INDICATIONS OF AGE. 343 



consisting of fibres and bloodvessels, and is largely supplied 

 with nerves. The cavity gradually disappears as age advances, 

 as there is more or less decomposition of dentine continu- 

 ally taking place. Immediately surrounding the cavity is 

 found the dentine, which consists of twenty-seven or 

 twenty-eight per cent, of animal matter, and seventy-two per 

 cent, of earthy matter. Hence it is seen to be harder than 

 bone. In the tubes which open from the pulp cavity is con- 

 tained some of the pulp. The tubes somewhat resemble the 

 canaliculi of bone, and the dentine itself, from the fact that it 

 contains processes from the tubes, has some little power of 

 sensibihty. Dentine is developed from the pulp in the j)ulp 

 cavity. As age increases it takes on a yellowish tinge, and 

 that last developed is the yellowest. Enamel contains 

 about ninety-seven per cent, of earthy material, and three 

 per cent, of animal matter, hence is exceedingly hard, being, 

 in fact, the hardest substance in the animal body. The 

 enamel covers the dentine, and is made up of a number of 

 six-sided rods, or hexagons, which are placed in a perpen- 

 dicular position, one extremity pointed outward, the other 

 extremity being placed upon the dentine ; these rods are 

 not exactly stmight, but have a somewhat wavy course, as 

 have the tubes. Lacuna? and canaliculi are found in enamel, 

 the same as in bone, but Haversian canals are absent. The 

 crusta petrosa is found on the outside, in connection with 

 the fang of the tooth ; it is softer than either enamel or 

 dentine, is considered to be the true bone of the teeth, 

 and possesses lacuna and canaliculi. The teeth are of 

 three classes, consisting of molars or grinders, incisors or 

 cutting teeth, and tusks or canine teeth. The teeth are 

 wider in the upper jaw than in the lower jaw ; they form 

 two oblong or parabolic arches, and are separated by a well- 

 marked interdental space. The horse, like other animals, 

 is provided with two sets of teeth, temporary and perma- 



