ORDER UNGULATA. 



1379 



only. There is but slight mutual interlocking of the carpal and 

 tarsal bones ; the structure of these joints being simpler than in the 

 other suborders, and resembling those of the Unguiculate orders. 

 In the Condylarthra the dental formula is nearly always the typical 

 one ; the cheek-teeth are brachydont, and usually bunodont, although 

 rarely lophodont. The premolars are simpler than the true molars, 

 which may be tritubercular like those of many Carnivora ; the can- 

 ines and incisors frequently also recall those of that order. The 

 humerus is peculiar among Ungulates in having an entepicondylar 

 foramen ; the femur has a third trochanter ; the astragalus, as in the 

 Carnivora, presents a uniformly convex distal articular surface ; and 

 there is no articular facet for the fibula either on this bone or on 

 the calcaneum. The feet usually have five digits, with sharply 

 pointed terminal phalangeals ; and the radius and ulna are distinct. 

 This suborder may be regarded as containing the ancestral types 

 from which the Artiodactyla and Perissodactyla have sprung. It 

 further presents such remarkable signs of affinity (especially in the 

 structure of the teeth, the form of the astragalus, and the presence 

 of the foramen in the humerus) with the Carnivora, that it seems 

 highly probable that we may look upon the Condylarthra as a side 

 branch from the original ancestral stock of the Carnivora, which is 

 most nearly represented by the more primitive Creodonts. 



Family Periptychid^e. — In this the most generalised family the 

 dentition is bunodont ; the digits are five on each foot ; the astra- 



Fig. i-z-^.—Periptychus rhabdodon. Right upper (a) and lower {b) cheek-dentition, grinding 

 surface ; from the Puerco Eocene of New Mexico. Two-thirds natural size. (After Cope.) 



galus has no trochlea ; and the premolars are very simple. In the 

 type genus Periptychus, from the Lowest, or Puerco, Eocene of New 



Mexico, the dental formula is I. - ^, C. -, Pm. -, M. -, and the 



incisors and lower canines are small. 



1 4 3 



The typical P. rhabdodon 



