142 THE WONDERS OF GEOLOGY. Lect. J I. 



proceed in the argument, and show the adaptation of the 

 muscles of the head to the apparatus here described ; and, 

 beginning with the jaw, review the whole animal frame, 

 and demonstrate how all its parts are alike wonderfully 

 constructed and fitted together, to perform the functions 

 necessary for the being to which it belongs. 



In the Elephant, which has but four teeth in each jaw, 

 the deficiency of prehensile incisor teeth being supplied 

 by that wonderful instrument, the proboscis, or trunk, the 

 structure of the dental organs is still further modified. 

 The teeth of animals are formed of three distinct substances, 

 which are variously disposed in the different orders, accord- 

 ing to the habits and economy of the species. The nucleus, or 

 germ of the tooth, is a congeries of blood-vessels and nerves, 

 called the pulp, by which the calcareous hard parts are 

 elaborated. The pulp is surrounded by a covering of a very 

 dense substance, composed of phosphate of lime, with 

 albumen and gluten, termed dentine, or tooth-ivory, which 

 is permeated throughout by very minute tubes. The den- 

 tine is encased in a still harder material, called enamel. In 

 the teeth of man, and of the carnivora, the enamel covers the 

 entire external surface of the crown. There is a third sub- 

 stance, a coarse kind of dentine, of an opaque and yellowish 

 appearance, termed crusta petrosa, or cement, w r hicb, in 

 the Elephant and other herbivora, is interstratified with 

 the enamel and dentine. The intermixture of these three 

 dental elements — the tooth-ivory, cement, and enamel — is 

 apparent on the worn surfaces of the teeth of elephants ; 

 and it differs in the several recent and fossil species.* 



In the African elephant, (Lign. 2 l,jfig. 1,) the worn surface 

 of the molar teeth presents a series of lozenge-shaped lines of 

 enamel, having the dentine on the inner margin of the ridges, 

 .and being surrounded by the crusta petrosa. In the Asiatic 



* See "Medals of Creation,'" vol. ii. p. 837 ; "Teeth of Mammalia.'* 



