COMPARATIVE ANATOMY. 



particularly the canine and molares, are 

 separated by considerable intervals. There 

 is no animal in which these parts are of 

 such equal height and such uniform ar- 

 rangement as in man. 



All the three kinds of teeth are found 

 in the quadrumana, the carnivora, the 

 pachydermata (excepting the two-horned 

 rhinoceros and elephant,) the horse, and 

 those ruminating animals which have no 

 horns. 



Cuvier states, that the teeth of an 

 animal, whose bones are found in a fos- 

 sil state, resemble those of man, in be- 

 ing arranged in a continued and unbroken 

 series. 



In the simiae, carnivora, and all such 

 as have canines longer than the other 

 teeth, there is at least one vacancy in 

 each jaw, for lodging the cuspidatus of 

 the opposite jaw. There is a vacancy be- 

 hind each canine in the bear. 



The horned ruminating animals not 

 only want entirely the upper incisors, but 

 they are also destitute of cuspidati, ex- 

 cept the stag, which has rudiments of these 

 teeth ; and the musk (moschus moschi- 

 fer) where they are very long, and cur- 

 ved in the upper jaw. 



Between the incisors and grinders of 

 the horse, a very large vacancy is left, 

 in the middle of which a small canine 

 tooth, termed the tusk, is found in the 

 male animal; but very rarely in the fe- 

 male. 



The elephant has grinders and two 

 tusks in the upper jaw ; but the former 

 only in the -lower. The immense tusks 

 belong properly to the male animal, as 

 they are so small in the female, generally 

 speaking, as not to pass the margin of the 

 lip. (Corse, in Phil. Trans. 1799, part 2. 

 p. 208.) 



The sloths have grinding and canine 

 teeth, without incisors. The dolphin and 

 porpoise have small conical teeth, all of 

 one size and shape, arranged in a conti- 

 nued line throughout the alveolar margin 

 of both jaws. The cachalot (physeter 

 macrocephalus) has these in the lower 

 jaw only. The teeth of the seal are all of 

 one form, viz. that of the canine kind ; 

 conical and pointed. 



The narwhal has no other teeth than 

 the two long tusks implanted in its os in- 

 termaxillare ; of which one is so frequent- 

 ly wanting. 



The structure of the incisor teeth, in 

 the rodentia, deserves attention on se- 

 veral accounts. They are covered by 

 enamel only on their anterior or convex 

 surface, and the same circumstance holds 

 good with respect to the tusks of the hip- 



popotamus. Hence, as the bone wears 

 down much faster than this harder co- 

 vering, the end of the tooth always con- 

 stitutes a sharp culling edge, which ren- 

 ders it very deserving of the name of an 

 incisor tooth. 



This partial covering of enamel refutes, 

 as Blake has observed (" Essays on the 

 Structure, &c. of the Teeth," p. 212,) the 

 opinion, that the enamel is formed by the 

 process of crystallization. 



The incisor teeth of these animals are 

 used in cutting and gnawing the "harder 

 vegetable substances, for which their 

 above-mentioned sharp edge renders 

 them particularly well adapted. Hence 

 Cuvier has arranged these animals in a 

 particular order, by the name of rodentia, 

 or the gnawers. As this employment 

 subjects the teeth to immense friction 

 and mechanical attrition, they wear away 

 very rapidly, and would soon be con- 

 sumed, if they did not possess a power 

 of growth, by which the loss is recom- 

 pensed. 



These teeth, which are very deeply 

 imbedded in the jaw, are hollow inter- 

 nally, just like a human tooth which is 

 not yet completely formed. Their cavity 

 is tilled with a vascular pulp, similar to 

 that on which the bone of a tooth is form- 

 ed ; this makes a constant addition of new 

 substance on the interior of the tooth, 

 which advances to supply the part worn 

 down. The covering of enamel extends 

 over that part of the tooth which is con- 

 tained in the jaw, as we might naturally 

 expect : for this must be protruded at 

 some future period, to supply the loss of 

 the anterior portion. Although these 

 teeth are very deeply implanted in the 

 maxillary bones, they can hardly be said 

 to possess a fang or root ; for the form 

 of the part is the same throughout ; the 

 covering of enamel is likewise continu- 

 ed ; and that part, which at one period is 

 contained in the jaw, and would form the 

 fang, is afterwards protruded, to constitute 

 the body of the tooth. 



The constant growth of these teeth 

 therefore proceeds in the same manner, 

 and is effected on the same principles, as 

 the original formation of any tooth ; and 

 can by no means furnish an argument for 

 the existence of vessels in the substance 

 of the part. 



We cannot help being struck with the 

 great size of these teeth, compared with 

 the others of the same animal, or even 

 with the bulk of the animal. Their 

 length in the lower jaw nearly equals 

 that of the jaw itself, although a small 

 proportion only of this length appears 



