[Contents]CHAPTER IIITHE DIFFERENT SHAPES OF TEETH“Man has thirty-two teeth, sixteen to each jaw,” Uncle Paul continued.Emile already had his finger in his mouth, passing it from one tooth to another, to count them. His uncle paused until he had finished the count.“But I have only twenty, all told,” declared the boy; “twenty, and not thirty-two.”“The other twelve will come some day, my boy; at present you have the right number of teeth for a child of your age. They do not all come at one time, but one after another. We begin with twenty, and no more. They are called milk teeth, or first teeth. When we are about seven years old they begin to fall out and are replaced by others stronger and set in more firmly. In addition to this second score of teeth there appear later twelve others, bringing the total number up to thirty-two. Those farthest back, in the inmost cavity of the mouth, come late, when we are eighteen or twenty years old, or even older, for which reason they are called wisdom teeth to signify that they appear at an age when the reason is well developed. These thirty-two last teeth constitute the second cutting. I call them last because they are never replaced by any others; if[14]we lose them, that is the end of our teeth; no more will come.”“I have two now that are loose,” said Emile.Human TeethHuman TeethI, incisors;C, canine tooth;m, small molars;M, large molars;a, cross-section showing,e, enamel;c, cement;i, ivory;p, dental pulp.“They must come out soon to leave room for the new teeth that are to take their place. The others will get loose, too, and the twenty that you have now will be succeeded by twenty others, to which, sooner or later, will be added twelve more which come only once. These last occupy the back part of the jaws, three on each side, top and bottom. Thus the final number will be thirty-two.“These thirty-two teeth are divided into three classes according to their shape and the work they must do. The same names being repeated top and bottom and right and left, I show you merely the eight teeth of half a jaw. In every tooth there are two parts to be distinguished, the crown and the root. The root is the part that is embedded in the jaw-bone like a nail hammered into wood; the crown is the part that comes into view, and it may be likened to the head of a nail. The root holds the[15]tooth in place, fixes it firmly; the crown cuts, tears, and grinds the food.“In the two front teeth in each half-jaw the crown grows thinner toward the top. The edge is straight and sharp, fitted for cutting food, dividing it into small mouthfuls. Therefore these teeth are called incisors, from the Latinincidere, meaning to cut. Their root is a simple pivot. The next tooth is called canine. Its root is a little longer than those of the preceding teeth, and its crown is slightly pointed. The dog, the cat, the wolf, and carnivorous animals in general have this tooth shaped like a powerful fang, which serves to catch and hold prey, but above all acts as a weapon in attack and defense. It is the canine teeth that you see crossing one another, long and pointed, two on each side, when you raise the upper lip of a cat or a dog. Because of these remarkable fangs of carnivorous animals, especially the dog, which in Latin iscanis, the name canine has been given to the teeth that in man are like them, if not in form and use, at least in the position they occupy.“The next five teeth are the most useful of all. They are called molars, from the Latinmola, a millstone, because they play the part of millstones in grinding the food. For this purpose their crowns are blunt and broad and slightly irregular, not flat like the horse’s molars or with sharp cutting edges like the wolf’s, because man’s food is not composed exclusively of either vegetables or flesh, but of both at the same time. For food as varied as man’s there[16]is need of molars fit for all sorts of service: they must grind like those of the herbivorous animals and cut like those of the carnivorous; in short, they must be like those of both. And, indeed, their wide crowns are suited to vegetable food, and their rather sharp irregularities are adapted to animal food.“The first two are called little molars or, in more learned language, bicuspids, because they have each two cusps or points. They are the least strong of the five and have only one root each. The two little molars, the canine tooth, and the two incisors (of each half-jaw) are the only teeth that are renewed. Multiply them by four and you will have the twenty teeth of the first cutting, teeth that begin to fall out toward the age of seven and are gradually replaced by others. That is the state of Emile’s teeth at present, there being but twenty of them.“The other three teeth, in each half-jaw, come only once. They are the large molars, of which the very end one is also called the wisdom tooth. As in the act of mastication the large molars have to bear strong pressure, the root is composed of several pivots or prongs reaching down each into a special cavity or socket. This makes them strong and firm, so that they can stand pressure both downward and sideways.“To sum up, the grown man has thirty-two teeth in all, sixteen to each jaw; namely, four incisors, two canines, and ten molars. These last are divided into four bicuspids or little molars and six large molars; the milk teeth do not include these last six.”[17]Here Jules had a question to ask. “Ivory and enamel,” said he, “those two substances of different degrees of hardness that you told us were arranged in such a wonderful way in horses’ and wolves’ teeth—are they in our teeth, too?”“Yes, they are there. Ivory forms the entire root, which must serve as a firm support, and it also fills the crown, while enamel merely covers the outside as a hard protecting layer.”“I am going to get the cat and look at her teeth,” said Emile. “Has she twenty, like me, or has she thirty-two?”Jaws and Teeth of a WolfJaws and Teeth of a Wolfi, incisors;c, canine teeth;m, small molars;r, large molars;s, salivary glands.“Neither twenty nor thirty-two, but thirty when full-grown. Dogs and wolves have forty-two; horses and donkeys forty-four. In fact, the number varies with different animals as much as the shape. Perhaps a few words on this subject will not be out of place.