XW1 



TEETH. 



TEID.E. 



1 -.12 



cavity, to their termination t the junction of the cement, and the 

 dentine on the enamel of the latter, or they may be aeen passing into 

 then external structures. The tubuli commence at a right angle with 

 the surface uf the pulp-cavity, and proceed outwards to wards the surface 

 of tlie tooth, giving out in their way numerous small branches, which, 

 nmelliiji with other similar branches from neighbouring tubes, anasto- 

 mose with them, or meeting with simple cells in the intert iibuUr tissue, 

 there terminate. Towards the surface of the dentine it is not uncom- 

 mon to see a tube alter its course, and by joining another, form a loop. 

 The tubes all commence in the pulp-cavity, and pass outwards towards 

 the surface of the dentine. Their course, as regards each other, is 

 divergent, so that the proportion of the intertubular tissue increases 

 relatively as their distance from the pulp-cavity U greater or less. This 

 preponderance of the intertubular ovrr the tubular tissue nesr the 

 periphery of the tooth is however in a considerable degree lessened by 

 the more frequent branching of the tubes, and by the occurrence of 

 cells near the surface of the dentine. If a single tuba be traced 

 through its whole extent, it will be found to make two undulations ; 

 and in addition to these, which are called the primary curves, a number 

 cf smaller undulations. In examining this structure a thin section 

 may be taken from the fang, and, with the aid of the microscope, 

 viewed by transmitted light. A tube will thru appear as a very definite 

 dark line pursuing its tortuous but definite course towards the surface, 

 giving out numerous minute branches on its way, and at last dividing 

 into two terminal branches, which end either by passing into a cell of 

 the intertubular tissue, or by anastomosis with a collateral tube, or 

 by passing into the cement. If a section of the dentine and enamel 

 be taken, then the tubes will be seen to give out comparatively few 

 branches till they come near to the latter, when they divide and anas- 

 tomose freely, and some few terminal branches may be traced entering 

 the enamel. It is by no means uncommon for a tube in its course to 

 suddenly dilate and give out branches from the dilatation, then again 

 contract, and pursue its original course. In such a case the dilatation 

 forms a cell in every way similar to the bone-cell. The point of the 

 greatest diameter of the dental tubes is at their commencement on the 

 walUof the pulp-cavity, thouvh in their course previous to the division 

 of the trunk into two terminal branches they suffer but little loss in 

 calibre. In tracing this structure in the teeth of various animals, we 

 find every form of branching; sometimes the branches are few, in 

 others extremely numerous ; in some instances they are given out from 

 one side of the tube only, in others from each side ; but whatever the 

 modification in the number or form of the branching given out, the 

 primary tube always commences by an open extremity on the walls 

 of the pulp-cavity, or upon the walls of a canal for a blood-vessel ; 

 and the direction taken by the tubes is invariably towards the periphery 

 of the tooth, always anastomosing in their way by the numerous 

 branches. In the temporary, and not unfrequently in the permanent 

 teeth, the tubes, instead of presenting an uninterrupted line, present 

 on their surface numerous indentations, just as though they were 

 composed of a series of hollow beads, which were united and made 

 to communicate with each other. 



fig. 7. 



Yiewi of the tubules of dentines. 



The second part composing the dentine is the intertubular tissue, 

 which occupies the spaces between the tubuli, everywhere surrounding 

 and investing them, and thereby contributing greatly in rendering the 

 whole dentine a solid dense mass, the area of the tubes and cells being 

 the only hollow portion. In a favourable specimen of this tissue Mr. 

 Tome* observed that it was composed of very minute granules, united 

 to each other on all sides, thus forming a soli.l mass, of which, in 

 character of formation, oolite would give a coarse illustration. The 

 granularity is best seen near the external surfaces of perfect dentine, 

 or in the tissue when developing. In the intertubular tissue, hemi- 

 spherical or elliptical cells are found, especially near the surface of the 

 dentine of the fang, where they form a layer joining the cement. 



