in tHe fœtal state, and are either shed before birth, or very shortly after. The last of the præmolars is called the flesh-tooth, or carnassier, or scissor-tooth, as the upper one acts on the lower one like a pair of scissors. It is greatly developed in the Cat tribe.
The true molars never exceed three in number on each side, above and below, and always end in two, three, or even four roots or fangs, sometimes considerably divergent from each other. They vary much in form and size, and are present in all Mammals except a few Ant-eaters, Whales, and the curious Duck-billed Platypus. They have four tubercles in most Monkeys, two sharp-pointed tubercles in Shrews and other Insectivorous animals; are three-pointed in some, and conical or flat in others. They are more or less numerous, according to the herbivorous or carnivorous nature of the animal, there being only one on each side in the Feline tribe.
In the Elephant there is only one molar on each side, above and below, and this forms a seeming exception to the non-renewal of these teeth, for as it gets worn away another is developed posteriorly, and gradually pushes the other out, so that there are sometimes two on one side at a time, but never more. The typical number of teeth is considered to be 44, and this number is never exceeded except in the fish-like Cetacea, and a few others of reptilian affinities. These teeth are arranged thus: Incisors 3—33—3 = 12; Canines 1—11—1 = 4; Præmolars 4—44—4 = 16; Molars 3—33—3 =12.
The mouth of Mammals is surrounded by fleshy lips, more or less protusile, and the cheeks in some form pouches for the reception of food taken hurriedly.
The extremities vary more than in Birds, in length, form, and structure, as noticed previously. The nails or claws are useful guides to assist in classifying Mammals. In some they are blunt and terminal, as in Monkeys; in others sharp, as in Shrews; much curved, powerful, sharp, and retractile in Cats ; long and strong, and well adapted for digging (fossorial), as in the Scaly Ant-eaters and Bears. In the herbivorous animals they are solid, as in the Horse;
