Apbh, 1, 1892.] 



KNOWLEDGE 



65 



of the molar teeth of Elephants, that they are often very 

 imperfectly understood, even by those who have spent half 

 thek lives among these animals. For instance, we find 



Fig. 3.— Last or Sixth Upper Molar Tootli of a 

 Mastodon ; half natural size. 



the veteran Elephant hunter, Sir S. Baker, in his " Wild 

 Beasts and their Ways," making the statement in regard 

 to Elephants that " both the Indian and African varieties 

 have only four teeth," whereas, as a matter of fact, every 

 Elephant has, during its whole life, six molars on each side 

 of both the upper and lower jaws. Instead, however, of 



Fig. 4. — Molar teeth of Indian (a) and African (i) Elephant. 

 In a the anterior hali is worn, and the remainder unworn. 

 Much reduced. After Owen. 



all these teeth being in use at one and the same time, as 

 are those of a cow or a horse, in existing Elephants there 



are never more than portions of two teeth in use at any 

 one time, although, in the extinct Mastodons, portions of 

 three may co-exist. In all Elephants, the more anterior of 

 these six teeth are smaller and of simpler structure than 

 the hinder ones, and the whole series is protruded in an 

 arc of a circle from back to front, the larger hind teeth 

 being pushed up and gradually coming into use as the 

 small anterior ones are worn away and finally discarded. 

 The hinder ones of these teeth (Fig. 4) are so large that 

 while the front portion is being worn away the back is still 

 bedded in the gum. In the earlier Elephants, or Mastodons, 

 these molar teeth are composed of a series of relatively low 

 and widely separated transverse ridges, more or less com- 

 pletely divided into inner and outer moieties, and with 

 large open valleys between them. Moreover, in all the 

 teeth, except the last, these ridges do not exceed four in 

 number, although in the sixth tooth (Fig. 3) they may be 

 as many as five or six. It was explained in the article on 

 teeth how such a molar tooth might have been derived from 

 the ordinary type of tooth presented to us by the molars of 

 the pig, in which the crown carries four columns, severally 

 placed at its corners. When a tooth like the one repre- 

 sented in Fig. 3 became worn down by use, the enamel 

 coating each of the columns would be cut thi-ough, so as 

 to expose a series of more or less trefoil-shaped surfaces of 

 ivory, each surrounded by a ring of the hard enamel. And 

 it will be obvious that a tooth thus constructed of 

 alternations of substances of dili'erent degrees of hardness 

 would act as an efficient mill-stone. Elephants do not 

 appear, however, to have been by any means satisfied with 

 this comparatively simple kind of tooth, for as we pass 

 upwards in the geological scale we find that there has been 

 a gradual increasing complexity in the structure of the molar 

 teeth of these animals, this being due to a graduated 

 increase in the height of their transverse ridges, accompanied 

 by an increase in the number of the ridires themselves. 

 There is, indeed, an almost perfect structural gradation, 

 now known to exist between the Mastodon tooth, repre- 

 sented in Fig. 8, to the teeth of true Elephants shown in 

 Fig. 4. Both the latter examples are in a somewhat worn 

 condition, but it will be readily seen that the lozenge- 

 shaped surfaces of ivory, surrounded by enamel, in the 

 tooth of the African Elephant, correspond to the transverse 

 ridges of the Mastodon's tooth. In the true Elephants, 

 however, the open valleys between these ridges (which 

 have now assumed the" form of tall, thin, and nearly 

 parallel lamina:') Lave been completely filled up by a third 

 constituent of the tooth, known as the cement. The 

 grinding surface of the tooth of such an Elephant con- 

 sequently consists of a solid mass, made up of alternating 

 vertical transverse layers of various substances, arranged 

 in the order of cement, enamel, ivory, enamel, cement; 

 and since each of these constituents differs in hardness, it 

 will be obvious that the millstone-like apparatus is now of 

 a far more efficient type than it was in the Mastodon. 

 Moreover, as the crowns of the molars of the true 

 Elephants are very much taller than are those of the 

 Mastodons, it is evident that they will require a longer 

 period of time before they become worn away, and that 

 they will therefore allow a longer life to their owner. 

 Even, however, among true Elephants there is a con- 

 siderable amount of difl'erence in regard to the number 

 and narrowness of the component plates of their molar 

 teeth, and it will be seen from Fig. 4, that in this respect 

 the African Elephant departs far less widely from the 

 Mastodon than does its Indian cousin. Since the food of 

 the latter consists to a large extent of boughs and twigs, 

 while that of the former is composed more of juicy leaves, 

 fruits, and roots, the necessity of a more complicated 



