THE MOUTH. 



347 



Fig. 155. 



contains, sparingly, the lacunae and canaliculi which characterise true 

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

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

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

 of the crusta petrosa, the lamellae 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-dentine Owen; 

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

 of the dental pulp, which shrinks or even disappears Gray.) 



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 which send 

 fibrillar prolongations into the dental tubuli. Towards 

 the base of the papilla, this membrane assumes the 

 texture of connective tissue, and is reflected upwards on 

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

 gum at the origin, of the crown. 



Gum. 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 papilla? and tesselakd 

 epithelium. It does not contain any glands. 



Alveola-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 tones. 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 merely to a 

 brief sketch of the general and constant characteristics 

 of its organisation. 



The 'dental follicle is constituted by an external en- 

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

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

 papilla which at a later period is termed the dental 

 pulp (B) ; this organ, destined for the secretion of the 

 dentine, then fills nearly the whole of the follicle. 

 In its upper part is observed the enamel organ, or germ 

 (enamel membrane), formed by a prolongation of the 

 gingival epithelium, and connected with the latter by a 

 small mass of cells named the gubernaculum dentis, 

 Most frequently there is, opposite the bottom of the 

 follicle, one or more papillae 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 papillae, or are buried in 



MAGNIFIED SECTION OP 

 A CANINE TOOTH, 

 SHOWING ITS INTI- 

 MATE STRUCTURE. 



Cavitas pulpae ; 5, 

 Opening by which 

 the vessels and 

 nerves communicate 

 with the pulp ; 6, 6, 

 Ivory, showing 

 fibrous structure ; 

 7, 7, Enamel ; 8, 8, 

 Cement. 



