SHEAR-LIKE MOUTH. 
33 
left hand, in which it is held, can be rested against the incisor teeth. 
The skilled practitioner can dispense with instruments having rounded 
guards near the cutting edge, and also with Brogniez’s “ odontriteur,” a 
chisel in which the blow is produced by an iron bolt sliding on the handle. 
The rasping and chiselling of the teeth sometimes produce their good results 
indirectly, by making one or more teeth sensitive, and thus throwing the 
patient off its feed, time is given for recovery from gastric affections. 
In old horses, chewing on one side of the mouth sometimes shortens 
the incisors of that side. This condition, described by Gunther as 
“ oblique mouth,” seldom causes trouble, but is interesting because often 
associated with irregular wear of the molars: 
(b) shear-like mouth. 
Shear-like mouth consists in a considerable increase in the obliquity 
of the wearing surfaces of the molars. Their outer edges in both jaws 
are too low, the inner too high, so that the wearing surfaces, if prolonged, 
Fig. 11.—Left-sided shear-moutli 
(from a photograph). 
Fig. 12.—Grinding surfaces 
in shear mouth, in normal mouth. 
would meet in an acute angle above the palate. In otliei words, the 
crowns lie not over, but alongside, one another, so that the mouth 
resembles that of a flesh feeder. (Pigs. 11 and 12.) The rows of teeth, 
therefore, do not grind, but cut, meeting one another like the blades of a 
pair of great shears, in which the inner blade is formed by the lower 
molars, the outer blade by the upper. When confined to single teeth, 
this change most frequently afiects the fourth molais, because they aie 
more liable to lateral displacements ; but, as a rule, one whole row is 
affected, constituting simple shear mouth ; occasionally both sides suffer 
(double shear mouth). 
The condition is brought about thus : The inner edge of the lower 
