Human Anatomy Vol 1

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INTRODUCIION

The thorax is an osseocartilaginous cavity or cage for
various viscera, providing them due support and pro-
tection. This cage is not static, but dynamic, as it moves
at its various joints, increasing or decreasing the various
diameters of the cavity for an extremely important
process of respiration, which is life for all of us.

RIBS OR COSTAE

1 There are 12 ribs on each side forming the greater

part of the thoracic skeleton.

The number may be increased by development of a

cervical or a lumbar rib; or the number may be

reduced to L1 by the absence of the twelfth rib.

2 The ribs are bony arches arranged one below the

other (Fig. 13.1). The gaps between the ribs are called

intercostal spaces (see Fig. 72.7).

The spaces are deeper in front than behind, and

deeper between the upper than between the lower

ribs.

3 The ribs are placed obliquely, the upper ribs being

less oblique than the lower. The obliquity reaches

its maximum at the ninth rib, and thereafter it

gradually decreases to the twelfth rib.

4 The length of the ribs increases from the first to the

seventh ribs, and then gradually decreases from the

eighth to twelfth ribs.

5 The breadth of the ribs decreases from above

downwards. In the upper ten ribs, the anterior ends

are broader than the posterior ends.

6 The first 7 ribs which are connected through their

cartilages to the sternum are called true ribs, or

aertebrosternal ribs. The remaining five are false ribs.

Out of these the cartilages of the eighth, ninth and

tenth ribs are joined to the next higher cartilage and

are known asaertebrochondral ribs.The anterior ends

of the eleventh and twelfth ribs are free and are called

floating ribs or aertebral ribs.

7 The first two and last three ribs have special features,

and are atypical ribs. The third to ninth ribs are

typical ribs.

Typicol Ribs

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The anterior end bears a concave depression. The

posterior end bears a head, a neck and a tubercle.

The shaft is convex outwards and there is costal

groove situated along the lower part of its inner

surface, so that the lower border is thin and the upper

border rounded.

Each rib has two ends, anterior and posterior. Its shaft

comprises upper and lower borders and outer and inner

surfaces.

Upper smaller facet of head

Neck of the rib

Non-articular part of tu

Angle of the rib

Articular part

of tubercle

Lower larger

facet of head

Costal

cartilage

Costal groove

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Fig. 13.1: A typical rib of the left side