Fig. 392.   Head of two horned Rhinoceros (R. bicornis).

Fig. 392. - Head of two-horned Rhinoceros (R. bicornis).

African species is the White Rhinoceros (R. simus), distinguished from the preceding by its colour, the shortness of its upper lip, and the great length of the anterior horn; and at least two other two-horned species are said to occur in the same country.

Fam. 3. Tapiridae. - The Tapirs are characterised by the possession of a short movable proboscis or trunk. The skull (fig. 391, A) is pyramidal, like that of the pigs, and the nasal bones project over the nasal cavity. The skin is hairy and very thick. The tail is extremely short. The fore-feet (fig. 388, A) have four toes each, but these are unsymmetrical (the little toe being smaller than the rest and not touching the ground), and the hind-feet have only three toes, all encased in hoofs. The dental formula of the Tapirs is:

i

3 - 3

;

1 - 1

; pm

4 - 4

; m

3 - 3

=

42.

3 - 3

1 - 1

3 - 3

3 - 3

The canines are of comparatively small size, and do not form projecting tusks; and the molars and praemolars are of the "bilophodont" type, the crown of each showing two transverse or oblique ridges separated by shallow valleys.

Several species of Tapirs are known, of which the most familiar is the American Tapir (T. Americanus), which inhabits the vast forests of South America. It is a large animal, something like a pig in shape, but brownish black in colour, and having a mane. It is nocturnal in its habits, and is strictly phytophagous. The proboscis is employed in conveying the food to the mouth, and the nostrils are placed at its extremity. It attains altogether a total length of from five to six feet. Another species, with longer hair (T. villosus), inhabits the Andes, and a still larger species (T. Malayanus) is found in Sumatra, Borneo, and Malacca. In this last, there is no mane, and the general colour is black; but the back, rump, and sides of the belly are white. The Elasmognathus Bairdii occurs in Central America, and one or more species of the genus Tapirus (T. Roulini and T. leucogenys) have been discovered in the elevated regions of Ecuador and New Granada.

Fig. 393.   Skull of Brontotherium ingens. (After Marsh.)

Fig. 393. - Skull of Brontotherium ingens. (After Marsh.)

Fam. 4. Brontotheridae. - We may provisionally place here the large fossil Mammals from the Miocene of North America, which Professor Marsh has described under the name of Bron-totheridae. In these, the fore-feet have four nearly equal toes, and the hind-feet three, thus resembling the Tapirs. The skull is elongated, and a pair of very large horn-cores are carried upon the maxillaries and the anchylosed nasal bones in both sexes. The dental formula in Brontotherium is:

i

2 - 2

; c

1 - 1

; pm

4 - 4

; m

3 - 3

=

38.

2 - 2

1 - 1

3 - 3

3 - 3

The incisors are small; and the canines are short and not separated from the praemolars by any diastema, these latter being much smaller than the molars. The neck was long, and there seems to have been a long tail. The nose was probably elongated and flexible, but there would not appear to have been a long proboscis. The Brontotheridae seem to be the successors of the Dinocerata of the Eocene. The chief genus is Brontotherium, with which the Symborodon and Miobasileus of Professor Cope are more or less entirely synonymous.

The genera Titanotherium, Megacerops, and Diconodon, also belong to this group.

Fam. 5. Palaeotheridae. - This family includes certain extinct Ungulates from the Eocene and Miocene Tertiary. They are characterised by the possession of three toes to all the feet, by having canines, and by the fact that the lower molars have a doubly crescentic form. The canines are longer than the other teeth, and the dental formula is:

i

3 - 3

; c

1 - 1

; pm

4 - 4

; m

3 - 3

-

44.

3 - 3

1 - 1

4 - 4

3 - 3

The chief genus in this family is Palaeotherium itself. Several species of this genus are known, varying in size from a sheep up to a horse. From the form and size of the nasal bones it is deduced, with great probability, that the Palaeotheridae. possessed a short movable proboscis or trunk.

Fig. 394.   Grinding surface of the molar and praemolar teeth of the upper jaw of Palaeotherium crassum. (After Owen.)

Fig. 394. - Grinding-surface of the molar and praemolar teeth of the upper jaw of Palaeotherium crassum. (After Owen.)

Fam. 6. Macrauchenidae. - This family comprises the single genus Macrauchenia from the late Tertiary deposits of South America. The animals included in this genus were of large size, with three-toed feet, and a third trochanter to the femur, but having cervical vertebrae of the type of those of the Came-lidae. The general form of the skull is horse-like, and the incisors have a coronal pit. The teeth form nearly a continuous series, and the dental formula is:

i

3 - 3

; c

1 - 1

; pm

5 - 5

; m

3 - 3

=

46.

3 - 3

1 - 1

4 - 4

3 - 3

Fig. 395.   Skull of the Horse (Equus caballus).

Fig. 395. - Skull of the Horse (Equus caballus).

Fam. 7. Solidungula or Eqiudae. - This family comprises the Horses, Asses, and Zebras, characterised by the fact that the feet, in living forms, have only a single perfect toe each, enclosed in a single broad hoof, without supplementary hoofs (figs. 355 and 397, D). The functional toe is the 3d, and the 2d and 4th digits are represented only by rudiments of their metapodials ("splint-bones"), hidden beneath the skin. There is a discontinuous series of teeth (fig. 395) in each jaw, and in the males, canines are present, but these are wanting in the females. The dental formula is: