THE TEETH. 



257 



CHAPTEK XIV. 



THE TEETH. 



The teeth are developed within their appropriate cavities or 

 wckets, which are found exactly corresponding with their number 

 in the upper and lower jaws, being narrower in the lower than in 

 the upper. Before birth they are nearly all in a state of incom- 

 plete growth, covered and concealed by the gums, but soon after- 

 wards they rise through it in pairs, the first set, or milk teeth, 

 being in course of time superseded by the permanent teeth as tn 

 all the mammalia. The following is the formula of the complete 

 dentition of the horse : — 



Incisors g, canine f , molars i|. 



Each tooth is developed within its corresponding cavity in the 

 jaw, and is made up of three distinct substances — cement, enamel, 

 and dentine. The cement of the 

 horse's tooth (sometimes called 

 crusta petrosa) closely corresponds 

 in texture with his bone, and, 

 like it, is traversed by vascular 

 canals. The enamel is the hardest 

 constituent of the tooth, and con- 

 sists of earthy matter arranged in 

 the animal matrix, but contained 

 in canals, so as to give the 

 striated appearance which it pre- 

 sents on splitting it open. Den- 

 tine has an organized animal ba- 

 sis, presenting extremely minute 

 tubes and cells, and containing 

 earthly particles, which are partly 

 blended with the animal matter in 

 its interspaces, and partly con- 

 tained in a granular state within 

 its cells. These three substances 

 are shown in the annexed section 

 of an incisor tooth, see Fig. 2, 

 which is of the natural size. 



Is the molar teeth the ar- 

 rangement of these three sub- 

 stances is the same, except that the 

 cement and enamel dip down into 

 two or more cavities instead of one, and are also reflected in a sinu- 

 ous manner upon the sides. This inequality in the hardness of the 



17 



Fig. 2.— section m incisor. 



c. Cement on external surface. 



c. Cement reflected within the cavity. 

 e. Enamel also reflected. 



d. Dentine. 



s. Tartar, colored black by decomposi- 

 tion of food, contained within th« 

 cavity. 



