MASTODON, Cuv.—The earliest appearance of this genus of proboscidian or elephantoid Mammal is in tertiary strata of miocene age, and by a species in which the fore part of the lower jaw was produced into a pair of deep sockets containing tusks ; but these are only slightly deflected from the line of the grinding teeth (fig. 112, C). This species of Mastodon, discovered in the miocene of Eppelsheim, was called langirostris by Kaup ; but he afterwards recognized it as the same with a species which had been previously called Masto don, arvernensis (Croizet and Jobert).* Both belong to that section of Mastodon in which the first and second true molars have each four transverse ridges,t and for which Dr. Falconer proposes the name Tetralophodon. In the newer tertiary deposits of North America remains of a Mastodon (M. Ohio ticus) have been discovered, in which the transverse ridges of the grinders are in shape more like those of the Dinothere than in any other Mastodon ; the first and second, moreover, are bilophodont, the third trilophodont ; but this is followed by two three-ridged molars and a last larger molar with four or five ridges.* For the Mastodons with penultimate and antepenultimate grinders with three ridges, Dr. Falconer pro poses the name Trilophodon. In the Mastodon Ohiotious the lower jaw has two tusks in the young of both sexes ; these are soon shed in the female, but one of them is retained by the male (fig. 112, B). The upper tusks are long and retained in both sexes (fig. 112, A).* An almost entire skeleton of a Mastodon (M. turicencis) has been discovered in the pliocene deposits of Aste, Pied mont, and has been described and figured by Professor Sis monda,t from whose beautiful Memoir fig. 112 is taken. The total length from the tail to the end of the tusks is 17 feet. The teeth have the same narrow shape and multi-mammillate structure as in M. arvernensis, but in the numerical character of transverse divisions of the crown this species agrees with M. Ohioticus.
The Mastodons were elephants with the grinding teeth less complex in structure, and adapted for bruising coarser vegetable substances. The grinding surface of the molars
(fig. 113), instead of being cleft into numerous thin plates, was divided into wedge-shaped transverse ridges, and the summits of these were subdivided into smaller cones, more or less resembling the teats of a cow, whence the generic name.f A more important modification appeared to distin guish the extinct genus, in respect of the structure of the molar teeth ; the dentine, or princi pal substance of the crown of the tooth (fig. 113, d) is cover ed by a thick coat of dense and brittle enamel (e); a thin coat of cement is continued from the fangs upon the crown of the tooth, but this substance does not fill up the interspaces of the divisions of the crown, as in the elephant's grinder (fig. 118, c). Such at least is the character of the molar teeth of the two species of Mastodon, which Cuvier has termed Mastodon gigantests and Mastodon angustidens (fig. 113). Fossil remains of proboscidians have subsequently been found principally in the tertiary deposits of tropical Asia, in which the number and depth of the clefts of the crown of the molar teeth, and the thickness of the intervening cement, are so much increased as to establish transitional characters between the lamello-tuberculate teeth of the elephants and the mammilated molars of the typical Mastodons, showing that the characters deducible from the molar teeth are rather the distinguishing marks of species than of genera in the pre sent family of mammalian quadrupeds.
The dentition of this family may be expressed by the formula— that is to say, in the Proboscidians in which the dentition most nearly approached to the typical one, thirty-four teeth were developed, as follows :—in the upper jaw, two deciduous incisors, followed by two per manent incisors developed as tusks ; six deciduous molars (three on each side, d 2, 3, 4, fig. 114); two premolars (one on each side, p 3, fig. 114), and six true molars (three on each side, m 1, 2, 3, figs. 114 and 115) ;—in the lower jaw, two incisors as tusks (uncertain whether preceded by deciduous tusks), deciduous molars, premolars, and molars, as in the upper jaw.