It is easy to understand the initial character of the foot of the early ancestral mammals. It had five toes. By the suppression or atrophy of first the innermost toe, then of the outermost, you find that mammals may first acquire four toes only, and then only three, and by repeating the process the toes may be reduced to two, or right away to one, the original middle toe. There is no special difficulty about tracing back the elephants in so far as this matter is concerned, since they have kept (like man and some other mammals) the full typical complement of five toes on each foot.

But I must explain a little more at length what was the "typical dent.i.tion,"--that is to say, the exact number and form of the teeth in each half of the upper and the lower jaw of the early mammalian ancestor of lower Eocene times, or just before. The jaws were drawn out into a snout or muzzle, an elongated, protruding "face," as in a dog or deer or hedgehog, and there were numerous teeth set in a row along the gums of the upper and the lower jaw. The teeth were the same in number, in upper and in lower jaw, and so formed as to work together, those of the lower jaw shutting as a rule just a little in front of the corresponding teeth of the upper jaw. There were above and below, in front, six small chisel-like teeth, which we call "the incisors." At the corner of the mouth above and below on each side flanking these was a corner tooth, or dog-tooth, a little bigger than the incisors, and more pointed and projecting. These we call "the canines," four in all. Then we turn the corner of the mouth-front, as it were, and come to the "grinders," cheek-teeth or molars. These are placed in a row along each half of upper and lower jaw. In our early mammalian ancestor they were seven in number, with broader crowns than the peg-like incisors and canines, the bright polished enamel of the crown being raised up into two, three or four cone-like prominences.

The back grinders are broader and bigger than those nearer the dog-tooth. The three hindermost grinders in each half of each jaw are not replaced by "second" teeth, whilst all the other teeth are.

[Ill.u.s.tration: Fig. 10.--The teeth in the upper and lower jaw-bone of the common pig--drawn from photographs. A and B represent the right half of the lower jaw (A) and the right half of the upper jaw (B) seen in horizontal position. _Inc._ are the incisors or chisel-like front teeth, three in number, in each half of each jaw and marked 1, 2, 3.

_C_ marks the canine or dog-tooth, which here grows to be a large tusk. The molars, "grinders," or cheek teeth are marked 1 to 7. Figs.

C and D give a side view of the left halves of the upper (C) and of the lower jaw-bone (D), with the teeth in place. The bone has been partly cut away so as to show the fangs or roots of the teeth, which are double in the molars, and even threefold in molar No. 7. The explanation of the lettering is the same as that given for Figs. A and B. The letter _p_ in Fig. B points to a "foramen" or hole in the upper jaw-bone. These drawings are introduced here as showing the _complete_ number of teeth which the ancestor of pigs, goats, elephants, dogs, tigers, men, and even whales possessed. The reduction in number and the alteration in the shape of the primitive full set of teeth is referred to in the present chapter on "Elephants," and in those on "Vegetarians and their Teeth" (p. 102), and on "A Strange Extinct Beast" (p. 92).]

Now this typical set of teeth--consisting of twenty-eight grinders, four canines, and twelve incisors--is not found complete in many mammals at the present day, though it is found more frequently as we go back to earlier strata.[6] Though some mammals have kept close to the original number, they have developed peculiar shape and qualities in some of the teeth as well as changes in size. The common pig still keeps the typical number (Fig. 10), but he has developed the corner teeth or canines into enormous tusks both in the upper and lower jaw, and the more anterior grinders have become quite minute. The cats (lions and tigers included) have kept the full number of incisors (see Figs. 21 and 22, pp. 103, 104); they have developed the four canines into enormous and deadly stabbing "fangs," and they have lost all the grinders but three in each half of the lower jaw and four in each half of the upper jaw (twelve instead of twenty-eight), and these have become sharp-edged so as to be scissor-like in their action, instead of crushing or grinding. Man and the old-world monkeys have lost an incisor in each half of each jaw (see Pls. VI and VII); they retain the canines, but have only five molars in each half of each jaw (twenty in all instead of twenty-eight). Most of the mammals--whatever change of number and shape has befallen their teeth in adaptation to their different requirements as to the kind of food and mode of getting it--have retained a good long pair of jaws and a snout or muzzle consisting of nose, upper jaw, and lower jaw, projecting well in front of the eyes and brain-case. Man is remarkable as an exception. In the higher races of men the jaws are shorter than in the lower races, and project but very little beyond the vertical plane of the eyes, whilst the nose projects beyond the lips. Another exception is the elephant. This is most obvious when the prepared bony skull and lower jaw are examined, but can be sufficiently clearly seen in the living animal. The lower jaw and the part of the upper jaw against which it and its grinders play is extraordinarily short and small. The elephant has, in fact, no projecting bony jaw at all, no bony snout, its chin does not project more than that of an old man, and even the part of the upper jaw into which its great tusks are set does not bend forward far from the perpendicular (Fig. 9).

