TEE MOUTH. 



347 



contains, sparingly, the lacunae and canaliculi which characterise true 

 bone : those placed near the surface have the canaliculi radiating from the 

 side of the lacunee towards the periodontal membrane; and those more 

 deeply placed join with the adjacent dental tubuli. In the thicker portions 

 of the crusta petrosa, the lamellse and Haversian canals peculiar to bone 

 are also found. As age advances, the cementum increases in thickness, 

 and gives rise to those bony growths, or exostoses, so common in the teeth 

 of the aged ; the pulp cavity also becomes partially filled up by a hard 

 substance, intermediate between dentine and bone (osteo-deniine—Oioen; 

 secondary dentine—Tomes). It appears to be formed by a slow conversion 

 of the dental pulp, which shrinks or even disappears— Gra;/.) 



Dental pulp. — The pulp, or papilla, is formed by a 

 fibrillar and nuclear mass that tills the internal dental ^'^' ^^^' 



cavity. It receives blood-vessels and nerves, and is 



enveloped in a very thin membrane which is entirely 



composed of several layers of beautiful cylindrical or 



prismatic cells, the most superficial of M'hich send 



fibrillar prolongations into the dental tubuli. Towards 



the base of the papilla, this membrane assumes tho 



texture of connective tissue, and is reflected upwards on 



the fang of the tooth to line the alveolus, and join tliC 



gum at the origin of the crown. 



€lum. — The gum is a portion of the buccal mucous 



membrane surrounding the neck of the tooth, and con- 

 curs in consolidating it in the alveolar cavity. Its 



structure is that of the membrane to which it belongs, 



being a thick dermis furnished with papill* and tesselatLd 



epithelium. It does not contain any glands. 



Alveolo-dental periosteum.- — This scarcely differs from 



the ordinary periosteum except in being a little softer. 



It lines the alveolus and covers the cementum of the fang. 

 Development. — Each tooth is developed in the 



interior of a closed sac named the dental follicle, and 



lodged in an excavation in the maxillary bones. The 



sac presents, according to the species of animal and kind 



of teeth, numerous variations, which we cannot stay to 



consider here : but must confine ourselves merelv to a 



MAGNIFIED SECTION" OB" 



brief sketch of the general and constant characteristics ^ canine tooth 



of its organisation. siiowiNa its inti- 



The dental follicle is constituted by an external en- mate structure. 

 veloping membrane of a cellule- vascular nature (Fig. 1, Crown ; 2, 2, Neck ; 



166, a). It shows at bottom the simple or compound 3, Fang, or root ; 4, 



papilla which at a later period is termed the dental Cavita=^ ^t '^^'hich 



pulp (b) ; this organ, destined for the secretion of the ^jf^ =^5^4 ^^^ 



dentine, then fills nearly the whole of the follicle. nerves communicate 



In its upper part is observed the enamel organ, or germ with the pulp ; 6, 6, 



{enamel membrane), formed by a prolongation of the ^^"^^T, ^'j^°J^\"^S 



gingival epithelium, and connected with the latter by a ^^ rj^ Enamel; 8, 8^ 



small mass of cells named the gubernaculum dentis. Cement. 

 Most frequently there is, opposite the bottom of the 



follicle, one or more papillse which, in some cases, adhere by their 

 whole length to one of the lateral walls of the follicular sac, and the free 

 extremities of which cross those of the dentine papiUas, or are buried in 



