GOOD SETS OF TEETH.

Lyttelton Times, Volume LVII, Issue 6506, 3 January 1882, Page 3

GOOD SETS OF TEETH.

The lion and tiger disdain all but living victims; the sneaking and cowardly hy«na feeds mainly on the bones and coarser parts of the animals whioh have been killed by the nobler beasts of prey. His jaws, whioh are extremely powerful, so much so that he can bite off the leg of a large dog at a single snap, have a lateral motion, as well as the vertical action to which the tiger is restricted, and the teeth, though of the same carnivorous type, are adapted for a different purpose. The oaninrs are smaller, and the molars, whioh are of great size, and surrounded at their base by a thiok ridge, whioh protects the gums from being injured by splinters and angular fragments, are capable of breaking the hardest bor«j into shivers.

The foregoing examples of carnivorous dentition are .of a sufficiently formidable nature, but many of the predatory fishes are quite as well armed as the tiger or the hyaena, while they possess the great additional advantage of a constant growth of new teeth to replace those which have been worn down or injured. The wolf-fish has already been described as an ugly customer, and the pike, the shark, the fishing frog, and the great barracouda, would all be bracketed high in a dental competition. Space permits us to describe the fishing-frog only, a hideous marine monster which is hidden in the ooze of the sea-bottom, and allures unwary fishes to their destruction by means of a flesh-like expansion, placed at the tip of a long slender filament, attached to the spine of the first dorsal fin. This bait serves to allure the prey within reach of the cavernous jaws, from which there is but small chance of escape, since the teeth, by an arrangement which is almost unique, are movable, being tied to the jaw by strong figments, which permit them to bend inwards towards the throat, and then rising to a vertical

position prorent the exit of the (boggling viotim. With hie filament, for enticing, and the above-mentioned dental apparatus for seizing and devolving his prey, it will probably be considered that the fishing-frog is tolerably well provided. It is only fair, however, to stale that ho usually has to fish for two, ae according to sf. Tan Beceden, by an arrangement not uncommon throughout nature, an* other fish, a species of Muraena, lives in the huge Gillsacs of this monster of the deep, and feeds ok a part of the provisions collected by his host.

The molar*, or grinding teeth are mainly characteristic of the herbivora. In theie teeth, the three substances of which all teeth are composed, enamel, cement, and dentine, are arranged alternatively in vertical plates, the edge* of which are presented at the grinding surface of the tooth. Of there mb* stances, the enamel is the hardest, and the cement the softest, and the unea«al wear causes the surface to be it pt c. rough. The mode of arrangement of tl.'-e three components varies greatly in different animals, and in some species is surprisingly complicated j the perfection of a grinding apparatus is attained by the molar teeth of the elephant, which may be compared with a self-dressing millstone. Host people are aware that the front teeth of horses are examined for the purpose of ascertaining their age, bnt probably few understand the nature of the test. The “mark” as it is termed, is an oblong fold of enamel, which dips dowa deeply into the crown of the tooth, forming a canty which is generally filled with a yellowish mass, composed of tartar and minute particles of the food. As the horses grow cider, the surface of the tooth is ground down by the constant wear of mastication, and the *' mark ” in course of time disappears.

The cavity is usually obliterated in the first incieor in the sixth year, in the second, at the seventh year, and in the third or outer incisors in the eighth rear, after which the horse is termed "aged ” by veterinarians. The incisors of the horse, once worn down or lost, are gone for ever, but in many suedes a provision exists by which the wear and tear of mastication is compensated by the perpetnal growth of certain i; embers of the dental series. This very conv. nient arrangement exists in all the rodents. cr gnawers, an order of which the beaver, the rat, and the rabbit are familiar examples, and al.-o in the elephant, walrus, wild boar, &c.

The incisors of tbe rodent? the seat of this perpetual growth, and e.ry one who will take the trout le to examine (he skull of a rabbit, will at- once gee how admirably they are adapted to the animal wants. They are of curred shape, tnd occupy sockets extending to tbe back part ol both jaws, the upper pair describing a larger part of a smaller circle, and th-i lower or.es a smaller part of a larger circle, Kach t> oth consists of a solid column of dentine, with a plate of enamel on its outer surface, and corsequently diminishes in hardness from front to back. The constant wear produced by the continual collision of the opposing surfaces, forms an cheque chisellifce surface, sloping from the hard enamel of the front, to the Sifter dent ne of the back part of tbe tooth. As these teeth are perpetually growing, they require constant exercise t' keep their growth within due bounds, arcl -he rat and others of fbi? most mischievous family might assign. ss an excuse for their ravages, the necessity of finding constant employment for their front teeth Serviceable as is this arrangement (and no one who has had any expo- ri •: c“ of 1 1 *>ae pests will doubt its efficiency), it is alter ded with some drawbacks.

Occasionally, as a conse-uscce of the accidental loss ef one of these teeth, or the misplaced union of a broken jaw, the lower incisors no longer meet the ones, and as they still continue to grow, tne poor animal is soon in a wretched plight. In the Humeri an Museum, many specimens of teeth which, which have been subjected to these conditions may be seen, some cf them contorted in a most extraordinary manner. As the curve of their sockets compels them to a circular growth, they frequently sweep round till the points enter the head, causing absorption of the bore, and the death of the poor animal from starvation. Similar disasters have been known to occur to the hippopotamus, which has perpetually-growing canine teeth—in one specimen the growth of the tooth has formed a complete ring, the point entering the formative pulp at the base. Another source of danger lies in the occasional liability to inflammation in the large vascular pulp, which supplies the material for these perpetual y-growing teeth. This is probably not a frequent occnrrer.ce, but it must sometimes arise, aud instances are recorded in which it has produced ungovernable madness in elephants. In XSi6 the proprietor of a very intelligent elephant, kept at Exeter Change, was compelled to call in the aid of a file of riflemen to put it to death, on account of its unmanageable conduct. The animal had been for some time subject to paroxysms of madness, which rendered it altogether uncontrollable, and its immense strength made it so dangerous, that it became absolutely necessary to destroy it. On examination alter death, it was found that the pulp at the base of the left tusk showed signs of repeated attacks of violent inflammation, and there can be little donbt but that a Brobdingnagian toothache was the cause of the ungovernable condition of the animal. Any one who has had experience of tho intense pain that may exist in the little speck of nervous matter which occupies the central cavity of a human tooth, will find it easy to conceive the raging agony which similar causes might produce in the immense vascular pulp of the elephant’s tusk. After the many elaborate and beautiful contrivances for procuring and masticating the fool which exist throughout nature, the teeth of creation’s lord may almost seem an anti-climax. As Professor Ichthysaurns observes, in Sir H. de la Becche’s amusing sketch, “ It seems wonderful how the creature could have procured its food.” The teeth of man are, however, in every respect well adapted to his requirements, and but for the mysterious and troublesome caries, which makes such ravages among them, we might regard our dental armament with an unmixed complacency. This malady is almost nnknown among animals living in a stav> of nature, but the race horse, the dog, and the pig are occasionally liable to it. From a variety of causes, many of them not very well understood, it has increased very much during the last two||gene rations, aud a perfect set of teeth Is fast becoming a rarity among adults. Happily, tho deterioration in our teeth, a deterioration which would involve the speedy extermination of any other order of living beings, has at present only imparted an increased activity to the occupation of the dentist, and there would probably be no grave cause for anxiety, even if the course of ages should evolve a race of men as toothless a» ant-eaters.