32 



AGE OF THE DOMESTIC ANIMALS. 



concavity backward, and they project slightly outward. The 

 external face is covered with small, longitudinal, parallel stria- 

 tions. The internal face has a conical eminence pointing toward 

 the free extremity of the tooth and separated from its borders by 

 deep gutters. The tusks have a pulp-cavity relatively much 

 larger than that of the incisors, which, however, also becomes 

 filled with a discolored dentine as the tooth advances in age. 

 As the tusks become used they show in their centre a dental 

 star, which sometimes is very dark in color. While the tusks 

 A B 



Fig. 19. 



Upper right-hand canine tooth of a horse. 

 A, external face ; B, internal face. 



Fig. 20. 



Longitudinal antero-posterior section of a 

 horse's canine tooth. C S, superior canine : 

 C I, inferior canine. 



may be subject to much use from the friction of food, the 

 tongue, lips, and the bit, they are always prominent, even in 

 very old horses. Goubaux and Barrier have seen one case in 

 which the tusks of the upper and lower jaw were in contact. 



Structure. — The tusks are composed of ivory or dentine, 

 inclosing a pulp-cavity and surrounded with enamel. 



There are no temporary tusks in the horse, although small, 

 rudimentary spicula sometimes are found before the permanent 

 teeth appear. 



