Human Anatomy Vol 1

THORAX

intercostal muscles and membranes from the upper

three intercostal spaces.

Trace the artery through the upper six intercostal

spaces and identify its two terminal branches. Trace its

vena comitantes upwards tillthird costal cartilage where

these join to form internal thoracic vein, which drains

into the brachiocephalic vein.

Follow the course and branches of both anterior and

posterior intercostal arteries including the course and

tributaries of azygos vein.

Feolures

The thoracic cage forms the skeletal framework of the
wall of the thorax. The gaps between the ribs are called
intercostal spaces. They are filled by the intercostal
muscles and contain the intercostal nerves, vessels and
lymphatics. There are nine intercostal spaces anteriorly
and eleven intercostal spaces posteriorly.

Interco IMuscles

These are:

1 The external intercostal muscle.
2 The internal intercostal muscle.
Each comprises intercartilaginous in front and intero-
sseous in posterolateral part.
3 The transversus thoracis muscle which is divisible
into three parts, namely the subcostalis, the inter-
costalis intimi (innermost intercostal) and the sterno-
costalis. The attachments of these muscles are given
in Table 14.1.

Exlent

The external intercostal muscle extends from the tubercle
of the rib posteriorly to the costochondral junction
anteriorly. Between the costochondral junction and the
sternum, it is replaced by the external or anterior

intercostal membrane. The posterior end of the muscle is

continuous with the posterior fibres of the superior

costotransaerse lignment (Fig. 14. 1).

The internal intercostal muscle extends from the lateral

border of the sternum to the angle of the rib. Beyond

the angle it becomes continuous with the internal or

posterior intercostal membrane, which is continuous with

the anterior fibres of the superior costotransaerse ligament.

The subcostalis is confined to the posterior part of

the lower intercostal spaces only.

The intercostalis intimi is confined to the middle two-

fourths of all the intercostal spaces (Fig. M.2).

The stemocostalis is present in relation to the anterior

parts of the upper intercostal spaces.

Direclion of res

In the anterior part of the intercostal space:

1 The fibres of the external intercostal muscle run

downwards, forwards and medially in front.

I nternal

intercostal

membrane

Vertebrae

External

intercostal

muscle

lnternal

intercostal muscle

External

intercostal membrane

Fig, 14.1: External and internal intercostal muscles with external

and internal intercostal membranes

Table 14.1: The attachments of the intercostal muscles (Figs 14.1 and 14.2)

Origin lnsertion

1.

2.

3.

Muscle

External intercostal

lnternal intercostal

Transversus thoracis

a. Subcostalis

b. lntercostalis intimi/

innermost intercostal

c. Sternocostalis

Lower border of the rib above the space

Floor of the costal groove of the rib above

lnner surface of the rib near the angle

Middle two-fourths of the ridge above the

costal groove

. Lower one{hird of the posterior surface of
the body of the sternum
. Posterior surface of the xiphoid
. Posterior surface of the costal cartilages ol
the lower 3 or 4 true ribs near the sternum

Outer lip of the upper border of the rib below

lnner lip of the upper border of the rib below

lnner sufface of two or three ribs below

lnner lip of the upper border of the rib below

Costal cartilages of the 2nd to 6th ribs