HUMAN BIOLOGY

94 Chapter 5

clavicle Collarbone.
femur Thighbone, largest
bone in the body.
humerus Long bone of the
upper arm.
pectoral girdle Portion
of the appendicular skel‑
eton that consists of the
scapulas (shoulder blades),
clavicles (collarbones), and
bones of the upper limbs.

pelvic girdle Portion of the
appendicular skeleton that
consists of bones of the
pelvis and lower limbs.
radius Long bone on the
inner (thumb) side of the
forearm.
scapula Shoulder blade.
ulna Long bone on the
outer (pinky finger) side of
the forearm.

the appendicular skeleton

the pelvic girdle and lower limbs support

body weight

For most of us, our shoulders and arms are much more

flexible than our hips and legs. Why? Although there are

similarities in the basic “design” of both girdles, this lower

part of the appendicular skeleton is adapted to bear the

n    The appendicular skeleton includes the bones that support

the limbs, upper chest, shoulders, and pelvis.

Append means “to hang,” and the appendicular skeleton

includes the bones of “hanging” body parts such as your

arms, hands, legs, and feet. It also includes a pectoral girdle

at each shoulder and the pelvic girdle at the hips.

the pectoral girdle and upper limbs provide

flexibility

Each pectoral girdle (Figure 5.7) has a large, flat shoul-

der blade—a scapula—and a long, slender collarbone, or

clavicle, that connects to the breastbone (sternum). The

rounded shoulder end of the humerus, the long bone

of the upper arm, fits into an open

socket in the scapula. Your arms

can move in a great many ways;

they can swing in wide circles and

back and forth, lift objects, or tug on

a rope. Such freedom of movement

is possible because muscles only

loosely attach the pectoral girdles

and upper limbs to the rest of the

body. Although the arrangement is

sturdy enough under normal con-

ditions, it is vulnerable to strong

blows. Fall on an outstretched arm

and you might fracture your clavi-

cle or dislocate your shoulder. In all

but the elderly the collarbone is the

bone most frequently broken.

Each of your upper limbs includes

thirty separate bones. The humerus

connects with two bones of the

forearm—the radius (on the thumb

side) and the ulna (on the “pinky fin-

ger” side). The upper end of the ulna

joins the lower end of the humerus to form the elbow joint.

The bony bump sometimes (mistakenly) called the “wrist

bone” is the lower end of the ulna.

The radius and ulna join the hand at the wrist joint,

where they meet eight small, curved carpal bones. Liga-

ments attach these bones to the long bones. Blood ves-

sels, nerves, and tendons pass in sheaths over the wrist;

when a blow, constant pressure, or repetitive movement

(such as typing) damages these tendons, the result can

be a painful disorder called carpal tunnel syndrome

(Section 5.6). The bones of the hand, the five meta­

carpals, end at the knuckles. Phalanges are the bones of

the fingers.

Figure 5.7 Bones of the pectoral girdle, the arm, and the hand

form the upper part of the appendicular skeleton. (© Cengage Learning)

clavicle

humerus

ulna

radius

carpals (8)

metacarpals (5)

phalanges (14)

sternum

scapula

5.4

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