily from structural
changes in bone, cartilage, and muscle tissues. For example,
the resilience of incompletely ossified bone in young children
allows their bones to withstand the mechanical stresses of
childbirth and learning to walk with relatively little risk of fracturing. The density of bone and cartilage in the young to
middle-age adult permits the carrying of great loads. Loss of
T
bone density in later adulthood can make a person so prone
to fractures that simply walking or lifting with moderate force
can cause bones to crack or break. The loss of skeletal tissue
density may result in a compression of weight-bearing bones
that causes a loss of height and perhaps an inability to maintain a standard posture. Degeneration of skeletal muscle
tissue in late adulthood also may contribute to postural
changes and loss of height.
THE BIG PICTURE
Skeletal System
he skeletal system is a good example of increasing structural hierarchy or complexity in the body.
Recall from Chapter 1 that “levels of organization” characterize body structure so that all of our anatomical components
logically fit together and function effectively (see Figure 1-2 on
p. 6). In studying skeletal tissues in Chapter 7, we proceeded
from the chemical level of organization (inorganic salts and
organic matrix) to a discussion of the specialized skeletal and
cartilaginous cells and tissues.
In this chapter, we have grouped skeletal tissues into discrete organs (bones) and then joined groups of individual
T
bones together with varying numbers and kinds of other
structures, such as blood vessels and nerves, to form a complex operational unit—the skeletal system. The “Big Picture”
becomes more apparent when we integrate the skeletal system with other organ systems, which ultimately allow us to
respond in a positive way to disruptions in homeostasis. The
skeletal system, for example, plays a key role in purposeful
movement, which, in turn, allows us to move away from potentially harmful stimuli. This organ system is much more
than an assemblage of individual bones—it is a complex and
interdependent functional unit essential for life.
MECHANISMS OF DISEASE
Fractures and Abnormal Spinal Curvatures
Bone Fractures
A bone fracture is defined as a partial or complete break in
the continuity of a bone that occurs under mechanical stress.
The most common cause of a fracture is traumatic injury.
Bone cancer or metabolic bone disorders can also cause fractures by weakening a bone to the point that it fractures under very little stress. An open fracture, also known as a compound fracture, is one in which broken bone projects
through surrounding tissue and skin, inviting possibility of
infection (Figure 8-27, A). A closed fracture, also known as a
simple fracture, does not produce a break in the skin and
therefore does not pose an immediate danger of bone infec-
tion (Figure 8-27, B). As Figure 8-27, C, shows, fractures also
are classified as “complete” or “incomplete.” A complete fracture involves a break across the entire section of bone,
whereas an incomplete fracture involves only a partial break,
in which bone fragments are still partially joined.
Fractures are also described anatomically according to the
bone involved (e.g., femur) and the region of bone in which
the fracture occurs (e.g., distal). There are many different
specific types of fractures. For example, a greenstick fracture
is one in which one side of the bone is bent and the other
side is broken. This type of fracture commonly occurs in
children because their growing bones are less brittle than in
the adult. A dentate fracture results in fragmented ends of
Skeletal System
the bone being jagged and opposing each other, fitting together like teeth on a gear. A hangman’s fracture is a fracture
of the posterior elements of the second vertebral bone of the
spine.
Sometimes the angle of the fracture line or crack is used
in labeling fracture types (Figure 8-27, D). A linear fracture
involves a fracture line parallel to the bone’s long axis. A fracture line at a right angle to the bone’s long axis is labeled a
transverse fracture. Oblique fractures occur at slanted, or diagonal, angles to the longitudinal axis of bone.
Clinical signs and symptoms of a fracture are loss of
function or false motion, pain, soft tissue edema, and deformity. These vary with the type and location of the fracture.
Treatment usually involves reduction or realignment of the
bone, immobilization, and restoring function through reha-
Chapter 8
249
bilitation. Repair of bone tissue is discussed in Skeletal Tissues (Chapter 7).
Abnormal Spinal Curvatures
The normal curvature of the spine is convex through the thoracic region and concave through the cervical and lumbar regions (see Figure 8-13). This gives the spine strength to support
the weight of the rest of the body and balance necessary to stand
and walk. A curved structure has more strength than a straight
one of the same size and material. Poor posture or disease may
cause the lumbar curve to be abnormally accentuated—a condition known as “sway back,” or lordosis (Figure 8-28, A). This
condition is frequently seen during pregnancy as the woman
adjusts to changes in her center of gravity. It may also be idiopathic, secondary to traumatic injury, or a degenerative process
Figure 8-27 Bone fractures. A, Open. B, Closed. C, Incomplete and complete. D, Linear, transverse, and
oblique.
Figure 8-28 Abnormal spine curvatures. A, Lordosis. B, Kyphosis. C, Scoliosis. D, X-ray film of scoliosis
curvature.
