FRACTURES OF THE JAWS. 81 



through the rent in the lining membrane into the tissues at the 

 root of the nose, and up on to the forehead. 



The grave lesion of an open fracture of the ethmoidal portion 

 of the base of the skull may occasionally be produced by the 

 violence which breaks the nose, and therefore prognosis in this 

 common accident must not always be too sanguine, since septic 

 meningitis may ensue. 



Fractures of the Maxilla (Upper Jaw). The maxilla is 

 quite superficial, and contains a large air cavity, the antrum, the 

 walls of which, at least anteriorly, are of no great thickness. 

 In spite of these anatomical facts, however, fractures of this bone 

 are not common. But violence, such as a kick from a horse, 

 however, may break it in spite of the protection afforded by the 

 prominent malar bone, the nose, and the symphysis menti. If 

 the fracture involves the antrum, air may escape into the tissues 

 of the cheek, giving rise to a characteristic crackling sensation 

 on palpation. If the aveolar border be fractured, teeth are apt 

 to be displaced, and the mucous membrane of the gum torn, the 

 fracture being then an open (compound) one. The infra-orbital 

 nerve running in its groove and canal is liable to primary or 

 secondary involvement. 



The floor of the orbit being formed chiefly by the upper surface 

 of the maxilla, it follows that a fracture of the bone including 

 this portion may cause extravasation of blood into the tissues of 

 the orbit, which, if sufficient in amount, may lead to proptosis. 



The lachrymal (or nasal) duct is also liable to laceration or 

 pressure in consequence of a fracture of the maxilla, passing as 

 it does through the inner part of the bone on its way to open into 

 the inferior meatus of the nose. 



Fractures of the Mandible (Lower Jaw). The mandible 

 is the only bone of the face which is moveable. The chin, and 

 each angle, form projections which are liable to be met by blows, 

 and yet a fracture at any one of these spots is not at all common, 

 probably owing to the greater thickness of the bone at these 

 points. The weakest part of the bone is in the body, rather 

 nearer the symphysis than the angle, where the incisive fossa, 



C.A.A. 6 



