258 ELEMENTARY ANATOMY. [LESS. 



reputed lowest are larger and more equal to the teeth next 

 in front of them than is the case with Europeans. 



When we descend to the creatures nearest to man in 

 bodily structure (the Apes of the old world), though we find 

 the number of teeth identical with that in him, yet a striking 

 difference is produced by the large size, especially in the 

 males, of the canines, which are true tusks for defence or for 

 attack. The last molar, or wisdom tooth, is also generally 

 larger relatively than in man, and in some forms is consider- 

 ably the largest molar of the lower jaw. 



The large size of the canines causes a separation between 

 the lower canine and the first lower pre-molar, and between 

 the upper canine and the outer incisor, in order to provide 

 space for their apices to pass. These interspaces are each 

 called a diastema, 1 and are wanting in man, where the teeth 

 are all normally close and contiguous. This contiguity and 

 absence of any diastema is a character which man shares 

 only with the little Lemur Tarsins, and with a certain extinct 

 hoofed quadruped, the Anoplotherium. 



Most Mammals have teeth of definite kinds incisors, 

 canines, or molars. This is not the case, however, with all, 

 as, for example, the Dolphins have teeth which are all 

 nearly alike. 



Below the class of Mammals, only rarely in certain Lizards 

 (e.g. the Agamas) do teeth simulate canines with small teeth 

 between them in the front of the mouth simulating incisors. 



25. The INCISORS of man are closely resembled by those 

 of the Apes, but in some Apes of the new world (Pithecia) 

 the lower incisors, instead of being nearly vertical, are long, 

 slender, approximated together, and inclined strongly forwards 



FIG. 225 GRINDING SURFACE OF THE TEETH OF THE RIGHT HALF OF THE 

 LOWER JAW OF THE LEMOROID Microcebus, showing the close apposition 

 of the canine to the two elongated incisors, which are almost horizontal in 

 position. 



as well as upwards a condition still more decided in the 

 Lemuroids. The most singular form of the Lemuroid 

 group (the Aye-aye Cheiromys] has but two incisors above 

 and two below. These, however, are very large, and grow 

 from permanent pulps during the whole of life, from deep 



1 From itac-TfjM', to separate. 



