Human Anatomy Vol 1

Poilition ot the lnlet of Thorox
The partition is in two halves, right and left, with a cleft
in between. Each half is covered by a fascia, known as
S ibson' s fascia or suprapleural membrane .Ilpartly separates
the thorax from the neck. The membrane is triangular in
shape. Its apex is attached to the tip of the transverse
process of the seventh cervical vertebra and the base to
the inner border of the first rib and its cartilage.
Morphologically, Sibson's fascia is regarded as the
flattened tendon of the scalenus minimus (pleuralis)
muscle. It is thus formed by scalenus minimus and
endothoracic fascia. Functionally, it provides rigidity
to the thoracic inlet, so that the root of the neck is
not puffed up and down during respiration. The
inferior surface of the membrane is fused to the cervical
pleura, beneath which lies the apex of the lung. Its

INTRODUCTION

superior surface is related to the subclavian vessels

and other structures at the root of the neck (Figs 12.10

and 72.77a and b).

Slructures Possing lhrough the Inlet of lhorox

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Trachea, oesophagus, apices of the lungs with pleura,

remains of the thymus. Figure 12.72 depicts the

structures passing through the inlet of tl're thorax.

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Brachiocephalic artery on right side"

Left common carotid artery and the left subclavian

artery on the left side. Right and left brachiocephalic

ve1ns.

Scalenus medius

Scalenus anterior

Brachial plexus

Scalenus medius

Cervical dome of pleura

Subclavian artery

Subclavian veln

Fig. 12.10: Thoracic inlet showing cervical dome of the pleura on left side of body and its relationship to inner border of first rib

Suprapleural

membrane

Apex of the lung

Subclavian artery

Subclavian vein

First rib

Figs 12.11a and b: The suprapleural membrane:

(b)

(a) Surface view, and (b) sectional view

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c

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a