88 



FIRST CLASS OF THE VERTEBRATED ANIMALS. 



lead the student to perceive the importance of these organs, and the different func- 

 tions which they are destined to fulfil. But a much more enlarged view is acquired by 

 studying the different forms of the teeth, in their relations to each other, as well as 

 to the nature and habits of the animals possessing them. It remains for us to give a 

 rapid outline of this part of the subject. 



On placing before our view the teeth of all known Mammalia, we soon perceive 

 that they admit of being classified under a small number of different forms. With 

 some of them, as we have already remarked, there is no difference between the root, 

 or rather, the parts inserted within the bones which bear the teeth, and the crown, 

 or part beyond these bones. Teeth of this nature have no real roots, in the proper 

 acceptation of the word ; that is to say, the crown is continued inwards as far as the 

 dentary capsule, which never produces anything but the crown, as long as it remains 

 free and active — a circumstance occurring with some animals during the whole course 

 of their lives. Among others, on the contrary, the roots are very distinct from the 

 crown ; they may be either simple or complex, but do not, in general, exhibit in 

 their forms that constancy of character which is always to be recognised in the 

 forms of the crown. This circumstance arises naturally from the different manner 

 in which each of them is formed. 



Restricting, therefore, our view of the teeth solely to their crowns, we find that 

 there exist three principal forms among them. These may be almost infinitely mo- 

 dified, and some transformed into others, in such a manner, that it becomes impossi- 

 ble rigorously to determine the precise point where the one form passes into the 

 other. This manner of classifying the teeth must be regarded as nothing more than 

 a purely artificial method, for enabling us to speak of their forms without too much 

 obscurity and confusion, by restraining, within their proper limits, the observations 

 necessary to be made. The crowns of all teeth may be regarded as conical, tren- 

 chant, or tuberculous. 



(1.) The Conical Teeth vary in form from the cylinder, more or less compressed, 

 terminated by a point, more or less obtuse, to the oval or ellipse. Some are straight, 

 some angular, others curved. Those of an elliptical, or oval form, are the least 

 common, and are observed among the Cachalots. The conical teeth, which comprise 

 the Canines of the Carnassiers, the tusks of the Elephants, Hippopotamus, &c. are the 

 most numerous. Finally, the cylindrical may be seen in the molars of such Edentata 

 as are possessed of teeth. Among the Conical teeth, only two kinds of composition 

 can be observed. Some are formed only of ivory and cortex, such as the ^lolars 

 of the Cachalots ; for although the external part of these teeth possesses a whiter 

 tinge than the central, it is not formed of enamel, as some have thought. Both 

 substances are ivory in reality, and it is the same with the tusks of the Elephant. 

 Others are covered with enamel, such as the Canines of the Carnassiers, and many 

 others. In this class of conical teeth are found by far the greater number of those 

 destitute of roots, such as nearly all tusks ; and of those, wherein the root is distinct 

 from the crown, only a small number have been observed with many roots, as the 

 Canines of the Moles, for example. 



(2.) The Trenchant or Cutting Teeth may be presented under a simple or com- 

 pound form. Among the former may be placed the Incisors of the Rodentia, which 



belong as much to the first division as to the serond, the Incisors of the Quadm- 

 mana, the Carnassiers, the Ruminantia, and others. In this division we may 

 place the false and carnassier molars of the Carnivorous animals. There are, how- 

 ever, many among the former which approach nearer to conical than to trenchant 

 teeth. All teeth of this class are composed of ivory and enamel, though some also 

 have cortex. These last are the incisors of the Rodentia, which present the singular 

 anomaly of having enamel only on their anterior surface. They are with simple or 

 multiple roots ; and those of the Rodentia alone are possessed of the same peculiarity 

 as tusks, in having no roots properly so called. 



(3.) The Tuberculous Teeth present the greatest variety of form, and are all 

 Molars. The simple tuberculous Molars are those of the Quadrumana, the hind- 

 most molars of some Carnassiers, the grinders of Squirrels and Rats, those of 

 the Babyroussa, or Indian Hog. The proper tuberculous Molars are found 

 in the Insectivora, &c. The compound tuberculous molars belong to a great num- 

 ber of Rodentia, such as the Beavers, the Pacas (^Cmlogeni/s), the Agoutis, the 

 Hares, the Guinea Pigs, and others. The simple tuberculous molars are always formed 

 of ivory and enamel, while they are all possessed of several roots. This observation 

 is equally applicable to the proper tuberculous molars. 



Among the compound tuberculous molars there are perhaps none which do not' 

 possess the cortex, in addition to the ivory and enamel. Some of these teeth are 

 found with several roots, as in the Beavers, Elephants, Horses, and Ruminantia; 

 and without roots, as in the Hares, the Cabiais, the Lagomys, and other Rodentia. 



