The Costal Cartilages
The Costal Cartilages
are bars of white, hyaline cartilage, which serve to prolong the ribs forward
to the front of the chest, and contribute very materially to the elasticity of
its walls. The first seven are connected with the sternum, the next three with
the lower border of the cartilage of the preceding rib. The cartilages of the
last two ribs have pointed extremities, which terminate in free ends in the
walls of the abdomen. Like the ribs, the costal cartilages vary in their
length, breadth, and direction. They increase in .length from the first to the
seventh, then gradually diminish to the last. They diminish in breadth, as well
as the intervals between them, from the first to the last. They are broad at
their attachment to the ribs, and taper toward their sternal extremities,
excepting the first two, which are of the same breadth throughout, and the
sixth, seventh, and eighth, which are enlarged where their margins are in
contact. In direction they also vary: the first descends a little, the second is
horizontal, the third ascends slightly, while all the rest follow the course of
the ribs for a short extent, and then ascend to the sternum or preceding
cartilage. Each costal cartilage presents two
surfaces, two borders, and two extremities. The anterior
surface is convex, and looks forward and upward: that of
the first gives attachment to the costo-clavicular ligament and the Subclavius
muscle; that of the second, third, fourth, fifth, and sixth, at their sternal
ends, to the Pectoralis major.! The others are covered by, and give partial
attachment to, some of the great fiat muscles of the abdomen. The posterior
surface is concave, and directed backward and downward, the
first giving attachment to the Sterno-thyroid, the third to the sixth inclusive
to the rrriangularis sterni, and the six or seven inferior ones to the
Tranversalis muscle and the Diaphragm. Of the two borders, the superior
is concave, the inferior convex: they afford attachment to the internal
Intercostal muscles, the upper border of the sixth giving attachment to the
Pectoralis major muscle. The contiguous borders of the sixth, seventh, and
eighth, and sometimes the ninth and tenth, costal cartilages present small,
smooth, oblong-shaped facets at the points where they articulate. Of the two
extremities, the outer one is
continuous with the osseous tissue of the rib to which it belongs. The inner extremity of the first is continuous with the sternum;
the six succeeding ones have rounded extremities,which are received into
shallow concavities on the lateral margins of the sternum. The inner
extremities of the eighth, ninth, and tenth costal cartilages are pointed, and
are connected with the cartilage above.
