416 UNGULATA 
The dentition, according to the usual interpretation, consists 
only of incisors and molars, the formula in all known species being 
2 4,¢9,p4, m3. The upper incisors have persistent pulps, and 
are curved longitudinally, forming a semicircle as in Rodents. 
They are, however, not flattened from before backwards as in that 
order, but prismatic, with an antero-external, an antero-internal, 
and a posterior surface, the first two only being covered with 
enamel; their apices are consequently not chisel-shaped, but sharp 
pointed. They are preceded by functional, rooted milk-teeth. 
The outer lower incisors, which should perhaps be regarded rather 
as canines, have long tapering roots, but not of persistent 
growth. They are straight, procumbent, with awl-shaped, trilobed 
crowns. Behind the incisors is a considerable diastema. The 
molars and premolars are all contiguous, and formed almost exactly 
Fic. 177.—Skull and dentition of Dendrohyraz dorsalis. x 3. 
on the pattern of some of the Perissodactyle Ungulates. The hyoid 
arch is unlike that of any known mammal. The dorsal and lumbar 
vertebrae are very numerous, 28 to 30, of which 21 or 22 bear 
ribs. The tail is extremely short. There are no clavicles. In 
the fore foot the three middle toes are subequally developed, 
the fifth is present, but smaller, and the hallux is rudimentary, 
although, in one species at least, all its normal bones are present. 
The ungual phalanges of the four outer digits are small, somewhat 
conical, and flattened in form. The carpus has a distinct os 
centrale. There is a slight ridge on the femur in the place of a 
third trochanter. The fibula is complete, thickest at its upper 
end, where it generally ankyloses with the tibia. The articulation 
between the tibia and astragalus is more complex than in other 
mammals, the end of the malleolus entering into it. The hind 
foot is very like that of Rhinoceros, having three well-developed 
toes. There is no trace of a hallux, and the fifth metatarsal is 
represented only by a small nodule. The ungual phalanx of the 
