206
UNIT TWO
It is composed of twelve pairs of
ribs,
which articulate
posteriorly with thoracic vertebrae. It also includes the
sternum
(ster
num), or breastbone, to which most of
the ribs are attached anteriorly.
The
appendicular skeleton
consists of the bones of the
upper and lower limbs and the bones that anchor the limbs
to the axial skeleton. It includes the following:
1.
Pectoral girdle.
The pectoral girdle is formed by a
scapula
(scap
u-lah), or shoulder blade, and a
clavicle
(klav
ı˘-k
l), or collarbone, on both sides of the body.
The pectoral girdle connects the bones of the upper
limbs to the axial skeleton and aids in upper limb
movements.
2.
Upper limbs.
Each upper limb consists of a
humerus
(hu
mer-us), or arm bone; two forearm bones—a
radius
(ra
de-us) and an
ulna
(ul
nah)—and a hand. The
humerus, radius, and ulna articulate with each other
at the elbow joint. At the distal end of the radius and
ulna is the hand. There are eight
carpals
(kar
palz),
or wrist bones. The F
ve bones of the palm are called
metacarpals
(met
ah-kar
palz), and the fourteen F
nger
bones are called
phalanges
(fah-lan
je¯z); singular,
phalanx,
(fa
lanks).
3.
Pelvic girdle.
The pelvic girdle is formed by two hip
bones attached to each other anteriorly and to the
sacrum posteriorly. They connect the bones of the
lower limbs to the axial skeleton and, with the sacrum
and coccyx, form the
pelvis,
which protects the lower
abdominal and internal reproductive organs.
4.
Lower limbs.
Each lower limb consists of a
femur
(fe
mur), or thigh bone; two leg bones—a large
tibia
(tib
e-ah), or shin bone, and a slender
F
bula
(F b
u-lah)—
and a foot. The femur and tibia articulate with each
other at the knee joint, where the
patella
(pah-tel
ah),
or kneecap, covers the anterior surface. At the distal
ends of the tibia and F
bula is the foot. There are seven
tarsals
(tahr
salz), or ankle bones. The F
ve bones of
the instep are called
metatarsals
(met
ah-tar
salz),
and the fourteen bones of the toes (like the F
ngers) are
called
phalanges.
Table 7.4
deF nes some terms used to
describe skeletal structures.
PRACTICE
16
Distinguish between the axial and appendicular skeletons.
17
List the bones of the axial skeleton and of the appendicular
skeleton.
7.6
SKULL
A human skull usually consists of twenty-two bones that,
except for the lower jaw, are F rmly interlocked along sutures.
Eight of these interlocked bones make up the cranium and
fourteen form the facial skeleton. The
mandible
(man
dı˘-b
l),
these sutures
(f g. 7.14)
. Extra small, round sesamoid bones
may develop in tendons, where they reduce friction in places
where tendons pass over bony prominences.
Divisions of the Skeleton
±or purposes of study, it is convenient to divide the skeleton
into two major portions—an axial skeleton and an appen-
dicular skeleton
(f
g. 7.15)
. The
axial skeleton
consists of
the bony and cartilaginous parts that support and protect the
organs of the head, neck, and trunk. These parts include the
following:
1.
Skull.
The skull is composed of the
cranium
(brain
case) and the
facial bones.
2.
Hyoid bone.
The hyoid (hi
oid) bone is located in the
neck between the lower jaw and the larynx
(f g. 7.16)
.
It does not articulate with any other bones but is F
xed
in position by muscles and ligaments. The hyoid bone
supports the tongue and is an attachment for certain
muscles that help move the tongue during swallowing.
It can be felt approximately a F
nger’s width above the
anterior prominence of the larynx.
3.
Vertebral column.
The vertebral column, or spinal
column, consists of many vertebrae separated by
cartilaginous
intervertebral discs.
This column forms
the central axis of the skeleton. Near its distal end, F
ve
vertebrae fuse to form the
sacrum
(sa
krum), part of
the pelvis. A small tailbone formed by the fusion of four
vertebrae and called the
coccyx
(kok
siks) is attached to
the end of the sacrum.
4.
Thoracic cage.
The thoracic cage protects the organs
of the thoracic cavity and the upper abdominal cavity.
Temporal bone
Occipital bone
Parietal bone
Sutural
bones
FIGURE 7.14
Sutural (wormian) bones are extra bones that
sometimes develop in sutures between the F
at bones of the skull.
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