THE TEETH OF RATS 



153 



deer, the cavicorn or sheath-horned bovines, ovines and cap- 

 rines, and the large series of antelopes of Africa and India — 

 all have precisely this form of jaw, this number and shape 

 and grouping of the teeth. Now let me call to mind the 

 lower jaw of a hare or rabbit or rat (Figs. 23 and 24). 



.y/ upp«<- 



Jaw. 



Fig. 24. — View in the horizontal plane of the teeth of the left half 

 of the lower and the left half of the upper jaw of the Coypu 

 rat to show the single great gnawing incisor on each side, the four 

 flat grinding molars and the wide gap between molars and incisors. 

 Compare with Figs. 22 and 27. 



There we find on each side the group of grinding cheek 

 teeth, with transverse ridges on their crowns, and a long, 

 toothless gap before we arrive at the front teeth. But 

 the front teeth are only two in number, one on each side, 