250
Unit 2
of the vertebral bodies. Kyphosis, or “hunchback,” is an abnormally increased roundness in the thoracic curvature (Figure 828, B). It is frequently seen in elderly people with osteoporosis
or chronic arthritis, those with neuromuscular diseases, or
compression fractures of the thoracic vertebrae. In a condition
called Scheuermann’s disease, kyphosis can develop in children
at puberty. Abnormal side-to-side curvature is called scoliosis
(Figure 8-28, C). This too may be idiopathic or a result of damage to the supporting muscles along the spine. It is a relatively
common condition that appears before adolescence.
All three abnormal curvatures can interfere with normal
breathing, posture, and other vital functions. The degree of
curvature and resulting deformity of the vertebral column determine the various treatments instituted. The traditional
treatment for scoliosis is the use of a supportive brace, called
the Milwaukee brace, that is worn on the upper body 23 hours
per day for up to several years. A newer approach to straighten
abnormal curvature is transcutaneous stimulation. In this
method, muscles on one side of the vertebral column are electrically stimulated to contract and pull the vertebrae into a
more normal position. If these methods fail, surgical intervention is used in which pieces of bone from elsewhere in the
skeleton, or metal rods, are grafted to the deformed vertebrae
to hold them in proper alignment. If treated early enough,
kyphosis resulting from poor posture can be corrected with
special exercises and instructions for appropriate posture.
Kyphosis resulting from pathological causes may also require
special braces or surgical intervention.
Skeletal System
Chapter 8
251
CASE STUDY
W
endy Jones, age 12, during a school physical examination, is noted to have uneven shoulder and hip
levels and a rotational deformity producing rib hump on
forward flexion.
1. Based on the above information, it would be expected
that Wendy has which one of the following?
A. Kyphosis
B. Lordosis
C. Osteoporosis
D. Scoliosis
2. The best test to confirm the diagnosis would be:
A. Spinal x-ray
B. Spinal CAT scan
C. MRI
D. Ultrasound
3. One of the treatments for this abnormal curvature
might be the use of a Milwaukee brace. Which one of
the following instructions should be included in the
teaching session for Wendy and her parents?
A. Wendy should remove the brace for only 1 hour a
day to bathe.
B. Wendy will need to wear the brace for approximately 2 months.
C. The brace is the best available method to treat
Wendy’s problem.
D. Wendy will be allowed to take the brace off every
night so that she can sleep but must put it back on
every morning.
CHAPTER SUMMARY
INTRODUCTION
A. Skeletal tissues form bones—the organs of the skeletal
system
B. The relationship of bones to each other and to other
body structures provides a basis for understanding
the function of other organ systems
C. The adult skeleton is composed of 206 separate
bones
DIVISIONS OF SKELETON (Figure 8-1; Table 8-1)
A. Axial skeleton—the 80 bones of the head, neck, and
torso; composed of 74 bones that form the upright axis
of the body and six tiny middle ear bones
B. Appendicular skeleton—the 126 bones that form the
appendages to the axial skeleton; the upper and lower
extremities
AXIAL SKELETON
A. Skull—made up of 28 bones in two major divisions:
cranial bones and facial bones (Figures 8-2 to 8-7;
Table 8-3)
1. Cranial bones
a. Frontal bone (Figure 8-8, C)
(1) Forms the forehead and anterior part of the
top of the cranium
(2) Contains the frontal sinuses
(3) Forms the upper portion of the orbits
(4) Forms the coronal suture with the two parietal bones
b. Parietal bones (Figure 8-8, A)
(1) Form the bulging top of the cranium
(2) Form several sutures: lambdoidal suture with
occipital bone; squamous suture with temporal bone and part of sphenoid; and coronal
suture with frontal bone
c. Temporal bones (Figure 8-8, B)
(1) Form the lower sides of the cranium and part
of the cranial floor
(2) Contain the inner and middle ears
d. Occipital bone (Figure 8-8, D)
(1) Forms the lower, posterior part of the skull
(2) Forms immovable joints with three other cranial bones and a movable joint with the first
cervical vertebra
e. Sphenoid bone (Figure 8-8, E)
(1) A bat-shaped bone located in the central portion of the cranial floor
(2) Anchors the frontal, parietal, occipital, and
ethmoid bones and forms part of the lateral
wall of the cranium and part of the floor of
each orbit
(3) Contains the sphenoid sinuses
f. Ethmoid bone (Figure 8-8, F)
(1) A complicated, irregular bone that lies anterior to the sphenoid and posterior to the
