28 



THE ELEPHANTS. 



somewhat similar to that of the dugong, 

 carries no incisors. The molars deserve 

 special attention. These teeth, the grinding 

 surface of which may attain a length of more 

 than 15 inches and a breadth of 4 inches, 

 may be considered as composed of a number 

 of very close-set transversely -placed tooth- 

 fragments, each of which has its own root, 

 pulp-cavity, dentine, and enamel-layer, while 

 all the crowns are united together by a bony 

 cement. These compressed tooth-fragments 

 are clearly seen to be separate at the roots. 

 At first they form separate transverse ridges; 

 afterwards the cement brings these ridges 

 to a uniform level, and when the tooth has 

 emerged from the socket and is brought into 

 operation it gets worn away horizontally so 

 as to present an almost level surface, on 

 which the folds of enamel are not, indeed, 

 very prominent, but yet form very distinct 

 lamellae. In different species these lamellae 

 exhibit a characteristic arrangement, and in 

 the fossil genera and species of the Probos- 

 cidea we can trace all the transitions from 

 molars with transverse ridges (Dinotherium), 

 or with series of tubercles (Mastodon), to the 

 more complicated forms of the elephants 

 proper. 



This structure has as its consequence the 

 gradual replacement of the molars as they get 

 worn away by use, and this renewal takes 

 place from behind forwards. A second molar, 

 larger and having more numerous plates, is 

 formed in a closed cavity behind the active or 

 functional molar, and this second molar, by a 

 rotatory movement which goes on in the pro- 

 cess of growth, pushes out the older one, 

 when it is used up, and takes its place. The 

 elephant thus has in most cases only a single 

 active molar in each half of the jaw, but there 

 may be as many as three: one in front just 

 ready to drop out and worn down to an insig- 

 nificant stump, a second in full operation, and 

 a third behind just beginning to emerge from 

 the socket. So far as our observations yet 

 go this renewal may be repeated five times in 



the Asiatic elephant. The first milk-molar, 

 which cuts the gum at the age of three 

 months and is replaced in the second year, 

 consists of only four plates or lamellae, while 

 the sixth has as many as twenty-seven. In the 

 fossil proboscideans we can prove a more or less 

 decided tendency to this successive replace- 

 ment of the molars carried on almost through- 

 out life, in place of the single shedding and 

 renewal which is the prevalent process in 

 other animals. 



Among the features of the internal organ- 

 ization we mention first of all the form and 

 size of the brain. The elephant has the 

 largest brain of all living and fossil animals. 

 This brain, besides being larger than that 

 of the whales, exhibits very numerous and 

 complex convolutions. These are two notable 

 facts, which, however, should not be exagger- 

 ated. The point of importance lies not in 

 the absolute size of the brain, but in the pro- 

 portion of its mass to that of the whole body. 

 Now, in proportion to the size of the body the 

 elephant has not a very large brain. To show 

 this it is enough, without making any accurate 

 measurements, to compare the contents of the 

 brain-case of the skull of an elephant and that 

 of a man after both have been sawn through. 

 The development of the convolutions of the 

 brain likewise stands in close relation with the 

 size of the animal. Large animals always 

 exhibit more complex convolutions than small 

 ones of the same family. The brain of the 

 elephant even exhibits some characters which 

 point to a lowly organization. The hemi- 

 spheres of the large brain (the cerebrum) do 

 not cover the small brain or cerebellum. The 

 stomach is simple, the ccecum enormous, the 

 uterus bicornuate. The elephants are distin- 

 guished from the other ungulate animals, 

 except the Hyracida or rock-badger family, 

 by their zonary placenta, which is not indeed 

 contracted like that of the Carnivora, but 

 nevertheless admits of the development of a 

 deciduous membrane in the uterus. 



In the moist primeval forests of their native 