The uses which animals make of these different forms of teeth are exceedingly 

 ■various. To some they are powerful arms, by means of which they attack their prey, 

 or any enemy that threatens them, or else defend themselves when attacked. In 

 others they seem rather to be intended to retain a prey, which has already been seized. 

 Some kinds are used for dividing the food like pincers ; others for cutting it like 

 scissors. Again, we find another class of teeth which grind like the stones of a mill, 

 or which triturate their food, like jagged pestles fitting into mortars as jagged as them- 

 selves. Sometimes they crush by a single jerk, or pressure. All these forms and 

 different modes of action find their final object in the ever-varied substances, which 

 may serve for the nourishment of animals. The kind of food which each animal re- 

 quires is determined by its nature ; this again regulates the influence which it exer- 

 cises upon other beings, and determines its station in the scale of creation. 



The different kinds of teeth are found combined together in different manners. In 

 many Carnassiers, we find conical, trenchant, and tuberculous teeth, all united in the 

 same individual. Among the greater number of the Ruminantia, we can discover 

 only the trenchant and tuberculous teeth. The conical teeth alone are found in some 

 Edentata, and in the Cachalots and Dolphins, while only the trenchant and conical 

 teeth are found in the common Seal. 



In fact, we find in almost all Mammalia at least some of these forms — simple teeth, 

 serai-compound, or compound, with one or more roots — conical, compressed, pointed, 

 with flat crowns, tuberculous or trenchant. At present it is unnecessary further to 

 enumerate the different possible combinations of teeth. A general idea of the sub- 

 ject may be obtained from the following 



SYNOPSIS OF THE MAMMALIA, EXHIBITING AN OUTLINE OF THE NATURE. FORM, AND POSITION 



OF THEIR TEETH. 



Instances. 



'of three kinds 

 not very strong- 

 ly defined 



(Anomalous) 



•completely lin- 

 ing the mar- 

 gins of both 

 jaws 



' of va- 

 rious 



forms 



'in both 

 jaws 



' Calcareous 



Teeth 



i 



molars 



{tubercles blunt Man, Orang-Outang. 

 pointed Lemurs, Flying-Cats. 

 very sharp ...Hedgehogs, Shrews, Moles. 



.molars compound Anoplotherium (fossil). 



fApes generally, the Ouistitis, 

 nearl}' all Carnassiers, Hip- 

 Hog, Tapir, 



not completely 

 lining the mar- 

 gins of both • 

 jaws, leaving a 

 . vacant space 



in the middle, both above and below 



of three kinds, well defined (Normal) <( 



popotamus, 



L Opossums. 



f really Rodentia, Asiatic Rhinoceros. 



\ apparently ...Horse, Kangaroo- Rat. 



f both above and below Sloths, Morse. 



I f Elephants, Mastodon (fossil), 



.in the front ...-<j below, and in the middle above < Dugong (adult), Manatus 



I ( (young). 



Labove, and in the middle below Ruminantia. 



f Armadilloes, Orycteropus, 



all Molars <. Megatherium (fossil), African 



' Rhinoceros, Manatus (adult). 



all Conical or Canines Dolphins generally. 



f the upper Narwhal, some Dolphins. 



\ the lower Cachalots ? 



u f in both jaws Ornithorhvnchus. 



Honiy / . 



(in the upper jaw only Whales. 



f Manis, Ant-eaters, Echidna, 



I some Dolphins ? 



I. Wanting 



These varied forms and positions, and even the number of the several kinds of teeth, 

 often afford the best specific characters for determining the Mammalia ; in all cases 

 thev offer the surest characteristics of the genera, and even of other divisions of a higher 

 order. In this way, one of the Mammalia may be immediately recognised by a simple 

 inspection of its teeth ; and, reciprocally, we may determine the nature of the animal 

 to which a single isolated tooth has belonged. The importance of this study towards 

 the knowledge of fossil animals, as well as for establisliing the generic groups of fos- 

 sils, has been forcibly illustrated in the celebrated work of the Baron Cuvier, on the 



Fossil Bones of Quadrupeds (^Sur les Ossemens Fossiles), and by MM. Frederit 

 Cuvier and llliger. The teeth may, indeed, be regarded as one of the most import- 

 ant subjects in Zoology, and one of the most certain marks for ascertaining the na- 

 ture of animals, and the relations established among them. They are, in fact, the 

 foundations of the science ; and, hence, should occupy an important place in any 

 system of classification, as they serve as an index to the order of facts and their re- 

 lations ; and, hence, may be considered as indispensable to the existence of the wbolo 



