310 



VETERINARY MEDICINE AND SURGERY. 



to guide us, there can seldom be any doubt as to the age of the animal. 

 There are, however, some well-authenticated instances of abnormal de- 

 velopment of the permanent incisors, but they are rare. 



High feeding encourages the growth of the teeth in common with the 

 rest of the frame. Hence thorough-breds are somewhat more forward in 

 their mouths than half-bred animals. 



The Mark.— Hitherto no notice has been taken of the " Mark," or 

 Infundibulum, not because the marks in the young mouth do not afford 

 some indication of the age ; but because fuller and more satisfactory 



Fig. 144. 

 Teeth at Six Years. 



evidence up to six years old is afEorded by the structural changes detailed 

 above. After six, however, recourse must be had to the indications given 

 by the marks and other slight, but gradual, alterations which take place 

 in the form of the teeth. 



The Mark or Infundibulum is a very peculiar hollow extending, when 

 the tooth first comes up, about half an inch down the temporary and 

 rather deeper down the permanent incisors. Figure 151. 



Thus in the tooth, as it originally ajipears, there are four walls of 

 enamel. The remainder of the tooth consists chiefly of dentine, less *■ 

 hard than enamel, and more like ivory. A small quantity of crusta 

 petrosa is also found on the outside. 



When an incisor first comes up, the hollow affords lodgment for the de- 

 hris of the food and the juices expressed from it, and therefore soon looks 



