ORAL EQUIPMENTS. 53 



be bettor adapted for crushing a bone or lacerating flesh. 

 Try and fancy a horse's molar tooth in the tiger's mouth. How 

 useless for its peculiar mode of life. In the skeleton of the 

 tiger we find the most marvellous and perfect combination of 

 lightness and strength. 



We find in the dog-like carnivora an approach towards 

 more omnivorous characters as in the hog, and in the bears a 

 still nearer approach. 



To particular teeth in both jaws the name " carnassial " 

 has been given (in the upper jaw the fourth premolar, and in 

 the lower the first rnolar), characterised by its sectorial or 

 cutting form. This is highly differentiated in the " cat tribe " 

 less specialised in the dog tribe, and amongst the bears the 

 sectorial condition has become altered into a more rounded 

 and tubercular form. The large canine tooth of the felidae 

 is also a sexual weapon, but I shall refer to this subject 

 later on. 



The next great class I have to refer to approaches at 

 both ends towards both the herbivora and the carnivora ; 

 it is named from the peculiarity of the incisor teeth which 

 are adapted for gnawing. They are called Rodents or 

 gnawers, and their incisors (centrals) grow from persistent 

 pulps, i.e., pulps or formative organs which never cease 

 elaborating fresh tooth substance throughout the creature's 

 life-time. The horse's molars do not continue to grow 

 throughout the whole life of the creature, but persist for some 

 considerable time, and are thus called " semi-persistent " as I 

 indicated before. The Rodent's molars as well as the incisors 

 grow from persistent pulps. In pattern their surfaces are 

 very complex and highly suitable for crushing such sub- 

 stances as woody fibres, and whatever in fact would require 

 gnawing by the incisors, as will be seen by the diagram. 

 Observe the transverse ridges of enamel, and see how well 

 adapted they are for their work. 



The jaws of this class as would be expected from my 

 remarks on correlation of growth, are also specialized to suit 

 the customary aliment. We see by the diagram a strongly 

 arched skull and jaws, but yet of a heavier build than the 

 carnivorous, and deep glenoid cavity and condyle, whose long 

 axis is from back to front to allow of the forward and back- 

 ward movement of gnawing. In many Rodents the anterior 

 face of enamel on the large scalpiform incisors is stained of a 

 deep orange or salmon colour. These large gnawing incisors, 

 which are kept constantly sharpened by wear from the 

 direction in which they meet one another, are exceedingly 