“First, here is the picture of a wolf’s mouth. If one did not already know, one could easily guess the animal’s diet by merely looking at its teeth. Those deeply indented molars, those strong, curved canines—surely they call for wild prey and show great strength. The whole set indicates clearly enough a[18]carnivorous appetite. Atiare the incisors, six in number. They are small and of slight use, for the animal does not cut its prey into little mouthfuls, but swallows it gluttonously in great strips. Atcare the canines, veritable daggers which the bandit plunges into the sheep’s neck. The little molars are atm. The large molars come next. The first, markedr, is the strongest, and it is with this that the wolf and the dog crack the hardest bones. Finally, the picture shows the salivary glands; that is, the organs that prepare the saliva and let it ooze into the mouth through the canalsas the animal eats. Without dwelling on this point, which would take me too far from my subject, I will merely say that saliva serves to soak the food and make a soft mouthful that can be easily swallowed, and it also plays an important part in the stomach in reducing to a fluid pap the food taken in; that is to say, it helps to digest the food.Jaws and Teeth of a CatJaws and Teeth of a Cat“Let us pass on to the cat, another typical flesh-eater. Six small incisors are ranged in the front of the jaw like a row of elegant but useless pearls. They are ornamental rather than useful to the animal. A mouse-hunter needs very long and pointed canines for piercing the prey seized by the claws. In this respect the cat is armed in a very formidable manner. What do you think of it, Louis?”[19]“I think,” he replied, “a rat must be very uncomfortable between those curved canines the picture shows us.”“One day,” said Emile, “when I was pulling the cat’s mustache, she gave me a bite that felt like the sharp prick of a needle. It was done so quickly I had no time to draw my hand back.”“The cat brought her canines into play and wounded you with one of them as quickly as a steel point could have done.“Now look at the molars. There are four above, the last one very small, and three below. Their cusps or points are still sharper than the wolf’s; so, too, the cat’s appetite—like that of its kindred, the tiger, the panther, the jaguar, and others—demands more flesh than that of the wolf and animals like it, such as the fox, the jackal, and especially the dog. Have you ever noticed how disdainful the cat is when you throw her only a piece of bread? Scarcely has she smelt it when she makes a movement of superb scorn, tail in the air, back raised, and looks at you as if to say: ‘Are you making fun of me? I want something else.’ Or, if very hungry, she reluctantly bites the bread, chews it awkwardly, and swallows it with distaste. The dog, on the contrary, our good Azor for example, catches the bread joyfully in his mouth without letting it touch the ground, and if he finds any fault with the piece it is for being too small. You call the cat a glutton. I take her part and maintain that it is not the vice of gluttony she shows, but that her teeth[20]must have meat. What could you expect her pointed canines and keen-edged molars to do with a crust of bread? They demand, above all, a prey that bleeds, a quivering bit of flesh.Jaws and Teeth of a HorseJaws and Teeth of a Horse“What a difference between the teeth of the hunter and those of the peaceful chewer of grass! Let us examine this picture of a horse’s head. Here the incisors, six in number, are powerful; they seize the forage and cut it, a mouthful at a time. The canines, of no use here, show only as little knobs on the jaw-bone. Next beyond comes a long vacant space called the bar; that is where the bit is held in the horse’s mouth. Back of the bar you see the real grinding mechanism, composed of twelve pairs of strong molars with square, flat crowns furnished with slightly projecting folds whose usefulness I have already pointed out to you. If I am not much mistaken, here we have a mill capable of grinding tough straw and fibrous hay.“Finally, here is a rabbit’s head. Each jaw is furnished with two enormous incisors set deep into the[21]bone, bent backward above, and ending each in a sharp-edged crown. What are such incisors as those made for?”“I know,” Jules quickly replied. “The rabbit is always nibbling. For want of better food it will gnaw the bark of a tree and even the wood. It uses its incisors to cut its food very fine, to gnaw it.”Jaws and Teeth of a RodentJaws and Teeth of a Rodenta, hamster’s jaws and teeth;b, upper incisor of a rabbit.“To gnaw it—that is the right word; hence we give the name of rodents or gnawers to the various animals having incisors of that kind. Such are the squirrel, the hare, the rabbit, the rat, and the mouse, those poor creatures which must gnaw the toughest vegetable substances and fill their bellies with wood, paper, rags even, when there is nothing better for supplying the mill that is kept always going. But it is not merely to satisfy their hunger that these animals are almost incessantly gnawing; there is another reason for their doing it. Their incisors grow all their lives and tend to lengthen indefinitely; consequently, the animal must wear them away by continual friction, as otherwise their crowns would at last so far overlap that they could not be made[22]to meet. Then the poor beast would be unable to seize its food and would perish. In order to be able to eat when hungry, the rat and the rabbit must eat when not hungry, so as to sharpen their incisors and keep them the right length. It is true that they often turn their attention to very poor fodder. A splinter of wood, a straw, a mere nothing suffices to maintain the play of their indefatigable incisors. Remember, children, the expressive termrodents(which meansgnawers), applied to a whole class of animals akin to the rabbit and the rat; remember their curious incisors, for we shall have occasion to speak of them again hereafter. For the present let us finish our examination of the rabbit’s teeth.“The canines are lacking; in their place the jaw shows a bar or, in other words, a large open space. At the extreme back of the mouth are the molars, few in number but strong, with flat crowns and several folds of enamel. In fact, they make an excellent grinding machine.“In giving you these details concerning the different shapes of teeth in different species of animals, I wished particularly to point out the following truth: Each species eats a particular kind of food for which the teeth are especially formed, so that one might say of any animal, ‘Show me its teeth and I will tell you what it eats.’ In many instances where we cannot examine the teeth we do not know what such and such a creature feeds on, and in our hasty judgment we mistake a friend for an enemy, a helper for a destroyer. If the animal[23]is ugly we condemn it on the spot and hate it, accusing it of any number of misdeeds. We declare war against it, and never suspect, in our foolishness, that it is a war at our own expense. But there is a very simple precaution by which we can avoid these regrettable mistakes: let us yield to no prejudice, however wide-spread, and before condemning an animal as harmful let us find out what sort of teeth it has. They will tell us the animal’s way of living, as you shall soon see for yourselves.”[24]
