NINETEEN YEARS.--All of the signs of the seventeen-year-old mouth are more prominent. The cups have usually disappeared from the upper incisors. [Footnote 1: This table is from dentition tables given in "Age of the Domestic Animals," by Huidekoper.] QUESTIONS 1. Name the different kinds of teeth; state the arrangement and number. 2. How is the age of an animal determined? 3. Give the time of replacement of the temporary incisor teeth. 4. How is the age of the animal determined between the fifth and ninth years? 5. What changes in the appearance of the table surfaces occur between ten and fifteen years of age? CHAPTER XX IRREGULARITIES OF THE TEETH Parrot-mouth, Lantern-jaw and Scissor-mouth.--The common deformities of the jaw and teeth are the overshot or parrot-mouth, the undershot or lantern-jaw, and the scissor-mouth. These different deformities result in unequal wear on the table surfaces of the incisors and molars. In both the overshot and undershot jaws, the incisor teeth become abnormally long. In the _parrot-mouth_, the wear occurs on the posterior face of the superior and the anterior face of the inferior incisors, the teeth becoming worn to rather a sharp edge, depending on the degree of the deformity. In the _lantern-jaw_, the wear occurs on the posterior face of the lower and the anterior face of the superior row of incisors, the teeth taking on somewhat the same shape as the parrot-mouth. The greater the deformity and the older the horse becomes, the more difficult it is for the animal to feed or graze on pasture. In all horses, the two rows of molar teeth are wider apart in the superior than in the inferior jaw. This results in the external border of the tables of the superior row of molars becoming longer, or projecting further downward than the internal border. The wear on the table surfaces of the inferior row of molars is just the opposite of the superior row. In the _scissor-mouth_ the wear takes place largely on the internal face of the superior and the external face of the inferior row of molars. The teeth become worn to more or less of a blunt cutting edge, and after a time the molars come together somewhat like the jaws of a pair of scissors. A horse with a badly deformed scissor-mouth is unable to grind the feed, and unless given special care, suffers severely from innutrition. _The treatment_ of deformed mouths consists in removing the irregular or unworn portion of the teeth by means of the tooth float and cutters. This attention should be given early before the free portion of the tooth has become excessively long and irregular. This should be followed by dressing the teeth every six or twelve months.