nasal bones
(2) Forms the anterior cranial floor, medial orbit
walls, upper parts of the nasal septum, and
sidewalls of the nasal cavity
(3) The cribriform plate is located in the ethmoid
2. Facial bones (Table 8-4)
a. Maxilla (upper jaw) (Figure 8-8, H)
(1) Two maxillae form the keystone of the face
(2) Maxillae articulate with each other and with
nasal, zygomatic, inferior concha, and palatine bones
(3) Forms parts of the orbital floors, roof of
the mouth, and floor and sidewalls of the
nose
(4) Contains maxillary sinuses
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Unit 2
b. Mandible (lower jaw) (Figure 8-8, M)
(1) Largest, strongest bone of the face
(2) Forms the only movable joint of the skull
with the temporal bone
c. Zygomatic bone (Figure 8-8, I)
(1) Shapes the cheek and forms the outer margin
of the orbit
(2) Forms the zygomatic arch with the zygomatic
process of the temporal bones
d. Nasal bone (Figures 8-8, L, and 8-10)
(1) Both nasal bones form the upper part of the
bridge of the nose, whereas cartilage forms
the lower part
(2) Articulates with the ethmoid, nasal septum,
frontal, maxillae, and the other nasal bone
e. Lacrimal bone (Figure 8-8, K)
(1) Paper-thin bone that lies just posterior and
lateral to each nasal bone
(2) Forms the nasal cavity and medial wall of the
orbit
(3) Contains groove for the nasolacrimal (tear)
duct
(4) Articulates with the maxilla, frontal, and ethmoid bones
f. Palatine bone (Figure 8-8, J)
(1) Two bones form the posterior part of the
hard palate
(2) Vertical portion forms the lateral wall of the
posterior part of each nasal cavity
(3) Articulates with the maxillae and the sphenoid bone
g. Inferior nasal conchae (turbinates)
(1) Form lower edge projecting into the nasal
cavity and form the nasal meati
(2) Articulate with ethmoid, lacrimal, maxillary,
and palatine bones
h. Vomer bone (Figure 8-8, G)
(1) Forms posterior portion of the nasal septum
(2) Articulates with the sphenoid, ethmoid, palatine, and maxillae
B. Hyoid bone (Figure 8-12)
1. U-shaped bone located just above the larynx and below the mandible
2. Suspended from the styloid processes of the temporal
bone
3. Only bone in the body that articulates with no other
bones
C. Vertebral column (Figure 8-13)
1. Forms the flexible longitudinal axis of the skeleton
2. Consists of 24 vertebrae plus the sacrum and coccyx
3. Segments of the vertebral column:
a. Cervical vertebrae, 7
b. Thoracic vertebrae, 12
c. Lumbar vertebrae, 5
d. Sacrum—in the adult, results from the fusion of
five separate vertebrae
e. Coccyx—in the adult, results from the fusion of
four or five separate vertebrae
4. Characteristics of the vertebrae (Figures 8-14;
Table 8-6)
a. All vertebrae, except the first, have a flat,
rounded body anteriorly and centrally, a spinous process posteriorly, and two transverse
processes laterally
b. All but the sacrum and coccyx have a vertebral
foramen
c. Second cervical vertebrae has an upward projection, the dens, to allow rotation of the head
d. Seventh cervical vertebra has a long, blunt spinous process
e. Each thoracic vertebra has articular facets for
the ribs
5. Vertebral column as a whole articulated with the
head, ribs, and iliac bones
6. Individual vertebrae articulate with each other in
joints between their bodies and between their articular processes
D. Sternum (Figure 8-15)
1. Dagger-shaped bone in the middle of the anterior
chest wall made up of three parts:
a. Manubrium—the upper handle part
b. Body—middle blade part
c. Xiphoid process—blunt cartilaginous lower tip,
which ossifies during adult life
2. Manubrium articulates with the clavicle and first rib
3. Next nine ribs join the body of the sternum,
either directly or indirectly, by means of the costal
cartilages
E. Ribs (Figures 8-15 and 8-16)
1. Twelve pairs of ribs, with the vertebral column and
sternum, form the thorax
2. Each rib articulates with the body and transverse process of its corresponding thoracic vertebra
3. Ribs 2 through 9 articulate with the body of the vertebra above
4. From its vertebral attachment, each rib curves outward, then forward and downward
5. Rib attachment to the sternum:
a. Ribs 1 through 8 join a costal cartilage that attaches it to the sternum
b. Costal cartilage of ribs 8 through 10 joins the cartilage of the rib above to be indirectly attached to
the sternum
c. Ribs 11 and 12 are floating ribs, since they do not
attach even indirectly to the sternum
APPENDICULAR SKELETON
A. Upper extremity (Table 8-7)
1. Consists of the bones of the shoulder girdle, upper
arm, lower arm, wrist, and hand
2. Shoulder girdle (Figure 8-17)
a. Made up of the scapula and clavicle