[Contents]CHAPTER IIITHE DIFFERENT SHAPES OF TEETH“Man has thirty-two teeth, sixteen to each jaw,” Uncle Paul continued.Emile already had his finger in his mouth, passing it from one tooth to another, to count them. His uncle paused until he had finished the count.“But I have only twenty, all told,” declared the boy; “twenty, and not thirty-two.”“The other twelve will come some day, my boy; at present you have the right number of teeth for a child of your age. They do not all come at one time, but one after another. We begin with twenty, and no more. They are called milk teeth, or first teeth. When we are about seven years old they begin to fall out and are replaced by others stronger and set in more firmly. In addition to this second score of teeth there appear later twelve others, bringing the total number up to thirty-two. Those farthest back, in the inmost cavity of the mouth, come late, when we are eighteen or twenty years old, or even older, for which reason they are called wisdom teeth to signify that they appear at an age when the reason is well developed. These thirty-two last teeth constitute the second cutting. I call them last because they are never replaced by any others; if[14]we lose them, that is the end of our teeth; no more will come.”“I have two now that are loose,” said Emile.Human TeethHuman TeethI, incisors;C, canine tooth;m, small molars;M, large molars;a, cross-section showing,e, enamel;c, cement;i, ivory;p, dental pulp.“They must come out soon to leave room for the new teeth that are to take their place. The others will get loose, too, and the twenty that you have now will be succeeded by twenty others, to which, sooner or later, will be added twelve more which come only once. These last occupy the back part of the jaws, three on each side, top and bottom. Thus the final number will be thirty-two.“These thirty-two teeth are divided into three classes according to their shape and the work they must do. The same names being repeated top and bottom and right and left, I show you merely the eight teeth of half a jaw. In every tooth there are two parts to be distinguished, the crown and the root. The root is the part that is embedded in the jaw-bone like a nail hammered into wood; the crown is the part that comes into view, and it may be likened to the head of a nail. The root holds the[15]tooth in place, fixes it firmly; the crown cuts, tears, and grinds the food.“In the two front teeth in each half-jaw the crown grows thinner toward the top. The edge is straight and sharp, fitted for cutting food, dividing it into small mouthfuls. Therefore these teeth are called incisors, from the Latinincidere, meaning to cut. Their root is a simple pivot. The next tooth is called canine. Its root is a little longer than those of the preceding teeth, and its crown is slightly pointed. The dog, the cat, the wolf, and carnivorous animals in general have this tooth shaped like a powerful fang, which serves to catch and hold prey, but above all acts as a weapon in attack and defense. It is the canine teeth that you see crossing one another, long and pointed, two on each side, when you raise the upper lip of a cat or a dog. Because of these remarkable fangs of carnivorous animals, especially the dog, which in Latin iscanis, the name canine has been given to the teeth that in man are like them, if not in form and use, at least in the position they occupy.“The next five teeth are the most useful of all. They are called molars, from the Latinmola, a millstone, because they play the part of millstones in grinding the food. For this purpose their crowns are blunt and broad and slightly irregular, not flat like the horse’s molars or with sharp cutting edges like the wolf’s, because man’s food is not composed exclusively of either vegetables or flesh, but of both at the same time. For food as varied as man’s there[16]is need of molars fit for all sorts of service: they must grind like those of the herbivorous animals and cut like those of the carnivorous; in short, they must be like those of both. And, indeed, their wide crowns are suited to vegetable food, and their rather sharp irregularities are adapted to animal food.“The first two are called little molars or, in more learned language, bicuspids, because they have each two cusps or points. They are the least strong of the five and have only one root each. The two little molars, the canine tooth, and the two incisors (of each half-jaw) are the only teeth that are renewed. Multiply them by four and you will have the twenty teeth of the first cutting, teeth that begin to fall out toward the age of seven and are gradually replaced by others. That is the state of Emile’s teeth at present, there being but twenty of them.“The other three teeth, in each half-jaw, come only once. They are the large molars, of which the very end one is also called the wisdom tooth. As in the act of mastication the large molars have to bear strong pressure, the root is composed of several pivots or prongs reaching down each into a special cavity or socket. This makes them strong and firm, so that they can stand pressure both downward and sideways.“To sum up, the grown man has thirty-two teeth in all, sixteen to each jaw; namely, four incisors, two canines, and ten molars. These last are divided into four bicuspids or little molars and six large molars; the milk teeth do not include these last six.”[17]Here Jules had a question to ask. “Ivory and enamel,” said he, “those two substances of different degrees of hardness that you told us were arranged in such a wonderful way in horses’ and wolves’ teeth—are they in our teeth, too?”“Yes, they are there. Ivory forms the entire root, which must serve as a firm support, and it also fills the crown, while enamel merely covers the outside as a hard protecting layer.”“I am going to get the cat and look at her teeth,” said Emile. “Has she twenty, like me, or has she thirty-two?”Jaws and Teeth of a WolfJaws and Teeth of a Wolfi, incisors;c, canine teeth;m, small molars;r, large molars;s, salivary glands.“Neither twenty nor thirty-two, but thirty when full-grown. Dogs and wolves have forty-two; horses and donkeys forty-four. In fact, the number varies with different animals as much as the shape. Perhaps a few words on this subject will not be out of place.“First, here is the picture of a wolf’s mouth. If one did not already know, one could easily guess the animal’s diet by merely looking at its teeth. Those deeply indented molars, those strong, curved canines—surely they call for wild prey and show great strength. The whole set indicates clearly enough a[18]carnivorous appetite. Atiare the incisors, six in number. They are small and of slight use, for the animal does not cut its prey into little mouthfuls, but swallows it gluttonously in great strips. Atcare the canines, veritable daggers which the bandit plunges into the sheep’s neck. The little molars are atm. The large molars come next. The first, markedr, is the strongest, and it is with this that the wolf and the dog crack the hardest bones. Finally, the picture shows the salivary glands; that is, the organs that prepare the saliva and let it ooze into the mouth through the canalsas the animal eats. Without dwelling on this point, which would take me too far from my subject, I will merely say that saliva serves to soak the food and make a soft mouthful that can be easily swallowed, and it also plays an important part in the stomach in reducing to a fluid pap the food taken in; that is to say, it helps to digest the food.Jaws and Teeth of a CatJaws and Teeth of a Cat“Let us pass on to the cat, another typical flesh-eater. Six small incisors are ranged in the front of the jaw like a row of elegant but useless pearls. They are ornamental rather than useful to the animal. A mouse-hunter needs very long and pointed canines for piercing the prey seized by the claws. In this respect the cat is armed in a very formidable manner. What do you think of it, Louis?”[19]“I think,” he replied, “a rat must be very uncomfortable between those curved canines the picture shows us.”“One day,” said Emile, “when I was pulling the cat’s mustache, she gave me a bite that felt like the sharp prick of a needle. It was done so quickly I had no time to draw my hand back.”“The cat brought her canines into play and wounded you with one of them as quickly as a steel point could have done.“Now look at the molars. There are four above, the last one very small, and three below. Their cusps or points are still sharper than the wolf’s; so, too, the cat’s appetite—like that of its kindred, the tiger, the panther, the jaguar, and others—demands more flesh than that of the wolf and animals like it, such as the fox, the jackal, and especially the dog. Have you ever noticed how disdainful the cat is when you throw her only a piece of bread? Scarcely has she smelt it when she makes a movement of superb scorn, tail in the air, back raised, and looks at you as if to say: ‘Are you making fun of me? I want something else.’ Or, if very hungry, she reluctantly bites the bread, chews it awkwardly, and swallows it with distaste. The dog, on the contrary, our good Azor for example, catches the bread joyfully in his mouth without letting it touch the ground, and if he finds any fault with the piece it is for being too small. You call the cat a glutton. I take her part and maintain that it is not the vice of gluttony she shows, but that her teeth[20]must have meat. What could you expect her pointed canines and keen-edged molars to do with a crust of bread? They demand, above all, a prey that bleeds, a quivering bit of flesh.Jaws and Teeth of a HorseJaws and Teeth of a Horse“What a difference between the teeth of the hunter and those of the peaceful chewer of grass! Let us examine this picture of a horse’s head. Here the incisors, six in number, are powerful; they seize the forage and cut it, a mouthful at a time. The canines, of no use here, show only as little knobs on the jaw-bone. Next beyond comes a long vacant space called the bar; that is where the bit is held in the horse’s mouth. Back of the bar you see the real grinding mechanism, composed of twelve pairs of strong molars with square, flat crowns furnished with slightly projecting folds whose usefulness I have already pointed out to you. If I am not much mistaken, here we have a mill capable of grinding tough straw and fibrous hay.“Finally, here is a rabbit’s head. Each jaw is furnished with two enormous incisors set deep into the[21]bone, bent backward above, and ending each in a sharp-edged crown. What are such incisors as those made for?”“I know,” Jules quickly replied. “The rabbit is always nibbling. For want of better food it will gnaw the bark of a tree and even the wood. It uses its incisors to cut its food very fine, to gnaw it.”Jaws and Teeth of a RodentJaws and Teeth of a Rodenta, hamster’s jaws and teeth;b, upper incisor of a rabbit.“To gnaw it—that is the right word; hence we give the name of rodents or gnawers to the various animals having incisors of that kind. Such are the squirrel, the hare, the rabbit, the rat, and the mouse, those poor creatures which must gnaw the toughest vegetable substances and fill their bellies with wood, paper, rags even, when there is nothing better for supplying the mill that is kept always going. But it is not merely to satisfy their hunger that these animals are almost incessantly gnawing; there is another reason for their doing it. Their incisors grow all their lives and tend to lengthen indefinitely; consequently, the animal must wear them away by continual friction, as otherwise their crowns would at last so far overlap that they could not be made[22]to meet. Then the poor beast would be unable to seize its food and would perish. In order to be able to eat when hungry, the rat and the rabbit must eat when not hungry, so as to sharpen their incisors and keep them the right length. It is true that they often turn their attention to very poor fodder. A splinter of wood, a straw, a mere nothing suffices to maintain the play of their indefatigable incisors. Remember, children, the expressive termrodents(which meansgnawers), applied to a whole class of animals akin to the rabbit and the rat; remember their curious incisors, for we shall have occasion to speak of them again hereafter. For the present let us finish our examination of the rabbit’s teeth.“The canines are lacking; in their place the jaw shows a bar or, in other words, a large open space. At the extreme back of the mouth are the molars, few in number but strong, with flat crowns and several folds of enamel. In fact, they make an excellent grinding machine.“In giving you these details concerning the different shapes of teeth in different species of animals, I wished particularly to point out the following truth: Each species eats a particular kind of food for which the teeth are especially formed, so that one might say of any animal, ‘Show me its teeth and I will tell you what it eats.’ In many instances where we cannot examine the teeth we do not know what such and such a creature feeds on, and in our hasty judgment we mistake a friend for an enemy, a helper for a destroyer. If the animal[23]is ugly we condemn it on the spot and hate it, accusing it of any number of misdeeds. We declare war against it, and never suspect, in our foolishness, that it is a war at our own expense. But there is a very simple precaution by which we can avoid these regrettable mistakes: let us yield to no prejudice, however wide-spread, and before condemning an animal as harmful let us find out what sort of teeth it has. They will tell us the animal’s way of living, as you shall soon see for yourselves.”[24]
CHAPTER IIITHE DIFFERENT SHAPES OF TEETH
