The superior thoracic aperture is essentially a hole surrounded by a bony ring, through which several vital structures pass.

The brachial plexus emerges between the anterior and middle scalene muscles, superior to the first rib, and passes obliquely and inferiorly, underneath the clavicle, into the shoulder and then the arm.

Impingement of the plexus in the region of the scalenes, ribs, and clavicles is responsible for thoracic outlet syndrome.

There are several other minor, but important, vessels and nerves passing through, and an abnormally large thyroid gland may extend inferiorly through the thoracic inlet into the superior mediastinum.

The apices of the lungs lie to either side of the oesophagus and trachea, and is separated from them by the other vessels and nerves listed above.