2O The Bones of the Head 





by the end of the first year. At birth the jaw is a ' mere shell of bone,' 

 with the sockets of the milk teeth, and until the teeth are cut there is 

 hardly any ramus. For a long while the alveolar part is larger than 

 the basilar, but in the adult these parts are of equal height, the mental 

 foramen being midway between the upper and lower borders of the 

 bone, the ramus passing up at a right angle. As old age advances the 

 teeth fall out, the alveolar process dwindles into a sharp and useful 

 cutting edge, covered with tough mucous membrane ; the mental fora- 

 men, in consequence, comes close to the upper border of the bone, and 

 the angle between the body and ramus widens out. 



Dislocation ot the jaw may result from over-action of the depres- 

 sors in an attack of yawning, or from a blow upon the chin when the 

 mouth is wide open. The condyle is carried forward upon the emi- 

 nentia articularis, where it remains fixed, a wide hollow appearing in 

 front of the mastoid process, and the mouth being wide open and fixed 

 in that position. When the luxation is on one side only, the chin is 

 thrust over to the opposite side. The coronoid process may be caught 

 against the malar bone. The jaw is firmly fixed in the new position 

 by the contraction of, and strain upon, its elevator muscles. 



Reduction is effected by making a fulcrum of the thumbs, well pro- 

 tected, between the molar teeth ; the symphysis being raised, the con- 

 dyle is unhitched, and, with a snap, the jaw resumes its proper position. 

 Simple pressure of the thumb downwards, backwards, upon the last 

 molar tooth, however, generally suffices, and it has this merit, that it 

 does not excite contraction of the temporal and internal pterygoid 

 muscles. Both in the dislocation and in the reduction the fibro-carti- 

 lage follows the condyle. 



Fracture may occur in any part ; a common situation being a 

 little in front of the insertion of the masseter, in 

 which case the digastrics, mylo-hyoids, genio- 

 hyo-glossi, genio-hyoids, and platysmas may draw 

 the anterior part downwards and inwards, whilst 

 the other piece may be drawn upwards and for- 

 wards by the temporal, internal pterygoid, and 

 masseter. The line which the fracture has taken, 

 however, may greatly influence the displacement 

 of the fragments. The treatment consists in maintaining the fragments 

 in apposition until union is firm. This may be done by locking the lower 

 jaw against the upper by a moulded splint and a four-tailed bandage ; 

 but sometimes it is necessary to fix and steady the fragments by a 

 strong wire suture. 



Resection may demand an incision along the lower border and 

 half-way up the back of the ramus not too far, lest the facial nerve 

 be cut the facial artery or arteries being promptly secured. The 

 muscles are detached to a great extent by using the blunt raspatory. 

 The genio-hyo-glossus, however, must be cut from the back of the 