“Man has thirty-two teeth, sixteen to each jaw,” Uncle Paul continued.Emile already had his finger in his mouth, passing it from one tooth to another, to count them. His uncle paused until he had finished the count.“But I have only twenty, all told,” declared the boy; “twenty, and not thirty-two.”“The other twelve will come some day, my boy; at present you have the right number of teeth for a child of your age. They do not all come at one time, but one after another. We begin with twenty, and no more. They are called milk teeth, or first teeth. When we are about seven years old they begin to fall out and are replaced by others stronger and set in more firmly. In addition to this second score of teeth there appear later twelve others, bringing the total number up to thirty-two. Those farthest back, in the inmost cavity of the mouth, come late, when we are eighteen or twenty years old, or even older, for which reason they are called wisdom teeth to signify that they appear at an age when the reason is well developed. These thirty-two last teeth constitute the second cutting. I call them last because they are never replaced by any others; if[14]we lose them, that is the end of our teeth; no more will come.”“I have two now that are loose,” said Emile.Human TeethHuman TeethI, incisors;C, canine tooth;m, small molars;M, large molars;a, cross-section showing,e, enamel;c, cement;i, ivory;p, dental pulp.“They must come out soon to leave room for the new teeth that are to take their place. The others will get loose, too, and the twenty that you have now will be succeeded by twenty others, to which, sooner or later, will be added twelve more which come only once. These last occupy the back part of the jaws, three on each side, top and bottom. Thus the final number will be thirty-two.“These thirty-two teeth are divided into three classes according to their shape and the work they must do. The same names being repeated top and bottom and right and left, I show you merely the eight teeth of half a jaw. In every tooth there are two parts to be distinguished, the crown and the root. The root is the part that is embedded in the jaw-bone like a nail hammered into wood; the crown is the part that comes into view, and it may be likened to the head of a nail. The root holds the[15]tooth in place, fixes it firmly; the crown cuts, tears, and grinds the food.“In the two front teeth in each half-jaw the crown grows thinner toward the top. The edge is straight and sharp, fitted for cutting food, dividing it into small mouthfuls. Therefore these teeth are called incisors, from the Latinincidere, meaning to cut. Their root is a simple pivot. The next tooth is called canine. Its root is a little longer than those of the preceding teeth, and its crown is slightly pointed. The dog, the cat, the wolf, and carnivorous animals in general have this tooth shaped like a powerful fang, which serves to catch and hold prey, but above all acts as a weapon in attack and defense. It is the canine teeth that you see crossing one another, long and pointed, two on each side, when you raise the upper lip of a cat or a dog. Because of these remarkable fangs of carnivorous animals, especially the dog, which in Latin iscanis, the name canine has been given to the teeth that in man are like them, if not in form and use, at least in the position they occupy.“The next five teeth are the most useful of all. They are called molars, from the Latinmola, a millstone, because they play the part of millstones in grinding the food. For this purpose their crowns are blunt and broad and slightly irregular, not flat like the horse’s molars or with sharp cutting edges like the wolf’s, because man’s food is not composed exclusively of either vegetables or flesh, but of both at the same time. For food as varied as man’s there[16]is need of molars fit for all sorts of service: they must grind like those of the herbivorous animals and cut like those of the carnivorous; in short, they must be like those of both. And, indeed, their wide crowns are suited to vegetable food, and their rather sharp irregularities are adapted to animal food.“The first two are called little molars or, in more learned language, bicuspids, because they have each two cusps or points. They are the least strong of the five and have only one root each. The two little molars, the canine tooth, and the two incisors (of each half-jaw) are the only teeth that are renewed. Multiply them by four and you will have the twenty teeth of the first cutting, teeth that begin to fall out toward the age of seven and are gradually replaced by others. That is the state of Emile’s teeth at present, there being but twenty of them.“The other three teeth, in each half-jaw, come only once. They are the large molars, of which the very end one is also called the wisdom tooth. As in the act of mastication the large molars have to bear strong pressure, the root is composed of several pivots or prongs reaching down each into a special cavity or socket. This makes them strong and firm, so that they can stand pressure both downward and sideways.“To sum up, the grown man has thirty-two teeth in all, sixteen to each jaw; namely, four incisors, two canines, and ten molars. These last are divided into four bicuspids or little molars and six large molars; the milk teeth do not include these last six.”[17]Here Jules had a question to ask. “Ivory and enamel,” said he, “those two substances of different degrees of hardness that you told us were arranged in such a wonderful way in horses’ and wolves’ teeth—are they in our teeth, too?”“Yes, they are there. Ivory forms the entire root, which must serve as a firm support, and it also fills the crown, while enamel merely covers the outside as a hard protecting layer.”“I am going to get the cat and look at her teeth,” said Emile. “Has she twenty, like me, or has she thirty-two?”Jaws and Teeth of a WolfJaws and Teeth of a Wolfi, incisors;c, canine teeth;m, small molars;r, large molars;s, salivary glands.“Neither twenty nor thirty-two, but thirty when full-grown. Dogs and wolves have forty-two; horses and donkeys forty-four. In fact, the number varies with different animals as much as the shape. Perhaps a few words on this subject will not be out of place.