ORDERS RUMINANTIA AND PACHYDERM ATA. 135 



known animals ; all of which agree in possessing the ruminat- 

 ing apparatus, as well as in having the hoof cleft (or rather 

 double) ; and nearly all in the following dental formula : 

 incisors -J, canines ^-j, molars, ^, the last being marked on the 

 surface with crescents, which are formed by ridges of enamel. 



X. PACHYDERMATA, or thick-skinned animals ; a group that 

 includes a great variety of dissimilar forms, which agree rather 

 in the absence of other characters, than in the possession of any 

 that are common to all. Thus the Elephant, Horse, and Pig, 

 would seem to possess very different types of structure, the 

 Elephant having the bones of its toes distinct, but included 

 together in a sort of horny skin, the Pig having four distinct 

 toes, with separate hoofs, and the Horse having all the bones 

 of the toes consolidated into a single row, which is terminated by 

 a single hoof. The characters afforded by the teeth are equally 

 various ; some having incisors, others none ; some having large 

 canines, others small ones, and others being destitute of them ; 

 and the number of molars also being subject to great variation. 

 Yet these very dissimilar forms are connected by intermediate 

 links, recent and fossil ( 28) ; and it appears as if we were to 

 unite with this order those whale-like animals, whose food is of 

 a vegetable character, ^-their whole conformation being very 

 different from that of the true Cetacea, and more closely resem- 

 bling that of certain aquatic Pachydermata. 



125. The foregoing arrangement of the orders of the vivipa- 

 rous Mammalia is more adapted to distinguish them from each 

 other, than to represent their relative positions in a natural 

 series. Thus, the Edentata and Rodentia are unquestionably 

 lower, in regard to their intelligence and their general conforma- 

 tion, than the Ruminantia and Pachydermata ; and the Roden- 

 tia are those, among the truly viviparous Mammals, which 

 approach the nearest to the non-placental group, in the low 

 development of their brain ; as well as in several points of their 

 general structure. It is impossible to represent their mutual 

 relations by any arrangement of them in a single line ; since 

 each group has connections, not only with those before and 

 behind it, but with others at a distance. Nevertheless it is 