[Ill.u.s.tration: Fig. 11.--A reconstruction of the extinct American mastodon (_Mastodon ohioticus_) from a drawing by Prof. Osborne. Other extinct species of mastodon are found in Europe.]

[Ill.u.s.tration: Fig. 12.--A. Skull, and B. restored outline of the head of the long-jawed extinct elephant called Tetrabelodon--the name referring to its four large tusks--two above and two below.]

The elephant (see Fig. 9) has no sign of the six little front teeth (incisors) above and below which we find in the typical dent.i.tion and in many living mammals, nor of the corner teeth (dog-teeth, or canines). In the upper jaw in front there is the one huge tusk on each side, and in the lower jaw no front teeth at all! Then as to the grinders. In the elephant these are enormous, with many transverse ridges on the elongated crown, and so big that there is only room for one at a time in each half of upper and lower jaw. Six of these succeed one another in each half of each jaw, and correspond (though greatly altered) to six of the seven grinders of the typical dent.i.tion. Are there amongst older fossil elephants and animals like elephants any which have an intermediate condition of the teeth, connecting the extremely peculiar teeth of the modern elephants with the typical dent.i.tion such as is approached by the pig, the dog, the tapir, and the hedgehog? There are such links. We know a great many elephants from Pleistocene and Pliocene strata--some from European localities, more from India, and some from America. A little elephant not more than 3 feet high when adult is found fossil in the island of Malta; other species were a little larger than the living African elephant. Whilst the Indian elephant has as many as twenty-four cross-ridges on its biggest grinding tooth (Fig. 8) there is a fossil kind which has only six such ridges. But besides true elephants we know from the Pliocene, Miocene, and Upper Eocene of the old world, the remains of elephant-like creatures (some as big as true elephants), which are distinguished by the name "Mastodon" (Fig. 11).

And, in fact, we are conducted through a series of changes of form by ancient elephant-like creatures which are of older and older date as we pa.s.s along the series, and are known as (1) Mastodon, (2) Tetrabelodon, (3) Palaeomastodon, (4) Meritherium, until we come to something approaching the general form of skull and skeleton and the typical dent.i.tion of the early mammalian ancestor. Mastodons of several species are found in Pliocene strata in Europe and Asia; detached teeth are found in Suffolk. One species actually survived (why, we do not know) in North America into the early human period, and whole skeletons of it are dug out from the mora.s.ses such as that of "Big-bone Lick." The Mastodons had a longer jaw and face than the elephants, though closely allied to them. They bring one nearer to ordinary mammals in that fact, and also in having (when young) two front teeth or incisors in the lower jaw. Their grinders had the crowns less elongated than those of the elephants, and there were only five cross-ridges--on the biggest--and these ridges tend to divide into separate cones (Fig. 8). So here, too, we are approaching the ordinary mammals, of which we may keep the pig and the tapir in mind as samples. But the Mastodons still had the great trunk and huge tusks of the elephants.

Next we must look at Tetrabelodon (Fig. 12), and it is this creature which has really revealed the history of the strange metamorphosis by which elephants were produced. The Tetrabelodon is known as "the long-jawed mastodon," because, as was shown in a wonderfully well-preserved skeleton from the lower Pliocene of the centre of France, set up in the Paris Museum, it had a lower jaw of enormous length, ending in two large horizontally directed teeth (Fig. 12).

