TEETH 



321 



the canine, the space often existing between them being called the 

 diastcma, and then come the molars. The primary arrangement 

 of the teeth is such that there is an alternation between those of 

 the upper and lower jaw : thus the teeth in one jaw do not usually 

 correspond in position with those of the other, but with the inter- 

 spaces between them. 



In some cases the enamel-organ, with its dental papilla, persists 

 in all the teeth, which then continue to grow throughout life 

 (e.g. Lepus) ; in others this is true of the incisors only (e.g. 

 Elephant, numerous Rodents, Fig. 237) ; but more usually growth 





FIG. 235. TEETH OF SHEEP (Ovis aries). 



(References as before, but the teeth of the lower instead of the upper jaw are 



figured from the surface. ) 



ceases after a certain time, and the teeth then form definite fangs 

 or roots, perforated by a small canal communicating with the reduced 

 pulp- cavity. 



The incisors are usually chisel-shaped, while the canines, in 

 those cases where they are most characteristically developed 

 (Carnivora), possess a pointed, conical form, and are more or less 

 curved. The cheek-teeth either have sharp, cutting crowns 

 (sccodont, e.g. Carnivora), or may possess infoldings of the enamel, 

 or tubercles, the crowns being broad and more or less flat, and 

 adapted for grinding the food. If the tubercles are conical, the 

 tooth is described as lunodont (e.g. Pig, Hippopotamus), and if 

 crescentic, selenodont (e.g. Horse, Ruminants) : in these cases the 

 relations of the enamel, dentine, and cement are such as to produce 



