The Complete Works of Aristotle

by Barnes, Jonathan, Aristotle

  Next after the chest comes the region of the belly, which is left unenclosed by [689a1] the ribs for a reason which has already been given; namely that there may be no impediment to the swelling which necessarily occurs in the food as it gets heated, not to the expansion of the womb in pregnancy.

  At the extreme end of what is called the trunk are the parts concerned in the [5] evacuation of the solid and of the fluid residue. In all sanguineous animals with some few exceptions, and in all Vivipara without any exception at all, the same part which serves for the evacuation of the fluid residue is also made by nature to serve in sexual congress, and this alike in male and female. For the semen is a kind of fluid [10] and residual matter. (The proof of this will be given hereafter, but for the present let it be taken for granted.) The like holds good of the menstrual fluid in women, and of the part where they emit semen. This also, however, is a matter of which a more accurate account will be given hereafter. For the present let it be simply stated as a fact, that the menstrual fluids of the female are also residual matter. Both of them, moreover, being fluid, it is only natural that things which are alike should be [15] discharged into the same parts. Of the internal structure of these parts, and of the differences which exist between the parts concerned with semen and the parts concerned with conception, a clear account is given in the History of Animals and in the Anatomies. Moreover, I shall have to speak of them later in the work On [20] Generation. As regards, however, the external shape of these parts, it is plain enough that they are adapted to their operations, as indeed of necessity they must be. There are, however, differences in the male organ corresponding to differences in the body generally. For all animals are not of an equally sinewy nature. This organ, again, is the only one that, independently of any morbid change, admits of augmentation and of diminution of bulk. The former condition is of service in [25] copulation, while the other is required for the advantage of the body at large. For, were the organ constantly in the former condition, it would be an incumbrance. The organ therefore has been formed of such constituents as will admit of either state. For it is partly sinewy, partly cartilaginous, and thus is enabled either to contract or [30] to become extended, and is capable of admitting air.

  All female quadrupeds are retromingent, because the position of the parts which this implies is useful to them in the act of copulation. This is the case with only some few males, such as the lynx, the lion, the camel, and the hare. No quadruped with a solid hoof is retromingent. [689b1]

  The posterior portion of the body and the parts about the legs are peculiar in man as compared with quadrupeds. Nearly all these latter have a tail, and this whether they are viviparous or oviparous. For, even if the tail be of no great size, yet they have a kind of stump as at any rate a small representative of it. But man is [5] tail-less. He has, however, buttocks, which exist in none of the quadrupeds. His legs also are fleshy (as too are his thighs and calves); while the legs in all other animals that have any, whether viviparous or not, are fleshless, being made of sinew and bone and spinous substance. For all these differences there is, so to say, one common [10] explanation, and this is that of all animals man alone stands erect. It was to facilitate the maintenance of this position that nature made his upper parts light, taking away some of their corporeal substance, and using it to increase the weight of the parts below, so that the buttocks, the thighs, and the calves of the legs were all [15] made fleshy. The character which she thus gave to the buttocks renders them at the same time useful in resting the body. For standing causes no fatigue to quadrupeds, and even the long continuance of this posture produces in them no weariness; for they are supported the whole time by four props, which is much as though they were lying down. But to man it is no easy task to remain for any length of time on his feet, [20] his body demanding rest in a sitting position. This, then, is the reason why man has buttocks and fleshy legs; and the presence of these fleshy parts explains why he has no tail. For the nutriment which would otherwise go to the tail is used up in the production of these parts, while at the same time the existence of buttocks does away with the necessity of a tail. But in quadrupeds and other animals the reverse [25] obtains. For they are of dwarf-like form, so that all the pressure of their weight and corporeal substance is on their upper part, and is withdrawn from the parts below. On this account they are without buttocks and have hard legs. In order, however, to cover and protect that part which serves for the evacuation of excrement, nature has [30] given them a tail of some kind or other, subtracting for the purpose some of the nutriment which would otherwise go to the legs. Intermediate in shape between man and quadrupeds is the ape, belonging therefore to neither or to both, and having on this account neither tail nor buttocks; no tail in its character of biped, no [690a1] buttocks in its character of quadruped. There is a great diversity of so-called tails; and this organ like others is sometimes used by nature for by-purposes, being made to serve not only as a covering and protection to the fundament, but also for other uses and advantages of its possessor.

