DISEASES OP SHEEP. 12 



and then fall out, and are replaced by permanent teeth i 

 the same order in which they appeared. The permaner 

 teeth differ froin the milk-teeth by the fact that the uppe 

 edge is not pointed, but straight and dull. They are als 

 stronger and broader than the milk-teeth, and no longe 

 milk-white, but yellowish. 



When the sheep is eighteen or twenty months old, th 

 milk-teeth fall out and are replaced by two permaner 

 teeth. The animal is then called two-toothed. 



When the sheep is three and a half years old, the tw 

 outer middle teeth fall out and are replaced by two perms 

 nent teeth. 



When the sheep is four and a half years old, the tw 

 corner teeth fall out and are replaced by two permaner 

 teeth ; and now all have changed. The animal is the: 

 called eight-toothed. 



In the sixth year the permanent teeth have obtained thei 

 full development, and are long and broad. The uppe 

 edge appears smooth and sharp. 



After the sixth year the incisors undergo differen 

 changes, from which the age of the sheep can be discovere' 

 with a tolerable degree of certainty. The edges of th 

 crown gradually become nicked and dented, until the; 

 wear down almost to the root. This takes place in th 

 some order as the changes of the teeth. In the sevent 

 year both tongs or gatherers become notched at the edge o 

 the crown, and in the eighth the nearest two become notchec' 

 although a more distant one may change instead, and tli 

 notches of the gatherers become deeper. In the nint; 

 year the crowns of the gatherers and the inner middl 

 teeth are indented very deeply, and the other teeth als 

 begin to show notches. In the tenth and twelfth years th 

 crowns of all incisors are broken and worn, so that noth 

 ing but the roots remain. 



11 F 