b. Clavicle forms the only bony joint with the trunk,
the sternoclavicular joint
c. At its distal end, the clavicle articulates with the
acromion process of the scapula
Skeletal System
3. Humerus (Figures 8-18 and 8-19)
a. The long bone of the upper arm
b. Articulates proximally with the glenoid fossa of
the scapula and distally with the radius and ulna
4. Ulna
a. The long bone found on the little finger side of
the forearm
b. Articulates proximally with the humerus and radius and distally with a fibrocartilaginous disk
5. Radius
a. The long bone found on the thumb side of the
forearm
b. Articulates proximally with the capitulum of the
humerus and the radial notch of the ulna; articulates distally with the scaphoid and lunate carpals
and with the head of the ulna
6. Carpal bones (Figure 8-20)
a. Eight small bones that form the wrist
b. Carpals are bound closely and firmly by ligaments
and form two rows of four carpals each
(1) Proximal row is made up of the pisiform, triquetrum, lunate, and scaphoid
(2) Distal row is made up of the hamate, capitate,
trapezoid, and trapezium
c. The joints between the radius and carpals allow
wrist and hand movements
7. Metacarpal bones
a. Form the framework of the hand
b. The thumb metacarpal forms the most freely
movable joint with the carpals
c. Heads of the metacarpals (the knuckles) articulate
with the phalanges
B. Lower extremity
1. Consists of the bones of the hip, thigh, lower leg, ankle, and foot (Table 8-8)
2. Pelvic girdle is made up of the sacrum and the two
coxal bones bound tightly by strong ligaments
(Figure 8-21)
a. A stable circular base that supports the trunk and
attaches the lower extremities to it
b. Each coxal bone is made up of three bones that
fuse together (Figure 8-22):
(1) Ilium—largest and uppermost
(2) Ischium—strongest and lowermost
(3) Pubis—anteriormost
3. Femur—longest and heaviest bone in the body (Figure 8-23)
4. Patella—largest sesamoid bone in the body
5. Tibia
a. The larger, stronger, and more medially and superficially located of the two leg bones
b. Articulates proximally with the femur to form the
knee joint
c. Articulates distally with the fibula and talus
6. Fibula
a. The smaller, more laterally and deeply placed of
the two leg bones
b. Articulates with the tibia
Chapter 8
253
7. Foot (Figures 8-24 and 8-25)
a. Structure is similar to that of the hand with adaptations for supporting weight
b. Foot bones are held together to form spring
arches
(1) Medial longitudinal arch is made up of the
calcaneus, talus, navicular, cuneiforms, and
medial three metatarsals
(2) Lateral longitudinal arch is made up of the
calcaneus, cuboid, and fourth and fifth
metatarsals
SKELETAL DIFFERENCES
IN MEN AND WOMEN
A. Male skeleton is larger and heavier than female skeleton
B. Pelvic differences (Figure 8-26; Table 8-9)
1. Male pelvis—deep and funnel shaped with a narrow
pubic arch
2. Female pelvis—shallow, broad, and flaring with a
wider pubic arch
CYCLE OF LIFE: SKELETAL SYSTEM
A. Changes in the skeletal framework result from changes
in bone, cartilage, and muscle tissue
B. Older adults
1. Loss of bone density
a. Prone to fractures
2. Loss of skeletal tissue density
a. Compression of weight-bearing bones
(1) Loss of height
(2) Postural changes
3. Degeneration of skeletal muscle tissue
a. Loss of height
b. Postural changes
REVIEW QUESTIONS
1. Describe the skeleton as a whole and identify its two
major subdivisions.
2. Identify and differentiate the bones in the cranium and
face.
3. Name and locate the fontanels and sutures of the skull.
4. Name the five pairs of bony sinuses in the skull.
5. Discuss the clinical (medical) importance of the cribriform plate of the ethmoid bone and the mastoid air
cells in the temporal bone.
6. Identify and discuss the normal primary and secondary
curves of the spine.
7. Describe and distinguish between the different kinds of
bone fractures and discuss symptoms and treatments
for broken bones.
8. Identify the bony components of the thorax.
9. Identify the bones of the shoulder and pelvic girdles.
10. Identify, compare, and organize the bones of the arm,
forearm, wrist, and hand with those of the thigh, lower
leg, ankle, and foot.
254
Unit 2
11. Discuss the arches of the foot and point out the functional importance of each.
12. Describe the role of the symphysis pubis during
childbirth.
13. Describe vertebroplasty.
CRITICAL THINKING QUESTIONS
1. How would you compare and contrast the differences
between the skeletal structure of males and females.
What are the physiological reasons for these differences?

Textbook Ch. 9 Skeletal System

Transcription

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