The narrow upper end of the thorax, which is continu-ous with the neck, is called the inlet of the thorax . It is kidney-shaped. Its transverse diameter is 10-12.5 cm. The anteroposterior diameter is about 5 cm.
Boundaries
Anteriorly: Upper border of the manubrium sterni. Posteriorly: Superior surface of the body of the first thoracic vertebra. On each side: First rib with its cartilage. The plane of the inlet is directed downwards and forwards with an obliquity of about 45 degrees. The anterior part of the inlet lies 3.7 cm below the posterior part, so that the upper border of the manubrium sterni lies at the level of the upper border of the third thoracic vertebra.
Diaphragm or Partition at the Inlet of the Thorax
The diaphragm is in two halves, right and left, with a cleft in between. Each half is also known as Sibson's fascia or suprapleural membrane. It partly 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 it is regarded as the flattened tendon of the scalenus minimus (pleuralis) muscle. Functionally, it provides rigidity to the thoracic inlet, so that the root of the neck is not
putted 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 superior surface is related to the subclavian vessels and other structures at the root of the neck .
Structures Passing through the Inlet of Thorax
Viscera Trachea, oesophagus, apices of the lungs with pleura, remains of the thymus. depicts the structures passing through the inlet of the thorax. Large vessels Brachiocephalic artery on right side. Left common carotid artery and the left subclavian artery on the left side. Right and left brachiocephalic veins. Smaller vessels Right and left internal thoracic arteries. Right and left superior intercostal arteries.. Right and left first posterior intercostal veins. Inferior thyroid veins. Nerves Right and left phrenic nerves. Right and left vagus nerves. Right and left sympathetic trunks. Right and left first thoracic nerves as they ascend across the first rib to join the brachial plexus. Muscles Sternohyoid, sternothyroid and longus colli.
Thoracic Inlet Syndrome: Two structures arch over the first rib: the subclavian artery and first thoracic nerve. These structures may be pulled or pressed by a cervical rib or by variations in the insertion of the scalenus anterior. The symptoms may, therefore, be vascular, neural, or both.
THE INFERIOR APERTURE/OUTLET OF THE THORAX
The inferior operture is the broad end of the thorax which surrounds the upper part of the abdominal cavity, but is separated from it by the diaphragm.
Boundaries
Anteriorly: Infrasternal angle between the two costal margins. Posteriorly: Inferior surface of the body of the twelfth thoracic vertebra. On each side: (i) Costal margin formed by the cartilages of seventh to twelfth ribs.
Diaphragm at the Outlet of Thorax The outlet is closed by a large musculotendinous partition, called the diaphragm—the thoracoabdo-urinal diaphragm—which separates the thorax from the abdomen.
Structures passing through the diaphragm There are three large, and several small, openings in the diaphragm which allow passage to structures from thorax to abdomen or vice versa.
Large Openings in the Diaphragm A. The aortic opening is osseoaponeurotic. It lies at the lower border of the twelfth thoracic vertebra.
It transmits: (i) the aorta, (ii) the thoracic duct, and (iii) the azygos vein. B. The oesophageal opening lies in the muscular part of the diaphragm, at the level of the tenth thoracic vertebra. It transmits: (i) the oesophagus, (ii) the gastric (vagus) nerves, and (iii) the oesoph-ageal branches of the left gastric artery, with some oesophageal veins that accompany the arteries. C. The vena caval opening lies in the central tendon of the diaphragm at the level of the eighth thoracic vertebra. It transmits: (i) the inferior vena cava, and (ii) branches of the right phrenic nerve.
Small Openings in the Diaphragm
(a) Each crus of the diaphragm is pierced by the greater and lesser splanchnic nerves. The left crus is pierced in addition by the hemiazygos vein. (b) The sympathetic chain passes from the thorax to the abdomen behind the medial arcuate ligament also called the medial lumbocostal arch. (c) The subcostal nerve and vessels pass behind the lateral arcuate ligament or lateral lumbocostal arch. (d) The superior epigastric vessels and some lym-phatics pass between the xiphoid and costal (7th costal cartilage) origins of the diaphragm.. This gap is known as Larry's space or foramen of Morgagni. (e) The musculophrenic vessels pierce the dia-phragm at the level of ninth costal cartilage.
(f) Several small veins pass through minute aper-tures in the central tendon.
SURFACE LANDMARKS OF THE.THORAX
Bony Landmarks
1. Suprasternal or jugular notch . It is felt just above the superior border of the manubrium between the sternal ends of the clavicles. It lies at the level of the lower border of the body of the second
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