DENTITION. MANUS. PES. O<O 



be either bunodont (p. 504), or lophodont (p. 504). Selenodont 

 teeth are a variety of the lophodont type in which the tubercles 

 have a crescentic form ; they are found mainly in the ruminant 

 division of the Artiodactyla. As a general rule the teeth have 

 short crowns and the neck of the tooth, i.e. the junction of the 

 crown and root lies at the top of the alveolus (brachyodont) ; but 

 in Equidae and some ruminant artiodactyls the crowns are much 

 lengthened and the neck of the tooth lies for some time in the 

 socket (hypsodont or hypselodont, p. 505). The hypsodont tooth 

 is clearly more adapted for prolonged use ; there is more 

 wear in it and its possessor is able to eat habitually drier and 

 harder food than creatures possessing brachyodont grinders. 

 The layers of hard enamel traversing the softer dentine and cement 

 give rise to a slight roughness of the surface which is of advantage 

 for trituration of the food. 



There is considerable modification of the manus and pes 

 within the group, more so than perhaps in any other organ ; and 

 as these modifications are combined with the ungulate characters 

 and are continuous or nearly so, i.e. the extreme modifications 

 are connected by intermediate gradations throughout the 

 group, there is comparatively little difficulty in fixing the sys- 

 tematic position of their possessors. To begin with, we may 

 describe a constant character which is found in all ungulates and 

 which is mentioned in the definition. The bones of the two 

 rows of the carpus and tarsus are not placed vertically below one 

 another, are not serial or successional as it is called, as they are 

 in most mammals, e.g. the elephant or Hyrax (Fig. 290), but the 

 bones of the distal row have been shifted towards the inner side, 

 so that in the carpus the os magnum is partly under the scaphoid 

 as well as under the lunar, and the uncif orm articulates not only 

 with the cuneiform but also with the lunar (Fig. 298). In the 

 pes the astragalus no longer articulates solely with the navicular 

 but it also has a surface of articulation for the cuboid (Fig. 299). 

 In this condition which is, as we have stated, characteristic of 

 ungulates, the two rows of carpal and tarsal bones are said to 

 interlock, and the interlocking gives greater strength to the 

 carpal and tarsal joints. 



The modifications in the manus and pes relate to the number 

 of digits present. In the manus the greatest number of complete 

 digits is four with occasionally a trace of the pollex, in the pes 