A separate organ u provided for the formation of each of these 

 three constituent parts of the tooth, though, when they are perfected, 

 they contain no vascular tissue but the pulp within the pulp-cavity ; 

 and it is doubtful whether, in the human subject, fresh material U ever 



formed from this after the tooth has once attained its complete develop- 

 incut The first appearance of the pulp of each tooth is in the form 

 of a minute process or papilla rising from the bottom of a groove in 

 the mucous membrane of the mouth behind the edge of the jaw. In 

 course of time, as the borders of the groove grow around it, the papilla 

 seems to sink into the mucous membrane ; and it now appears as if 

 rising from the base of a follicle, or of a flask-like depression, in the 

 edge of the jaw. And lastly, processes of membrane, or ojwrcula, 

 grow from the sides of the mouth of the follicle, and as they appmne.li 

 each other and adhere by their mutually opposed edges, they gradually 

 close it, and convert it into a capsule or sac, to the base of which 

 the first-formed papilla is affixed. In the first-appearing tooth tho 

 papillary state may be se n in the human embryo an inch in length : 

 the capsular stage is completed at about the fifteenth week of embryonic 

 life. 



These three stages of the formative organs of the tooth, namely, the 

 papillary, the folliculor, and tho capsular, being completed, the sub- 

 stances of the tooth itself begin to be produced. The dentine i.< 

 developed from the papilla, which gradually assumes tho form and 

 relations of the proper tooth-pulp ; the enamel, from a special organ 

 developed at that part of the capsule which is opposite to the papilla ; 

 and the bone probably from the interior of the capsule it-elf. The 

 composition of the enamel and osseous portions of the teeth differs. 

 The following analysed are given by Von Bibra : 



The osseous portion includes the dentine aud ceuient. 



TEETHING. [DENTITION.] 

 TEFFLUS. [CARABUS.] 



TEID^E, a family of Saurian Reptiles. [SA.URIA]. The following 

 is a synopsis of the genera : 



I. Throat with two cross folds, with larger 6-sided scales between. 

 A. Ventral shields small, long, smooth. Tongue contractile. 



1. TViiw. Toes 5-5. Femoral pores distinct Two species. 



2. C'allujiitla. Femoral pores none. Toos 5-5. Oue species. 



U. Ventral shields broad, smooth. 

 * Tongue elongate, sheathed at the base. Teeth compressed. 



3. Amciva. Toes 5-5. Teeth 3-lobed. Six species. 



* Tongue not sheathed, free at the base, 



4. CncmidophoriM. Teeth compressed longitudinally, 3 lobed. Toos 



5-5. Six species. 



5. Dicrodon. Teeth compressed transversely, bifid. Toes 5-5. One 



species. 



6. A cranium Teeth compressed transversely, bifid. Toes 5-4. Oue 



species. 



II. Throat with a collar of large shields. 

 a. Collar and ventral shields keeled. Tail round. 



7. Acanthopyga. Scales of back large, of sides granular. One 



species. 



8. Centropyx. Scales of back and sides moderate, in many series. 



One species. 



4. Collar and ventral shields smooth, elongate. Tail round. 



9. fmminia, Scales of back rhombic, keeled, equal One species. 

 c. Collar and ventral shields smooth, elongate. Tail compressed. 



10. Crocodilurui. Scales of back equal, similar. One species. 



11. data. Scales of back unequal. Throat with a collar of largo 



scales. One species. 



1'2. Ada. Scales of back unequal Throat with two plaits. One 

 species. 



This family is well-illustrated by the Taut Teyuixin of the British 

 Museum Catalogue. It is the Lacerta Tcyuiiin, Linn. ; Sept marmoratut, 

 Laurenti; Lacerla Monitor,la&T.; Tupinambis Monitor, Oaud.; Monitor 

 Mcriantf, Ue lilainville, Van Hasselt and Kuhl, Ac, ; Tyut Monitor, 

 Merr., &c. ; Monitor Teffitixin, Kit/ing. ; Podinema Tegmxiu, WagL, 

 Wiegm. ; Tcguixin Monitor, Gray ; Monitor Tegaixin, Eichw. ; Tejut 

 Tryuinn, Scbinz. ; Le Grand Sauvegarde d'Amerique, CUT. ; Variegated 

 Lizard, Shaw ; Great American Safeguard, Griffith's Cuvier. 



The warm countries of America are the native places of the Teidre, 

 which arrive at a considerable size, often measuring as much as 

 4 or 5 feet in length. Messrs. Dumc'ril aud Bibron state that they 

 ordinarily inhabit the fields and the borders of woods, although they 

 never climb trees; but they al-o appear to frequent sandy, and con- 

 sequently arid tracts, where they are said to excavate burrows, in 



