The eleventh order of Mammals is that of the Proboscidea, comprising no other living animals except the Elephants, but including also the extinct Mastodon and Deinotherium.
The order is characterised by the total absence of canine teeth; the molar teeth are few in number, large, and transversely ridged or tuberculate; incisors are always present, and grow from persistent pulps, constituting long tusks (fig. 417). In living Elephants there are two of these tusk-like incisors in the upper jaw, and the lower jaw is without incisor teeth. In the Deinotherium this is reversed, there being two tusk-like lower incisors and no upper incisors. In the Mastodons, the incisors are usually developed in the upper jaw, and form tusks, as in the Elephants, but sometimes there are both upper and lower incisors, and both are tusk - like. The nose is prolonged into a cylindrical trunks movable in every direction, highly sensitive, and terminating in a finger-like prehensile lobe (fig. 417). The nostrils are placed at the extremity of the proboscis. The feet are furnished with five toes each (fig. 419), but some of those toes may not be provided with hoofs. The feet are furnished with a thick pad of integument, forming the palms of the hands and the soles of the feet. There are no clavicles. The testes are abdominal throughout life. There are two teats, and these are placed upon the chest. The placenta is deciduate and zonary.
Fig. 417. - Skull of the Indian Elephant (Elephas Indicus): i Tusk-like upper incisors ; m Lower jaw, with molars, but without incisors ; n Nostrils, placed at the end of the proboscis. (After Owen.)
The recent Elephants are exclusively confined to the tropical regions of the Old World, in the forests of which they live in herds. Only two living species are known - the Asiatic Elephant (Elephas Indicus) and the African Elephant (E. Afri-canus). There can be no doubt, however, but that the Mammoth (Elephas primigenius) existed in Europe within the human period.
In both the living Elephants the "tusks" are formed by an enormous development of the two upper incisors. The milk-tusks are shed early, and never attain any very great size. The permanent tusks grow throughout the life of the animal, and often reach six or seven feet in length, and from fifty to seventy pounds in weight, or even up to one hundred and fifty pounds in aged males. In the Indian Elephant, and its variety the Ceylon Elephant, the males alone have well-developed tusks, but both sexes have tusks in the African species, those of the males being the largest. The lower incisors are absent, and there are no other teeth in the jaws except the large molars, which are of very large size, and are composed of transverse plates of enamel, surrounding tracts of dentine, and bound together by cement. As the tooth wears down, the enamel plates come to project, enclosing islands of dentine, which are narrow and elongated in the Indian Elephant (fig. 418, A), but are lozenge-shaped in the African Elephant (fig. 418, B). In reality, there are six molars on each side of each jaw, but owing to their large size, and the manner in which they succeed each other, there is never more than one (or part of two) in use on each side of each jaw at one time. The first three teeth of the grinder - series, which would ordinarily be supposed to be premolars, are in reality true molars, as they have no predecessors or successors. None of the molars, in fact, undergo vertical displacement, but the whole series gradually moves forward in the jaw, and the place of each tooth as it slowly advances is taken by the tooth next behind it in the series, each succeeding tooth being usually larger than its predecessor, and having more numerous plates of enamel.
Fig. 418. - A, Left ramus of lower jaw of Elephas Indicus, viewed from above (after Cuvier). B, Grinding-surface of molar tooth of Elephas Africanus (after Giebel).
The Indian Elephant is the only species which is now caught and domesticated, and as it rarely breeds in captivity, the demand for it is supplied almost entirely by the capture of adult wild individuals, which are taken chiefly by the assistance of those which have been already tamed. The Indian Elephant is distinguished by its concave forehead, its small ears, and the characters of the molars. Its skull is pyramidal, and it has five hoofs on the fore-feet, and only four on the hind-feet. Its colour is generally pale brown. (The so-called "White Elephants" are merely albinos.) The African Elephant, on the other hand, has a strongly convex forehead and great flapping ears. Its colour is darker, its skull is rounded, and it has four hoofs on the fore-feet, and only three on the hind-feet. The African Elephant is chiefly hunted for the sake of its ivory, and there is too much reason to believe that the pursuit will ultimately end in the destruction of these fine animals. A great deal, however, of the ivory of commerce comes from Siberia, and is really derived from the tusks of the now extinct Mammoth, which formerly inhabited the north of Asia in great numbers.
The Elephants are all phytophagous, living entirely on the foliage of shrubs and trees, and other vegetable matters, which they strip off by means of the prehensile trunk. As the tusks prevent the animal from drinking in the ordinary manner, the water is sucked up by the trunk, which is then inserted into the mouth, into which it empties its contents.
Closely allied to the true Elephants are the Mastodons, characterised by the fact that the crowns of the molar teeth have nipple-shaped tubercles placed in pairs (fig. 420). Generally speaking, the two upper incisors formed long curved tusks, as in the Elephants, but in some cases there were two lower incisors as well. The various species of Mastodon all belong to the later Tertiary and Post-tertiary periods.
Fig. 419. - Hind-foot of the Indian Elephant (Elephas Indicus). (After Cuvier.)
The last of the Proboscidea is a remarkable extinct animal, the Deinotherium. This extraordinary animal has hitherto only been found in Miocene deposits, and little is known of it except its enormous skull. Molars and praemolars were present in each jaw, and the upper jaw was destitute of canines and incisors. In the lower jaw were two very large tusklike incisors, which were not directed forwards as in the true Elephants, but were bent abruptly downwards (fig. 421). The animal must have attained an enormous size, and it is probable that the curved tusks were used either in digging up roots, or in mooring the animal to the banks of rivers, for it was probably aquatic or semi-aquatic in its habits. The whole of the praemolars and molars were in use at one time, and their crowns are crossed by strong transverse ridges, which give them a marked Tapiroid character, while in some respects they resemble the teeth of the Mastodons. It is placed by De Blainville in the Sirenia, being regarded as a Dugong with tusk-like lower incisors; but this view has been rendered untenable by the discovery of limb-bones of a distinctly Proboscidean type.
Fig. 420. - A, Skull of Mastodon giganteum ; of Mastodon giganteum.
B, Side-view of the second true molar (After Owen.)
Fig. 421. - Skull of Deinotherium giganteum. Miocene Tertiary.
Fig. 422. - A, Side-view of the third molar of Deinotherium giganteum; B, Grinding surface of the same. Miocene Tertiary. (After Kaup.)
The genus Deinotherium, as just mentioned, is exclusively confined to the Miocene period.
The genus Mastodon is characteristic in Europe of the Miocene and Pliocene; but in North America it is represented in the Post-pliocene, and it occurs also in deposits of the same age in South America.
No Elephant has yet been discovered in the Miocene rocks of Europe, but six species are known from Miocene (Pliocene ?) strata in India. In the Pliocene period Europe possessed its Elephants (viz., E. priscus and E. meridionalis); but the best known of the extinct Elephants, as well as the most modern, is the Mammoth (E. primigenius). This enormous animal is now wholly extinct, but it formerly abounded in the northern parts of Asia and over the whole of Europe. It occurred also in Britain, and unquestionably existed in the earlier portion of the human period, its remains having been found in a great number of instances in connection with human implements. From its great abundance in Siberia, it might have been safely inferred that the Mammoth was able to endure a much colder climate than either of the living elephants. This inference, however, has been rendered a certainty by the discovery of the body of more than one Mammoth embedded in the frozen soil of Siberia. These specimens had been so perfectly preserved that even microscopical sections of some of the tissues could be made; and in one case even the eyes were preserved. From these specimens we know that the body of the Mammoth was covered with long woolly hair.