232
UNIT 2
Covering, Support, and Movement of the Body
7
and the
coronoid process
, separated by a deep concavity, the
trochlear notch
(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
radial notch
, where the ulna
articulates with the head of the radius.
Distally the ulnar sha² narrows and ends in a knoblike
head
(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.
Radius
±e
radius
(“rod”) is thin at its proximal end and wide
distally—the opposite of the ulna. ±e
head
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
radial tuberosity
, which anchors the biceps muscle
of the arm. Distally, where the radius is expanded, it has a medial
ulnar notch
(Figure 7.28d), which articulates with the ulna, and
a lateral
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.
Homeostatic Imbalance
7.5
Colles’ fracture
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.
Hand
±e skeleton of the hand
(Figure 7.29)
includes the bones of
the
carpus
(wrist); the bones of the
metacarpus
(palm); and the
phalanges
(bones of the fingers).
Carpus (Wrist)
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
carpals
(kar
9
palz), closely united by liga-
ments. Because gliding movements occur between these bones,
the carpus as a whole is quite flexible.
Trapezoid
Trapezium
• Scaphoid
Triquetrum
• Lunat
e
• C
apitate
• Hamat
e
V
IV
III
II
I
V
IV
III
II
I
Phalanges
Metacarpals
Carpals
Carpals
(a) Anterior view of right hand
(b) Posterior view of right hand
Radius
Ulna
Sesamoid
bones
• Base
• Shaf
t
Proximal
• Middle
• Distal
• Head
Ulna
Triquetrum
• Lunat
e
• C
apitate
• Hamat
e
• Pisif
orm
Carpals
Figure 7.29
Bones of the right hand.
(For a related image, see
A Brief Atlas of the Human
Body
, Figure 27.)
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