PERISSODACTYLA. 761 



Families of Perissodactyla 



Family Tapiridse. In the Tapirs ( Tapirus] there are four digits in 

 the manus, but the third finger is still practically median, as the 

 fifth digit scarcely reaches the ground. The hind-foot has three 



digits. The dentition of the genus is 3 ^. The orbit and 



temporal fossa are continuous. The nose and upper lip form a 

 short proboscis. The thick skin has but scanty hair. In habit, 

 the tapirs are shy and nocturnal, fond of forests and water, 

 feeding on tender shoots and leaves. The distribution is some- 

 what remarkable, for four species live in Central and South 

 America, while a fifth is Malayan. The genus was once 

 widespread, but has survived in these two far-separated regions. 



FIG. 410. Side view of horse's skull. 



P., Parietal ; FR., frontal ; NA.^ nasal ; PMX., premaxilla ; MX., maxilla; 

 /., jugal ; L., lachrymal; SQ., squamosal ; PP., paroccipital process; 

 CO., condyle; CA. t canine. 



Family Equidse. In the modern horses (Equus) there is on each 

 foot one functional digit the third, with splints representing the 

 metacarpals and metatarsals of the second and fourth. Professor 

 Cossar Ewart has demonstrated in the embryo of the horse the 

 rudiments of the three phalanges of the second and fourth digits. 

 The vestigial phalanges of these digits subsequently fuse with 

 one another and with the respective metacarpals or metatarsals, 

 forming " buttons" at the end of the splints. The ulna and 

 fibula are incomplete, but the former is quite complete in the 



foetus. The dentition is ^^, but the first premolar is rudi- 

 mentary, and soon lost in both sexes, and the canines are rarely 

 present in the mare. The orbit is complete. 



The modern horses are connected by a very complete series of forms 

 with ancestral Eocene types, but it is not clearly proved that these 

 forms were actually in the line of descent of the genus Equus. The 

 progress shows an increase of size, a diminution in the number of 



