Human Anatomy Vol 1

BONES AND JOINTS OF THORAX

Clavicle

Sternal head of

sternocleidomastoid

Manubrium

Pectoralis major

Body of sternum

Costal cartilages

Xiphoid process

with a foramen

Aponeurosis of

oblique muscles

Rectus abdominis

Fig. 13.9: The sternum:Anterior aspect, with muscle attachment

Posterior Su ce

1 The first cartilage gives origin to the sternothyroid

muscle.

2 The second to sixth cartilages receive the insertion

of the sternocostalis.

3 The seventh to twelfth cartilages give attachment to

the transversus abdominis and to the diaphragm.

1 The borders give attachment to the internal

intercostal muscles and the external intercostal

membranes of the spaces concerned (see Fig. 1,4.L).

2 The fifth to ninth cartilages articulate with one

another at the points of their maximum convexity,

to form synovial joints.

Lale End

The lateral end of each cartilage forms a primary
cartilaginous joint with the rib concerned.

Me I End
1 The first cartilage forms a primary cartilaginous joint
with the manubrium.
2 The second to seventh cartilages form synovial joints
with the sternum.
The eighth, ninth and tenth cartilages are connected
to the next higher cartilage by synovial joints.
The ends of the eleventh and twelfth cartilages are
pointed and free.

Weakest area of rib is the region of its angle. This

is the commonest site of fracture.

Cervical rib occurs in 0.5% of persons. It may

articulate with first rib or may have a free end. It

may cause pressure on lower trunk of brachial

plexus, resulting in paraesthesia along the medial

border of forearm and wasting of intrinsic muscles

of hand (seeFig.72.14).It may also cause pressure

on the subclavian artery.

In rickets there is inadequate mineralisation of

bone matrix at the growth plates due to increased

bone resorption. Due to deposition of

unmineralised matrix there is widening of the

wrist and rachitic rosary, i.e. prominent

costochondral junctions in thoracic cage.

The stemum is a flat bone, forming the anterior median

part of the thoracic skeleton. In shape, it resembles a

short sword. The upper part, corresponding to the

handle is called the manubrium. The middle part,

resembling the blade is called the body. The lowest

tapering part forming the point of the sword is the

xiphoid process or xiphisternum.

The stemum is about 17 cm long. It is longer in males

than in females (Figs 13.9 to 13.11).

Manubrium

Sternal angle

Anterior surface of

body of sternum

Xiphoid process

Linea alba

Clavicular notch

Notch for first

costal cartilage

Notch for second

costal cartilage

Notch for third

costal cartilage

Notch for fourth

costal cartilage

Notch for fifth

costal cartilage

Notch for sixth

costal cartilage

Notch for seventh

costal cartilage

Fig.10.10: The sternum: Anterior aspect