Instead of a lower jaw a foot long, as in an elephant or in the common kind of mastodon--this long-jawed kind had a lower jaw 5 feet or 6 feet long! The tusks of the upper jaw were large, and nearly horizontal in direction, bent downwards a little on each side of the long lower jaw. This lower jaw seemed incomprehensible, almost a monstrosity--until it occurred to me that it exactly corresponds to the elongated upper lip and nose which we call the elephant's trunk--and that the trunk of "Tetrabelodon" must have rested on his long lower jaw. In descending to Tetrabelodon we leave behind us the elephants with hanging unsupported trunk; the lower jaw here is of sufficient length to support the great trunk. When the lower jaw shortened in the later mastodons and elephants the trunk did not shorten too, but remained free and depending, capable of large movement and of grasping with its extremity. Photographs, casts, and actual specimens of the extraordinary skull of the long-jawed mastodon or Tetrabelodon and of the creatures mentioned below may be seen in the Natural History Museum.

Lastly we have the wonderful series of discoveries made about twelve years ago by Dr. Andrews (of the Natural History Museum) of elephant-like creatures in the upper Eocene of the Fayoum Desert of Egypt. Palaeomastodon (the name given by Dr. Andrews to one of them) is a "pig-like" mastodon, with an elongated, bony face, the tusks of moderate size, and the lower jaw not projecting more than a few inches beyond them, so that the proboscis is quite short and rests well on it (Fig. 13). This animal had six moderate sized grinders (molars or cheek-teeth) on each side of each jaw in position simultaneously, as may be seen in the complete skull shown in Fig. 14. Of other teeth it had only the two moderate-sized front tusks above and two very big, chisel-like "incisors" in the front of the lower jaw. Exactly how these were used and for what food no one has yet made out.

[Ill.u.s.tration: Fig. 13.--Head of the ancestral elephant--Palaeomastodon--as it appeared in life. It shows, as compared with the earlier ancestor, an elongation both of the snout and the lower jaws. The tusk in the upper jaw has increased in size, but is still small as compared with that of later elephants. (After a drawing by Prof. Osborne.)]

[Ill.u.s.tration: Fig. 14.--Restored model of the skull and lower jaw of the ancestral elephant Palaeomastodon from the upper Eocene strata of the Fayoum Desert, Egypt. It shows the six molar teeth of the upper and lower jaw (left side), the tusk-like upper incisors and the large chisel-like lower incisors in front.]

The remains, which finally bring the elephants into line with the ordinary mammals with typical dent.i.tion, were discovered also by Dr.

Andrews and named "Meritherium" by him, signifying "the beast of the Lake Meris." This creature is not bigger than a tapir, and had the shape of head and face which we see in that and the ordinary hoofed animals (Fig. 15). It had no trunk, and whilst it had six small and simplified mastodon-like grinders in each half of each jaw, it had six incisors in the upper jaw and a canine or corner tooth on each side.

In the lower jaw there were only two large incisors besides the cheek-teeth or grinders. Not the least interesting point about Meritherium is that it tells us which of the front upper teeth have become the huge tusks of the later elephants. Counting from the middle line there are in Meritherium three incisors right and three left. The second of these upper teeth on each side is much larger than the others. It is this (seen in Fig. 15) which has grown larger and larger in later descendants of this primitive form and become the elephant's tusk, whilst all the others have disappeared.

[Ill.u.s.tration: Fig. 15.--Head of the early ancestor of elephants--Meritherium--as it appeared in life. Observe the absence of a trunk and the enlarged front tooth in the upper jaw, which is converted in later members of the elephant-stock or line of descent into the great tusk. (After a drawing by Prof. Osborne.)]

We now know the complete series of steps connecting elephants with ordinary trunkless, tuskless mammals. The transition from the "beast of Meris" on the one hand to the common typidentate mammalian ancestor, and on the other hand to the elephants, is easy, and requires no effort of the imagination. His short muzzle (upper and lower jaw), first elongated step by step to a considerable length, giving us Palaeomastodon (Fig. 13). Then the lower jaw shrunk and became shorter than it was at the start, and the rest of the muzzle (the front part of the upper jaw, carrying with it the nostrils), drooped and became the mobile muscular elephant's trunk!

FOOTNOTES:

[Footnote 5: I am inclined to think that the line between Pliocene and Pleistocene or Quaternary ought, in this country, to be drawn between the White and Red Crag of Suffolk. Glacial conditions set in and were recurrent from the commencement of the Red Crag deposit onwards.]

