UNGULATA. 513 



ing in the entire order. There are always two sets of enamelled 

 teeth, so that the animal is diphyodont. The molar teeth are 

 massive and have broad crowns, adapted for grinding vegetable 

 substances. 



The order Ungulata is divided into two primary sec- 

 tions : the Perissodactyla, in which the toes or hoofs are odd 

 in number (one or three), and the Artiodactyla> in which the 

 toes are even in number (two or four). 



SECTION A. PERISSODACTYLA. The section of the Perisso- 

 dactyle 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. 197, A, D), and the 

 fore-feet in all except the Tapirs. The dorso-lumbar vertebrae 

 are never less than twenty-two in number. The femur has a 

 third trochanter. The horns, if present, are not paired. 

 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. 198). In neither case are the horns ever supported by 

 bony horn-cores. The stomach is simple, and is not divided 

 into several compartments; and there is a large and capacious 

 caecum. 



The three existing genera of Perissodactyle Ungulates 

 namely, the Horse, Tapir, and Rhinoceros, are widely removed 

 from one another in many important characters; but the 

 intervals between them are filled up by an extensive series of 

 fossil forms, commencing in the Lower Tertiary Strata. 



Fam. i. Rhinocerida. This family comprises only a single 

 genus, the genus Rhinoceros, unless, indeed, the little Hyrax 

 is to be retained in this order. The Rhinoceroses are ex- 

 tremely 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 - - molars, with tuberculate crowns. 



There are no canines, but there are usually incisor teeth in 

 both jaws. The feet are furnished with three toes each, 

 encased in hoofs. The nasal bones support one or two horns, 

 which are not paired. 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. The Rhino- 

 ceroses live in marshy places, and subsist chiefly on the foliage 



VOL. II. 2 K 



