234
UNIT 2
Covering, Support, and Movement of the Body
7
Te carpals are arranged in two irregular rows of four bones
each (Figure 7.29). In the proximal row (lateral to medial) are
the
scaphoid
(skaf
9
oid; “boat-shaped”),
lunate
(lu
9
nāt; “moon-
like”),
triquetrum
(tri-kwet
9
rum; “triangular”), and
pisiform
(pi
9
sĭ-form; “pea-shaped”). Of these, all but the pisiform par-
ticipate in forming the wrist joint. Te carpals of the distal row
(lateral to medial) are the
trapezium
(trah-pe
9
ze-um; “little ta-
ble”),
trapezoid
(tra˘
9
peh-zoid; “four-sided”),
capitate
(“head-
shaped”), and
hamate
(ham
9
āt; “hooked”).
Tere are numerous memory-jogging phrases to help you
recall the carpals in the order given above. If you don’t have one,
try:
S
ally
l
t
he
p
arty
t
o
t
ake
C
indy
h
ome. As with all such
memory jogs, the first letter of each word is the first letter of the
term you need to remember.
Homeostatic Imbalance
7.6
Te arrangement of its bones is such that the carpus is concave
anteriorly and a ligament roofs over this concavity, forming the
notorious
carpal tunnel
. Besides the median nerve (which sup-
plies the lateral side of the hand), several long muscle tendons
crowd into this tunnel. Overuse and inflammation of the tendons
cause them to swell, compressing the median nerve, which causes
tingling and numbness of the areas served, and movements of the
thumb weaken. Pain is greatest at night. Tose who repeatedly
flex their wrists and fingers, such as those who work at computer
keyboards all day, are particularly susceptible to this nerve im-
pairment, called
carpal tunnel syndrome
. Tis condition is treated
by splinting the wrist during sleep or by surgery.
Metacarpus (Palm)
Five
metacarpals
radiate from the wrist like spokes to form the
metacarpus
or palm of the hand (
meta
5
beyond). Tese small
long bones are not named, but instead are numbered I to V from
thumb to little finger. Te
bases
of the metacarpals articulate
with the carpals proximally and each other medially and laterally
(Figure 7.29). Teir bulbous
heads
articulate with the proximal
phalanges of the fingers. When you clench your fist, the heads of
the metacarpals become prominent as your
knuckles
.
Metacarpal I, associated with the thumb, is the shortest and
most mobile. It occupies a more anterior position than the other
metacarpals. Consequently, the joint between metacarpal I and
the trapezium is a unique saddle joint that allows
opposition
, the
action of touching your thumb to the tips of your other fingers.
Phalanges (Fingers)
Te
fingers
, or
digits
of the upper limb, are numbered 1 to 5
beginning with the thumb, or
pollex
(pol
9
eks). In most peo-
ple, the third finger is the longest. Each hand contains 14 mini-
ature long bones called
phalanges
(fah-lan
9
jēz). Except for the
thumb, each finger has three phalanges:
distal
,
middle
, and
prox-
imal
. Te thumb has no middle phalanx. [Phalanx (fa
9
langks; “a
closely knit row of soldiers”) is the singular term for phalanges.]
Check Your Understanding
25.
Which bones play the major role in forming the elbow joint?
26.
Which bones of the upper limb have a styloid process?
27.
Where are carpals found and what type of bone (short,
irregular, long, or flat) are they?
For answers, see Appendix H.
The Pelvic (Hip) Girdle
Name the bones contributing to the os coxae, and relate
the pelvic girdle’s strength to its function.
Describe differences in the male and female pelves and
relate these to functional differences.
Te
pelvic girdle
, or
hip girdle
, attaches the lower limbs to the
axial skeleton, transmits the full weight of the upper body to
the lower limbs, and supports the visceral organs of the pelvis
(Figures 7.30 and 7.31 and
Table 7.4
, p. 237). Unlike the pec-
toral girdle, which is sparingly attached to the thoracic cage,
the pelvic girdle is secured to the axial skeleton by some of the
strongest ligaments in the body. And unlike the shallow glenoid
cavity of the scapula, the corresponding sockets of the pelvic
girdle are deep and cuplike and firmly secure the head of the
femur in place. Tus, even though both the shoulder and hip
joints are ball-and-socket joints, very few of us can wheel or
swing our legs about with the same degree of freedom as our
arms. Te pelvic girdle lacks the mobility of the pectoral girdle
but is far more stable.
Te pelvic girdle is formed by the sacrum* (a part of the
axial skeleton) and a pair of
hip bones
, each also called an
os
coxae
(ahs kok
9
se), or
coxal bone
(
coxa
5
hip). Each hip bone
unites with its partner anteriorly and with the sacrum posteri-
orly
(Figure 7.30)
.
Each large, irregularly shaped hip bone consists of three sep-
arate bones during childhood: the ilium, ischium, and pubis
(Figure 7.31)
. In adults, these bones are firmly fused and their
boundaries are indistinguishable. Teir names are retained,
however, to refer to different regions of the composite hip bone.
At the point of fusion of the ilium, ischium, and pubis is a
deep hemispherical socket called the
acetabulum
(as
0
ĕ-tab
9
u-
lum; “vinegar cup”) on the lateral surface of the pelvis (Fig-
ure 7.31). Te acetabulum receives the head of the femur, or
thigh bone, at this
hip joint
.
Ilium
Te
ilium
(il
9
e-um; “flank”) is a large flaring bone that forms
the superior region of a coxal bone. It consists of a
body
and a
superior winglike portion called the
ala
(a
9
lah). When you rest
your hands on your hips, you are resting them on the thickened
superior margins of the alae, the
iliac crests
, to which many
muscles attach. Each iliac crest ends anteriorly in the blunt
ante-
rior superior iliac spine
and posteriorly in the sharp
posterior
superior iliac spine
.
Located below these are the less prominent
anterior
and
posterior inferior iliac spines
. All of these spines are attachment
points for the muscles of the trunk, hip, and thigh. Te anterior
*Some authorities do not consider the sacrum part of the pelvic girdle, but here we
follow the convention in
Terminologia Anatomica
.
previous page 268 Human Anatomy and Physiology (9th ed ) 2012 read online next page 270 Human Anatomy and Physiology (9th ed ) 2012 read online Home Toggle text on/off