  [5] There are differences in the feet of quadrupeds. For in some of these animals there is a solid hoof, and in others a hoof cloven into two, and again in others a foot divided into many parts.

  The hoof is solid when the body is large and the earthy matter present in great abundance; in which case the earth, instead of forming teeth and horns, is separated [10] in the character of a nail, and being very abundant forms one continuous nail, that is a hoof, in place of several. This explains why these animals, as a rule, have no huckle-bones; a second reason being that the presence of such a bone in the joint of the hind leg somewhat impedes its free motion. For extension and flexion can be made more rapidly in parts that have but one angle than in parts that have several. But the presence of a huckle-bone, as a connecting bolt is the introduction as it were [15] of a new limb between the two. Such an addition adds to the weight of the foot, but renders the act of progression more secure. Thus it is that in such animals as have a huckle-bone, it is only in the posterior and not in the anterior limbs that this bone is found. For the anterior limbs, moving as they do in advance of the others, require to be light and capable of ready flexion, whereas firmness and extensibility are what [20] are wanted in the hind limbs. Moreover, a huckle-bone adds weight to the blow of a limb, and so renders it a suitable weapon of defence; and these animals all use their hind legs to protect themselves, kicking out against anything which annoys them. In the cloven-hoofed quadrupeds the lighter character of the hind legs admits of there being a huckle-bone; and the presence of the huckle-bone prevents them from having a solid hoof, the bony substance remaining in the joint, and therefore being deficient in the foot. As to the polydactylous quadrupeds, none of them have [25] huckle-bones. For if they had they would not be polydactylous, but the divisions of the foot would only extend to that amount of its breadth which was covered by the huckle-bone. Thus it is that most of the animals that have huckle-bones are cloven-hoofed.

  Of all animals man has the largest foot in proportion to the size of the body. This is only what might be expected. For seeing that he is the only animal that [30] stands erect, the two feet which are going to bear all the weight of the body must be both long and broad. Equally intelligible is it that the proportion between the size of the fingers and that of the whole hand should be inverted in the case of the toes and feet. For the function of the hands is to take hold of objects and retain them by [690b1] pressure; so that the fingers require to be long. For it is by its flexed portion that the hand grasps an object. But the function of the feet is to enable us to stand securely, and for this the undivided part of the foot requires to be of larger size than the toes. And it is better for the extremity to be divided than to be undivided. For in an undivided foot disease of any one part would extend to the whole organ; whereas, if [5] the foot be divided into separate digits, there is not an equal liability to such an occurrence. The digits, again, by being short would be less liable to injury. For these reasons the feet in
man are many-toed, while the separate digits are of no great length. The toes, finally, are furnished with nails for the same reason as are the fingers, namely because the tips are weak and therefore require special protection. [10]

  11 · We have now done with practically all the sanguineous animals that live on land and bring forth their young alive. Of the oviparous Sanguinea, some have four feet, while others have none. The latter form a single genus, namely the serpents; and why these are footless has been already explained in the remarks On [15] the Progression of Animals. But in other respects serpents resemble the oviparous quadrupeds in their conformation.

