864 



TEETH. 



wholesome food, and to afford pleasure in the 

 reception of it, whilst it deters from the use of 

 such as would be deleterious. This is more 

 obvious in the lower animals than it is in man, 

 who is frequently led by habit and fashion to 

 a preference for substances which are high- 

 flavoured over those which are most whole- 

 some, and who is still more frequently induced 

 to gratify his gustative sense by the reception 

 of an amount of food which appetite alone 

 would not incite him to take in. Of the 

 pernicious results of such excess, this is not 

 the place to speak. 



The only ulterior purposes which the sense 

 of taste appears to perform in the economy, 

 are to aid in exciting the flow of saliva, and 

 in certain cases to excite the act of vomiting. 

 Although the secretion of saliva is greatly 

 affected by other causes, as, for example, by 

 the movement of the jaws, tongue, &c., yet 

 it is much influenced by the sapid qualities of 

 the food introduced into the mouth, being 

 greatly increased by the taste of savoury food. 

 It is also augmented by the sight or odour of 

 such food ; but it is probable that the latter 

 sensations influence it not so much directly 

 as indirectly, namely, through the ideas which 

 they call up, for the idea alone, if called up 

 with sufficient vividness, is sufficient to make 

 " the mouth water." The sense of nausea, as 

 already remarked, seems intermediate between 

 taste and touch ; but it is connected most 

 closely with the former. We experience more 

 or less of difficulty in swallowing all substances 

 whose taste is peculiarly repugnant to us, and 

 we find ourselves compelled to regurgitate 

 them when the impression becomes of a 

 certain intensity. This is one of the auto- 

 matic actions in which it appears requisite 

 that a sensation, not a mere impression, should 

 participate. 



(William B. Carpenter.) 



TEETH. COMPARATIVE ANATOMY. (Sing. 

 a tooth ; Tunth, Teut. ; Dens, Lat. ; Dente, Ital. ; 

 Dent, Fr.; Tand, Dan. ; Tain, Old English ; 

 Zahn, Germ. ; Dant, Welsh ; Dend, Erse ; 

 odovs-cdovTos, Gr. ; Dantis, Lithuanic; Dantas, 

 Sanscrit . * ) A tooth is a hard body attach ed to 

 the mouth or commencement of the alimentary 

 canal, always exposed, save where its develop- 

 ment is permanently arrested, as in the rudi- 

 mental tusk of the Narwhal; commonly cal- 

 cined, the exceptions being few, e. g., the 

 horny teeth of the Lamprey and Platypus. 

 Teeth vary not only in their tissue, but still 

 more in number, size, form, structure, position, 

 and mode of attachment, in different animals : 

 they are principally adapted for seizing, tear- 

 ing, dividing, pounding, or grinding the food ; 

 in some they are modified to serve as wea- 

 pons of offence and defence ; in others as aids 

 in locomotion, means of anchorage, instru- 



* These synonyms are cited as illustrative of the 

 coincidence in one of the primary words of a natural 

 class of languages that prevails from the East Indies, 

 through the west of Asia and across Europe, and as 

 indicative of the unity of stock of the great Indo- 

 European family of mankind. 



ments for uprooting or cutting down trees, 

 or for transport and working of building 

 materials ; they are characteristic of age and 

 sex ; and in man they have secondary rela- 

 tions subservient to beauty and to speech. 



Teeth are always most intimately related to 

 the food and habits of the animal, and are 

 therefore highly interesting to the physiolo- 

 gist : they form for the same reason most 

 important guides to the naturalist in the 

 classification of animals ; and their value, as 

 zoological characters, is enhanced by the 

 facility with which, from their position, they 

 can be examined in living or recent animals ; 

 whilst the durability of their tissues renders 

 them not less available to the palaeontologist 

 in the determination of the nature and affi- 

 nities of extinct species, of whose organisation 

 they are often the sole remains discoverable 

 in the deposits of former periods of the earth's 

 history. 



Although there are many analogous struc- 

 tures in the inverterbrate classes, true calcified 

 teeth are peculiar to the Vertebrata, and ma}' 

 be defined as bodies primarily, if not perma- 

 nently, distinct from the skeleton, consisting 

 of a cellular and tubular basis of animal 

 matter containing earthy particles, a fluid, and 

 a vascular pulp. 



In general, the earth is present in such 

 quantity as to render the tooth harder than 

 bone, in which case the animal basis is gela- 

 tinous, as in other hard parts where a great 

 proportion of earth is combined with animal 

 matter. In a very few instances among the 

 vertebrate animals, the hardening material 

 exists in a much smaller proportion, and the 

 animal basis is albuminous ; the teeth here 

 agree, in both chemical and physical qualities, 

 with horn. 



True teeth consist commonly of two or 

 more tissues, characterised by the proportions 

 of their earthy and animal constituents, and 

 by the size, form, and direction of the cavities 

 in the animal basis which contain the earth, 

 the fluid, or the vascular pulp. 



The tissue which forms the body of the 

 tooth is called "dentine," (Dentinum, Lat.; 

 Zahnbein, Zahnsubstanz, Germ. ; I'lvoire*, Fr.) 



The tissue which forms the outer crust 

 of the tooth is called " cement " (ccementum, 

 crusta petrosa, Lat.). 



* The learned author of the article Secretions," 

 in the " Dictionnaire Universel d'Histoire Naturelle," 

 8vo, 1848, adopts the term " Dentine " in preference 

 to Cuvier's name " ivoire," and after defining its 

 properties, observes, " Sur ces divers rapports, le 

 mot dentine, par lequel M. R. Owen les designe, me 

 parait tres heureux." The term " ivory " unavoid- 

 ably recalls the idea of the peculiar modification of 

 " dentine," which characterises the tusks of the ele- 

 phant, mammoth, and mastodon; but, besides this 

 objection to its more general application, the word 

 is used in a still wider sense in the " Le9ons d' Ana- 

 tomic Comparee : " " Les unes (dents), en eflfet, ont 

 la partie enfoncee dans 1'alveole denuee d'email; 

 cette partie, ou la racine, ne se compose gene'ralement 

 que de Yivoire interieure, recouvert tres rarement 

 ft ivoire exterieure (les dents de cachalot) ; " torn. iv. 

 Ed. posth. 1836, p. 200. The example cited of the 

 tissue here denominated " ivoire exterieure " is the 

 " cement." See my " Odontography," p. 355, pL 89. 



