protect the heart and lungs and provide attachment points
for muscles, especially those involved in breathing.
The Scapula and Clavicle Form
the Pectoral Girdle
The next set of bones in the upper body is the shoulder
girdles or
pectoral girdles
(
PEK-to-ral
), which attach the
upper limbs to the axial skeleton (see
Figure 5.11b,c
).
The
clavicle
(
KLAV-i-kul
), or collarbone, attaches to the
manubrium of the sternum and the
scapula
, or shoulder
blade. The
coracoid process
(
KOR-a-koyd
) of the scapu-
la serves as a point of attachment for muscles and its
gle-
noid cavity
forms the shoulder joint with the head of the
humerus (upper arm bone).
the two bones of the forearm, the
ulna
and
radius
. The
ulna is medial to the radius. The proximal end of the ra-
dius is rounded and articulates with the humerus, to al-
low approximately 180° of forearm rotation. Distal to the
ulna and radius are the bones of the wrist, the
carpals
(8
bones), which are arranged in two rows of 4 bones each.
The distal row attaches to the bones of the palm of the
hand (
metacarpals
), whose distal heads form the knuck-
les. Finally, the metacarpals attach to the bones of the fin-
gers, the
phalanges
(fa-LAN-jez). There are 2 phalanges
in the thumb and 3 in each finger (Figure 5.11).
CONCEPT CHECK
Each Arm Contains 22 Bones
Attached to the scapula is the
humerus
(
HU-mer-us
), the
longest bone in the upper body (
Figure 5.11d
). The hu-
merus has a rounded head that fits into the glenoid cavity
of the scapula. The distal end of the humerus attaches to
1.
What
is the difference between true ribs, false
ribs, and floating ribs?
2.
What
bones are attached to the scapula?
3.
What
are the bones of the arm, in order from
proximal to distal?
Bones of the Lower Body Form
the Pelvic Girdle and legs
LEARNING OBJECTIVES
1.
Describe
the features of the pelvis.
2.
List
the bones of the legs.
3.
Name
the bones of the feet.
long with those of the shoulder, arms, and
hand, the bones of the lower body form the
appendicular skeleton—a total of 126 bones.
The bones of the lower body have two ma-
jor functions: They support the weight of the entire body
while you are standing, and they provide the mobility that
allows you to walk, run, and jump.
Coxal Bones and Sacrum Form
Walls of the Pelvis
We start our tour of the lower body with the
pelvic girdle
,
which consists of the two hip bones. The hip bones, also
called the
coxal bones
(or
os coxa),
attach to the sacrum of the
vertebral column posteriorly and with each other anteriorly
to form the
pubic symphysis
(
PU-bik SIM-fi-sis
). Each cox-
al bone is composed of an
ilium,
an
ischium,
and a
pubis
that
have fused to form a single unit. Centrally, on each coxal
bone is the
acetabulum
(
as-e-TAB-u-lum
), the “socket” for
the hip joint that articulates with the femur from the leg.
The bowl-shaped
pelvis
(plural is
pelves)
is formed
by the coxal bones, sacrum, and coccyx. The
pelvic brim
forms the boundary between the upper pelvis (false pelvis)
and the lower pelvis (true pelvis). The false pelvis is part
of the abdomen and contains the urinary bladder and the
uterus. The true pelvis surrounds the pelvic cavity. Blood
vessels and nerves to the legs pass through openings in the
lower pelvis called the
obturator foramina
.
There are a number of structural differences between
the male and female pelves. This is predominantly be-
cause the female must pass the baby through the pelvis
during childbirth (Table 5.1):
The angle formed inferior to the pubic bones at the
pubic symphysis (pubic arch) is wider in women (> 90°)
than in men (< 90°).
132
CHAPTER 5
The Skeletal System
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