Inferior thoracic aperture; Thoracic outlet - Apertura thoracis inferior
The inferior thoracic aperture (thoracic outlet, lower opening) is formed by the twelfth thoracic vertebra behind, by the eleventh and twelfth ribs at the sides, and in front by the cartilages of the tenth, ninth, eighth, and seventh ribs, which ascend on either side and form an angle, the subcostal angle, into the apex of which the xiphoid process projects. The lower opening is wider transversely than from before backward, and slopes obliquely downward and backward, it is closed by the diaphragm which forms the floor of the thorax.
This definition incorporates text from a public domain edition of Gray's Anatomy (20th U.S. edition of Gray's Anatomy of the Human Body, published in 1918 – from http://www.bartleby.com/107/).
General Anatomy > Bones; Skeletal system > Axial skeleton > Thoracic skeleton > Thoracic cage > Inferior thoracic aperture; Thoracic outlet