DENTITION OF HORSES. 413 



At four years old the horse has the lateral permanent in- 

 cisors in apposition, and the fourth and sixth molars are 

 level, or nearly level, with the other teeth. 



The tusks of the horse are often through the gums at four 

 years of age, but they are not usually fully developed before 

 five years, and occasionally they are not well up before five 

 years and a half. As a means of judging the age these teeth 

 are of little importance. 



Fig. 9 represents the state of the incisor teeth on the 

 completion of the fourth year. Remarkably well-developed 

 tusks were an exceptional feature in the mouth of the ani- 

 mal from which the illustration was taken; in other respects 

 the teeth present the appearances which are ordinarily ob- 

 served at the age of four years. 



The only milk-teeth now remaining are the four corner 

 incisors, which are much worn and quite different from the 

 broad, permanent teeth, with which they are not likely to 

 be confounded. In the lateral incisors the wear has affected 

 the anterior edge of the tooth, and the cavity extends com- 

 pletely across the table, which is therefore not fully formed. 

 In the central incisors there is a line of worn surface quite 

 round the central cavity, and the table may be properly de- 

 scribed as fully formed. 



Incidentally it may be remarked that between the com- 

 mencement and completion of the fourth year the dental 

 changes include the cutting of four permanent incisors, two 

 in each four tusks, and eight molars two on each side of 

 both jaws, making sixteen teeth, which are all advancing at 

 the same time. 



Between four years and five the corner temporary incisors 

 are removed and the permanent teeth occupy their places. 

 Indications of the change are seen at four years off in the 

 upper corner incisors, and in a few months the temporary 

 teeth are displaced and the permanent organs are in the 

 mouth, but their edges do not meet until the fifth year is 

 completed, and even then the contact is limited to the an- 

 terior part, and a triangular space similar to that which can 

 be seen between the upper and lower corner teeth in the 

 mouth of the yearling may be recognized when the lips are 