[Footnote 6: Mammals having the number and form of teeth which I have just described as typical--or such modification of it as can easily be produced by suppression of some teeth and enlargement of others--are called Typidentata. On the other hand, the whales, the sloths, ant-eaters, and armadilloes, as also the Marsupials, are called Variodentata, because we cannot derive their teeth from those of the Typidentate ancestor. They form lines of descent which separated from the other mammals before the Typidentate ancestor of all, except the groups just named, was evolved.]

CHAPTER VII

A STRANGE EXTINCT BEAST

The terraces of gravel deposited by existing rivers and the deposits in caverns in the limestone regions of Western Europe--the so-called "Pleistocene" strata--contain, besides the flint weapons of man and rare specimens of his bones, the remains of animals which are either identical with those living at the present day (though many of them are not living now in Europe) or of animals very closely similar to living species. Thus we find the bones of horses like the wild horse of Mongolia, of the great bull (the Urus of Caesar), of the bison, of deer and goats, of the Siberian big-nosed antelope, of the musk-ox (now living within the Arctic circle), of the wild boar, of the hippopotamus (like that of the Nile), and of lions, hyenas, bears, and wolves. The most noteworthy of the animals like to, but not identical with, any living species are the mammoth, which is very close to the Indian elephant, but has a hairy coat; the hairy rhinoceros, like, but not quite the same as, the African square-mouthed rhinoceros; and the great Irish deer, which is like a giant fallow-deer. These three animals are really extinct kinds or species, but are not very far from living kinds. In fact, the most recent geological deposits do not contain any animals so peculiar, when compared with living animals, as to necessitate a wide separation of the fossil animal from living "congeners" by the naturalist who cla.s.sifies animals and tries to exhibit their degrees of likeness and relationship to one another by the names he adopts for them. The mammoth is a distinct "species" of elephant. It requires, it is true, a "specific" or "second" name of its own; but it belongs to the genus elephant. Hence we call it _Elephas primigenius_, whilst the living Indian elephant is _Elephas Indicus_. The reader is referred to the preceding chapter for further notes about elephants.

The strata next below the Pleistocene gravels and cave deposits are ascribed to the "Pliocene age"--older than these are the "Miocene" and the "Eocene," and then you come to the Chalk, a good white landmark separating newer from older strata.

We know now in great detail the skeletons and jaws of some hundreds of kinds of extinct animals of very different groups found in the Eocene, the Miocene, the Pliocene, and the Pleistocene layers of clays, sands, and gravels of this part of the world. Nothing very strange or unlike what is now living is found in the Pleistocene--the latest deposits--but when we go further back strange creatures are discovered, becoming stranger and less like living things as we pa.s.s through Pliocene to Miocene, and on--downwards in layers, backwards in time--to the Eocene.

Though the past history of the Mediterranean sea shows that it was formerly not so extensive as it is now, and that there were junctions between Europe and Africa across its waters, yet the deeper parts of that sea are very ancient, and some of the islands have long been isolated. In Malta the remains of extraordinary species of minute elephants have been found, one no larger than a small donkey, and in the island of Cyprus an English lady, Miss Dorothea Bate, has discovered the bones of a pigmy hippopotamus (like that still living in Liberia) no larger than a sheep. Miss Bate some three years ago heard of the existence of a bone-containing deposit of Pleistocene age in limestone caverns and fissures in the island of Majorca, and with the true enthusiasm of an explorer determined to carry on some "digging" there and see what might turn up. In the following spring she was there, and obtained a number of bones, jaws, and portions of skulls, which appeared at first sight to be those of a small goat. Its size may be gathered from the fact that its skull is six inches long.

These and the bones of a few small finches were all that rewarded her pains. The bones of fossil goats (of living species) are found in caves at Gibraltar and in Spain; so at first the result seemed disappointing. But on carefully clearing out the specimens and examining them in London, Miss Bate found that the supposed goat bones obtained by her in Majorca were really those of a new and most extraordinary animal, to which (in a paper published in the "Geological Magazine" in September, 1910) she has given the name "_Myotragus balearicus_."

[Ill.u.s.tration: Fig. 16.--Side-view of the skull and lower jaw of a goat. _inc. i._ The three lower incisor teeth of the left side. _can.

i._ The little canine teeth grouped with them. _p._ The toothless front part of the upper jaw. _m. s._ Upper molars or "grinders." _m.

i._ Lower molars or grinders. Compare this and the following figures with Fig. 10, showing the more complete "dent.i.tion" of the pig.]

