Part 4: THE THORAX
The thorax contains the heart, lungs, and other important structures within a skeletal framework that also protects some of the abdominal organs. The skeleton consists of the thoracic vertebrae and intervertebral discs, the ribs and costal cartilages, and the sternum (see fig. 19-1). The thoracic cavity communicates with the front of the neck by the superior thoracic aperture, or thoracic inlet, which is bounded by the upper margin of the first thoracic vertebra posteriorly, the first pair of ribs and their cartilages laterally, and the upper border of the manubrium sterni anteriorly. The aperture slopes inferior and anterior following the obliquity of the first ribs. It is occupied on each side by the apices of the lungs and pleurae and by the neurovascular bundles for the upper limbs. More medially, it is occupied by the vessels of the head and neck and by viscera. The thoracic cavity communicates with the abdomen by the inferior thoracic aperture which is closed by the diaphragm. The outlet is bounded by the twelfth thoracic vertebra, the twelfth pair of ribs, the free edges of the lower six pairs of costal cartilages, and the xiphisternal joint. Costal cartilages 7 to 10 unite and form the costal margin medially. The right and left costal margins meet at the infrasternal, or subcostal, angle, the apex of which is the xiphosternal joint. The xiphoid process descends into the infrasternal angle. The epigastric fossa, or "pit of the stomach," is a slight depression in front of the xiphoid process.
At birth the thorax is nearly circular in section, but between infancy and puberty it gradually becomes more elliptical until, in the adult, it is shallower from front to back than from side to side. The ratio between the anteroposterior and transverse diameters is the thoracic index. The shape of the chest varies from broad (hypersthenic individuals) with a wide infrasternal angle to narrow (asthenic individuals) with a narrow infrasternal angle.
ADDITIONAL READING
Edwards, E. A., Malone, P. D., and Collins, J. J., Operative Anatomy of the Thorax, Lea & Febiger, Philadelphia, 1972. Anatomical drawings of operative approaches used in thoracic surgery.
Kubik, S., Surgical Anatomy of the Thorax, ed. by J. E. Healey, W. B. Saunders Company, Philadelphia, 1970. Color photographs and key drawings of dissections of the thorax.