DEFICIENCY OF LENGTH OF THE CROWN. 141 



seven or eight years old, a slight increase of wearing on one side 

 of the jaw will frequently make, in the tahle-mark, a deviation 

 of a year or two in the appearance of the animal's age, whi(;li is 

 readily corrected by a further examination from the other side. 



DEFICIENCY OF LENGTH OF THE FREE PORTION OF THE INCISORS. 



Deficiency of length is seen only in very old horses; the 

 teeth are always in apposition, except in the case of cribbing 

 horses, when they may be so worn off as not to reach those 

 of the other jaw. The diminution in the length may be so 

 great that nothing but a mere stub remains. This condition is 

 frequently accompanied by cementoma, or tumors thrown out by 

 the irritated alveolar periosteum (Fig 148). 



MOLAR TEETH. 



As in the case of the incisors, the irregularities of the molar 

 teeth are due to excess and deficiency of length. This may 

 occur on one or both sides of the jaw, on all of the tables of an 

 arch, or only on certain teeth. 



DEFICIENCY OF LENGTH OF THE CROWN. 



Inferior Jaw. — The abnormal use of the molars rarely ex- 

 tends to all of them in an arch ; sometimes those in the centre 

 of the arch are the most worn (Fig. 149), giving it a concavity, 

 in which the corresponding elongated teeth of the upper jaw fit ; 

 or sometimes they are worn most at the extremities of the arch, 

 with an inverse condition of the upper jaw (Fig. 150) ; in molars 

 which have been excessively worn the crown may have disap- 

 peared, leaving the roots as distinct and apparently supernu- 

 merary teeth (Fig. 149). In this case, as was noticed in tlie 

 study of the structure of teeth, when they are worn down, they 

 produce an irritation of their alveolar cavities which causes an 

 excessive deposit of callous bone or cement, which unites them 

 toaether and aids them in their function, but sometimes causes 

 annoying bony tumors ; however, the new function is not as 

 complete as the original one, as the hard enamel has disappeared 



