228
UNIT 2
Covering, Support, and Movement of the Body
7
superior angle
and the lateral border at the
lateral angle
. Te
medial and lateral borders join at the
inferior angle
. Te inferior
angle moves extensively as the arm is raised and lowered, and is
an important landmark for studying scapular movements.
Te anterior, or costal, surface of the scapula is concave and rela-
tively featureless. Its posterior surface bears a prominent
spine
that
is easily felt through the skin. Te spine ends laterally in an enlarged,
roughened triangular projection called the
acromion
(ah-kro
9
me-
on; “point of the shoulder”). Te acromion articulates with the acro-
mial end of the clavicle, forming the
acromioclavicular joint
.
Projecting anteriorly from the superior scapular border is
the
coracoid process
(kor
9
ah-coid);
corac
means “beaklike,” but
this process looks more like a bent little finger. Te coracoid
process helps anchor the biceps muscle of the arm. It is bounded
by the
suprascapular notch
(a nerve passage) medially and by
the glenoid cavity laterally.
Several large fossae appear on both sides of the scapula and
are named according to location. Te
infraspinous
and
supraspi-
nous fossae
are inferior and superior, respectively, to the spine.
Te
subscapular fossa
is the shallow concavity formed by the
entire anterior scapular surface. Lying within these fossae are
muscles with similar names.
Check Your Understanding
22.
What two bones construct each pectoral girdle?
23.
Where is the single point of attachment of the pectoral girdle
to the axial skeleton?
24.
What is the major shortcoming of the flexibility allowed by
the shoulder joint?
For answers, see Appendix H.
The Upper Limb
Identify or name the bones of the upper limb and their
important markings.
Tirty separate bones form the bony framework of each upper
limb (see Figures 7.27 to 7.29, and
Table 7.3
on p. 233). Each of
these bones may be described regionally as a bone of the arm,
forearm, or hand. (Keep in mind that anatomically the “arm” is
only that part of the upper limb between the shoulder and elbow.)
Arm
Te
humerus
(hu
9
mer-us), the sole bone of the arm, is a typical
long bone
(Figure 7.27)
. Te largest, longest bone of the upper
limb, it articulates with the scapula at the shoulder and with the
radius and ulna (forearm bones) at the elbow.
At the proximal end of the humerus is its smooth, hemispheri-
cal
head
, which fits into the glenoid cavity of the scapula in a man-
ner that allows the arm to hang freely at one’s side. Immediately
inferior to the head is a slight constriction, the
anatomical neck
.
Just inferior to this are the lateral
greater tubercle
and the more
medial
lesser tubercle
, separated by the
intertubercular sulcus
,
or
bicipital groove
(bi-sip
9
ĭ-tal). Tese tubercles are sites of attach-
ment of the rotator cuff muscles. Te intertubercular sulcus guides
that move the upper limbs. Tese girdles are very light and allow
the upper limbs a degree of mobility not seen anywhere else in
the body. Tis mobility is due to the following factors:
Because only the clavicle attaches to the axial skeleton, the
scapula can move quite freely across the thorax, allowing the
arm to move with it.
Te socket of the shoulder joint (the scapula’s glenoid cavity)
is shallow and poorly reinforced, so it does not restrict the
movement of the humerus (arm bone). Although this ar-
rangement is good for flexibility, it is bad for stability: Shoul-
der dislocations are fairly common.
Clavicles
Te
clavicles
(“little keys”), or collarbones, are slender, S-shaped
bones that can be felt along their entire course as they extend hori-
zontally across the superior thorax (Figure 7.25). Each clavicle is
cone shaped at its medial
sternal end
, which attaches to the sternal
manubrium, and flattened at its lateral
acromial end
(ah-kro
9
me-
al), which articulates with the scapula. Te medial two-thirds of the
clavicle is convex anteriorly; its lateral third is concave anteriorly. Its
superior surface is fairly smooth, but the inferior surface is ridged
and grooved by ligaments and by the action of the muscles that attach
to it. Te
trapezoid line
and the
conoid tubercle
, for example, are an-
choring points for a ligament that connects the clavicle to the scapula.
Besides anchoring many muscles, the clavicles act as braces:
Tey hold the scapulae and arms out laterally, away from the
narrower superior part of the thorax. Tis bracing function be-
comes obvious when a clavicle is fractured: Te entire shoulder
region collapses medially. Te clavicles also transmit compres-
sion forces from the upper limbs to the axial skeleton, for exam-
ple, when someone pushes a car to a gas station.
Te clavicles are not very strong and are likely to fracture, for
example, when a person uses outstretched arms to break a fall.
Te curves in the clavicle ensure that it usually fractures anteri-
orly (outward). If it were to collapse posteriorly (inward), bone
splinters would damage the subclavian artery, which passes just
deep to the clavicle to serve the upper limb. Te clavicles are
exceptionally sensitive to muscle pull and become noticeably
larger and stronger in those who perform manual labor or ath-
letics involving the shoulder and arm muscles.
Scapulae
Te
scapulae
, or
shoulder blades
, are thin, triangular flat bones
(Figure 7.25a and
Figure 7.26
). Interestingly, their name derives
from a word meaning “spade” or “shovel,” for ancient cultures
made spades from the shoulder blades of animals. Te scapulae lie
on the dorsal surface of the rib cage, between ribs 2 and 7.
Each scapula has three borders. Te
superior border
is the
shortest, sharpest border. Te
medial
, or
vertebral
,
border
parallels
the vertebral column. Te thick
lateral
, or
axillary
,
border
abuts
the armpit and ends superiorly in a small, shallow fossa, the
gle-
noid cavity
(gle
9
noid; “pit-shaped”). Tis cavity articulates with
the humerus of the arm, forming the shoulder joint.
Like all triangles, the scapula has three corners or
angles
.
Te superior scapular border meets the medial border at the
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