FIG. 70.

that with which it presses, and an impulse is accordingly thrown into it, sufficient to detach it, and project it to a greater or less distance. But while the process is of course very much facilitated by the fulcrum being firm and elastic-a fact well known to operadancers and vaulters by profession, who commonly use spring-boards to assist them in their bounds it cannot be effected by terrestrial animals from the water, nor even from soft, boggy ground, unless their bodies be very light, or their feet very broad, because the points by which they in general press upon their fulcrum, compared with the weight of their whole body, namely, the extremity of their legs, are so small as to be resisted only by the very narrow columns of this fulcrum, which therefore, instead of re-acting upon them, immediately give way to the pressure which they sustain. Such, however, is not the case with fishes, the broad flat part of the tail of which, or if the tail be tapering, at least the broad flat part of the body which leads to the tail, is brought directly to bear upon the water; so that a very considerable column of resistance, in proportion to

the whole bulk and weight of the animal, is called into reaction. Nor is it peculiar to fishes to

employ their tail in the process of leaping; some quadrupeds, as the kangaroos, using their tails, in conjuction with their very long hind legs, to assist their bounds. Thus they not only employ an additional limb, the sudden extension of which, after flexion, adds to their impulse; but, pressing with an additional joint upon the fulcrum, they thus di

FIG. 71.

THE KANGAROO.

minish any tendency which it may have to yield to the pressure which they impose upon it. Both in the kangaroo and the jerboa, or jumping rat, and also in the hare, rabbit, squirrel, and others, the muscles of the hind legs are also greatly developed, in order to give the force necessary to effect their extended leaps; while the

142

LEAPING OF INSECTS.

This is the case with the velvet springtail, which leaps, by jerking its tail downwards from under its body, in the same manner as the grasshopper, the froghopper, or the flea, by jerking down its legs; that is to say, by suddenly extending them, after they have been brought to a state of full flexion. Wonderful as may be the leaping of fishes, and much as the bounds recorded of these animals exceed those which man is capable of making, they fall very short of what we witness every day in insects the grasshoppers and fleas, for example, being capable, with ease, of springing some hundred times their own length. Looking at the comparative lightness of these animals, however, and the favourable nature of the fulcrum on which they rest in making their springs, it is by no means certain that they employ more muscular power in their vaultings than fishes; while, on the other hand, it is pretty clear that they do not in general exercise them with anything like so definite a purpose, or so much precision.

It would be improper to leave this subject without remarking, that while some invertebrate aquatic animals-for example, the cuttleare enabled to leap out of the water by the sudden extension, after flexion, not of their tails, but of their numerous arms or other processes from their bodies; others-for example, the oyster-effect the same action by sudddenly bringing together the valves of their shells, by a strong muscle situated near the hinge, by which means a portion of the previously-contained water is rapidly expelled, and made to bear downwards upon that in the immediate vicinity of the animal, which, reacting of course upon the sudden pressure, communicates an impulse which forces it above the surface. The feats of the oyster, however, in this way are very insignificant, and it is not easy to say for what purpose they are performed.

In conclusion, we would briefly remark, that so nicely and admirably are the organs of locomotion in quadrupeds adapted to each other, that an anatomist, from the inspection of any one bone of the very many which compose the skeleton-in man no less than two hundred and forty-six-is enabled to infer the general form and relations of all the rest, as well as of the ligaments which connect, and the muscles which move them. Nay, more:-so intimately

SENSES OF ANIMALS.

143

does the structure of this shell, as it were, of the body correspond with that of the internal parts, that from this one bone he may almost give a description of every organ of the animal-of its propensities and habits. Can this correspondence be the work of a blind chance? or does it imply a unity of design, an extent of benevolence, and a vastness of power, indicative of a ruling Providence the Architect alike of the star of the firmament, and of the mite which plays in the sunbeam-whose hand is traced equally in the immensities of magnitude and of minuteness the Almighty Father of the Universe, and of everything that astounds and delights us in its construction?

Senses of Animals.-The next function of which we have to speak is Sensation; and it will be convenient, in the first place, to devote a few pages to a short description of the senses in particular, and of the several organs by which, in different animals, the functions of smell, sight, hearing, taste, and touch, are respectively performed. We shall then pass to a general view of Sensation, Emotion, Instinct, and Thought; and conclude our subject with an account of Voice and Speech in Man, particularly as distinguished from the cries, song, and buzzing of inferior animals.

Smell.-In quite the lowest orders of animals the organ, if any, specifically appropriated to smell is in general very obscure, although some of them in which this is the case the cuttle, for exampledisplay this function very remarkably. It is, perhaps, in most of them, merely a modification of touch, and performed equally by every part of the surface of the body. In the snail the seat of smell has been commonly considered to be the short feelers; but apparently without any good reason.

144

ACUTE SMELL IN FISHES AND REPTILES.

