26 THE SURGICAL ANATOMY OF THE HORSE 



the actual length of the tooth has diminished on account of the 



diminution in length of the fang. 



The maximum length is attained when the animal is about five 



years old. 



The Incisors 



These are in three pairs, termed respectively the centrals, middles, 

 and corners. They are named incisors because they are adapted for 

 cutting. Each is made up of a crown, which is compressed from before 

 to behind, and a fang, the upper portion of which is somewhat three- 

 sided. A little lower down the fang becomes circular, whilst near the 

 apex it is in the form of an ellipse, the long axis of which lies in an 

 antero-posterior direction. These differences in shape of the tooth at 

 various situations are used as an indication of the age of the animal, 

 since the outline of the free wearing surface will vary according to 

 the part of the tooth which is in use. 



The table of the crown presents a marked depression called the 

 infundibulum. This was formerly used as an indication of the animal's 

 age, since its disappearance from the tooth was supposed to occur 

 constantly at definite periods during the life of the animal. This theory 

 is negatived by the fact that considerable variations are met with 

 in the depth of the cavity. 



The enamel covers the exposed portion of the incisor and also in part 

 the fang. It also dips into and lines the infundibulum. Thus when 

 the table has been slightly worn two rings of enamel are visible on 

 its surface, namely, an outer ring by which the whole surface is 

 surrounded, and an inner ring surrounding the infundibulum. 



The cement is deposited in a layer, which presents considerable 

 variations in thickness, over the enamel. 



Distinction between Temporary and Permanent Incisors 

 Temporary teeth are much smaller and whiter. They possess a well- 

 defined neck, the anterior aspect of the crown presents z faint striation. 



