Tissues and Organs of the Skeletal System
Functions of the Skeleton
The skeleton functions in support, protection, movement, blood formation, electrolyte balance, acid-base
balance, and detoxification of the body.
The Shapes of Bones
Long bones include those in the appendages that produce body movement.
Examples of long bones are the femur and the humerus
Short bones are equal in length and width, such as those of the
wrist and ankle. Example of short bones are the carpals and tarsals
Flat bones, such as in the skull, protect soft tissues. Examples of flat bones are the parietal and frontal bones
Irregular bones have elaborate shapes that don’t fit any
of the previous categories. Example: the vertebrae.
Sesamoid bones example – the patella
General Features of Bones
The features of a long bone include its outer layer of compact bone, a medullary cavity containing
bone marrow, and spongy bone at its ends.
The shaft of a long bone is referred to as the diaphysis; the expanded ends are the epiphyses.
The epiphyses are covered with articular cartilage, and the outer bone is covered by periosteum.
The inside is lined with endosteum.
Lamellae are arranged in concentric circles around haversian canals. This is the basic structural unit
of compact bone, collectively called an osteon.
Within the lamellae lie the lacunae with osteocytes. Canaliculi extend between adjacent lamellae.
Perforating (Volkmann's) canals enter the bone from the outside and inside, and feed into the haversian
canals, carrying nerves and blood vessels.
Spongy bone consists of slender rods, plates, and spines called trabeculae. Bone marrow occupies the
spaces within the trabeculae.
Processes that are sites of muscle
and ligament attachment:
Tuberosity: Large rounded projection that
may be roughened.
Crest: Narrow, usually prominent, ridge of bone.
Trochanter: Very large, blunt, irregularly shaped process.
Line: Narrow ridge of bone that is less prominent than a crest.
Tubercle: Small rounded process.
Epicondyle: Raised area on or above a condyle.
Spine: Sharp, slender, often pointed process.
Processes that help to form joints:
Head: Bony expansion carried on a
Facet: Smooth, nearly flat articular surface.
Condyle: Rounded articular projection.
Ramus: Armlike bar of a bone.
Depressions and openings that allow blood vessels
and nerves to pass:
Meatus: Canal-like passageway.
Sinus: Cavity within a bone, filled with air and lined with mucous membrane.
Fossa: Shallow, basinlike depression in a bone, often serving as an articular surface.
Fissure: Narrow, slitlike opening.
Foramen: Round or oval opening through a bone.
1. The skull (cranium) bones are locked into position with sutures.
Several large cavities occur in the skull: the cranial cavity, orbits, nasal cavity, buccal cavity,
middle- and inner-ear cavities, and paranasal cavities.
3. Four bones contain paranasal sinuses: frontal, sphenoid, ethmoid, and maxillary.
Bones of the skull have foramina, which are holes that allow for the passage of nerves and blood vessels. The spinal cord
connects with the brain through the foramen magnum.
Eight cranial bones directly contact the meninges around the brain.
The frontal bones anterior, forms the forehead, superior to orbits. Feature
the supraorbital margin, supraorbital foramen, and glabella. The coronal suture marks the edge of the frontal bone.
The parietal bones (X2) posterolateral to frontal bone, sides
of cranium; extend from the coronal suture to the lambdoidal suture. The sagittal suture articulation between the two
parietal bones at the top of the skull.
The temporal bones form the lower lateral walls of the cranium. Four regions:
Squamous region – close to parietal and includes: Squamous suture, zygomatic
process and mandibular fossa.
Tympanic region – around the external ear opening includes: external auditory
meatus and styloid process.
Mastoid region – in the area posterior to the ear. Includes mastoid process
and stylomastoid foramen (can be seen in the inferior view of the skull).
Petrous region – forms the lateral portion of the skull base. Includes
jugular foramen, carotid canal, internal acoustic meatus and foramen lacerum (can be seen in the inferior view of the skull).
