72 PRINCIPLES OF VETERINARY SCIENCE 



The enamel forms a thin ivory-white cap over the dentin of the 

 crown. In herbivora it is folded into the table surface. In the 

 virgin tooth it covers the entire table surface, but soon wears off 

 on the grinding portion, leaving only projecting edges. Enamel is 

 a secretion of epithelial cells and cannot be reproduced when it 

 is once destroyed. It is the hardest tissue of the body. The 

 cement is the external covering of the root. In complex teeth, 

 like those of the horse, it fills in spaces between the enamel folds 



¥ia. 19. — Skull of two-year-old colt, sculptured to show embedded parts of 

 temporary and permanent teeth. The upper first premolar (wolf tooth) is 

 present, but not visible; the lower one is indicated by the arrow. Temporary 

 premolars are numbered 1, 2, 3; permanent premolars are designated by Roman 

 numerals; Dc, upper temporary canine; C, lower permanent canine, which was 

 not ready to erupt; 1X2, Di3, second and third temporary incisors; Ii, first 

 permanent incisor, not quite ready to erupt. (Sisson, Anatomy of Domestic 

 Animals.) 



of the crown also and in old horses it increases in amount around 

 the roots of teeth to strengthen them. The alternate arrange- 

 ment of substances of different degrees of hardness keeps the 

 teeth of herbivora always rough and peculiarly adapts them for the 

 cutting and grinding of coarse vegetable foods. 



All farm animals first develop a set of deciduous, temporary 

 or milk teeth, which are smaller, softer, and whiter than the per- 

 manent teeth that replace them. 



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