Costal cartilages
Definition
:
They are unossified anterior
parts of embryonic cartilaginous ribs
These are flattened bars of
hyaline cartilages extending from the anterior ends of rib
The location of the primary
ossification center is near the posterior angle , this ossification extends
toward the anterior end so anterior part of ribs remain cartilaginous at birth
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Differences
features of costal cartilages from 1-12:
The first seven costal cartilage pairs are connected with
the sternum;
The next three cartilages are each articulated with the lower
border of the cartilage of the preceding rib;
The last two cartilage posses free pointed tips in the muscular
wall of the abdomen.
Length of
cartilages : .
They increase
in length from the first to the seventh, then gradually decrease to the
twelfth.
Breadth of
the costal cartilage:
Their breadth, as well as that of the intervals between them,
diminishes from the first to the last. They are broad at their attachments 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.
Direction of
costal cartilage :
They also vary in direction: the first descends a little to the
sternum, the second is horizontal, the third ascends slightly, while the others
are angular, following the course of the ribs for a short distance, and then
ascending to the sternum or preceding cartilage.
Gross
features of costal cartilage :
Each costal cartilage presents two surfaces, two borders, and
two extremities.
Surfaces
The anterior
surface is convex, and looks forward and upward: that of the first
gives attachment to the costoclavicular ligament and the subclavius
muscle; those of the first six or seven at their sternal ends, to the pectoralis
major. The others are covered by, and give partial attachment to, some of the
flat muscles of the abdomen.
The posterior
surface is concave, and directed backward and downward; that of the
first gives attachment to the Each costal cartilage presents two surfaces,
two borders, and two extremities.
Surfaces
The anterior
surface is convex, and looks forward and upward: that of the first
gives attachment to the costoclavicular ligament and the subclavius
muscle; those of the first six or seven at their sternal ends, to the pectoralis
major. The others are covered by, and give partial attachment to, some of the
flat muscles of the abdomen.
The posterior
surface is concave, and directed backward and downward; that of the
first gives attachment to the sternothyroideus, those of the third to the
sixth inclusive to the transversus thoracis muscle, and the six or seven
inferior ones to the transversus abdominis muscle and the diaphragm.
Borders
Of the two
borders the superior is concave, the inferior convex; they
afford attachment to the intercostales interni the upper border of the sixth gives attachment
also to the pectoralis major
The inferior borders
of the sixth, seventh, eighth, and ninth cartilages present heel-like
projections at the points of greatest convexity. These projections carry smooth
oblong facets which articulate with facets on slight projections from the upper
borders of the seventh, eighth, ninth, and tenth cartilages, respectively.
Extremities
The lateral
end of each cartilage is continuous with the osseous tissue of the rib to which
it belongs.
The medial
end of the first is continuous with the sternum; the medial ends of the six
succeeding ones are rounded and are received into shallow concavities on the
lateral margins of the sternum.
The medial
ends of the eighth, ninth, and tenth costal cartilages are pointed, and are
connected each with the cartilage immediately above.
Those of the
eleventh and twelfth are pointed and free.
In old age
the costal cartilages are prone to undergo superficial ossification
, those of the third to the sixth inclusive to the transversus
thoracis muscle, and the six or seven inferior ones to the transversus
abdominis muscle and the diaphragm.
Borders
Of the two
borders the superior is concave, the inferior convex; they
afford attachment to the intercostales interni: the upper border of the
sixth gives attachment also to the pectoralis major.
The inferior borders
of the sixth, seventh, eighth, and ninth cartilages present heel-like
projections at the points of greatest convexity. These projections carry smooth
oblong facets which articulate with facets on slight projections from the upper
borders of the seventh, eighth, ninth, and tenth cartilages, respectively.
Extremities
The lateral
end of each cartilage is continuous with the osseous tissue of the rib to which
it belongs.
The medial
end of the first is continuous with the sternum; the medial ends of the six
succeeding ones are rounded and are received into shallow concavities on the
lateral margins of the sternum.
The medial
ends of the eighth, ninth, and tenth costal cartilages are pointed, and are
connected each with the cartilage immediately above.
Those of the
eleventh and twelfth are pointed and free.
In old age
the costal cartilages are prone to undergo superficial ossification
Functions:
They impart elasticity and
mobility of the thorax which prevent many crushing injuries from fracturing the
ribs and sternum
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