Covering, Support, and Movement of the Body
, separated by a deep concavity, the
(Figure 7.28c). Together, these two processes grip
the trochlea of the humerus, forming a hinge joint that allows the
forearm to be bent upon the arm (ﬂexed), then straightened again
(extended). When the forearm is fully extended, the olecranon
“locks” into the olecranon fossa (Figure 7.27d), keeping the fore-
arm from hyperextending (moving posteriorly beyond the elbow
joint). ±e posterior olecranon forms the angle of the elbow when
the forearm is ﬂexed and is the bony part that rests on the table
when you lean on your elbows. On the lateral side of the coronoid
process is a small depression, the
, where the ulna
articulates with the head of the radius.
Distally the ulnar sha² narrows and ends in a knoblike
(Figure 7.28d). Medial to the head is the
ulnar styloid process
from which a ligament runs to the wrist. ±e ulnar head is sepa-
rated from the bones of the wrist by a disc of ﬁbrocartilage and
plays little or no role in hand movements.
(“rod”) is thin at its proximal end and wide
distally—the opposite of the ulna. ±e
of the radius is
shaped somewhat like the head of a nail (Figure 7.28). ±e su-
perior surface of this head is concave, and it articulates with the
capitulum of the humerus. Medially, the head articulates with the
radial notch of the ulna (Figure 7.27c). Just inferior to the head
is the rough
, which anchors the biceps muscle
of the arm. Distally, where the radius is expanded, it has a medial
(Figure 7.28d), which articulates with the ulna, and
radial styloid process
(an anchoring site for ligaments
that run to the wrist). Between these two markings, the radius is
concave where it articulates with carpal bones of the wrist.
±e ulna contributes more heavily to the elbow joint, and the
radius is the major forearm bone contributing to the wrist joint.
When the radius moves, the hand moves with it.
is a break in the distal end of the radius. It is a
common fracture when a falling person attempts to break his or
her fall with outstretched hands.
±e skeleton of the hand
includes the bones of
(wrist); the bones of the
(palm); and the
(bones of the ﬁngers).
A “wrist” watch is actually worn on the distal forearm (over the
lower ends of the radius and ulna), not on the wrist at all. ±e
true wrist, or carpus, is the proximal part of the structure we
generally call our “hand.” ±e carpus consists of eight marble-
size short bones, or
palz), closely united by liga-
ments. Because gliding movements occur between these bones,
the carpus as a whole is quite ﬂexible.
(a) Anterior view of right hand
(b) Posterior view of right hand
Bones of the right hand.
(For a related image, see
A Brief Atlas of the Human
, Figure 27.)