Section A. Perissodactyla

The section of the Perissodactyle Ungulates includes the Rhinoceros, the Tapirs, the Horse and its allies, and some extinct forms, all agreeing in the following characters:

The hind-feet are odd-toed in all (fig. 388, B), and the fore-feet in all except the Tapirs and Brontotheridae. The dorso-lumbar vertebra are never less than twenty-two in number. The femur has a third trochanter. The horns, if present, are not paired (except in the extinct genus Diceratherium, and in the family of the Brontoiheridae). Usually there is only one horn, but if there are two, these are placed in the middle line of the head, one behind the other (fig. 392). In neither case are the horns ever supported by bony horn-cores. The sto7nach is simple, and is not divided into several compartments; and there is a large and capacious caecum.

The three existing groups of Perissodactyle Ungulates namely, the Horses, Tapirs, and Rhinoceroses - are widely removed from one another in many important characters; but the intervals between them are largely filled up by an extensive series of fossil forms, commencing in the Lower Tertiary strata.

The section of the Perissodactyle Ungulates includes the following seven families:

Tarn. 1. Coryphodontidae. - This family comprises only a number of extinct Tapir-like animals, belonging to the Eocene period. The skull is of the Perissodactyle type, hornless, with small nasal bones. The brain is remarkably small, and the dentition is complete, the dental formula being:

i

3 - 3

; c

1 - 1

; pm

4 - 4

; m

3 - 3

=:

44.

3 - 3

1 - 1

4 - 4

3 - 3

The canines are not excessively developed, and the molars are of the Tapiroid type, having two transverse crests or ridges. The limbs are short, and both the fore-feet (fig. 389) and the hind-feet are furnished with five complete toes, all of which carried hoofs. The genus Coryphodon is the principal or only one comprised in the family; and as it contains the only Ungulates with the complete number of five digits on each foot, it might with propriety be raised to the rank of a distinct section, equal with the sections of the Perissodactyla and

Fig. 389.   Fore foot of Coryphodon. (After Marsh.) Eocene Tertiary.

Fig. 389. - Fore-foot of Coryphodon. (After Marsh.) Eocene Tertiary.

Artiodactyla, to which the name of Teleodactyla might be applied.

Fam. 2. Rhinocerotidae. - This family comprises only a single living genus, the genus Rhinoceros, unless, indeed, the little Hyrax is to be retained in this order. The Rhinoceroses are extremely large and bulky brutes, having a very thick skin, which is usually thrown into deep folds. The muzzle is rounded and blunt, and there are

7 - 7

7 - 7

grinders, with tuberculate crowns.

The typical dental formula is:

i

1 - 1

(or

0 - 0

); c

0 - 0

; pm

4 - 4

; m

3 - 3

+

32

or

28.

1 - 1

0 - 0

0 - 0

4 - 4

3 - 3

There are no canines; and the incisors are often wanting in the adult (as in the living two-horned species), or may be increased in number (as in the extinct Acerotheriuni). The crowns of the praemolars and molars (fig. 390) exhibit two principal tracts of dentine, not filled up by cement.

Fig. 390.   Teeth of the upper jaw of Rhinoceros Indicus (after Cuvier). m1, m3 Molars;pm1, pm4 Praemolars ; i Incisor.

Fig. 390. - Teeth of the upper jaw of Rhinoceros Indicus (after Cuvier). m1, m3 Molars;pm1, pm4 Praemolars ; i Incisor.

The skull (fig. 391, B) is pyramidal, and the nasal bones are generally enormously developed. The nasal bones usually support one or two horns, which are not paired in any living form. The horn is composed of longitudinal fibres, which are agglutinated together, and are of the nature of epidermic growths, somewhat analogous to hairs. When two horns are present, the hinder one is carried by the frontal bones, and is placed in the middle line of the head behind the anterior horn. The posterior horn is usually much shorter than the anterior one; and if not, it differs in shape. In the extinct genus Diceraiherium of Marsh, from the Miocene of Oregon, there are two horns placed transversely and symmetrically upon the nasal bones. This singular form further differs from the typical Rhinoceroses in having four toes to the fore-feet, whilst the hind-feet have only three.

The development of the nasal bones in the Rhinoceroses varies greatly in accordance with the varying condition of the horns. In the extinct Acerotherium, in which there are no horns, the nasal bones are greatly reduced in size. In the horned forms, on the other hand, not only are the nasal bones prolonged forwards over the nasal cavity; but the septum narium may be partially or completely ossified, thus strengthening the basement of the anterior horn in the bicorn species.

Fig. 391.   A, Side view of the skull of Tapirus Americanus;, B, Side view of the skull of Rhinoceros bicornis. (After Giebel.)

Fig. 391. - A, Side-view of the skull of Tapirus Americanus;, B, Side-view of the skull of Rhinoceros bicornis. (After Giebel.)

The Rhinoceroses live in marshy places, and subsist chiefly on the foliage of trees. They are exclusively confined at the present day to the warmer parts of the Old World; but several extinct species formerly ranged over the greater part of Europe. Of the one-horned species, of which there are three, the best known is the Indian Rhinoceros (R. Indicus or unicornis), which was probably the "Unicorn" of the ancients. Another species with one horn (R. Sondaicus) inhabits the Malay Peninsula, Java, Sumatra, and Borneo. Of the two-horned species, one (R. Sumatrensis) is found in Sumatra and the Malay Peninsula, and is remarkable for the comparative absence of cutaneous folds. The best known, however, is the African Rhinoceros (R. bicornis) which occurs abundantly in Cape Colony and in the southern parts of the African continent, extending its range to Nubia (fig. 392). Another