[Ill.u.s.tration: Fig. 17.--Horizontal view of the teeth in the lower and upper jaw of the goat. In front of the lower jaw the group of three incisors (_inc. i._) and one canine is seen, whilst the toothless bony plate (_p._) of the upper jaw, against which they work, is seen in the right-hand half of the figure. The molars, "grinders," or cheek-teeth are numbered 1 to 6 in each jaw.]

[Ill.u.s.tration: Fig. 18.--Side view of the skull of a typical "rodent"

mammal, the Coypu rat (_Myocastor coypus_) from South America. _inc.

s._ Upper incisor. _inc. i._ Lower incisor. _m. s._, _m. i._ Upper and lower molars, grinders or cheek-teeth.]

I must ask the reader now to look at the figures here given (Figs. 16 and 17) of the skull and the lower jaw of a goat. The lower jaw might (except for size) pa.s.s for that of a sheep, ox, antelope or deer. They are all alike. There are on each side six grinding cheek-teeth (molars), and then as we pa.s.s to the front we find a long toothless gap until we come to the middle line where the two halves of the jaw unite. There we see a little semicircular group of eight chisel-like teeth, which work against the toothless pad of the upper jaw opposed to them, and are the instruments by which these animals, with an upward jerk of the head, "crop" the gra.s.s and other herbage on which they feed, to be afterwards triturated by the grinding cheek teeth. A vast series of living and of fossil animals, called the Ruminants--including the giraffes, the antler-bearing forms called deer, the cavicorn or sheath-horned bovines, ovines and caprines, and the large series of antelopes of Africa and India--all have precisely this form of jaw, this number and shape and grouping of the teeth. Now let me call to mind the lower jaw of a hare or rabbit or rat (Figs. 18 and 19). There we find on each side the group of grinding cheek-teeth, with transverse ridges on their crowns, and a long, toothless gap before we arrive at the front teeth. But the front teeth are only two in number, one on each side, close to each other, very large, and each with a tremendously long, deeply set root. They meet a similar pair of teeth in the upper jaw, and give the hare, rabbit, rats, mice, beavers, and porcupines the power of "gnawing" tough substances.

These animals are hence called Rodents, or gnawers, and the two great front teeth are called "rodent-teeth." No two arrangements of teeth could be much more unlike than are the group of eight little chisel-like teeth of the lower jaw of the Ruminants and the two enormous gnawing teeth of the Rodents. Apparently the two rodent incisors, or front teeth, of the lower jaw of the rat correspond to the two middle incisors of the Ruminant's lower jaw; the other front teeth of the Ruminant have atrophied, disappeared altogether. The rodent condition has been developed from that of an ancestor which had several front teeth and not two large ones only; but we have not at present found the intermediate steps.

[Ill.u.s.tration: Fig. 19.--View in the horizontal plane of the teeth of the left half of the lower and the left half of the upper jaw of the Coypu rat to show the single great gnawing incisor on each side, the four flat grinding molars and the wide gap between molars and incisors. Compare with Figs. 17 and 22.]

The reader should compare the teeth of the goat and the large rat here pictured with the more typical and complete series of the pig, given in Fig. 10, p. 84. The pig's teeth are the same in number as those of the ancestral primitive typidentate mammal, and their form is near to that of the ancestor's teeth.

Now I come to the extraordinary interest of Miss Bate's goat-like or antelope-like animal from Majorca. Although it is shown by its skull (Fig. 20) and other bones to be distinctly one of the sheath-horned Ruminants, very like a small goat or antelope, the lower jaw, of which there are several specimens, does not present in front the little group of eight small chisel-like "cropping" teeth, but, instead, two enormous rodent teeth placed side by side, very deeply fixed in the jaw, and quite like those of some rat-like animals in shape. Hence the name given to this little marvel by Miss Bate--"Myotragus," "the rat-goat." This strange little animal also differs from goats and antelopes in having proportionately much thicker and shorter "feet"

(cannon-bones) than they have.

