110 



INTRODUCTION. 



termed a capsule, which is, in fact, an apparatus for their production, 

 seated in the alveolar cavity of the maxillary bones.* Like every other 

 part of the system, the teeth are the result of a process of secretion. 

 The apparatus, by which the material of the teeth is elaborated, and 

 which, at the same time, also determines their form, is, itself, more or 

 less complicated, according to the structure of its product. It consists, 

 then, of a pulp and two membranes. 



The pulp, or bulb, consists of a spongy, or tuft-like, mass of blood- 

 vessels and nerves, and is destined for the secretion of the ivory of the 

 tooth. Its form is that of the tooth which it produces : it is, indeed, the 

 mould, upon which the ivory is modelled. The first capsular membrane 

 is the enamel membrane : it envelopes the bulb, following its form and 

 contour ; but terminates at its base, corresponding to the neck of the 

 tooth, which part is the boundary of the enamel in teeth with true 

 roots. This membrane is brittle and translucid ; from its inner surface 

 (although F. Cuvier was unable to detect any vessels), it deposits, 

 particle by particle, on the ivory moulded by the bulb, the enamel with 

 which it is invested ; which, being fully accomplished, it becomes then 

 opaque and elastic, and, at last, finally obliterated. To the transparency 

 of this membrane, to its subsequent thinness, and to its total obliteration, 

 when the crown of the tooth is duly formed, the cause of its having 

 hitherto been overlooked is, doubtless, to be attributed. It is, however, 

 easily to be distinguished from the contiguous parts on the molars of 

 ruminants, and especially their posterior molars, immediately after birth. 

 To look for this membrane when the teeth are developed, is, of course, 

 useless. 



The second membrane is that which deposits the cortical substance, 

 or crusta petrosa ; and which is even to be discovered where this sub- 

 stance does not enter into the composition of the teeth ; but in such cases 

 it is very thin, and seems to act merely as a protecting envelope to the 

 capsule. As the substance secreted differs little from the ivory, so, in 

 its structure, this membrane approaches the bulb, being highly vascular. 

 In compound teeth its function is very important. Following the sinuosi- 

 ties of the enamel-covered ivory, it fills, like an external pulp, the inter- 

 stices of the folds, and completes, by its secretion, the composition, which 

 the internal pulp and the enamel membrane have previously elaborated. 



* " Les machoires presentant d'abord une seule alveole commune, vaste, mais peu profonde, dans 

 1'interieur de laquelle se developpent les sacs dentaires. Peu a peu il s'eleve des cloisons osseuses, 

 imparfaites au commencement, et parfaites a une 6poque plus reculee, qui divisent 1' alveole primitive 

 en plusieurs compartiments. Ces cloisons, qui formaient originairement une gaine ample a la dent 

 toute entiere, n'entourent plus tard que sa racine, a laquelle elles sont alors etroitement appliquees. 

 A mesure que celle-ci se developpe les arcades alveolaires augmentent considerablement de hauteur, 

 pour se retrecir ensuite, apres la chute des dents ; cette diminution du diametre vertical des arcades 

 dentaires tient au r6trecissement et a 1'acclusion des alveoles." Traite Gen. d'Anat. Comp., par J. F. 

 Meckel. Vol. viii., p. 338. 