  In all these animals there is a head with its component parts; its presence being determined by the same causes as obtain in the case of other sanguineous animals; and in all, with the single exception of the river crocodile, there is a tongue inside the [20] mouth. In this one exception there would seem to be no actual tongue, but merely a space left vacant for it. The reason is that a crocodile is in a way a land-animal and a water-animal combined. In its character of land-animal it has a space for a tongue; but in its character of water-animal it is without the tongue itself. For in some fishes, as has already been mentioned, there is no appearance whatsoever of a [25] tongue, unless the mouth be stretched open very widely indeed; while in others it is indistinctly separated from the rest of the mouth. The reason for this is that a tongue would be of but little service to such animals, seeing that they are unable to chew their food or to taste it beforehand, the pleasurable sensations they derive from it occurring during swallowing. For it is in their passage down the gullet that solid edibles cause enjoyment, while it is by the tongue that the savour of fluids is [30] perceived. Thus it is during swallowing that the oiliness, the heat, and other such qualities of food are recognized. Now the Vivipara too have this power of perception (and in fact the satisfaction from most solid edibles and dainties is derived almost entirely from the dilatation of the oesophagus during swallowing—that is why the [691a1] same animals are not intemperate both with regard to tasty drinks and with regard to dainty foods); but while other animals have in addition the sensation of taste, [5] tongueless animals lack it and have the other sensation only.

  In some oviparous quadrupeds, namely in lizards, the tongue is bifid, as also it is in serpents, and its terminal divisions are of hair-like fineness, as has already been described. (Seals also have a forked tongue.) This is why all these animals are fond of dainty food. The teeth in the four-footed Ovipara are of the saw-like kind, like the [10] teeth of fishes. The organs of all the senses are present and resemble those of other animals. Thus there are nostrils for smell, eyes for vision, and ears for hearing. The latter organs, however, do not project from the sides of the head, but consist simply [15] of the duct, as also is the case in birds. This is due in both cases to the hardness of the integument; birds having their bodies covered with feathers, and these oviparous quadrupeds with horny plates. These plates are equivalent to scales, but of a harder character. This is manifest in tortoises and river crocodiles, and also in the large serpents. For here the plates become stronger than the bones, being of the same substance as these.

  [20] These animals have no upper eyelid, but close the eye with the lower lid. In this they resemble birds, and the reason is the same as was assigned in their case. Among birds there are some that also blink by means of a membrane which comes from the corner of the eye. But none of the oviparous quadrupeds blink; for their [25] eyes are harder than those of birds. The reason for this is that keen vision is of very considerable service to birds, flying as they do in the air, whereas it would be of comparatively small use to the oviparous quadrupeds, seeing that they all live in holes.

  Of the two separate portions which constitute the head, namely the upper part and the lower jaw, the latter in man and in the viviparous quadrupeds moves not [30] only upwards and downwards, but also from side to side; while in fishes and birds and oviparous quadrupeds, the only movement is up and down. The reason is that [691b1] this latter movement is the one required in biting and dividing food, while the lateral movement serves to reduce substances to a pulp. To such animals, therefore, as have molars this lateral motion is of service; but to those animals that have none it would be quite useless, and they are therefore invariably without it. For nature never [5] makes anything that is superfluous. While in all other animals it is the lower jaw that is movable, in the river crocodile it is exceptionally the upper. This is because the feet in this creature are so excessively small as to be useless for seizing and holding prey; on which account nature has given it a mouth that can serve for these [10] purposes in their stead. For that direction of motion which will give the greater force to a blow will be the more serviceable one in holding or in seizing prey; and a blow from above is always more forcible than one from below. Seeing, then, that both the prehension and the mastication of food are offices of the mouth, and that [15] the former of these two is the more essential in an animal that has neither hands nor suitably formed feet, these crocodiles will derive greater benefit from a motion of the upper jaw than from a motion of the lower jaw. The same considerations explain why crabs also move the upper division of each claw and not the lower. For their claws are substitutes for hands, and so require to be suitable for the prehension of [20] food, and not for its division; for such division and biting is the office of teeth. In crabs, then, and in such other animals as are able to seize their food in a leisurely manner, inasmuch as their mouth is not called on to perform its office while they are still in the water, the two functions are assigned to different parts, prehension to the [25] hands or feet, biting and division of food to the mouth. But in crocodiles the mouth has been so framed by nature as to serve both purposes, the jaws being made to move in the manner just described.

