SEVENTH LECTURE. 



THE DENTITION OF HORSES, CATTLE, SHEEP, 

 PIGS, AND DOGS; AND DENTAL DISEASES. 



340. The teeth are the principal agents in mastication ; and, althougli 

 composed of the hardest structures in the body, are, in the first 

 instance, developed by a very interesting process, from one of the 

 softest structures — the mucous, or lining membrane of the mouth. 



341. The Tooth is divided into the crown, neck, and root, and 

 is made up of three structures — ivory, or dentine; enamel; Sind cement, or 

 ci'usta petvosa. The dentine is whitish-yellow in colour, and forms the 

 bulk of the tooth. It is found in the middle, in contact with the pulp, 

 and consists of about 72 per cent, earthy matter, and about 28 per cent, 

 animal matter. The enamel — the hardest substance of the three — 

 is of a pale bluish-white, and contains 95 per cent, earthy, and 5 per 

 cent, animal matter. It acts as a protection, covering the external 

 parts of the crown, and is interspaced in irregular curves between the 

 dentine and cvnsta petrosa The crusta petrosa is yellowish-white, and 

 found on the outside of the tooth, in connection with the root, or 

 fang, and is softer than either the dentine or enamel ; in fact, it .is the 

 bone of the tooth, and is composed of 67 per cent, earthy, and 33 per 

 cent, animal matter. 



342. There are two sets of teeth, viz. : Temporary, or Milk 

 Teeth, which are much smallev and whiter than the second set — the 

 Permanent (see par. 346). 