The occipital bone at the posterior base of the cranium. Includes lambdoid
suture, foramen magnum, occipital condyles, hypoglossal canal and external occipital crest and protuberance.
sphenoid is a bat-shaped bone that lies at the anterior base of the brain. Includes the greater and lesser wings,
the latter of which forms part of the orbit, superior orbital fissures, sella turcica, optic canals, foramen rotundum and
ethmoid anterior to the sphenoid forms the roof of the nasal cavity, and its perpendicular plate forms the superior
portion of the nasal septum. Includes the crista galli, cribiform plates, perpendicular plate, lateral masses and superior
and middle nasal conchae.
B. Facial Bones
facial bones form the face.
The maxillae (X2) are the largest facial bones and form the upper jaw.
processes mark the spaces between the upper teeth each tooth fits into an alveolus. Other features of the maxillae include:
infraorbital foramen, inferior orbital fissure, the hard palate, palatine processes, and incisive foramen.
The palatine bones (X2) posterior to the palatine process. Form the posterior
part of the hard palate and part of the orbit
The zygomatic (X2) lateral to maxilla, form the cheekbones and part of lateral
orbit. Include 3 processes that are named after the bones with which they articulate.
The lacrimal bones (X2) form part of the medial wall of each orbit between
the maxilla and ethmoid. It contains the lacrimal fossa that houses a lacrimal sac where tears collect.
The nasal bones (X2) form the bridge of the nose.
The vomer (1) in the median plane of the nasal cavity. Forms the posterior
and inferior nasal septum.
Inferior nasal conchae (X2) thin bones found medially from the lateral walls
of the nasal cavity
The mandible (1) is the strongest bone of the skull and forms the lower jaw.
Articulate with the temporal bone with freely movable joints. The mandible supports the lower teeth and allows mastication.
Includes the mandibular body, mandibular ramus, mandibular condyle, coronoid process, mandibular angel, mental foramen, mandibular
foramen, alveolar margin and mandibular symphysis.
C. Bones Associated with the Skull
1. Also associated with the skull are the middle-ear auditory ossicles and the hyoid bone
which is not a part of the skull and located in the throat.
Vertebral Column and Thoracic Cage
vertebral column supports the skull and trunk, protects the spinal cord, and acts as a shock absorber during movement. The
column extends from the skull to the pelvis. It surrounds and protects the spinal cord. Intervertebral discs of fibrocartilage
separate the vertebrae.
Structure of a Vertebra
body of each vertebra is a mass of spongy bone surrounded by compact bone, and is the weight-bearing portion. Other
features of a general vertebra include: vertebral foramen, pedicle, lamina, spinous process, transverse process, superior
and inferior articulating processes.
Characteristics of Vertebrae (fig. 10.14; table 10.1)
seven cervical vertebrae (C1-C7) are unique with their bifid spinous processes and presence of transverse foramina.
The transverse processes are wide and contain foramina. Vertebra C7 spinous process is visible through the skin and it is
called vertebra prominens.
The first cervical vertebra (C1) is the atlas that holds up the weight of the
head. It lacks a body and its two lateral processes contain concave depression that connects with the occipital condyles.
This joint allows the "yes" movement of the head.
C2, the axis, has a distinctive dens or odontoid process that serves as the pivot
point for turning the head. The articulation between C1+C2 allows the "no" movement.
12 thoracic vertebrae (T1-T5) correspond to the 12 pairs of ribs attached to them.
The thoracic vertebrae have the following distinctive features: downward sloping spinous process, larger body, articular
surfaces for attachment to ribs, and a costal facet on the transverse process where ribs attach.
five lumbar vertebrae (L1-L5) feature a thick, stout body, and a blunt, squarish spinous process that extends directly
backwards. The superior articular facets face posteromedially and the inferior ones are directed anterolaterally. These structure
features reduce the mobility of the lumbar area and thus the lumbar vertebrae are especially resistant to twisting.
five sacral vertebrae are fused into a single bone (the sacrum) by age 26. The anterior surface forms the wall of the
pelvic cavity, and four pairs of pelvic foramina are found on this anterior surface.
the posterior side the medial sacral crest is a residue of the spinous process of the fused vertebrae. The sacral
foramina (opening for the spinal nerves) are located at both sides of the transverse ridges. The sacral canal is the continuous
of the vertebral canal and it terminates near the coccycx with an enlarged opening called the sacral hiatus.
