IX] 



SURGICAL DISEASES AND CONFORMATION 



117 



of the molar and parts of the incisors called 

 crusta petrosa ; this continues to grow after the 

 tooth has formed. It contains about 66 per cent, 

 earthy matter. 



Permanent incisors do not have a well-marked 

 neck, as do the milk incisors, are larger and 

 longer, are not so white, but have a bluish tint, 

 and are more curved on their outer surface. 



The angle formed by the incisors, which can 

 be seen by looking at a mouth sideways with the 

 lips held open, is called the angle of incidence. 

 This angle decreases as the horse gets older. 



The cups in the tables of the upper incisors 

 are deeper than in the lower, therefore those in 

 the lower wear away before those in the upper. 



The centre incisors are called middle or centre 

 incisors ; those next outside are called the inter- 

 mediate or lateral incisors ; and those outside the 

 corner incisors. 



471. Average Period of Eruption. 



Tooth Eruption Shedding 



Temp. Mid. Inc. . . Birth to 8 days . . 2 to 2i years 

 Temp. Inter. Inc. . . 4, 6 or 8 weeks . . 3 to 3| years 

 Temp. Cor. Inc. . . 7 to 8 months . . 4 to 4| years 



The milk incisors are often said to erupt at 

 approximately 8 days, 8 weeks and 8 months 

 respectively. 



Tooth 



Perm. Mid. Inc. 

 Perm. Inter. Inc. 

 Perm. Cor. Inc. 



Eruption 



2 to 2 J years 



3 to 3^ years 



4 to 4i years 



These teeth will be fully grown in six 

 months after eruption, so that at five years of 

 age a horse should have a full mouth of 

 incisors. 



Tooth Eruption 



Canines, Permanent (no temp.) . . 4 to 4^ or 5 years 



Shedding 



2i to 3 years 

 2i to 3 years 

 3i to 4 years 



Tooth Eruption 



Molars, 

 permanent 



1st . . 2i to 3 years 



2nd . . 2i to 3 years (a little after the 1st) 



3rd . . 3J to 4 years 



4th . . 10 months to 1 yr. (1st molar in mouth) 



5th . . 1 i to 2 years 



6th . . 3i to 4 years 



The teeth of the lower jaw generally erupt 

 earlier than those of the upper. Some horses' 

 molars are earlier in eruption than normal, and 

 incisors later. The molars will erupt much 

 earlier if the horse is fed on grain, as a race- 

 horse is, whilst the incisors will erupt much 

 earlier if the horse is at pasture in a sandy 

 district. A thoroughbred horse fed on hard 



grain, and developed rapidly for racing in the 

 modern "young events," will have many of his 

 molars six months earlier. 



472. Table of teeth from birth to five years 

 (an average) : At birth or soon after, temp. mid. 

 incisor, 1st and 2nd temp, molars ; at 3 months, 

 temp. mid. incisor, temp, inter, incisor, 1st, 

 2nd and 3rd temp, molars ; at 6 months, temp, 

 mid. incisor, temp, inter, incisor, 1st, 2nd and 

 3rd temp, molars ; at 9 months, all temp, 

 incisors, 1st, 2nd and 3rd temp, molars ; at 

 1 year, all temp, incisors, 1st, 2nd, 3rd temp, 

 molars and 4th perm, molar ; at 2 years, all temp, 

 incisors, Ist, 2nd and 3rd temp, molars, 4th and 

 5th perm, molars ; at 3 years, perm. mid. 

 incisor, temp, inter, incisor and cor. incisor, 1st 

 and 2nd perm, molars, 3rd temp, molar, 4th and 

 5th perm, molars; at 4 years, perm. mid. and 

 inter, incisors, temp. cor. incisors, 1st and 2nd 

 perm, molars, 3rd temp, molar, 4th, 5th and 

 6th perm, molars ; at 5 years, all perm, incisors, 

 all canines, all perm, molars. 



Therefore, at four and a half to five years of 

 age a horse has a full mouth. From this time 

 on we tell his age by examining the cups in 

 the tables of the incisors, by the shape of the 

 tables, by the angle of incidence, and by the 

 length of the teeth. 



Molar teeth are matured at nine years of age, 

 and from that time on they commence to grow 

 up from the bottom of the jaw, and the lower 

 edge of the rami of the lower jaw bone (inferior 

 maxilla) becomes thinner. 



473. A glance at a longitudinal section of a 

 tooth (see P. 102) shows us that a tooth wears 

 away from mastication, and gradually becomes 

 shorter, causing the shape and nature of a table 

 to vary very much. This takes place in the 

 canines and also in the molars. At first there is 

 no cup in the incisors, then a cup appears, then 

 it goes again. Dishonest dealers make a young 

 horse appear six years of age by filing the 

 incisors and showing the cups. The expert, 

 though, will examine the molars to detect this. 

 Again, old horses are made to appear younger 

 by filing the incisors shorter and making cups, 

 and darkening them with silver nitrate. The 

 expert can tell the difference by the angle of 

 these teeth and by the shape. 



Table of Incisors.— At 6 years, lower jaw 

 cups in mid. incisors disappear ; at 7 years, lower 

 jaw cups in inter, incisors disappear ; at 8 years, 

 lower jaw cups in cor. incisors disappear ; at 9 

 years, the back corner of upper cor. incisors 

 begins to point down below and behind the 

 cor. of the lower cor. incisors ; at 10 years, upper 

 jaw cups in mid. incisors disappear ; at 11 years, 

 upper jaw cups in inter, incisors disappear ; at 

 12 years, upper jaw cups in cor. incisors dis- 

 appear. 



After twelve years of age it is difficult to 

 judge accurately the age of a horse. Successful 



