214 MANUAL OF MODERxN FARRIERY. 



to much more friction thau tlie cutting teetli in grinding 

 down the harder j^ortions of their foo^^ and nature has 

 made ample provision for their strength and endurance. 



We have given a representation of the section of a grinder 

 (plate V. fig. 12) to show its interior structure The teeth 

 are prepared and formed in cavities within the jaw-bones. 

 In the unborn animal a delicate membraneous bag, contain- 

 ing a jellj-like substance, is situate in the small cell within 

 the jaw-bone. By degrees this substance assumes the form 

 of a tooth, and then the jelly within the membrane begins 

 to change to a bony consistence ; then a hard crystallization 

 is formed on the outside of this membraneous covering. 

 This is the enamel of the tooth. In the formation of each 

 grinder of the horse in the upper jaw, there are originally 

 five of these membraneous bags filled Avith jelly, and four 

 in the lower jaw. This jelly is gradually superseded by 

 bony matter, whicli is deposited by little vessels penetrating 

 into it. These vessels are represented by the black streaks 

 in the darker central portions of the figure, around each of 

 which the crystallization of enamel can be distinctly traced, 

 so that there would be five distinct bones or teeth. The 

 white spaces in the figure represent a very powerful cement, 

 which unites all these distinct bones into one compact body, 

 thus making one tooth of the five as they originally ap- 

 peared to be ; this being accomplished, an outer coating of 

 enamel invests the whole of the sides, but not the top, 

 which completes the tooth. It will thus be manifest that 

 this is a beautiful and perfect contrivance to prevent the 

 wearing down of the grinders by the constant friction to 

 which they are subjected by chewing the harder portions of 

 their food. Thus it will be seen there are columns of 

 enamel penetrating through the entire substance of the 

 tooth ; this, together with the bony matter and cement by 