  Another part present in all these animals is a neck, this being the consequence of their having a lung. For the windpipe by which the air is admitted to the lung is of some length. Since the portion between the head and the shoulders is called the neck, a serpent can scarcely be said with the same right as the rest of these animals to have a neck, but only to have something analogous to that part of the body—if, [30] indeed, the neck must be determined by the limits just stated. It is a peculiarity of serpents, as compared with other animals allied to them, that they are able to turn [692a1] their head backwards without stirring the rest of the body. The reason of this is that a serpent, like an insect, has a body that admits of being curled up, its vertebrae being cartilaginous and easily bent. The faculty in question belongs then to serpents as a necessary consequence of this cause; but it is for the sake of their good too—for [5] it enables them to guard against attacks from behind. For their body, owing to its length and the absence of feet, is ill-suited for turning round and protecting the hinder parts; and merely to lift the head, without the power of turning it round, would be of no use whatsoever.

  The animals with which we are dealing have, moreover, a part which corresponds to the chest; but neither here nor elsewhere in their body have they any [10] breasts, as neither has any bird or fish. This is a consequence of their having no milk; for a breast is a receptacle for milk and, as it were, a vessel to contain it. This absence of milk is not peculiar to these animals, but is common to all such as are not internally viviparous. For all such produce eggs, and the nutriment which in Vivipara has the character of milk is in them engendered in the egg. Of all this, however, a clearer account will be given in the treatise On Generation. As to the [15] mode in which the legs bend, a general account, in which all animals are considered, has already been given in the work on Progression. These animals also have a tail, larger in some of them, smaller in others, and the reason for this has been stated in general terms in an earlier passage.

  Of all oviparous animals that live on land there is none so lean as the [20] chamaeleon. For there is none that has so little blood. The explanation of this is to be found in the psychical temperament of the creature. For it is of a timid natur
e—hence its many changes of appearance. But fear is a refrigeration, and results from deficiency of natural heat and scantiness of blood.

  We have now done with such sanguineous animals as are quadrupeds and also [692b1] such as are footless, and have stated with sufficient completeness what external parts they possess, and for what reasons they have them.

  12 · The differences of birds compared one with another are differences of magnitude, and of the greater or smaller development of parts. Thus some have long [5] legs, others short legs; some have a broad tongue, others a narrow tongue; and so on with the other parts. There are few of their parts that differ, taking birds by themselves. But when birds are compared with other animals the parts present differences of form also.

  Birds, then, are feathered, and this is a character common to them all and [10] peculiar to them. For the parts of animals are covered in some cases with hair, in others with scales, in others with scaly plates; but birds have feathers. Their feathers, too, are split and distinct in kind from the undivided feathers of insects; for the bird’s feather is divided, these are not; the bird’s feather has a shaft, these have none.

  [15] A second strange peculiarity which distinguishes birds from all other animals is their beak. For as in elephants the nostril serves in place of hands, and as in some insects the tongue serves in place of mouth, so in birds there is a beak, which, being bony, serves in place of teeth and lips. Their organs of sense have already been considered.

  [20] All birds have a neck naturally extending from the body; and the purpose of this neck is the same as in such other animals as have one. This neck in some birds is long, in others short; its length, as a general rule, being pretty nearly determined by that of the legs. For long-legged birds have a long neck, short-legged birds a short one, to which rule, however, the web-footed birds form an exception. For to a bird [693a1] perched up on long legs a short neck would be of no use whatsoever in collecting food from the ground; and equally useless would be a long neck, if the legs were short. Such birds, again, as are carnivorous would find length in this part interfered [5] greatly with their habits of life. For a long neck is weak, and it is on their superior strength that carnivorous birds depend for their subsistence. No bird, therefore, that has talons ever has an elongated neck. In web-footed birds, however, and in those other birds belonging to the same class, whose toes though actually separate are shaped like a snub nose, the neck is elongated, so as to be suitable for collecting [10] food from the water; while the legs are short, so as to serve in swimming.