The coccyx (tailbone) consists of 3-5 small vertebrae fused into a single triangular bone in the adult. It is
attached to the sacrum by ligaments.
Thoracic Cage – bony thorax
thoracic cage consists of the thoracic vertebrae, sternum, and ribs.
sternum is a flat bone and it is consists of the manubrium, body (gladiolus), and xiphoid process. The sternum has
3 landmarks: the jugular notch at the level of the 3rd thoracic vertebra, the sternal angel where
the manubrium is meeting the sternal body (at the level of the 2nd ribs and xiphisternal joint where the
sternal body and the xiphoid fuse (at the level of the 9th thoracic vertebra.
ribs protect the thoracic organs and the spleen, liver, and portions of the kidneys.
There are 12 pairs of ribs. The Ribs have a head, tubercle, neck, and superior and inferior articulating facets. All
ribs articulate posteriorly with the vertebral column via their heads and tubercles and then curve downward toward the anterior
side of the body.
Ribs 1–7 are true ribs, and attach directly to the sternum with their own costal cartilages. Ribs 8–10
are false ribs because they attach to the cartilage of rib 7; ribs 11 and 12 are floating ribs and do not join the sternum.
The appendicular skeleton
Pectoral Girdle (shoulder) and Upper Limb
pectoral girdle supports the arm. It consists of the clavicle and scapula.
The clavicle or collarbone is a slightly S-shaped bone. Its sternal end, which attaches to the sternal manubrium,
is rounded, and its acromial end is flattened where it articulate with the scapula. On the posteroinferior surface
there is the conoid tubercle on which a ligament is attached.
The triangular scapula or shoulder blades have a flattened body and 2 processe – the acromion and
the coracoid. The first connects to the clavicle and the latter serves as an attachment point for some of the arm muscles.
The suprascapulare notch is found at the base of the coracoid process and it allows passage of nerves.
The scapula has several fossa (depressions): the anterior subscapular fossa and the posterior infraspinous
and supraspinous fossae.
scapula also features the glenoid cavity a socket that receives the head of the arm (humerus).
scapula articulates with the clavicle and humerus.
upper extremity is divided into four regions: brachium, antebrachium, carpus, and manus.
brachium (arm) contains only one long bone, the humerus. The round head of the humerus articulates with the glenoid
cavity of the scapula. Other features include: anatomical neck, surgical neck, greater (lateral) and lesser
(medial) tubercles, an intertubercular groove that guides the tendon of the biceps muscle, deltoid tuberosity
in the midpoint of the shaft where the deltoid is attached, capitulum which is the lateral point of attachment with
the radius, trochlea which is the attachment point with the ulna, and lateral and medial epicondyles.
the trochlea the coronoid fossa is found and the olecranon fossa is found on the posterior side. These 2 allow
the process of the ulna to move freely. The radial fossa (lateral to the coronoid one) houses the radius head when
the elbow flexes.
The antebrachium, or forearm, contains two bones, the radius and the ulna. When in anatomical position, the
radius is in lateral position and the 2 bones are parallel.
proximal head of the radius articulates with the humerus head and ulna. Features of the radius include: a radial tuberosity
– a point of attachment for the biceps tendon, styloid process – a point of attachment for the wrist ligaments
and an ulnar notch where the radius articulates with the ulna.
proximal ulna bears a deep C-shaped notch where it wraps around the trochlea of the humerus. The olecranon and coronoid
process mark either side of the notch and the 2 processes grip the trochlea of the humerus. The radial notch articulates
with the head of the radius. A styloid process can be found at the distal edge of the ulna and it serve as a point
of attachment for the wrist ligaments.
carpus, or wrist, contains eight small bones (carpals) arranged in two rows. The 8 carpals are: scaphoid, lunate, triquetral,
pisiform, trapezium, trapezoid, capitate, and hamate.