Insects in general smell very acutely; and in them the seat of this function has been at different times supposed to be their stigmata, or air-holes, their palpi, or commonly-reputed organs of taste, and their antennæ, or organs of touch in general. In the crustaceans, as the cray-fish and lobsters, which are among the few of this order that have a sufficiently obvious olfactory nerve, it is manifestly their smaller antennæ, at the root of which the nasal cavities are situated. In these animals, however, as well as in all aquatic animals, smell is rather a modification of taste than a distinct function, the vehicle of the impression being not air, but water. Such is also the case in fishes; in them the nasal cavities are situated, in general, on the sides of the snout, and are lined by a plaited membrane, sometimes not unlike the teeth of a comb, for the distribution of the proper nerve. The distance at which some fishes scent their prey is immense; and they are so acutely sensible of odorous bodies, that the very perfection of the function is often fatal to them. Some kinds of fish are so strongly allured by aromas, that by smearing the hand over with them, and immersing it in water, they will often flock towards the fingers, and may be easily taken. In all fishes, external openings, or nostrils, are very apparent. They generally constitute, it is true, only blind sacs; but their inner surface is of considerable extent, and upon their lining membrane, a pair of large nerves, analogous to the olfactory nerves of man, are distributed.

In reptiles, the nasal cavities have both an internal and external opening; the former being, in frogs, turtles, and serpents, in the palate; but in lizards, in some of which, as the crocodile, they are exceedingly long, in the pharynx, or muscular bag, at the back part of the mouth. Most reptiles, also, have a kind of a movable lid at the aperture of their nasal cavities, by which they close them when under water; this medium being apparently but ill-adapted in them to the function of smell. The proper vehicle of the impression in reptiles, as well as in birds and mammiferous animals, is air; and this the former draw through their nasal cavities during inspiration, effecting the operation by depressing their lingual bone, and thus enlarging the cavity of the mouth.

In birds, the nasal cavities are in general very large, their external aperture being in the upper mandible, and their internal in the pharynx. The olfactory nerve is very large in carnivorous birds, and its great size, together with the great length of the nasal cavities, serve to explain the immense distance at which some of them

-the vulture, for example — are known to scent carrion: it is said to be capable of doing this over the whole breadth of the Mediterranean!

The nasal cavities of mammiferous animals run in general horizontally; but in the cetaceous tribes their direction is perpendicular,

SENSE OF SMELL IN MAN.

145

the outer opening being at the top of their heads. Many animals of this kind as the porpoise, the whale, and the narwal-are generally regarded as destitute of smell, since they have no proper olfactory nerve; and certainly the hard and dry lining of their nostrils, like that of the proboscis of the elephant, is apparently very little adapted to this sensation. The projecting bones, by which the nasal cavities are, in most animals, more or less divided, are, in quadrupeds, extremely complicated, being, in most herbivorous species, both variously convoluted, and pierced sometimes like lattice-work, and, in most carnivorous, lamellated like the leaves of a book—a structure calculated, by increasing the surface, together with the great length in general of their snout, and the large size of their olfactory nerves, immensely to increase the acuteness of their smell. The "intellectual noses," as they are called by Lord Byron, of dogs are proverbial; and the distance from which many other quadrupeds, particularly such as are carnivorous, are sometimes attracted by the smell, is wonderful; white bears, for example, being found to come swimming to the Greenland ships, when a whale is cutting up, from all quarters, and far out of sight. Some quadrupeds, as the hog, the peccari, and the tapir-have a remarkable power of moving the extremity of their snout; but this is probably less for the purpose of smell than for that of burrowing, &c., their snout being to them, as its proboscis is to the elephant, a kind of hand.

In man, the sense of smelling is performed by means of a soft pulpy membrane, called the Schneiderian membrane, full of pores and small vessels, and lining the whole internal cavity of the nostrils; it is thickest upon the septum, or partition between the nostrils, but thinner in the sinuses, or cavities, hollowed out in the bones about the ncse. The nerves of the nose being almost naked, require a defence from the atmospheric air, which is continually drawn through the nostrils, and blown out again by respiration. Nature has, therefore, supplied this part with a thick, insipid mucus, very fluid in its first separation, but, by the air, condensed into a thick, dry, and more consistent crust. By this mucus the nerves are defended from drying and from pain. It is poured out from many small vessels, and deposited partly in numerous cylindrical pits, and partly in the round visible cryptæ or cells scattered all over the nostrils. The mucus is accumulated in the night-time; but in the day it either flows spontaneously, or may be more powerfully expelled by blowing the nose. By becoming dry and harsh, it irritates the very sensible nerves of the lining membrane, and is then removed by sneezing. The tears descend into the nose by a channel proper to the muscles, and moisten and dilute the mucus.

Sight. With respect to sight, it is equally doubtful, as with respect to smell, whether there be any specific organ for this func

t