168 A MANUAL OF DENTAL ANATOMY. 



bone of the alveolus to the cementum of the tooth, becoming 

 lost at each extremity in the one tissue or other. 



The osteoblasts form both matrix and bone corpuscles : 

 in Professor Klein's words " each osteoblast by the peripheral 

 portion of its cell substance gives origin to the osseous ground- 

 substance, while the central protoplasm round the nucleus 

 persists with the latter as the nucleated bone-cell. The bone- 

 cell and the space in which it lies become branched. For 

 a row of osteoblasts we then find a row of oblong or round 

 territories, each composed of matrix, and in it a nucleated 

 branched cell. The outlines of individual territories are 

 gradually lost, and we have then a continuous osseous 

 lamina, with its bone-cells. The ground substance is from 

 the outset a network of fibrils ; it is at first soft, but soon 

 becomes impregnated with inorganic salts, the process com- 

 mencing at the ' point of ossification.' The bone cells, with 

 their processes, are situated in corresponding lacunae and 

 canaliculi, just as in the adult osseous substance." 



Thus just as calcification in an enamel cell or in an odon- 

 toblast commences upon its surface, and proceeds inwards 

 till it has more or less completely pervaded it, so in the case 

 of the osteoblast the deposition of calcareous salts proceeds 

 from without inwards. To use a rough comparison we 

 might imagine a calcifying osteoblast as like an egg-shell, 

 the central cavity of which was being gradually obliterated 

 by the addition of successive layers on its interior (it is not 

 to be understood that any such lamination is to be detected 

 in an individual osteoblast). In a certain number of osteo- 

 blasts this process of calcification does not proceed with 

 such regularity as to obliterate their centres, and at the 

 same time to fuse together their exteriors, but as it pro- 

 gresses with some degree of irregularity towards the centre, 

 tracks of uncalcified matrix are left, and finally it stops 

 short of obliterating the central portion of the cell. Al- 

 though for the purpose of description I have spoken of the 



