the cervical sympathetic is implicated.

#Thoracic or Dorsal Region.#--When the disease is confined to the
thoracic region, stiffness of the back and boarding of the vertebral
muscles are prominent features. On being asked to pick up an object
from the floor, the patient reaches it by bending his knees and hips,
while he keeps his back rigid. He refuses to make any movement that
involves jolting of the spine, such, for example, as jumping from a
chair to the ground. Children often attempt to take the weight off the
diseased vertebrae by placing the palms of the hands on the edge of a
chair so that the weight is borne by the arms.

Angular deformity is often well marked, and may implicate several
vertebrae. In order to maintain the head erect, the spine above and
below the seat of disease becomes unduly arched forward--compensatory
lordosis. In advanced cases the ribs become approximated, and the
lower end of the sternum is projected forward. The antero-posterior
diameter of the thorax is thus increased, while its vertical diameter
is diminished. These changes, together with the telescoping of the
vertebral bodies, lead to the deformity characteristic of the
tuberculous hunch-back (Fig 216). The alterations in the shape of the
chest may lead to functional disturbances of the heart and lungs.

[Illustration: FIG. 216.--Hunch-back Deformity following Pott's
disease of Thoracic Vertebrae.

(Photograph lent by Sir George T. Beatson.)]

_Dorsal Abscess._--As already mentioned, the earliest stage of abscess
is well seen in skiagrams (Fig. 213), especially in children. When
there is an extension of the suppurative process, the pus may pass
directly backwards along the posterior branches of the intercostal
vessels and nerves, and come to the surface behind the transverse
processes, or it may travel forward between the pleura and the ribs,
and, passing along the course of the lateral cutaneous branches of the
intercostals, come to the surface opposite the middle of the rib. In
the latter case, the abscess is liable to be mistaken for one
associated with tuberculous disease of the rib, particularly as the
rib is usually found to be bare. In rare cases the pus opens into the
pleura, giving rise to empyema. When the disease is on the anterior
surface of the bodies of the lower thoracic vertebrae, the pus may
spread down through the pillars of the diaphragm and reach the sheath
of the psoas muscle.

_Treatment_ is on the usual