toward the uninjured side. The capsule of the joint, as a rule, is not torn, but becomes greatly distended (Plate 17). This dislocation does not occur in children. The prognosis is favorable, although a marked tendency to recurrence is frequently observed. It is termed habitual

dislocation of the lower jaw.

It follows from what has been said that a special manipulation is necessary to effect reduction. The surgeon inserts his two thumbs into the mouth and lays them on the alveolar processes of the lower jaw; the bone is then pressed first downward and then somewhat backward. In this way the articular extremity is pushed back until it rests on the articular tubercle, and finally into the glenoid fossa, and the dislocation is

reduced. The sudden goid muscle in dislocation of the lower disappearance of the jaw.

muscular resistance,

which produces the fixation of the head of the bone, is plainly felt as the luxation is reduced.

(B) Backward Dislocation

Backward dislocation of the lower jaw is an extremely rare occurrence, and is observed almost exclusively in The accident occurs after yawning or spasmodic

women.

contraction, during a fall, etc. The condyloid process is forced behind the small tympanic tubercle which forms the posterior boundary of the glenoid fossa and enters the tympanico-stylo-mastoid fossa. The mouth is tightly closed; the teeth of the lower jaw are behind those of the

upper jaw and tightly clenched. The articular process is found beneath the external auditory meatus in front of the mastoid process. Reduction is effected by pressing the jaw backward, and then downward and forward, or the teeth may be forcibly separated with any suitable instrument. [Anesthesia is usually necessary.-ED.]

IV. FRACTURES AND DISLOCATIONS OF THE VERTEBRAL COLUMN

(A) FRACTURES OF THE VERTEBRAL COLUMN

1. Fracture of the Body of a Vertebra

We may speak of a typical fracture of the body of a vertebra, such as that occurring in the region of the fifth and sixth cervical, of the last thoracic, and of the first lumbar, these being the most frequent. The accident is always produced by great violence. That the force must be great is readily understood when we consider that the vertebral column, in addition to a considerable degree of rigidity, possesses marked elasticity and mobility, since one-fourth of its entire length consists of the elastic and extremely movable intervertebral discs. The degree of mobility that can be attained by exercise is shown by the astonishing performances of so-called india-rubber men, who are able to bend almost double in the cervical region, at the junction between the thoracic and lumbar portions, and in the lumbar region of the column. These points also correspond with the most frequent sites of fracture, evidently because a bending force here finds the most favorable point of attack. This may be further illustrated by the fact that a rod of variable flexibility, like the vertebral column, when subjected to a breaking strain, usually breaks at a point where one of the more flexible segments joins a more rigid one; i. e., in the region of the twelfth thoracic and first lumbar, and particularly in the region of the lower cervical vertebræ.

rare.

Direct fracture of the body of a vertebra is extremely In all such cases of fracture of a vertebra by a violent blow or a wagonwheel, indirect violence is always a causal factor.

Indirect fractures very commonly affect the bodies of the

PLATE 18.

Fracture of the Cervical Portion of the Column with Contusions of the Cord.-Fracture in the region of the sixth and seventh cervical vertebræ. From a woman thirty-three years old, admitted to the Greifswalder Klinik on June 28, 1893; died on July 5th. At the autopsy a complete transverse contusion of the cord was found. During life consciousness was preserved and there were sensory and motor paralyses of the trunk and lower extremities, with partial paralysis of the upper extremities. The limits of sensation were found, in front, at the level of the third rib on both sides. There was also retention of urine. In the region of the sixth cervical vertebra a distinct prominence was felt which could be reduced under anesthesia. The injury was treated by the extension method, weights being attached to the head by means of a jury-mast (Glisson's sling). The patient was kept on a surgical bed provided with a water-mattress and a contrivance for raising and lowering. Death from paralysis of respiration.

The illustration shows the fracture of the two vertebræ and the dislocation backward and upward of the seventh, which encroached on the spinal canal and pressed upon the cord. (Author's observa

tion.)

vertebræ and are produced by excessive flexion or extension, by compression, or by a dislocating force-usually by a combination of all these factors. The accident is always produced by an overwhelming force, such as a fall on the back, the head, the buttocks, or the feet, or a cave-in, etc. In some cases it occurs while the vertebral column as a whole is fixed by the action of the muscles. Indirect fractures of the vertebræ by compression are comparatively frequent among coal-miners. The injury is usually produced while the miner is bent over in a sitting posture, with the buttocks resting on the heels, by a mass of stones or coal falling on his head and neck from an inconsiderable height. Thus he is gradually bent over forward and compressed, excessive forward flexion of the vertebral column takes place until the head comes in contact with the knees, and a fracture is produced.