231
CHAPTER SEVEN
Skeletal System
Hip Bones
Each hip bone develops from three parts—an ilium, an ischium,
and a pubis
(f
g. 7.48)
. These parts fuse in the region of a
cup-shaped cavity called the
acetabulum
(as
e
˘-tab
u-lum).
This depression, on the lateral surface of the hip bone,
receives the rounded head of the femur or thigh bone.
The
ilium
(il
e-um), the largest and most superior por-
tion of the hip bone, fl
ares outward, forming the prominence
of the hip. The margin of this prominence is called the
iliac
crest.
The smooth, concave surface on the anterior aspect of
the ilium is the
iliac fossa.
Posteriorly, the ilium joins the sacrum at the
sacroiliac
joint.
Anteriorly, a projection of the ilium, the
anterior supe-
rior iliac spine,
can be felt lateral to the groin. This spine
provides attachments for ligaments and muscles and is an
important surgical landmark.
A common injury in contact sports such as football is bruising the soft tis-
sues and bone associated with the anterior superior iliac spine. Wearing
protective padding can prevent this painful injury, called a
hip pointer.
F
st. The metacarpals articulate proximally with the carpals
and distally with the phalanges. The metacarpal on the lat-
eral side is the most freely movable; it permits the thumb to
oppose the F
ngers when grasping something. These bones
are numbered 1 to 5, beginning with the metacarpal of the
thumb (F
g. 7.45).
The
phalanges
are the F nger bones. Three are in each
F nger—a proximal, a middle, and a distal phalanx—and two
are in the thumb. (The thumb lacks a middle phalanx.) Thus,
each hand has fourteen F nger bones.
Table 7.9
summarizes
the bones of the pectoral girdle and upper limbs.
It is not uncommon for a baby to be born with an extra F
nger or toe,
but because the extra digit is usually surgically removed early in life,
hands like the ones in
F
gure 7.46
are rare. Polydactyly (“many digits”)
is an inherited trait. It is common in cats. A lone but popular male cat
brought the trait from England to colonial Boston. Polydactyly is also
common among the Amish people.
PRACTICE
31
Locate and name each of the bones of the upper limb.
32
Explain how the bones of the upper limb articulate.
7.11
PELVIC GIRDLE
The
pelvic girdle
consists of the two hip bones, also known
as coxal bones, pelvic bones or innominate bones, which
articulate with each other anteriorly and with the sacrum
posteriorly
(f g. 7.47)
. The sacrum, coccyx, and pelvic girdle
form the bowl-shaped
pelvis.
The pelvic girdle supports the
trunk of the body; provides attachments for the lower limbs;
and protects the urinary bladder, the distal end of the large
intestine, and the internal reproductive organs. The body’s
weight is transmitted through the pelvic girdle to the lower
limbs and then onto the ground.
TABLE
7.9
|
Bones of the Pectoral Girdle and Upper Limbs
Name and Number
Location
Special Features
Clavicle (2)
Base of neck between sternum and scapula
Sternal end, acromial end
Scapula (2)
Upper back, forming part of shoulder
Body, spine, acromion process, coracoid process, glenoid cavity
Humerus (2)
Arm, between scapula and elbow
Head, greater tubercle, lesser tubercle, intertubercular groove, anatomical neck,
surgical neck, deltoid tuberosity, capitulum, trochlea, medial epicondyle, lateral
epicondyle, coronoid fossa, olecranon fossa
Radius (2)
Lateral side of forearm, between elbow and wrist
Head, radial tuberosity, styloid process, ulnar notch
Ulna (2)
Medial side of forearm, between elbow and wrist
Trochlear notch, olecranon process, coronoid process, head, styloid process, radial notch
Carpal (16)
Wrist
Two rows of four bones each
Metacarpal (10)
Palm
One in line with each F
nger and thumb
Phalanx (28)
±inger
Three in each F
nger; two in each thumb
FIGURE 7.46
A person with polydactyly has extra digits.
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