223
CHAPTER SEVEN
Skeletal System
of the next higher vertebra. The neck of the rib is fl attened,
lateral to the head, where ligaments attach. A
tubercle,
close
to the head of the rib, articulates with the transverse process
of the vertebra.
The costal cartilages are composed of hyaline cartilage.
They are attached to the anterior ends of the ribs and con-
tinue in line with them toward the sternum.
Sternum
The
sternum
(ster
num), or breastbone, is located along
the midline in the anterior portion of the thoracic cage. It
is a fl
at, elongated bone that develops in three parts—an
The F rst seven rib pairs, called the
true ribs
(vertebro-
sternal ribs), join the sternum directly by their costal carti-
lages. The remaining F ve pairs are called
false ribs
because
their cartilages do not reach the sternum directly. Instead,
the cartilages of the upper three false ribs (vertebrochondral
ribs) join the cartilages of the seventh rib, whereas the last
two rib pairs have no attachments to the sternum. These last
two pairs (or sometimes the last three pairs) are called
oat-
ing ribs
(vertebral ribs).
A typical rib
(f g. 7.39)
has a long, slender shaft, which
curves around the chest and slopes downward. On the poste-
rior end is an enlarged
head
by which the rib articulates with
a facet on the body of its own vertebra and with the body
TABLE
7.8
|
Bones of the Vertebral Column
Bones
Number
Special Features
Bones
Number
Special Features
Cervical
vertebrae
7
Transverse foramina; facets of atlas articulate with
occipital condyles of skull; dens of axis articulates
with atlas; spinous processes of second through sixth
vertebrae are biF
d
Lumbar
vertebrae
5
Large bodies; thinner transverse processes
that project laterally; short, thick spinous
processes that project posteriorly nearly
horizontal
Thoracic
vertebrae
12
Transverse processes project posteriorly at sharp
angles; pointed spinous processes that slope
downward; facets that articulate with ribs
Sacrum
4–5 vertebrae
fused
Posterior sacral foramina, auricular surfaces,
sacral promontory, sacral canal, sacral hiatus,
anterior sacral foramina
Coccyx
3–5 vertebrae
fused
Attached by ligaments to the margins of the
sacral hiatus
Sacral canal
Tubercle
of median
sacral crest
Auricular
surface
Posterior sacral
foramen
Sacral hiatus
Coccyx
Sacrum
Superior articular process
Sacral promontory
Anterior sacral
foramen
(a)
(b)
FIGURE 7.37
Sacrum and coccyx. (
a
) Anterior view. (
b
) Posterior view.
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