i8 9 5. THE TEETH OF THE HORSE. 255 



and the third at one month before birth. The first or central is cut 

 a few days after birth, the second at six weeks, and the third at eight 

 or nine months. The first is shed at two and a half years, the second 

 a year later, and the third at four and a half years. About five months 

 before birth, the first and second deciduous incisors point vertically 

 up and down like the three deciduous molars, but at birth they show 

 marked indications of that forward slope so characteristic of the 

 incisors of the horse. The permanent incisors cut the gum a few 

 weeks after the loss of their respective milk predecessors, and sub- 

 serve the requirements of the animal till death. 



The canine teeth in the male, called tusks or tushes, have the form 

 of curved cylinders, tapering off to a blunt biting edge (Fig. L.). The 

 lower are larger than the upper, are less sharply curved, and develop 

 earlier. The crown of the lower canine is situated so far in front of 

 that of the upper that the two teeth do not bite with one another. 

 The canines very rarely cut the gum in the female, but not 

 infrequently they may be felt under the gum, especially in the lower 

 jaw. They are usually of small size (Fig. M.), and are very 

 irregular in shape, as are most teeth that are absorbed without 

 eruption ; but the characteristic tooth tissues, enamel, dentine, and 

 cement are present, and are disposed in the same manner as in 

 the canines of the male. Calcification of the permanent canines 

 begins at about two years, and eruption usually takes place, in the 

 male, at four-and-a-half to five years, although in some cases the 

 canines are cut at three years, and in others they only appear at six. 

 The eruption of the canines is thus of less value for the determination 

 of age than was formerly supposed. 



The deciduous canines (Fig. N.) are straight, blunt, very slender, 

 and about half an inch in length and are of equal size in the two sexes. 

 They begin to calcify about a fortnight before birth, and are absorbed 

 at three to four years, without ever cutting the gum. They are 

 developed in the lower jaw, not behind the corner milk incisors (di 3), 

 but to the inner side of those teeth. In the upper jaw they are lodged 

 in the conspicuous suture between the maxilla and premaxilla. For 

 some inscrutable reason, veterinarians are agreed in insisting on the 

 non-homology of these " splinters of bone," as they term them, with 

 the milk canines ; but a microscopic examination demonstrates the 

 presence of dentine and cement, and a thin cap of enamel at the 

 anterior extremity, and the dissection of a large number of specimens 

 cannot fail to convince the comparative anatomist of the true value of 

 these rudiments. 



The first premolar is not constant in its occurrence, and is almost 

 always small and irregular in shape (Fig. O.). It occurs more 

 frequently in the upper jaw, and rarely in both jaws simultaneously. 

 It is not preceded by a milk tooth, and, although it appears with 

 the deciduous molars of the remaining three premolars, and is in 

 most cases dislodged when the first deciduous molar (dm 2) is 



