THE FACE. 63 



Area of Distribution of the Fifth Nerve. When the ophthalmic division 

 is affected the pain in neuralgia is over the brow and up toward the vertex of the 

 skull; it also involves the eye. The points of exit of the supra-orbital branch at 

 the supra-orbital foramen and of the nasal branch toward the lower portion of the 

 nose are tender to pressure. 



When the maxillary division is affected, there is pain in the cheek and ala of 

 the nose. The tender points are the exit of the infra-orbital nerve at and below 

 the infra-orbital foramen, at the exit of the malar branch on the malar bone, and 

 the upper gums and hard palate. 



When the mandibular division is affected the pain involves the lower jaw and 

 the side of the head nearly to the top (auriculotemporal branch). The lower gums 

 and tongue are also painful. Pain on pressure is felt over the mental foramen and in 

 the course of the auriculotemporal nerve in front of and above the ear. 



THE LOWER JAW. 



The mandible or inferior maxilla is subject to fractures, dislocation, and tumors. 

 In its composition it is very dense, so that in dividing it a groove should be cut 

 with a saw before the use of the bone-cutting forceps is attempted, otherwise 



FIG. 71. Lower jaw of child and adult, showing the mental foramen. 



splintering of the bone will ensue. It is the last bone to decay. Its horseshoe 

 shape and exposed position render it unusually liable to fracture. The strongest 

 portion is what one would expect to be the weakest, viz., the symphysis. Its 

 weakest part (or rather the part where it is most often broken) is the region of the 

 mental foramen. The bone is weakened at this point not only by the foramen 

 but also by the deep socket of the canine tooth. 



The position of the mental foramen, normally between the two bicuspids 

 (beneath the second in the negro Humphry), varies in its vertical location between 

 the alveolar border and lower edge of the body, according to age. In infancy it is 

 low down, in young adults it is midway, and in old people it is high up. 



The body of the jaw is composed of two parts, one above and one below the 

 external oblique line, which runs from the base of the anterior border of the 

 coronoid process downward and forward to end at the mental tubercle, to one side 

 of the symphysis. The part above this oblique line is the alveolar and the part 

 below is the basal portion of the body. 



The mental foramen opens on the oblique line separating the alveolar and basal 

 portions. In early adult life the two portions, basal and alveolar, are about even in 

 size, so that the foramen is below the middle of the jaw. As the teeth are lost 

 the alveolar process atrophies ; this naturally leaves the basal portion with the mental 



