PRACTICAL CONSIDERATIONS : THE FACE. 



245 



Fig. 266. 



The inferior maxilla has no epiphysis, and, as might therefore be expected, the 

 ends of the bone at and near the articular surfaces are usually exempt from disease, 

 in marked contrast to the long bones, in which those regions especially suffer. 



The inferior maxilla is not a very vascular bone ; the mucous membrane of the 

 gum is in close contact with it ; it occupies a peculiarly exposed position, and is 

 subject to frequent minor traumatisms ; it is readily infected through carious teeth 

 or tooth-sockets. Such a tooth or an open socket communicates directly with the 

 cancellous tissue of the bone, thus probably permitting in the lower, as in the upper, 

 jaw the direct contact of the toxic agent in phosphorus necrosis. Similar conditions 

 are found in no other bones of the skeleton. 



As a result of the conditions just enumerated, osteitis and necrosis are common, 

 are associated with much pain, and are often very slow in their progress. 



The excessive pain, dysphagia, dribbling of saliva, and occasional aphasia and 

 marked nervous symptoms are thought to be due to reflex irritation associated 

 with compression of the inferior dental nerve in the dental canal by the products 

 of inflammation. Such irritation of a cranial nerve confined within a bony canal is 

 rare, and associates the above symptoms with those occasioned by pressure from 

 similar causes on the other branches of the fifth pair and on the seventh. 



Fracture of the lower jaw may occur at any point. The whole bone is to a great 

 extent protected from fracture by its horse- 

 shoe shape, which gives it some of the 

 properties of a spring, by its density of struc- 

 ture, by its great mobility, and by the buffer- 

 like interarticular cartilages that protect its 

 attached extremities (Treves).' 



The neck of the condyloid process and 

 the coronoid process are so deeply situated 

 and so sheltered in the temporal fossa by 

 the zygomatic arches that they are seldom 

 broken. 



The ramus is protected (though to a 

 less extent) by the masseter externally and 

 the internal pterygoid internally, and is not often fractured, 

 symphysis are thickened, and thus resist fracture. 



About three centimetres (approximately one and a quarter inches) laterally to 

 the symphysis the bone is weakened by the presence of the mental foramen and the 

 large socket for the canine tooth. It is most often broken there or thereabouts 

 either by direct or bv indirect violence. Most fractures of the body of the bone 

 are compound on account of the firm adhesion of the gum, which is usually torn ; 

 hence necrosis and non-union following infection from the mouth-fluids are not un- 

 common results. (For the displacement accompanying this fracture see section 

 on Muscles, page 493. ) The deformity, in so far as it is produced by anatomical 

 forces, is apt to consist of depression of the anterior and larger fragment by the 

 digastric, the genio-hyo-glossus, and the genio-hyoid, and elevation of the posterior 

 and smaller fragment by the temporal, the masseter, and the internal pterygoid. 



The dental nerve, while escaping injury at the time of the accident, may later 

 be compressed by callus, and, if irritated, may, by reason of its anatomical associa- 

 tions with the regions in front of the pinna or in the external auditory meatus, give 

 rise to " faceache" or to "earache." If paralyzed, and the patient puts a cup to 

 his lips, he feels with his lower lip only half of it ; in paralysis of the fifth nerve itself 

 it seems to him exactly as though it were broken (Owen). 



The capsule of the temporo-77iaxillary joint is thinnest anteriorly and strongest 

 externally ; hence suppuration is most likelv to extend in a forward direction. 

 The strong external lateral ligament arising from the lower edge of the zygoma and 

 running backward and downward seems to prevent the condyle being pressed back- 

 ward against the bony meatus and the middle ear (Fig. 247). As Treves observes, 

 if it were not for this provision, blows upon the chin would be far more dangerous 

 than they are. 



In spite of its great mobility and its frequent use, the joint is rarely the subject 



Mandible, showing lines of fractures. 



The angle and the 