The manus, or hand, contains 19 bones in two groups, metacarpal (palm)
bones and phalanges (fingers).
bones of the palm are the metacarpals, each having a base, body, and head.
The finger bones are called the phalanges; there are two phalanges in the pollex (thumb) and three in each of the other
The Pelvic Girdle and Lower Limb
The pelvic girdle supports the trunk on the legs and encloses and protects the pelvic viscera. Each half of the pelvic
girdle is called the os coxae/coxal bone; these two join in the front in the symphysis pubis. The adult os coxae
form by the fusion of the ilium, ischium, and pubis.
The ileum forms the major portion of the coxal bone. It connects with the sacrum at the sacroiliac joint.
The superior margin of the iliac bone is the iliac crest. The iliac crest terminates anteriorly with the anterior
superior spine and posteriorly with the posterior superior spine. The iliac fossa mark the internal surface
and the arcuate line outline the pelvic brim (pelvic edge).
ischium forms the inferior and posterior part of the coxal bone. The ischial tuberosity has a part in "receiving"
the body weight when sitting. Also can be found the ischial spine and the lesser and greater sciatic notches.
The pubis/pubic bone is the most anterior portion of the coxal bone. The fusion of the pubic bone and the ischium
form the obturator foramen. The pubic bones meet anteriorly at the pubic crest in a cartilage joint called pubic
symphysis. On the lateral side of the pubic crest the pubic tubercule is found and to which the inguinal ligament
3 hip bones fuse together at the acetabulum socket which receives the femoral head.
and female pelvises are shaped somewhat differently, allowing for childbirth in females. (Table 11.1)
lower extremity is adapted for weight-bearing and locomotion; it includes the femoral region, the patella, crural
region, tarsus, and foot.
femur, or thigh bone, is the longest and strongest bone of the body. Features of the femur include: fovea capitis,
greater and lesser trochanters, linea aspera, medial and lateral condyles articulation point with
the tibia, an intercondylar fossa, medial and lateral epicondyles and patellar surface.
patella (kneecap) is a triangular bone with a broad superior base, a pointed inferior apex, and two articular facets.
crural region contains two bones, the tibia (shinbone) and the fibula. The tibia is the larger and stronger
of the two lower leg bones, and the only one that bears weight. Features of the tibia are: medial and lateral condyles
that receive the distal end of the femur to form the knee joint, an intercondylar eminence, tibial tuberosity
an attachment point of the patellar ligament, anterior border/margin, and medial and lateral malleoli.
fibula lies parallel to the tibia and takes no part in forming the knee joint. The proximal head articulates with the
lateral condyle of the tibia. It terminates distally in the lateral mallelus
which form the outer part of the ankle.
The foot is composed of 7 tarsal bones, 5 metatarsals, and 14 phalanges.
7 tarsal bones of the ankle include the calcaneus (heel), the talus between the calcaneus and tibia, the navicular,
cuboid, and three cuneiforms; they are treated as part of the foot.
The metatarsals articulate with the tarsal bones on one end and the phalanges on the other.
