318 ORDER PACIIYDERMATA. FAMILY ELEPUANTID^E. 



ant marks of resemblance, are here so various, as to require a 

 separate description for each family ; it can only be stated re- 

 garding the former, that they are chiefly formed for a vegetable 

 diet (though some species are omnivorous) ; whilst the extremi- 

 ties are constructed for support only, the clavicles being absent, 

 the bones of the fore-arm consolidated, so that the power of 

 rotation is altogether lost, and the toes included in a callous 

 skin, or in proper hoofs. The order may be subdivided into four 

 sections ; distinguished by the following characters : 1. The AN- 

 ISODACTYLA, in which there are several hoofs, forming a single 

 series round the bottom of the foot. 2. The ZYGODACTYLA, with 

 feet composed of two principal hoofs on which the animals walk, 

 separated as in the Ruminants by a cleft. 3. The SOLIDUNGULA, 

 in which the foot has but a single entire hoof. 4. The SIRENIA, 

 or CETACEA HERBIVORA of many authors, in which the posterior 

 extremities are wanting, and the anterior converted into paddles. 

 286. Of the Anisodactyla the first family is that of the 

 ELEPHANTID^E, or Elephant tribe ; and this at present consists of 

 but a single genus. The Elephants, of which only two species 

 the Asiatic and the African at present exist, are distinguished, 

 not only by their proboscis, but by the absence of front teeth in 

 the lower jaw, and by the possession of two enormous tusks, 

 which project downwards from the upper. These, like the long 

 incisors of the Rodentia, grow from a pulp which is continually 

 forming new ivory (ANIM. PHYSIOL., 177) ; and may be re- 

 garded as closely analogous to the teeth which are character- 

 istic of that order. The analogies between the largest and the 

 smallest of the terrestrial Mammalia do not, however, stop here. 

 They may be traced, also, in the structure of the molar teeth, 

 which are formed of alternating vertical plates of enamel, bone, 

 and crusta petrosa, arranged transversely to the jaw, as in the 

 Rodentia ( 216). These grinders succeed one another, from 

 behind forwards, each tooth, as it is worn, giving way to 

 another, which is pushed into its place; so that the Elephant 

 may have one, or two, of these large grinders on each side, 

 according to the period of their development. The molars are 

 said to be thus changed eight times ; the first tusks of the young 