“First, here is the picture of a wolf’s mouth. If one did not already know, one could easily guess the animal’s diet by merely looking at its teeth. Those deeply indented molars, those strong, curved canines—surely they call for wild prey and show great strength. The whole set indicates clearly enough a[18]carnivorous appetite. Atiare the incisors, six in number. They are small and of slight use, for the animal does not cut its prey into little mouthfuls, but swallows it gluttonously in great strips. Atcare the canines, veritable daggers which the bandit plunges into the sheep’s neck. The little molars are atm. The large molars come next. The first, markedr, is the strongest, and it is with this that the wolf and the dog crack the hardest bones. Finally, the picture shows the salivary glands; that is, the organs that prepare the saliva and let it ooze into the mouth through the canalsas the animal eats. Without dwelling on this point, which would take me too far from my subject, I will merely say that saliva serves to soak the food and make a soft mouthful that can be easily swallowed, and it also plays an important part in the stomach in reducing to a fluid pap the food taken in; that is to say, it helps to digest the food.Jaws and Teeth of a CatJaws and Teeth of a Cat“Let us pass on to the cat, another typical flesh-eater. Six small incisors are ranged in the front of the jaw like a row of elegant but useless pearls. They are ornamental rather than useful to the animal. A mouse-hunter needs very long and pointed canines for piercing the prey seized by the claws. In this respect the cat is armed in a very formidable manner. What do you think of it, Louis?”[19]“I think,” he replied, “a rat must be very uncomfortable between those curved canines the picture shows us.”“One day,” said Emile, “when I was pulling the cat’s mustache, she gave me a bite that felt like the sharp prick of a needle. It was done so quickly I had no time to draw my hand back.”“The cat brought her canines into play and wounded you with one of them as quickly as a steel point could have done.“Now look at the molars. There are four above, the last one very small, and three below. Their cusps or points are still sharper than the wolf’s; so, too, the cat’s appetite—like that of its kindred, the tiger, the panther, the jaguar, and others—demands more flesh than that of the wolf and animals like it, such as the fox, the jackal, and especially the dog. Have you ever noticed how disdainful the cat is when you throw her only a piece of bread? Scarcely has she smelt it when she makes a movement of superb scorn, tail in the air, back raised, and looks at you as if to say: ‘Are you making fun of me? I want something else.’ Or, if very hungry, she reluctantly bites the bread, chews it awkwardly, and swallows it with distaste. The dog, on the contrary, our good Azor for example, catches the bread joyfully in his mouth without letting it touch the ground, and if he finds any fault with the piece it is for being too small. You call the cat a glutton. I take her part and maintain that it is not the vice of gluttony she shows, but that her teeth[20]must have meat. What could you expect her pointed canines and keen-edged molars to do with a crust of bread? They demand, above all, a prey that bleeds, a quivering bit of flesh.Jaws and Teeth of a HorseJaws and Teeth of a Horse“What a difference between the teeth of the hunter and those of the peaceful chewer of grass! Let us examine this picture of a horse’s head. Here the incisors, six in number, are powerful; they seize the forage and cut it, a mouthful at a time. The canines, of no use here, show only as little knobs on the jaw-bone. Next beyond comes a long vacant space called the bar; that is where the bit is held in the horse’s mouth. Back of the bar you see the real grinding mechanism, composed of twelve pairs of strong molars with square, flat crowns furnished with slightly projecting folds whose usefulness I have already pointed out to you. If I am not much mistaken, here we have a mill capable of grinding tough straw and fibrous hay.“Finally, here is a rabbit’s head. Each jaw is furnished with two enormous incisors set deep into the[21]bone, bent backward above, and ending each in a sharp-edged crown. What are such incisors as those made for?”“I know,” Jules quickly replied. “The rabbit is always nibbling. For want of better food it will gnaw the bark of a tree and even the wood. It uses its incisors to cut its food very fine, to gnaw it.”Jaws and Teeth of a RodentJaws and Teeth of a Rodenta, hamster’s jaws and teeth;b, upper incisor of a rabbit.“To gnaw it—that is the right word; hence we give the name of rodents or gnawers to the various animals having incisors of that kind. Such are the squirrel, the hare, the rabbit, the rat, and the mouse, those poor creatures which must gnaw the toughest vegetable substances and fill their bellies with wood, paper, rags even, when there is nothing better for supplying the mill that is kept always going. But it is not merely to satisfy their hunger that these animals are almost incessantly gnawing; there is another reason for their doing it. Their incisors grow all their lives and tend to lengthen indefinitely; consequently, the animal must wear them away by continual friction, as otherwise their crowns would at last so far overlap that they could not be made[22]to meet. Then the poor beast would be unable to seize its food and would perish. In order to be able to eat when hungry, the rat and the rabbit must eat when not hungry, so as to sharpen their incisors and keep them the right length. It is true that they often turn their attention to very poor fodder. A splinter of wood, a straw, a mere nothing suffices to maintain the play of their indefatigable incisors. Remember, children, the expressive termrodents(which meansgnawers), applied to a whole class of animals akin to the rabbit and the rat; remember their curious incisors, for we shall have occasion to speak of them again hereafter. For the present let us finish our examination of the rabbit’s teeth.“The canines are lacking; in their place the jaw shows a bar or, in other words, a large open space. At the extreme back of the mouth are the molars, few in number but strong, with flat crowns and several folds of enamel. In fact, they make an excellent grinding machine.“In giving you these details concerning the different shapes of teeth in different species of animals, I wished particularly to point out the following truth: Each species eats a particular kind of food for which the teeth are especially formed, so that one might say of any animal, ‘Show me its teeth and I will tell you what it eats.’ In many instances where we cannot examine the teeth we do not know what such and such a creature feeds on, and in our hasty judgment we mistake a friend for an enemy, a helper for a destroyer. If the animal[23]is ugly we condemn it on the spot and hate it, accusing it of any number of misdeeds. We declare war against it, and never suspect, in our foolishness, that it is a war at our own expense. But there is a very simple precaution by which we can avoid these regrettable mistakes: let us yield to no prejudice, however wide-spread, and before condemning an animal as harmful let us find out what sort of teeth it has. They will tell us the animal’s way of living, as you shall soon see for yourselves.”[24]
“Man has thirty-two teeth, sixteen to each jaw,” Uncle Paul continued.
Emile already had his finger in his mouth, passing it from one tooth to another, to count them. His uncle paused until he had finished the count.
“But I have only twenty, all told,” declared the boy; “twenty, and not thirty-two.”
