82 CLINICAL APPLIED ANATOMY. 



the canine socket, and the mental foramen all tend to lessen the 

 solidity of the jaw. 



All the fractures of the body of the mandible involve the 

 mucous membrane of the gum, and are therefore open (compound) 

 fractures. Hence haemorrhage into the mouth is a usual, if not 

 a universal, sign. There is generally some displacement in these 

 fractures, but the amount depends very greatly upon the force 

 applied, whether direct or indirect. As a result the regular 

 curved line of the teeth, or their horizontal level, may be altered, 

 a tooth or teeth may be missing, and one may even have dropped 

 between the fragments. In the most typical displacement, the 

 larger or anterior of the fragments ^^ 7 here the fracture is on one 

 side of the symphysis, is drawn backwards and downwards by 

 the depressor muscles, the digastric, mylo-hyoid, genio-hyoid and 

 genio-hyo-glossus, and the posterior or smaller portion pulled 

 upwards and outwards by the elevator muscles, the masseter, 

 internal pterygoid, and temporal. If there is a fracture on both 

 sides of the symphysis, there will be a tendency for the median 

 fragment to be drawn backwards and downwards by the depressor 

 muscles, and as a consequence the tongue may fall back, covering 

 the upper opening of the larynx, and inducing dyspnoea or even 

 suffocation. 



The inferior dental nerve runs in a canal in the body of the 

 mandible, but is not as a rule torn when the bone is fractured, 

 owing to the fact that displacement is not great. If it is 

 lacerated, the lower lip and the anterior teeth may be anaesthetic. 

 Later, if the nerve becomes secondarily involved in callus, its 

 functions may be interfered with, or there may be much neuralgic 

 pain over its distribution. Fracture of the ramus is rare owing 

 to the protection afforded by the masseter and internal pterygoid 

 muscles. Further, if fracture is present, these muscles, acting 

 practically as splints on either side, prevent much, if any, dis- 

 placement of the fragments. The condyle may be broken by 

 indirect violence, such as a fall upon the chin. The coronoid 

 process is well protected by the zygoma, and is rarely broken 

 without this arch being fractured at the same time. 



