DISEASES OF DOMESTIC ANIMALS. 141 



THE TEETH. 



Odontology is a treatise on the teeth. The teeth are hard and 

 bone-like, and are the principal agents in mastication. They are a 

 combination of inorganic salts, with the previously existing animal 

 matter, and contain about seventy-six per cent, of earthy material, 

 phosphate of lime, phosphate of magnesia, etc., the same as in bone. 

 The teeth are the means afforded us to tell the age of the animal. 

 We find they vary much in different animals, in size, structure, 

 number and position, and also in motion, as for grinding, tearing, 

 pounding, etc. In the horse there is a large grinding surface; in 

 the carnivora they are sharp and pointed ; in the omnivora they are 

 both sharp and tabled. They are intimately related with the struc- 

 tures and habits of the animal, their form depending upon the 

 nature of food upon which the animal lives. Teeth are of two 

 kinds, simple and complex. Simple in the human being and the 

 dog, being covered with one coat of enamel. They are complex in 

 the horse and ox, there being several processes of enamel brought into 

 wear at the same time. This is why the lower animals are not 

 troubled with the toothache. The tusk of a horse is a simple tooth, 

 having but one coat of enamel ; the others are complex, because 

 they have external and internal enamel, bringing different tissues 

 into wear at the same time. In describing a tooth we say it has a 

 body or crown, which is above the gums ; a table, or the grinding 

 surface ; the neck, or that surrounded by the gums ; and a root or 

 fang, which is inserted in the alveoli. Running up the centre of 

 the fang is a cavity which contains the pulp, a highly nervous sub- 

 stance. The sulcus, in which the teeth are inserted, are called 

 aveolar processes, and exist only with the tooth, for if a tooth is 

 taken out the cavity disappears. There are three substances in the 

 tooth — dentine or ivory, enamel, cementum or crusta petrosa. These 

 vary in proportton in the different teeth. Dentine is a yellowish 

 white substance which appears homogeneous to the eye, but under 

 the microscope it is found to be made of tubuli. These begin at 

 the pulp cavity and radiate towards the surface, they are imbedded 

 in a matrix and form a greater part of the body and fang of the 

 tooth. The enamel is the hardest structure in the body, and forms 

 a protective covering for the teeth. It contains about ninety-three 

 to ninety-five per cent, of earthy material ; it is a bluish white 

 substance, covers the crown of the tooth, and in complex teeth it 

 also forms an internal ring which brings the different parts into 

 wear at the same time. It is small in quantity, and is made up of 

 hexagonal prisms, it also covers the little depression of the tooth. 

 There are three classes of teeth, the incisors or cutting, are situated 

 in front, six above and six below ; the canine, or tusks, are in the 

 interdental space ; the molars or grinders are twenty-four in num- 

 ber. The horse has two sets of teeth, the deciduous or milk teeth, 

 which are temporary, and the permanent. The temporary are 

 twenty-four in number, the permanent forty. The incisors show a 

 centre which is greater in the young horse, it is called the infundi- 

 bulum, by means of which we are able to determine its age pretty 

 correctly up to a certain age. This funnel-shaped cavity is usually 

 covered with tartar. Sometimes the teeth are dressed, but it is 

 easy to tell the difference, the black mark has no ring of enamel. 

 There is a little difference in the incisors of the upper and lower 

 jaw, the upper have two grooves, the lower only one. The same is 



