in the Hippopotamus, the Rhinoceros, and the Tapir, the separation of the toes is more apparent externally, but still the phalanges, which are three in number to each of the four toes, are excessively strong and bulky when compared with their length. A kind of grada tion is likewise to be traced through these genera, whereby the foot of the Elephant be comes gradually transformed into the cloven hoof of the hog tribe, owing to the progressive diminution in size of the inner and outer toes, and the gradual conversion of the terminal phalanges of the central toes into that prismatic form which adapts them to fit the horny enve lopes that encase them like shoes.
Throughout all the hog genera the weight of the body is entirely supported on the two cen tral digits, the bones whereof are propor tionally strong and well developed, while the phalanges of the inner and of the outer toe, which do not touch the ground, remain per thanently of very rudimentary size.
Teeth.—In no order of Mammiferous ani mals do the teeth present so much diversity of structure and irregularity of disposition as among the Pachydermatous races ; it will be therefore necessary, in adverting to this part of their economy, to describe the principal modifi cations which the dental organs assume in different genera, before we proceed to investi gate the manner of their formation; and this we do more willingly, because from the character and arrangement of the teeth we can alone sa tisfactorily determine what have been the habits of extinct genera, the list of which is already considembly more extensive than that of living forms. Professor Owen, to whose labours in this department science is already so deeply in debted, has in his recent work on the Com parative Anatomy of the Teeth* examined this part of our subject with all the minuteness re quired for geological researches, and from his kindness we are enabled to lay the following abstract before our readers.
In the genus Sus, the wild progenitor of our domestic breeds of Hogs, Sus scrofa, the com plete set consists of forty-four teeth, viz.— IF In the wild Boar both the upper and lower lii.
nnines curve forwards, outwards, and up wards ; their sockets inclining in the same di ,ection, and being strengthened above by a idge of bone which is sometimes extraordina ily developed, these. teeth become converted nto most formidable weapons. These teeth, vhich have the chamcter of true tusks, are ree-sided ; the broadest convex side being irected obliquely inwards and forwards, while outer and posterior sides are nearly flat; and le hinder surface being destitute of any cover ig of enamel ; whilst the two other sides are Itcased with that material, the tusk wears ob quely from behind upwards and forwards to point, while its posterior margins present enamel edges that are always sharp and tren-: chant. Each of these tusks in the lower jaw
of the German wild Boar will measure eight inches in length along its curve ' and in the wild Boars of Assam they have 'been noticed measuring one foot, so that when wielded by such strong and brawny muscles as those of a Hog's neck, it is easy to conceive that terrific wounds may be inflicted by such instruments.
In the Baberoussa or " Horned Hog" the developement of the canines is still more ex traordinary. Those of the upper jaw seem as if their sockets had been pulled out or pro duced from the alveolar border of the upper maxillary bone, and then abruptly bent up wards, giving the tooth a direction upwards and backwards. The tooth pierces the integu ments of the upper lip like a horn, and its growth being unchecked by any opposing tooth, sometimes forces the lip again through the in tegument and into the substance of the skull. The lower tusks have the ordinary direction, but rise rather more vertically and much higher than in the wild Boar. These strangely situated teeth are well adapted by their position to de fend the eyes and assist in the act of forcing the head through the dense entangled under wood of a tropical forest, as suggested in Ilome's Comparative Anatomy, vol. I, p. 221, but their use has not been determined by actual observation.
In the next group of Pachydermata ( Chero potamidee) the dental formula of the existing type of the family Dicotyles, the Peccari, is as follows. _ 'The upper canines are moderately long, narrow, and compressed, with an entire covering of enamel ; while the lower are long, slightly curved, and have no enamel posteriorly. To this type of dentition belonged the Hyracothe rium and the Charopotamus, both extinct genera, the former having been about half the size of the existing Peccari, vvhile the latter was about one-third larger. The Hippophyus, likewise an extinct genus, found in the Himmalayan tertiary deposits, and of about the size of the Chwropotamus, appertained to the same family.