Essentials of Anatomy and Physiology

upper arm does not move. The radius crosses over the
ulna, which permits the hand to perform a great vari-
ety of movements without moving the entire arm.
The carpalsare eight small bones in the wrist;
gliding jointsbetween them permit a sliding move-
ment. The carpals also articulate with the distal ends
of the ulna and radius, and with the proximal ends of
the metacarpals, the five bones of the palm of the
hand. All of the joints formed by the carpals and
metacarpals make the hand very flexible at the wrist
(try this yourself: flexion to extension should be almost
180 degrees), but the thumb is more movable than the
fingers because of its carpometacarpal joint. This is a
saddle joint, which enables the thumb to cross over
the palm, and permits gripping.
The phalangesare the bones of the fingers. There
are two phalanges in each thumb and three in each
of the fingers. Between phalanges are hinge joints,
which permit movement in one plane. Important
parts of the shoulder and arm bones are described
in Table 6–3.

THE HIP AND LEG

The pelvic girdle (or pelvic bone) consists of the two

hip bones(coxae or innominate bones), which articu-

late with the axial skeleton at the sacrum. Each hip

bone has three major parts: the ilium, ischium, and

pubis, and these are shown in Fig. 6–13, which depicts

both a male and a female pelvis. The iliumis the

flared, upper portion that forms the sacroiliac joint.

The ischiumis the lower, posterior part that we sit

on. The pubisis the lower, most anterior part. The

two pubic bones articulate with one another at the

pubic symphysis, with a disc of fibrous cartilage

between them. Notice the pubic angle of both the

male and female pelvises in Fig. 6–13. The wider

female angle is an adaptation for childbirth, in that it

helps make the pelvic outlet larger.

The acetabulumis the socket in the hip bone that

forms a ball-and-socket joint with the femur.

Compared to the glenoid fossa of the scapula, the

acetabulum is a much deeper socket. This has great

The Skeletal System 123

Manubrium

Body of sternum

Costal

cartilages

Xiphoid process

12th thoracic vertebra

1st rib

1st thoracic vertebra 2nd

3rd

4th

5th

6th

7th

8th

9th

10th

11th

12th

Figure 6–11. Rib cage. Anterior view.

QUESTION:With what bones do all of the ribs articulate?