If the remains of this strange little creature had turned up in more ancient strata--in Pliocene or Miocene--it would have not been quite so astonishing. But it would be still very remarkable, since it has all the characters of a goat-like creature in the shape of its skull, its bony horn-cores, its limb-bones, and its cheek-teeth; and yet, as it were monstrously and in a most disconcerting way, protrudes from its lower jaw two great rats' teeth. Nothing like it or approaching it or suggesting it, is known among recent or fossil Ruminants. They all without exception have a lower jaw with the teeth of the exact number and grouping which you may see in a sheep's lower jaw. We know hundreds of them, both living and fossil, many from the Pleistocene, others from Pliocene deposits, and even from the still older Miocene, but all keep to the one pattern of lower jaw and lower jaw teeth. It is only in this little island of Majorca, surrounded by very deep water and not known to have nurtured any other animal so large in size either in recent or geologic times, that we come upon a Ruminant with horns like a goat's, but with great rat-like front teeth in place of the semicircle of eight little cropping toothlets. The wonderful thing is that the bones found by Miss Bate are light and well preserved, evidently not very ancient--probably late Pleistocene in age.

[Ill.u.s.tration: Fig. 20.--Drawing of the skull of the rat-toothed goat, Myotragus--the new extinct beast discovered in limestone fissures in the island of Majorca by Miss Bate. 1. Side view of the skull and lower jaw. 2. Appearance of the two rat-like teeth as seen when the end of the lower jaw is viewed from above.]

The questions that arise are: Where did the rat-goat come from? How did this utterly peculiar change in a Ruminant's teeth come about?

With regard to the second question, it is a matter of importance that although we have hitherto not discovered any Ruminants with this modification of the teeth, still less any cavicorn or sheath-horned Ruminant so altered, yet it is by no means rare amongst herbivorous mammals to find such rat-like teeth making their appearance, whilst the smaller side-teeth of the incisor group or front teeth disappear.

The Australian kangaroos and wombats are a case in point--so is the lemur-like aye-aye of Madagascar (an insect eater). So is the Hyrax or "damian" of the Cape, and also the very ancient Plagiaulax from the prae-chalk Purbeck clay. But perhaps the best case for comparison with the ruminants is that of the rhinoceroses. There are a great many species and even genera of fossil and recent rhinoceroses. An old Miocene kind (called Hyracodon) has eight little teeth in the front of the lower jaw. In a Pliocene kind of rhinoceros (called _R.

incisivus_) these are reduced to two, the middle two, which are of great size and project far forward--like those of the rat-goat of Majorca. Among living rhinoceroses the Indian species have these two front teeth, but smaller, whilst the square-mouthed African rhinoceros has none at all! This helps us, as a parallel, to understand "the strange case" of Myotragus. But, of course, the rhinoceroses are a distinct line of animal descent--remote from Ruminants. They are (like horses and tapirs) odd-toed hoofed beasts--not even-toed ones, as are pigs, camels, and ruminants.

On first considering the question of the origin of the rat-goat of Majorca, some naturalists will, no doubt, be tempted to suggest that it is a case of a sudden "sport," a "mutation" as they now call it, and not a result of gradual slowly developed reduction of the now lost teeth and correspondingly gradual enlargement of the two middle ones, taking many thousand generations to bring about. The fact that the rat-goat is found on an island cut off from compet.i.tion with other animals will favour this view. On the other hand, there is the important and really remarkable fact that familiar as man has been for ages with Ruminants of many kinds--such as sheep, goats, cattle, deer--there is absolutely no case on record of an "oddity" or "monstrosity" resembling the rat-goat's condition occurring in the teeth of any of the hundreds of thousands of these animals killed and eaten by man, and therefore closely examined. Professor Bateson, who a few years ago ransacked the museums of Europe for instances of "discontinuous variation," or "sports," and wrote a valuable book on the subject, did not discover any example of the kind. Apart from the view, which is very generally held, that such sudden "mutations" as "rat-teeth in a ruminant" are--even should they occur--not perpetuated, we are not really in any way driven to suppose that the rat-goat of Majorca originated in that island. It is true that we know nothing like it in the Pliocene and Miocene of the Mediterranean region which could have been its immediate ancestor. But probably the ancestors of the rat-goat were slowly developed from a Miocene sheath-horned ruminant, a primitive sort of antelope in some part of North-west Africa, or in an extension of it now submerged in the Atlantic, and stragglers of this curious and now lost Ruminant stock were left in Majorca when in Miocene or early Pliocene times that island became detached from its Hispano-African connection.

CHAPTER VIII

VEGETARIANS AND THEIR TEETH