The<unk>  is essentially a hole surrounded by a bony ring, through which several vital structures pass. The<unk>  is bounded by: the first thoracic vertebra (T1) posteriorly; the first pair of ribs laterally, forming lateral C-shaped curves posterior to anterior; and the costal cartilage of the first rib and the superior border of the manubrium anteriorly. Dimensions The adult<unk>  is around 6.5 cm antero-posteriorly and 11 cm transversely. Because of the obliquity of the first pair of ribs, the aperture slopes antero-inferiorly. Relations The clavicle articulates with the manubrium to form the anterior border of the<unk> . Superior to the<unk>  is the root of the neck, and the superior mediastinum is inferiorly related. The brachial plexus is a superolateral relation of the<unk> . 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.
Thoracic inlet
Subclavian loop
Subclavian triangle
Thoracic diaphragm
Cervical rib
Boracic lint
Posterior triangle of the neck
Anterior triangle of the neck