“The other twelve will come some day, my boy; at present you have the right number of teeth for a child of your age. They do not all come at one time, but one after another. We begin with twenty, and no more. They are called milk teeth, or first teeth. When we are about seven years old they begin to fall out and are replaced by others stronger and set in more firmly. In addition to this second score of teeth there appear later twelve others, bringing the total number up to thirty-two. Those farthest back, in the inmost cavity of the mouth, come late, when we are eighteen or twenty years old, or even older, for which reason they are called wisdom teeth to signify that they appear at an age when the reason is well developed. These thirty-two last teeth constitute the second cutting. I call them last because they are never replaced by any others; if[14]we lose them, that is the end of our teeth; no more will come.”
“I have two now that are loose,” said Emile.
Human TeethHuman TeethI, incisors;C, canine tooth;m, small molars;M, large molars;a, cross-section showing,e, enamel;c, cement;i, ivory;p, dental pulp.
Human Teeth
I, incisors;C, canine tooth;m, small molars;M, large molars;a, cross-section showing,e, enamel;c, cement;i, ivory;p, dental pulp.
“They must come out soon to leave room for the new teeth that are to take their place. The others will get loose, too, and the twenty that you have now will be succeeded by twenty others, to which, sooner or later, will be added twelve more which come only once. These last occupy the back part of the jaws, three on each side, top and bottom. Thus the final number will be thirty-two.
“These thirty-two teeth are divided into three classes according to their shape and the work they must do. The same names being repeated top and bottom and right and left, I show you merely the eight teeth of half a jaw. In every tooth there are two parts to be distinguished, the crown and the root. The root is the part that is embedded in the jaw-bone like a nail hammered into wood; the crown is the part that comes into view, and it may be likened to the head of a nail. The root holds the[15]tooth in place, fixes it firmly; the crown cuts, tears, and grinds the food.
“In the two front teeth in each half-jaw the crown grows thinner toward the top. The edge is straight and sharp, fitted for cutting food, dividing it into small mouthfuls. Therefore these teeth are called incisors, from the Latinincidere, meaning to cut. Their root is a simple pivot. The next tooth is called canine. Its root is a little longer than those of the preceding teeth, and its crown is slightly pointed. The dog, the cat, the wolf, and carnivorous animals in general have this tooth shaped like a powerful fang, which serves to catch and hold prey, but above all acts as a weapon in attack and defense. It is the canine teeth that you see crossing one another, long and pointed, two on each side, when you raise the upper lip of a cat or a dog. Because of these remarkable fangs of carnivorous animals, especially the dog, which in Latin iscanis, the name canine has been given to the teeth that in man are like them, if not in form and use, at least in the position they occupy.
“The next five teeth are the most useful of all. They are called molars, from the Latinmola, a millstone, because they play the part of millstones in grinding the food. For this purpose their crowns are blunt and broad and slightly irregular, not flat like the horse’s molars or with sharp cutting edges like the wolf’s, because man’s food is not composed exclusively of either vegetables or flesh, but of both at the same time. For food as varied as man’s there[16]is need of molars fit for all sorts of service: they must grind like those of the herbivorous animals and cut like those of the carnivorous; in short, they must be like those of both. And, indeed, their wide crowns are suited to vegetable food, and their rather sharp irregularities are adapted to animal food.
“The first two are called little molars or, in more learned language, bicuspids, because they have each two cusps or points. They are the least strong of the five and have only one root each. The two little molars, the canine tooth, and the two incisors (of each half-jaw) are the only teeth that are renewed. Multiply them by four and you will have the twenty teeth of the first cutting, teeth that begin to fall out toward the age of seven and are gradually replaced by others. That is the state of Emile’s teeth at present, there being but twenty of them.
“The other three teeth, in each half-jaw, come only once. They are the large molars, of which the very end one is also called the wisdom tooth. As in the act of mastication the large molars have to bear strong pressure, the root is composed of several pivots or prongs reaching down each into a special cavity or socket. This makes them strong and firm, so that they can stand pressure both downward and sideways.
“To sum up, the grown man has thirty-two teeth in all, sixteen to each jaw; namely, four incisors, two canines, and ten molars. These last are divided into four bicuspids or little molars and six large molars; the milk teeth do not include these last six.”[17]
Here Jules had a question to ask. “Ivory and enamel,” said he, “those two substances of different degrees of hardness that you told us were arranged in such a wonderful way in horses’ and wolves’ teeth—are they in our teeth, too?”
“Yes, they are there. Ivory forms the entire root, which must serve as a firm support, and it also fills the crown, while enamel merely covers the outside as a hard protecting layer.”
“I am going to get the cat and look at her teeth,” said Emile. “Has she twenty, like me, or has she thirty-two?”
Jaws and Teeth of a WolfJaws and Teeth of a Wolfi, incisors;c, canine teeth;m, small molars;r, large molars;s, salivary glands.
Jaws and Teeth of a Wolf
i, incisors;c, canine teeth;m, small molars;r, large molars;s, salivary glands.
“Neither twenty nor thirty-two, but thirty when full-grown. Dogs and wolves have forty-two; horses and donkeys forty-four. In fact, the number varies with different animals as much as the shape. Perhaps a few words on this subject will not be out of place.
“First, here is the picture of a wolf’s mouth. If one did not already know, one could easily guess the animal’s diet by merely looking at its teeth. Those deeply indented molars, those strong, curved canines—surely they call for wild prey and show great strength. The whole set indicates clearly enough a[18]carnivorous appetite. Atiare the incisors, six in number. They are small and of slight use, for the animal does not cut its prey into little mouthfuls, but swallows it gluttonously in great strips. Atcare the canines, veritable daggers which the bandit plunges into the sheep’s neck. The little molars are atm. The large molars come next. The first, markedr, is the strongest, and it is with this that the wolf and the dog crack the hardest bones. Finally, the picture shows the salivary glands; that is, the organs that prepare the saliva and let it ooze into the mouth through the canalsas the animal eats. Without dwelling on this point, which would take me too far from my subject, I will merely say that saliva serves to soak the food and make a soft mouthful that can be easily swallowed, and it also plays an important part in the stomach in reducing to a fluid pap the food taken in; that is to say, it helps to digest the food.
