SUBSTANCE. 301 



are very short, and the crowns of the teeth are of equal length,, 

 there is no interspace or 'diastema' in the dental series of either 

 jaw, and the teeth derive some additional fixity by their close apposi- 

 tion and mutual pressure. No inferior Mammal now^ presents this 

 character ; but its importance, as associated w^ith the peculiar attri- 

 butes of human organization, has been somewhat diminished by 

 Cuvier's discovery of a like contiguous arrangement of the teeth 

 in the jaws of the extinct Anoplotherium, 



128. Substance. — The teeth of the Mammalia usually consist 

 of hard or unvascular dentine, defended at the crown with an in- 

 vestment of enamel, and everywhere surrounded by a coat of cement. 

 The coronal cement is of extreme tenuity in Man, Quadrumana and 

 terrestrial Carnivora ; it is thicker in the Herbivora, especially in 

 the complex grinders of the Elephant, and is thickest in the teeth 

 of the Sloths, Megatherioids, Morse, and Cachalot. Vertical folds 

 of enamel and cement penetrate the crown of the tooth in the 

 Ruminants, and in most Rodents, and Pachyderms, characterizing 

 by their various forms the genera of the two last orders : but these 

 folds never converge from equidistant points of the circumference 

 of the crown towards its centre. The teeth of the quadrupeds of 

 the order Bruta, {Edentata, Cuv.), have no true enamel; this is 

 absent, likewise, in the molars of the Dugong, the Zeuglodon and 

 the Cachalot. (1) The tusks of the Narwhal, Walrus, Elephant, 

 Mastodon, and Dinotherium, consist of modified dentine, which, in 

 the large proboscidian animals, is properly called ' ivory,' (2) and is 

 covered by cement. 



The central part of the fully-formed tooth in man and most other 

 animals contains an irregular kind of osseous substance, which is most 

 abundant in the Cachalot, (3) and forms around foreign bodies which 

 may gain admission to the pulp-cavity of tusks. A fifth substance 

 which, from the number and regular position of the vascular canals 



(1) M. Fr. Cuvier divides the teeth of Mammalia, according to their composition, into 

 four classes : the first consist of ivory, (dentine), enamel and cement ; the second of ivory 

 and enamel ; the third of ivory and cement ; the fourth of ivory only. ' Dents des Mammiferes,' 

 p. xxi. I have met with no Mammalian teeth, in which cement is absent, and believe that 

 the second and fourth of the above-cited classes of teeth, have no existence in Nature. 



(2) " Hoc solum est ebur," Plinius, Hist. Nat. lib. xi. c. 37. 



(3) PI. 89, fipf. 2, c. 



