THE ANATOMY OF THE HORSE 



33 



years of age, the second pair of nippers in each jaw of the 

 colt gives way to two larger, permanent teeth, so that the 

 four-year-old shows four pairs of permanent front teeth. 



At four and one-half to five years of age the last pair 

 of the front teeth of the colt, in each jaw, is supplanted by 



a pair of permanent 

 ones. At this age 

 what are called tusks 

 appear in the mouth 

 of the male ; they also 

 occur occasionally in 

 the mare. These tusks 

 have roundish points, 

 and there are two in 

 each jaw, one on a 

 side, a short distance 

 back of the front teeth. 

 After the fifth year 

 the age of the horse is 

 determined by the ap- 

 pearance of the wear- 

 ing surface of the 

 teeth, each tooth when normal having its age surface. 

 At six years the cups of the two central teeth are worn off. 

 At seven years the second pair shows the worn surface. 

 At eight years all of the teeth have been worn about 

 level, and the mouth-mark loses its value. The six perma- 

 nent teeth in each jaw at first meet each other in vertical 

 position, the ends butting squarely against each other. As 

 age increases, however, the teeth gradually take a more in- 

 clined or slanting-out position in each jaw, so that they 

 come together at a sharper angle. The older teeth are also 

 more worn on the ends, and are longer than the younger 

 teeth. In a horse from 12 to 16 years of age the ends of 

 the teeth have become somewhat three-sided. 



The spinal column of the horse consists of fifty-four 

 bones, or vertebrse. Seven of these, the cervical, are in 

 the neck; eighteen, the thoracic, are in the back; six, the 



Fig, 14. — Four years of age. 



