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CHAPTER EIGHT
Content Review
1. The pectoral girdle consists of the clavicle and the scapula. Each pectoral girdle
supports one upper limb and provides attachment sites for many muscles that move
the limb. The pelvic girdle is composed of right and left ossa coxae only, whereas the
pelvis consists of the ossa coxae, the sacrum, and the coccyx. The pelvis protects and
supports the viscera in the inferior part of the ventral body cavity.
2. The scapula is triangular in shape and has three borders. The superior border is the
horizontal edge of the scapula that is superior to the spine. The medial border
(sometimes called the vertebral border) is the scapular edge closest to the vertebrae.
The lateral border (sometimes called the axillary border) is closest to the axilla.
3. The anatomical neck is an almost indistinct groove that marks the location of the
former epiphyseal plate. The anatomical neck is located between the head and two
prominent projections called the greater and lesser tubercles, respectively. The
surgical neck, a common fracture site of the humerus, is a narrowing of the bone
immediately distal to the tubercles, at the transition from the head to the shaft.
4. 4. The eight carpal bones of the wrist are arranged in two rows of four bones each.
From the lateral to the medial side, the carpal bones of the proximal row are the
scaphoid, lunate, triquetrum, and pisiform bones. Again beginning on the lateral side,
the bones of the distal row of carpal bones are the trapezium, trapezoid, capitate, and
hamate bones.
5. The glenoid cavity is a shallow, cup-shaped fossa on the lateral side of the scapula
where the head of the humerus articulates with the scapula. It has tubercles on its
superior and inferior edges that represent the attachment sites for muscles that
position the shoulder and arm. The acetabulum is a deep, curved depression on the
lateral surface of the os coxae where the ballshaped head of the femur articulates with
the pelvis.
6. Between the ages of 13 and 15 years, the ilium, ischium, and pubis fuse to form the os
coxae of the pelvic girdle. The three bones that form the os coxae all contribute a
portion to the acetabulum. Thus, the acetabulum represents a region where these
bones have fused.
7. The true pelvis lies inferior to the pelvic brim. It encloses the pelvic cavity and forms
a deep, inferior bowl that contains the pelvic organs. The false pelvis lies superior to
the pelvic brim. It is enclosed by the ala of the iliac bones. It forms the inferior region
of the abdominal cavity and houses abdominal organs.
8. The fibula is a laterally placed bone in the leg that does not bear any weight, but
serves as the attachment site for several muscles. Additionally, its distal tip, called the
lateral malleolus, extends inferiorly to the ankle joint, where it provides lateral
stability to the ankle.
9. The arches of the foot prevent the muscles, nerves, and blood vessels that supply the
inferior surface of the foot from being squeezed between the metatarsals and the
ground. In addition, the segmented structure of the foot can best support the weight of
the body if the foot is arched, much like the strength exhibited in the arch of a bridge.
10. In the fourth week, limb buds appear as small ridges along the lateral sides of the
embryo. Upper limb buds appear early in the fourth week, and lower limb buds
appear a few days later. The limb buds have a core of lateral plate mesoderm (which
forms bones, tendons, cartilage, and connective tissue) covered by a layer of
ectoderm. Early in week 5, the upper limb forms a paddle-shaped hand plate. A foot
plate forms in the lower limb bud in the sixth week. Digital rays are longitudinal
thickenings that will form digits in both the hand plate (late sixth week) and the foot
plate (early seventh week). Between the digital rays, the tissue undergoes
programmed cell death to form fingers and toes; this occurs in the seventh week and
is complete by the eighth week. During the late seventh through early eighth weeks,
the upper limb rotates laterally so that the future elbow is directed posteriorly, while
the lower limb rotates medially to direct the future knee anteriorly. By week 8,
primary ossification centers begin to form. By week 12, limb bone ossification is
accelerating.