Jaws and Teeth of a CatJaws and Teeth of a Cat
Jaws and Teeth of a Cat
“Let us pass on to the cat, another typical flesh-eater. Six small incisors are ranged in the front of the jaw like a row of elegant but useless pearls. They are ornamental rather than useful to the animal. A mouse-hunter needs very long and pointed canines for piercing the prey seized by the claws. In this respect the cat is armed in a very formidable manner. What do you think of it, Louis?”[19]
“I think,” he replied, “a rat must be very uncomfortable between those curved canines the picture shows us.”
“One day,” said Emile, “when I was pulling the cat’s mustache, she gave me a bite that felt like the sharp prick of a needle. It was done so quickly I had no time to draw my hand back.”
“The cat brought her canines into play and wounded you with one of them as quickly as a steel point could have done.
“Now look at the molars. There are four above, the last one very small, and three below. Their cusps or points are still sharper than the wolf’s; so, too, the cat’s appetite—like that of its kindred, the tiger, the panther, the jaguar, and others—demands more flesh than that of the wolf and animals like it, such as the fox, the jackal, and especially the dog. Have you ever noticed how disdainful the cat is when you throw her only a piece of bread? Scarcely has she smelt it when she makes a movement of superb scorn, tail in the air, back raised, and looks at you as if to say: ‘Are you making fun of me? I want something else.’ Or, if very hungry, she reluctantly bites the bread, chews it awkwardly, and swallows it with distaste. The dog, on the contrary, our good Azor for example, catches the bread joyfully in his mouth without letting it touch the ground, and if he finds any fault with the piece it is for being too small. You call the cat a glutton. I take her part and maintain that it is not the vice of gluttony she shows, but that her teeth[20]must have meat. What could you expect her pointed canines and keen-edged molars to do with a crust of bread? They demand, above all, a prey that bleeds, a quivering bit of flesh.
Jaws and Teeth of a HorseJaws and Teeth of a Horse
Jaws and Teeth of a Horse
“What a difference between the teeth of the hunter and those of the peaceful chewer of grass! Let us examine this picture of a horse’s head. Here the incisors, six in number, are powerful; they seize the forage and cut it, a mouthful at a time. The canines, of no use here, show only as little knobs on the jaw-bone. Next beyond comes a long vacant space called the bar; that is where the bit is held in the horse’s mouth. Back of the bar you see the real grinding mechanism, composed of twelve pairs of strong molars with square, flat crowns furnished with slightly projecting folds whose usefulness I have already pointed out to you. If I am not much mistaken, here we have a mill capable of grinding tough straw and fibrous hay.
“Finally, here is a rabbit’s head. Each jaw is furnished with two enormous incisors set deep into the[21]bone, bent backward above, and ending each in a sharp-edged crown. What are such incisors as those made for?”
“I know,” Jules quickly replied. “The rabbit is always nibbling. For want of better food it will gnaw the bark of a tree and even the wood. It uses its incisors to cut its food very fine, to gnaw it.”
Jaws and Teeth of a RodentJaws and Teeth of a Rodenta, hamster’s jaws and teeth;b, upper incisor of a rabbit.
Jaws and Teeth of a Rodent
a, hamster’s jaws and teeth;b, upper incisor of a rabbit.
“To gnaw it—that is the right word; hence we give the name of rodents or gnawers to the various animals having incisors of that kind. Such are the squirrel, the hare, the rabbit, the rat, and the mouse, those poor creatures which must gnaw the toughest vegetable substances and fill their bellies with wood, paper, rags even, when there is nothing better for supplying the mill that is kept always going. But it is not merely to satisfy their hunger that these animals are almost incessantly gnawing; there is another reason for their doing it. Their incisors grow all their lives and tend to lengthen indefinitely; consequently, the animal must wear them away by continual friction, as otherwise their crowns would at last so far overlap that they could not be made[22]to meet. Then the poor beast would be unable to seize its food and would perish. In order to be able to eat when hungry, the rat and the rabbit must eat when not hungry, so as to sharpen their incisors and keep them the right length. It is true that they often turn their attention to very poor fodder. A splinter of wood, a straw, a mere nothing suffices to maintain the play of their indefatigable incisors. Remember, children, the expressive termrodents(which meansgnawers), applied to a whole class of animals akin to the rabbit and the rat; remember their curious incisors, for we shall have occasion to speak of them again hereafter. For the present let us finish our examination of the rabbit’s teeth.
“The canines are lacking; in their place the jaw shows a bar or, in other words, a large open space. At the extreme back of the mouth are the molars, few in number but strong, with flat crowns and several folds of enamel. In fact, they make an excellent grinding machine.
“In giving you these details concerning the different shapes of teeth in different species of animals, I wished particularly to point out the following truth: Each species eats a particular kind of food for which the teeth are especially formed, so that one might say of any animal, ‘Show me its teeth and I will tell you what it eats.’ In many instances where we cannot examine the teeth we do not know what such and such a creature feeds on, and in our hasty judgment we mistake a friend for an enemy, a helper for a destroyer. If the animal[23]is ugly we condemn it on the spot and hate it, accusing it of any number of misdeeds. We declare war against it, and never suspect, in our foolishness, that it is a war at our own expense. But there is a very simple precaution by which we can avoid these regrettable mistakes: let us yield to no prejudice, however wide-spread, and before condemning an animal as harmful let us find out what sort of teeth it has. They will tell us the animal’s way of living, as you shall soon see for yourselves.”[24]