sill or ho tree layer Ofmutts petty.** • tale it Cnereettlad by it waving lino met, wttlito vilitelt it the proper bone of the tooth, hut the substitute or the lid. ter is penetrated by two prtaltietiwie of ttutinel, in the interior of rani of which is crusts petrol:, 'the crusts 'lotto**. width fills these in. terital reductions or eitmod. rt seine. times not completely depotidt-cl before the tooth etas the gum r. henna Volitive are ten in the centre of the tooth, wh Ili br• totioe tilletl with a dietk.etihetelire, toimpo.‘ Mt 01 the *Mutat final, and other reign modem, This tielittim happens to any cunsultinble extent in tlie Rrmitirrig or the horse, In the row and sheep these env ides are wno/dlIy tilled with the dark talcrntitiowrs matter. the crusts pelts.** be. ing toblinecl to the exterior surfaer or the teellt,on1 net exists there so Oen %tinily as in the home The kiwer grinders of the home differ very ninth in their thrmation from those of the upper jaw, Ossification etimmen. ors in these by Rine or the points, whielt increase into as malty small shells w fel they unite without any the tttiVnIle in000arr doe It between, to ill. ternal pentInelitilte or the enamel. that substance hi, however, deposited iu a etniveltiteil Manner on the bent of the teeth. so that the same roil is *named. as if iirtatitrtions of the cortex Mellow.. had Ceitted in the tenter of the part The trusts petrosa fills tip the irregularities or this why tog line or enamel, An horiaental section or such a tooth pre. setits the three substances arranged within roll other the trusts petty** is external t then trines the enamel, includes itet14111 but the proper bone of the tooth.
The incisors ot the horse have * pro. &lotion or mono in their erntre i but the cavity which this term*. emitaining nie ertietit petroem, le Meetly tilled by the particles of food, &e. As three proorwl or enamel descend only to a certain VC. tool in the tooth, they disappear At last. Item the tonstent wear or the part tit Inas. tiestion, This is tmpttopt'rtiy called the filling up of the teeth t and haute * crite rion of the home's age.
The grinding teeth or the elephant tom %sin the unlit eomplete intermishity the dote substatwes. and have a pri,ter proportion or trod% petrosit than those or any ether animal,. The pulp form* a ',timber or brinot list protesrs. Itiog parallel to each other, and placid trim• between the inner and mitt:r aim. me of the alveoli. The bone tooth Is 'brined on these in separate shells, ciiiiimencing at their loose extremities, and extending towards the basis, where they are connected together. The capsule lends FM e(11101 1111111ber of 11101111/111110lIS pl'01111CliellS Whiell fill!, cover die bony shells with enamel, and then Invest them with eruct petrosa; which hitter sub. stalice unites and consolidates the differ.
cat portions, The bony shells vary In number kom four to twenty.three, lie. cording to the size of the tomb, and the age of the animal they have been de scribed under the term of dentictili, and have been represented as separate teeth in the first instance. It must, however, he remembered, that they are formed on peeresSeS of one single pulp.
\Viten the crusty petrosa Is completely deposited, the dill'erent lnmicohl are C011. 14011(131c(1 together. The bony shells nee united at their base to the neighbouring ones ; the investments of C11411101 are joined in like nmannert and the intervals tire filled with the third substance, which really deserves the 1111111e bestowed on it by ettvier, of cement, The pulp is then elongated, for the purpose of forming the roots or fangs of the tooth. From the peculiar mode of dentition of this animal, which will be explained in a subsequent note, the front portion of' the tooth has cut the gem, and is employed in mastica tion, befiire the back part is completely formed, even before smile of the posterior dentictili have been consolidated. The hack of the tooth clues not appear du the mouth until the anterior part has been worn down even to lieditlig.
A horizontal section of the elephant's tooth presents it series of narrow bands of bone of the tooth, surrounded by cm.. responding portions °rename', iletweel, these are portions of crusty petrosit and the whole circunikrence of the section is composed of a thick layer of the some substance.
A vertical section in the longitudinal direction exhibits the pr.:c.os of bone upon the different denticuli, running tip from the fangs : u vertical layer Of 1213. niel is placed before, and another be. hind each of these. If the tooth is not yet worn by mastication, the two havers of enamel are continuolis at the port where the bone, terminates in it point and the front layer of one denticulus is contintt oes with the black layer of the succeeding one at the root of the tooth ; so that the enamel, ascending on the anterior, and descending. on the posterior, surface of each dentemlus forms a continued line through the whole tooth. Crusts petrosa intervenes between the ascending and &rending poll lous of the enamel, AN tile 1111111lee Of the tooth Is worn down in mastication, the promise* of enamel, resisting by their superior hard. mess, form prominent ridges on the grinding 1011'1110C, Which must adapt It ex. c.elleutly for bruising and comminuting any hard substance.
The grinding buses, when worn suffi ciently to expose the einunel, present very dilrerent appearance In the Asiatic African elephants. The processes of enamel in the former specks represent flattened ovals, placed accrosis the tooth. In the latter they Ibrm a series of lozen. get', which touch each other In the mid. me or the tooth.