DENTAL INDICATIONS OF AGE OF A HORSE 197 



not at all in others, the cause of which remains still 

 a question. 



The horizontal direction of the teeth, which in- 

 creases with the years of a horse, will be easily 

 understood by a reference to Plate v, fig. 18. This 

 figure represents the under incisor teeth of a horse 

 known by the name of " Old Billy," which attained 

 his SEVENTY-SIXTH year, and was perhaps the oldest 

 horse that ever lived. The cranium, with the muscles 

 preserved, is deposited in the Museum of the 

 Manchester Natural History Society, from which I 

 made the drawing. The whole of the incisors are 

 much elongated horizontally, but not perpendicularly 

 elevated more than those of a horse at six years of 

 age. The upper surface of the nippers and dividers 

 are of a quadrangular form, the inner margins being 

 a little rounded, while the corner teeth are oblong 

 oval, nearly the form of an egg, with the most acute 

 end outwards. The tushes are conical, a little 

 blunted on the crown, and turned backward, with an 

 elongated, shallow, curved groove on their inner sides. 

 It will be seen that the outer edge of all the cutting 

 teeth is nearly parallel, the corner teeth being only a 

 little less produced than the others. It does not 

 appear that the jawbones themselves have been 

 lengthened, the teeth alone having shot forward ; con- 

 sequently, their surface is lying obliquely, and hence 

 their elongated form from front to back, as more 

 particularly developed in the corner teeth. The 

 tushes are considerably larger in proportion than in 

 a horse under twenty years of age. 



The portion of the tooth which is buried in the 

 gums is called "the root"; the nippers are placed 

 parallel to the axis of the jaw, that is, perpendicular 

 to it ; the dividers are somewhat oblique, and the 



