readily be separated. Next to these, on each side, are situated the canine teeth or tusks, which are longer than the other teeth, and being pointed are specially adapted for tearing food. In the back of the jaws are placed another form of teeth, called molars, or grinders. Their use is to masticate the food; in animals that live on vegetables the molars are flattened at the top; but in the carnivora, their upper surfaces are furnished with sharp-pointed protuberances. The numbers, form, and disposition of the teeth constitute most important characteristics for separating the various orders of the mammalia from one another. The nose is a cartilaginous body, pierced with two holes, which are called nostrils. Through these the animal is affected by the sense of smell; in some animals this organ is prominent, whilst in others it is flat, compressed, turned upwards, or bent downwards. In beasts of prey the nose is frequently longer than the lips; and in some other animals, as the elephant, it is elongated into a movable trunk or proboscis, whilst in the rhinoceros it is armed with a horn. The eyes of quadrupeds are generally defended by movable lids, on the outer margins of which are fringes of hair called eyelashes. The opening of the pupil is in general circular; but in some species, as in those of the cat and hare, it is contracted into a perpendicular line; in the horse, the ox, and a few others, it forms a transverse bar. The ears are openings, generally accompanied with a cartilage which defends and covers them, called the external ear. In aquatic animals the latter are wanting, sound being transmitted merely through orifices in the head, which have the name of auditory holes. The most defenceless animals are extremely delicate in the sense of hearing, as are also most beasts of prey. Most of the mammiferous animals walk on their toes, which at the extremities are usually divided into five digits. In some, however, the feet end in a single corneous substance, called a hoof. The toes of a few of the mammalia end in broad flat nails, and of most others in pointed claws. Those that are destined to pass a considerable portion of their lives in water have the toes connected by a membrane. Others again, as in the bat, have the digitations of the anterior feet greatly elongated, the intervening space being filled by a membrane, which extends round the hinder legs and tail, by means of which they are enabled to rise into the air. In man, the hand comprises fingers separate free and flexible; but apes and some other kinds of animals, have fingers both to the hands and feet. These, therefore, are the only animals that can hold moveable objects in a single hand. Others, such as rats and squirrels, have the fingers sufficiently small and flexible to enable them to pick up objects, but they are compelled to hold them in both hands. Others, again, have the toes shorter, and must rest on the hind-feet, as is the case with dogs and cats when they want to hold a substance firmly on the ground with their paws. There are still others that have their toes united and drawn under the skin
