Anatomy

The inferior thoracic aperture is much larger than the superior thoracic aperture

Superior thoracic aperture

The superior thoracic aperture refers to the superior opening of the thoracic cavity. It is also referred to anatomically as the thoracic inlet and clinically as the thoracic outlet...

. In layman's terms, it is the round opening whose edges are the lowest ribs. It is closed by the diaphragm, which separates the thoracic

Thoracic cavity

The thoracic cavity is the chamber of the human body that is protected by the thoracic wall ....

 and abdominal cavities

Abdominal cavity

The abdominal cavity is the body cavity of the human body that holds the bulk of the viscera. It is located below the thoracic cavity, and above the pelvic cavity. Its dome-shaped roof is the thoracic diaphragm , and its oblique floor is the pelvic inlet...

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The inferior thoracic aperture is bounded by:

• the 12th thoracic vertebra
  Thoracic vertebrae
  In human anatomy, twelve thoracic vertebrae compose the middle segment of the vertebral column, between the cervical vertebrae and the lumbar vertebrae. They are intermediate in size between those of the cervical and lumbar regions; they increase in size as one proceeds down the spine, the upper...
  
   posteriorly,
• 11th and 12th pairs of ribs laterally,
• costal cartilages of ribs 7 through 10 anteriorly,
• and the xiphisternal joint
  Xiphisternal joint
  The xiphisternal joint is a location near the bottom of the sternum, where the body of the sternum and the xiphoid process meet.It is in line with the T9 vertebrae....
  
   - (i.e.: the articulation between the xiphoid process
  Xiphoid process
  The xiphoid process, or xiphisternum or metasternum, is a small cartilaginous process of the lower part of the sternum which is usually ossified in the adult human. By age 15 to 29, the xiphoid usually fuses to the body of the sternum with a fibrous joint. Unlike the synovial articulation of major...
  
   and the inferior border of the sternal body) anteriorly.

Structures passing through the inferior thoracic aperture between the thorax and abdomen include the inferior vena cava

Inferior vena cava

The inferior vena cava , also known as the posterior vena cava, is the large vein that carries de-oxygenated blood from the lower half of the body into the right atrium of the heart....

 and esophagus

Esophagus

The esophagus is an organ in vertebrates which consists of a muscular tube through which food passes from the pharynx to the stomach. During swallowing, food passes from the mouth through the pharynx into the esophagus and travels via peristalsis to the stomach...

, both of which pass through the diaphragm, and the abdominal aorta

Abdominal aorta

The abdominal aorta is the largest artery in the abdominal cavity. As part of the aorta, it is a direct continuation of the descending aorta .-Path:...

 and thoracic duct

Thoracic duct

In human anatomy, the thoracic duct of the lymphatic system is the largest lymphatic vessel in the body. It is also known as the left lymphatic duct, alimentary duct, chyliferous duct, and Van Hoorne's canal....

 which pass posterior to the diaphragm through the aortic hiatus

Aortic hiatus

The aortic hiatus is a hole in the human diaphragm. It is the lowest and most posterior of the large apertures.It is located approximately at the level of the twelfth thoracic vertebra .-Structure:...

.