Toes are made of phalanges, with the great toe (hallux) having two phalanges.
springy arches can be found in this region: medial longitudinal, lateral longitudinal and transverse arches
and bone markings list
1. Frontal bone - Coronal suture, superorbital foramen,
2. Parietal bone - Coronal suture
3. Temporal - a. squamous region of temporal
– squamous suture, zygomatic process
b. Tympanic region of temporal – external
auditory meatus, styloid process, mastoid process
4. Sphenoid bone – part of greater wing
5. around orbit
Zygomatic bone, lacrimal bone,
ethmoid bone, nasal bone
6. Maxilla bone - Infraorbital foramen
7. Mandible - Mandibular body,
angle, ramus, notch and condyle, coronoid process, mental foramen
B. Anterior view
1. Frontal bone - Glabella, superorbital foramen
2. in and around orbit
a. Superior to orbit – superorbital margin and foramen
b. Lateral to orbit – zygomatic, temporal and sphenoid
c. Medial to orbit – frontonasal suture, lacrimal
bone, nasal bone, part of maxilla.
d. Inferior to orbit – maxilla bone with infraorbital
e. Inside orbit – sphenoid bone with the optic canal,
superior and inferior orbital fissures.
3. Nasal area - Nasal bones, ethmoid bones, vomer
4. Mandible - Mandibular body and symphysis,
C. inferior view
1. - Maxilla bone - palatine process
2. Palatine bone
3. Sphenoid bone - Greater wings
5. Temporal bone
6. Occipital bone - Foramen magnum, occipital condyles
1. Frontal bone
2. Ethmoid bone -
Cribiform plate, crista galli, olfactory foramina
3. Sphenoid bone - Lesser and greater wings, sella
turcica, optic canal
4. Temporal bone - Internal
acoustic canal, jugular foramen, carotid canal
5. Occipital bone - Foramen
1. Parietal bone - sagittal suture
2. Occipital bone - lambdoid suture
3. Parietal bone – mastoid process
Know to identify vertebrae from different regions of the column.
On each vertebra – spinous process, transverse process, body, superior
and inferior articular process, vertebral (spinal) foramen, inferior notch
Special markings – transverse foramen (cervical), transverse costal
Sacrum and coccyx – superior articular process, sacral canal, median
sacral crest, sacral foramina, sacral hiatus, transverse ridge, coccyx.
Bony thorax (rib cage)
Sternum – manubrium, body, xiphoid process, jugular notch, clavicular
Ribs – head of rib, angle of rib. True, false and floating ribs
Pectoral (shoulder) girdle
Clavicle – acromial (lateral) end,
sternal (medial) end
Posterior view –
spine, supraspinous fossa, infraspinous fossa, glenoid cavity, acromion, coracoid process
Anterior view – subscapular fossa
Proximal anterior – head, greater and
lesser tubercle, deltoid tuberosity
Distal – radial fossa, coronoid fossa,
lateral and medial epicondyle, trochlea, capitalum
Proximal – olecranon process, trochlear
notch, coronoid process, radial notch
Distal – head, styloid process
Radius – proximal – head, neck,
Distal – styloid process
Carpals, metacarpals, phalanges (proximal,
middle and distal)
ilium, pubis, ischium
Posterior view –
iliac crest, posterior superior and inferior iliac spines, greater sciatic notch, ischial tuberosity
Anterior view –
iliac fossa, acetabulum, pubic symphysis, obturator foramen, articular surface
Proximal – head, neck, greater and lesser trocheanter.
Distal – lateral and medial epicondyle, lateral and medial condyle, intercondylar fossa
Anterior view – base, apex
Posterior view – medial and lateral articular facet
Proximal – medial
and lateral condyle
Distal – medial mallelus
Fibula – distal – lateral mallelus
Foot - tarsals (calcaneus)
Phalanges – proximal, medial, distal
and Their Classification
Joints are classified according to their relative freedom of movement.
A diarthrosis is freely movable.
An amphiarthrosis is slightly movable.
A synarthrosis is immovable.
Joints are also classified according to how the adjacent bones are joined
fibrous joints, fibers of collagen join two bones and there is no joint cavity. Most are immovable (synarthrotic).
Two types: Sutures are immovable fibrous joints limited to the skull. Syndesmoses are the most movable of the
fibrous joints and are joined by an interosseous short ligament. Example: tibia and fibula connection at the ankle.
cartilaginous joints, two bones are joined by cartilage and there is no joint cavity. Most slightly movable (amphiarthrotic).
