266 HORNS OF TITANOTHERIUM CHAP. 



together with the long and divergent horn cores, must have given 

 to the living animal a most bizarre appearance. It is an interest- 

 ing fact that this animal, though a Perissodactyle, agrees with the 

 Artiodactyla in the nineteen dorso-lumbar vertebrae, of which seven- 

 teen bear ribs. 



The genus further agrees with the Artiodactyles in the 

 structure of the carpus. The toes of the fore -limb are four, 

 those of the hind-limb three ; but while the hind-limb is un- 

 doubtedly Perissodactyle in the arrangement of its component 

 parts, the fore -limb shows a hint of an Artiodactyle mode of 

 structure. This limb is paraxonic, the axis of the limb passing 

 between the two middle digits. It may be that this genus 

 represents more nearly than any other Perissodactyle or Artio- 

 dactyle the primitive stem from which both have diverged, though, 

 of course, it is not old enough to be very near to the actual 

 ancestor. The molar dentition is the typical one ; the incisors 

 seem to vary as to their presence or absence, and, if present, in 

 their numbers. In comparing the older with the more recent 

 forms it is noteworthy that there has been an increase of size 

 exactly as there has been during the evolution of the Camels and 

 some other groups of Ungulates. As already mentioned, the size 

 of the horn cores also increases until it culminates in the extra- 

 ordinary species, T. platyceras and T. ramosum, in which these are 

 half as long as the skull, flattened in form, and connected at 

 their bases by a " web " of bone. Arrived at this amount of 

 specialisation the genus Titanotherium apparently exhausted its 

 capacities for modification and ceased to be. The many 

 generic names may be explained by sexual differences on the one 

 hand and an incomplete knowledge of connecting links on the 

 other. 1 



Palaeosyops is somewhat like a Tapir in build, the skull 

 especially resembling that of the Tapir. As in Titanotherium 

 the molar teeth, instead of having an outer wall formed by fused 

 cusps, have a W-shaped outer wall on one side and two or one 

 cusps on the opposite side. It is, moreover, an Eocene form, and 

 in correspondence with its greater age is more primitive in some 

 points of structure, for example, in the absence of horns and in 

 the full dental formula. The fore-limbs are four-toed, the hind 



1 See especially Osborn and Wortman, Bull. Amer. Mvs. Nat. Hist. vii. 1895, 

 p. 333, and Osborn, ibid. viii. 1896, p. 157. 



