330 MAMMALIA. 



of the femur is much reduced. There are four digits in the 

 manus, nos. Ill and IV being more nearly equal in size than in 

 the tapirs ; the calcaneum is notably elongated, and there are 

 only three digits in the pes. 



When alive these animals must have had a very flexible nose, 

 but they do not appear to have possessed any true proboscis 

 like that of the tapir. The later and larger forms probably 

 attained great longevity ; for the epiphyses of their vertebrae 

 remain long separated in the adult as in the existing 

 elephants. 



Titanotherium (fig. 190). This genus is known by nearly complete 

 skeletons from the White River Formation (Lower Miocene) of Dakota. 

 The skull is long and depressed, much like that of a rhinoceros, and the 

 orbital cavity is directly continuous with the temporal fossa, not even 

 limited by any postorbital process of the frontal region. The zygomatic 

 arch is massive, and there is a large infraorbital foramen. A pair of bony 

 prominences or horn-cores arise from the maxillse in front of the orbits ; 

 while the well-developed nasals, which are firmly co-ossified, form the 

 inner margin of their base. These prominences contain large air-cavities, 

 and they vary considerably according to age, species, and probably sex. 

 The premaxillae are very small, and do not usually extend forwards so far 

 as the end of the nasals. The brain-cavity is very small, and a cast of it 

 shows that the much-convoluted and well-developed cerebral hemispheres 

 did not extend at all over the cerebellum. The premolars are as complex 

 as the molars, and small canines are always present ; but the incisors vary 

 from three pairs to none, and several generic names have been proposed 

 to indicate their different states of development. The epiphyses of the 

 vertebrae are loosely united in most specimens, as in the elephants. The 

 neck is stout, of moderate length, while the cervical and most of the dorsal 

 vertebrae are distinctly opisthocoelous. The atlas is much expanded trans- 

 versely, and the odontoid process of the axis is conical ; there are 17 dorsal 

 and 3 lumbar vertebrae, the latter smaller than the former ; and the tail 

 is very slender. The dorso-lumbar region is thus shorter by 3 or 4 

 vertebrae than is usual in perissodactyls. The limbs are intermediate 

 in proportions between those of the elephant and the rhinoceros. The 

 scapula is large, with a prominent spine and small coracoid process. The 

 humerus is stout, with very prominent radial crest ; the radius and ulna 

 are separate, the latter with a much-compressed olecranon process; the 

 four digits of the manus (nos. n to v) are remarkably uniform in size. 

 In the pelvis the ilium is greatly expanded. The femur has almost lost 

 its third trochanter ; the tibia and fibula are relatively short, complete 

 and separate, but the latter bone is very slender ; the calcaneum is much 

 elongated, and the cuboid facette on the astragalus is relatively large ; the 