2 types: In a synchondrosis, the bones are joined by hyaline cartilage. Example: the attachment of a rib to the sternum.
In a symphysis, two bones are joined by a fibrocartilage pad. Example: an intervertebral disc.
bones of a synovial joint are separated by a joint cavity containing lubricating synovial fluid. All synovial
joints are freely movable (diarthrotic). The adjoining surfaces of bones are covered with hyaline cartilage, further reducing
friction within the joint.
articular capsule encloses the cavity and is made up of an outer fibrous capsule lined with synovial membrane.
Certain joints contain a pad of fibrocartilage called a meniscus that absorbs shock and pressure. Synovial joints
are reinforced on the outside by tendons and ligaments and sometimes on the inside by ligaments.
of Synovial Joints
In gliding (plane) joints, articular surfaces are mostly flat. Example: between the carpal or tarsal bones.
Hinge joints - rounded process of one bone fits into concave surface. They are uniaxial, like a door hinge. Examples:
the knee, finger, and toe joints.
In pivot joints, one bone has a knobby projection that fits into the ringlike ligament on the other. Example: between
the first two vertebrae.
Condyloid (ellipsoid) joints exhibit an oval convex surface on one bone that fits into a similar depression on the
next. They have biaxial movement. Example: the metacarpophalangeal joints.
5. The body's single saddle joint occurs at the base of the thumb. Each bone in the joint is concave in one
direction and convex in the other.
Ball-and-socket joints are highly movable, multiaxial joints. Examples: the shoulder and hip joints.
of synovial joints
Flexion is movement that decreases the angle of a joint; extension straightens the joint; and hyperextension
increases the angle beyond 180 degrees.
Abduction is movement of a body part away from the midsagittal line, while adduction is movement toward the
Elevation is movement that raises a bone vertically (e.g., by opening the mouth), and depression is the opposite.
4. During circumduction, one end of an appendage remains stationary while the other end makes a circular motion.
Rotation is a movement in which a bone turns on its longitudinal axis.
Supination and pronation are limited to the forearm. Supination is rotating the arm so the palm is upward. Pronation
is rotating the arm so the palm is downward
Opposition is movement of the thumb toward the fingers, and reposition is movement back to anatomical position.
Dorsiflexion and plantar flexion are limited to the feet. Dorsiflexion is a movement in which the toes are raised.
Plantar flexion is hyperextension of the foot so that the toes point downward.
Inversion and eversion are also limited to the feet. Inversion is a movement in which the soles turn medially.
Eversion is a turning of the soles laterally.
of Selected synovial joints
temporomandibular joint (TMJ) is the insertion of the mandibular condyle into the mandibular fossa of the temporal bone. The
synovial cavity of the TMJ is divided into superior and inferior chambers by the articular disc (a meniscus). Two ligaments
support the joint: the temporomandibular ligament and the sphenomandibular ligament. (Fig 13.9)
coxal (hip) joint occurs where the head of the femur fits into the acetabulum of the os coxae. The hip joint has a deeper
socket and is much more stable than the shoulder. An acetabular labrum serves to further deepen the socket. Ligaments that
support the coxal joint are: the iliofemoral, pubofemoral, ischiofemoral, and transverse acetabular ligaments, plus the ligamentum
teres at the fovea capitis. (Fig. 13.8)
The knee joint (tibiofemoral
joint) is the largest and most complex diarthrosis of the body. The patella and patellar ligament also form a gliding patellofemoral
joint with the femur. The joint cavity contains two cartilages, called the lateral meniscus and the medial meniscus, joined
by a transverse ligament. The posterior "pit" of the knee, called the popliteal region, is supported by intracapsular (anterior
and posterior cruciate) ligaments inside the capsule, and extracapsular (oblique popliteal, arcuate, popliteal, lateral collateral,
and medial collateral) ligaments outside.