MAMMALIAN ORDERS. 



287 



167 



The metacarpals of the two functional toes coalesce to form a single 



' cannon-bone,' fig. 166, 57, as do the corresponding metatarsals, 



ib. 69. The Camel-tribe have 



the upper incisors reduced to a 



single pair ; in the rest of the 



Ruminants the upper incisors 



are replaced by a callous pad, 



figs. 167, 168. The lower ca- 

 nines, fig. 168, c, are contiguous, 

 and, save in the Camel-tribe, 

 similar, to the six lower inci- 

 sors, ^ forming part of the same ^^^^^^^^, ^^^^^^ ^.^^^^^ 

 terminal series of eight teeth, 



between which and the molar series there is a wide interval. The 

 true molars have their grinding surface marked by two double 

 crescents, the convexity of which is turned inward in the upper, 

 ^g. 168, *, and outward in the under jaw, fig. 169, *. 



168 



ir.9 



Raiuinant dentition, Sheep. 



Many fossil Artiodactyles, with similar molars {Dicliodon, 

 Microtherium, Sic), appear to have differed from the existing 

 Ruminants chiefly by retaining structures which in them are 

 transitory and embryonic, as, e.g., upper incisors and canines, 

 first premolars, and separate metacarpal and metatarsal bones; 

 these are among the lost links that once connected more intimately 

 the Ruminants with the Hog and Hippopotamus. 



The third division of the GyrenccpJuila enjoy a higlier degree 



