VIL] THE EXTERNAL SKELETON. 261 



The same is the case in some Mammals of other orders, 

 as in the Ox, Deer, and Sheep ; as also in the extinct Ele- 

 phant-like creature Dinotherium, which had only two in- 

 cisors, but these extended downwards from the front end 

 of the lower jaw. 



Incisors may be present in the form of enormous tusks in 

 the upper jaw but wanting altogether in the lower, as in the 

 Elephant. They may similarly be present in the upper jaw 

 only, but exhibit a flat grinding surface flush with the gum, 

 as in the Walrus. 



The upper incisors may be separated by an interval from 

 their fellows of the opposite side, as in Loris. 



FIG. 231. Fr.oNT VIEW OF UPPER INCISORS AND CANINES OF THREE GENERA 

 OF SLOW LEMURS (natural size). 



i, Loris; 2, Nycticebus ; 3, Perodicticus. 



The front lower incisor may be enormous, and represent, 

 by its notched outline, several incisors fused into one. More- 

 over with age the teeth may become anchylosed to the jaw. 



m' 



FIG. 232. DENTITION OF SHREW-MOUSE (Sorex). 



i upper incisors ; i', notched lower incisor ; c, upper canine ; c', lower canine ; 

 pm, upper pre-molars ; pm ', lower pre-molar ; m, upper molars: m', lower 

 molars. 



These peculiarities are exhibited by the Shrew-Mice, which, 

 as before remarked, are not " mice " at all, but closely allied 

 to the Mole and Hedgehog. 



Generally having but a single fang, whether with or without 

 a permanent pulp, an incisor tooth may yet have a double 

 fang, as is the case in the Flying Lemur and in Petrodroimts. 



26. The CANINE TEETH of man, as their name implies, find 

 in the Dog (and other flesh-eating beasts) an enlarged repre- 

 sentative, as also in the Apes. Such tusks, however, are far 



