PERISSODACTYLA. 761 
Families of Perissodactyla 
- Family Tapiridee.—In the Tapirs (Zagzrus) 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 ee 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. 
Fic. 410.—Side view of horse's skull. 
P., Parietal; FR., frontal; WA., nasal; PALX., premaxilla; JX., maxilla; 
J., jugal; Z., lachrymal; SQ., squamosal; PP., paroccipitai process ; 
CO., condyle; CA., canine. 
Family Equide.—In the modern horses (Zgzus) 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 oe 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 Zguus. The 
progress shows an increase of size, a diminution in the number of 
