XIII 



PHYLUM CHORDATA 



489 



maims and pes, all reaching l^he ground. The surface is naked, 

 with only a few hairs in certain positions ; the skin is of great 

 thickness. 



In the Perissodactyles the third digit is either the only complete 

 one in both fore- and hind-foot (Horses), or there are only three 

 digits second, third, and fourth in each (Rhinoceroses), or there 

 are four in the fore-foot and three in the hind (Tapirs). The 

 " Horses " (Equidae, Fig. 1130) have the distal divisions of the limbs 

 slender, the metacarpals and metatarsals nearly vertical to the 

 surface of the ground ; the single hoof massive and with a broad 

 lower surface. Though the head is elongated, the nasal region is 

 not produced into a proboscis. The tail is short or moderately 

 long, and is either beset throughout with a large number of very 

 long, coarse hairs, or with a tuft of such specially developed hairs 

 at the extremity. A mane of similar large hairs usually runs 

 along the dorsal surface of the neck. There is a wart-like callosity 

 above the wrist, and in the true Horses a second a little below 

 the heel or "hock." 



The Tapirs (Fig. 1131) have the body more massive than the 

 Horses, and the limbs, especially the distal segments, shorter and 



FIG. 1131. American Tapir (Tapirus terrestris). (From the Cambridge Natural History.) 



stouter. The nasal region is produced into a short proboscis. 

 The surface is beset with a scanty covering of hairs. The tail is 

 vestigial. 



In the Rhinoceroses (Fig. 1132) the body is extremely massive, 

 the limbs short and stout, each digit provided with a hoof-like 

 nail. There is a short, soft muzzle. Either one or two remarkable 

 median horns are borne on the nasal region, not attached directly 

 to the skull : these are epidermal structures which are formed of 

 a dense aggregation of slender fibre-like elements. The eyes are 



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