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FRACTURE OF THE LOWER JAW. 
(2.) FRACTURE OF THE LOWER JAW. 
* 
Of all the bones of the head the under jaw is the most frequent seat 
of fracture : this is true of all classes of animals, and notably of the 
horse. The causes are external violence, kicks and falls; occasionally 
the excessive action of the muscles of mastication, as when the mouth 
gag is applied to horses suffering from brain disease, or in the simul¬ 
taneous application of the mouth gag and twitch. Hertwig considers 
that, under these circumstances, the animals are unable rightly to 
estimate the degree of contraction of the masseter muscles. Hering saw 
a case in the horse, caused by the clumsy use of the tooth chisel. In 
dental operations fractures may occur under the same circumstances as 
in the upper jaw. Transverse fracture of the body of the jaw in calves 
not infrequently results from violent manipulation during delivery. In 
a similar way fracture of the symphisis of the lower jaw may be caused 
by parturition hooks being inserted in the angle behind the body of the 
jaw. In staghounds they result from the prey striking out at the moment 
when the dog has fastened on to the hind-limb. 
The fracture is sometimes subcutaneous, and remains confined to one 
branch of the lower jaw ; but not infrequently both branches break, and 
usually at the neck, where teeth are wanting. Vormeng noted breakage 
of both branches in the middle line, an accident which occurs more 
frequently in foals than in older animals. Fractures of the border of 
the alveoli of the lower incisors are often seen, in consequence of the 
animal biting, being kicked, or falling and striking fixed objects. 
Fractures of the joint or coronoid process, although occasionally reported, 
occur less frequently. 
Subcutaneous fractures of one branch of the lower jaw are not so 
readily diagnosed; suddenly developed difficulty in mastication is the 
chief symptom. In fractures in the region of the molars the teeth may 
continue to hold the fragments together in such a way that neither 
crepitation nor unusual mobility of the parts can be detected. In such 
cases one or more teeth may be found to be loose. 
Symptoms. In transvere fractures of the body of the bone the chin 
and lower incisors hang limply and are abnormally mobile, while crepi¬ 
tation may be detected. Fractures of the coronoid process or joint, or 
in their neighbourhood, often interfere seriously with mastication, and 
may be mistaken for inflammation of the articulation. The broken 
fragments of the coronoid process are drawn upwards by the temporalis 
muscle, and can be detected on palpation. 
Prognosis. Fractures in the median line and subcutaneous injuries 
of one branch unite regularly and completely in from three to five weeks. 
Double-sided fractures present the greatest difficulty, and often affect 
