The thoracic or dorsal vertebrae are twelve in number and are so articulated with one another as to form a single, regular curve with its concavity forwards and convexity backward. Any sudden change in the direction of the curve is an evidence of disease; this is seen in the angular curvature of Pott's disease or caries of the spine. The ribs are connected with the vertebras by the articulation of the head of the rib with the body of the vertebra, and the tubercle of the rib with the transverse process. The transverse process is connected with the body by the pedicle and with the spinous process by the lamina. The spinal cord is exposed in operations by removal of the spinous process and laminae, hence the name laminectomy.

The spinous processes are the guides which indicate the position and condition of the vertebrae. Their tips are not covered by muscles but lie close beneath the skin and are readily felt and any abnormality detected. In the normal body the grooves on each side of the spinous processes are filled up with muscle, but in certain diseases, as in infantile paralysis and lateral curvature, they become atrophied and the spine becomes twisted, hence on the convex side of the abnormal lateral curve, to the outer side of the spines, the projection formed by the transverse processes and tubercles of the ribs can be both seen and felt.

The external curve formed by the tips of the spinous processes of the thoracic region in the normal person is not so great as is the curve formed by the anterior portion of the bodies of the thoracic vertebrae. This is because the spinous processes at the upper and lower portions of the chest project out almost at right angles to the long axis of the body, while those of the middle portion slope downward. Hence the tips of the spinous processes of the seventh cervical, first dorsal, and twelfth dorsal vertebrae are opposite the bodies of the same vertebrae, while the others are opposite the bodies of the vertebrae next below. (The spine will be considered more at length in the section devoted to the Back).

Soft Parts

The bony thorax is lined by the pleurae, the ribs are united to each other by the intercostal muscles, and over all are muscles, superficial fascia, and skin. In addition, in front are the mammary glands and behind are the scapulae.