4i6 



UNGULATA 



The dentition, according to the usual interpretation, consists 

 only of incisors and molars, the formula in all known species being 

 * 2 j c o> V h m f • 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 



Fio. 177.— Skull and dentition of Dendrohyrax dorsalis. x g. 



on the pattern of some of the Perissodactyle Ungulates. The hyoid 

 arch is unlike that of any known mammal. The dorsal and lumbar 

 vertebras 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 



